hacking old valve/tube radio into guitar amp,question's,

just bought this 1950's radio, EVEREADY SKY QUEEN, with the intention of turning it into a guitar amp, being a newbie at this i need all the help i can get, where do i start, dont even know if it can be done with this set,
valve's in it are= DK96, DF96, DAF96, DL96,
it also has a mains transformer fitted, 240 volts,
any help appreciated,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0088.jpg

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0089.jpg

http://lmgtfy.com/?q=converting+a+tube+radio+into+a+guitar+amp

Some old wireless receivers can be a death trap with things like live chassis.
Be careful.

Does it work? If so then you might break into the circuit after the radio receiver stage to use it as an amp, some radios had a pair of sockets provided for this intended for a record player.

Most of the capacitors will have blown by now. Is there the usual paper in oil mess everywhere under the chassis?

Test the electrolytics, these can be replaced.

You can probably recover the case, chassis, some of the bottles and maybe the transformers.

Unfortunately the valves are in the 1969 Mullard book as "earlier types not in common use" The "D" prefix means 0.5 to 1.5V heaters, this means the transformer might not support "normal" 6.3V heaters. The 2nd letter, "K" is octode or heptode, the "L" is an output tetrode or pentode, the 3rd "9" is B7G base, the final numbers particular to design/type.

I think you have a cool case and workable chassis but I dont think much else will be of any value in a guitar amp...

I think you have a cool case and workable chassis but I dont think much else will be of any value in a guitar amp...

What would it look like with a tweed cover?

Transformers, tube sockets, chassis, pots and switch and case. About all I would bother with.

ooop's,, listed the wrong valve's, these are the one's in the radio ,

6516ND
6AT6
6064NJ
6AM6KJ
and one with no marking's,

sorry about that,

http://lmgtfy.com/?q=converting+a+tube+radio+into+a+guitar+amp

thank you,

ooop's,, listed the wrong valve's, these are the one's in the radio ,

6516ND
6AT6
6064NJ
6AM6KJ
and one with no marking's,

sorry about that,

Good grief. I have no idea what they are.
Let's ask Frank
http://www.mif.pg.gda.pl/homepages/frank/vs.html
from http://frank.pocnet.net/

Silly question - is this a battery powered radio?
Ever Ready made batteries, still do in fact.
They even made some mains/portable sets.
I note the way the back opens on a hinge as if it is intended to open regularly to replace the HT accumulator (oh yes, nasty primitive rechargeable jobbie) and heater cells.
In which case you may well have really weird heater voltages and HT (B+) from the transformer.
Which will leave you with just a nice box and chassis.
Unless it still works, in which case you should be able to find the audio amp section and add an input, if it doesn't have one already - look for a pair of "banana plug" sockets, which might look like an olde aerial connectoid.

this set did start out as HT battery powered but has been severley hacked in the past, in the pic you can see the mains transformer, plus it has one more valve than standard, plus there seem's to be a lot going on around the mains transformer, diode's etc, no banana skts, i'll try and find out what the valve's are,

6516ND - 6AM5 = EL91, The 6AM5 is a miniature audio output pentode. In single ended configuration it will produce 1.4 Watts
http://www.r-type.org/exhib/aaa1132.htm

6AT6 - Double Diode-Triode, 6AT6 is about like a 5751, a single triode 6V lower gain 12AX7
http://www.r-type.org/exhib/aaa0358.htm

6064NJ - The 6064 is a special quality version of the EF91. The special quality valve has a more rugged build than the commercial EF91. US designation 6AM6.
http://www.r-type.org/exhib/aam0047.htm

6AM6KJ - EF91 is also known as 6AM6, and it is a nice RF pentode also usable for audio - and it also makes a very nice liner triode, with a mu of about 70 and gm at about 7mA/V, which makes it eminently usable for a variety of applications in audio.
Datasheet here: http://www.mif.pg.gda.pl/homepages/f...154/e/EF91.pdf
Triode curves here: http://www.tubes.mynetcologne.de/roe..._as_triode.pdf

What size is the speaker? How big is the cabinet? I think the case/controls/speaker look cool. Could you fit a 5e1 inside the box and use the radio controls? That is what I would try to do.

printer2,, thank's for the information,,

What size is the speaker? How big is the cabinet? I think the case/controls/speaker look cool. Could you fit a 5e1 inside the box and use the radio controls? That is what I would try to do.

it's about 12" x 12" x 6", no idea what a 5e1 is though,

Check out my 5F1 Kit in the Vendor Section. A 5E1 is the precursor to the 5F1. These old model numbers are often casually tossed around here even as some are unfamiliar with them.

Google 5E1 and click on images to see a layout and schematic for it specifically.

With some fabrication skills, either small amp could be made to fit inside your box and inside your existing chassis as it were.

The essential components are Power Transformer, Output Transformer, Three tubes. 12 resistors 7 capacitors. Volume Pot, Switch, fuse holder, jacks,

A tone control can be easily added.

Sorry, I meant 5f1 and was specifically thinking about one of Hackworth1's kit.

***it's about 12" x 12" x 6", no idea what a 5e1 is though,***

5 = 1950's
e = this letter refers to which circuit version
1 = this is the model

1 = champ model
2 = princeton model
3 = deluxe model

and so on . .

stripped the chassis down,,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0088-1.jpg

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0089-1.jpg

here's pic's of the power transformer, what are all the associated part's hanging off it,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0093.jpg

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0094.jpg

this is a pic of the valve with no marking's on it, written on the chassis is EL90 where it was fitted, how do i find out what it is,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0090.jpg

what's the metal shield for on this valve, (i am new to all this)

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0092.jpg

Metal shield serves as electromagnetic shielding to prevent interference. Some tubes are more prone to picking up unwanted signals from outside sources than others. These tubes get a cover shield.

You might need to discern at some point the voltages produced by that Power Transformer. Wall Voltage is introduced by two primary wires. The transformer produces secondary voltages via its electromagnetic coils. Atempting to read these voltages with a mulitmeter must be undertaken with some background of study and then due care because you could potentially electrocute yourself.

It appears that you have a rather esoteric assortment of parts that are not well suited for guitar amplification, but I could be wrong.

A 5F1 could fit in that Chassis however.:wink:

i've this old 1950's record player, just wondering if it would be an easier project for me as there's no radio circuit etc involved, the valves are,
6AT6
EL84
6X4

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0096.jpg

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0100.jpg

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0099.jpg

IMHO, relative to your desire to endeavor to assemble a guitar amp from a variety of old parts you have on hand, this assortment does not present itself as an improvement over the last assembly.

I might point out that old capacitors are particularly useless. They are good for about ten years give or take - before they need replacement. One would not want to risk using them in a new project.

hackworth1, thanks for your comments but i'm determined to make an amp out of the junk i have on hand, one way or another,

I have no problem with the parts you have, electrolytic caps may be good, may not and you will get some hum. They may be good for now and start causing problems in a year, by that time you may have built another amp or two learning as you go. This collection of parts is just a stepping stone.

I would suggest this page. and schematic. I would change C2 to the other side of C1. The 2.2k cathode resistors can be anywhere from 2.2k down to 820 ohms. R9 the 330k resistor can be up to 500k or down to 100k, the lower value will reduce gain though. You want to ground the amp with a three prong plug rather than shown in this schematic. The AX84 doc may have it otherwise you have to do a little looking around how to do it.

http://music-electronics-forum.com/t5573/

http://harmony.demont.net/myharmonies/Jaybird/modeloneschematic.jpg

Rather than the 12AX7 you can use the two 6AT6's you have along with the EL84 and 6X4. Mind you this is assuming you have a power transformer with the right voltage and current to drive the tubes (from the radio). You will have to find out which are the primary and secondary windings, the high voltage one is the one with the most resistance and most likely a tap in the centre , the lowest one is the heater, one with a higher resistance but no centre tap is probably your mains. Be careful checking out your transformer you do not want to hurt yourself or the transformer.

The EL84 takes a bit of heater current but the transformer you had fed enough tubes so it might handle it. To find out hook the heaters of the EL84 and the two 6AT6's in parallel across the 6V winding and when the tubes heat up measure the voltage. If you are within 10% of 6.3V you are doing good.

Look up the spec sheets of the tubes for the pin numbers of the parts (you need to learn what a cathode. grid, and plate are). A good place to start.

http://ax84.com/p1/P1_Theory_Document.zip

Look up point to point amps for ideas to lay out the circuit. Space between parts is your friend.

http://www.lh-electric.net/projects/tiny3w.html

You want the power transformer to be oriented 90 degrees from the direction of the output transformer.




Not sure from your pictures, does the record player have its own power transformer? if yes then use it.

printer2, really appreciate the time and trouble you've taken to help me, with the information you've supplied i might be able to do it, once i get my head round everything,,

the record player has one transformer you can see mounted on the valve bracket with the resistor on it and the other transformer in the pic is connected to the speaker, how can i tell which is the power transformer and which is the output transformer,

another newbie question, i've seen speaker's with transformer's mounted on them, why is that,?

I thought there were two but wanted to make sure. The one on the speaker is the output transformer. They mount the transformer on the speaker as it is a convenient place to put it.

What I would suggest is to read the AX84 document and try to understand it. Then take the record player and draw out the parts with their values as a schematic. I have a feeling you can use it as it is and add another tube up front from the radio to add more gain. Just draw the tubes where they are and the rest of the circuit attached to them something like this.

http://i406.photobucket.com/albums/pp142/printer2_photo/guitar%20amp/TweedBFdualpotlayout.jpg

i've printed out the ax84 doc, and will study it, i'll post a pic of my circuit when i figure it out, here's my small stash of future hack's, reel to reel tape player's, radiogram gut's, and a few valve radio's, really stoked about getting into this valve amp building,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0101.jpg

i've printed out the ax84 doc, and will study it, i'll post a pic of my circuit when i figure it out, here's my small stash of future hack's, reel to reel tape player's, radiogram gut's, and a few valve radio's, really stoked about getting into this valve amp building,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0101.jpg

OK, I don't like you now.

well there's actually 4 of the radio's i'm not going to hack, as they are complete, when i get more proficient at valve circuit's i'll restore them, but the reel to reel tape recorder's etc are broken so i'll use them for part's etc,

http://lmgtfy.com/?q=converting+a+tube+radio+into+a+guitar+amp

How in tarnation did you do that Google link?

this is a pic of the valve with no marking's on it, written on the chassis is EL90 where it was fitted, how do i find out what it is,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0090.jpg


EL90 is the Euro-designation for 6AQ5, which is what this tube looks like based on the picture (7 pin, sort of cylindrical plates). The 6AQ5 is the little brother to the 6V6, for use with maximum plate voltage of 250V. It has been used in guitar amps and would give you a good sounding low-wattage amp if you surrounded it with the right circuitry.

Fender used it in the first version of the Musicmaster Bass amp; Gibson used it in the GA-17, and I'm sure there are others.

steven

steven,, thanks for that,,^^^

this is one of the salvaged transformer's from a valve radiogram i'd like to use as the power transformer in the amp i'd like to build, but i dont know what is the power in, heater winding's, etc, anyone know which is which, i put my avo on and these are the reading's , any help appreciated,
F+G= 6K OHM
F+H= 5.75K OHM
G+H= 9.5K OHM

A+B= dead short
C+E= 1.75K OHM
C+I= 2.75K OHM
E+I= 2.75K OHM



http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/TRANS.jpg

think i've sorted it out,

F+G= 6K, supply in 240vac
G+H= 9.5K @ 27 VAC
F+H= 5.75K @ 250 VAC

A+B= dead short @ 8 VAC
C+E= 1.75K @ 450 VAC
C+I= 2.75K @ 240 VAC
E+I= 2.75K @ 240VAC

what i can use these voltage's for in a single ended amp, i'm not sure,,

any idea's,????

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/TRANS.jpg

stripped the chassis down,,

here's pic's of the power transformer, what are all the associated part's hanging off it,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0093.jpg

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0094.jpg

The pics are a bit blurry, but the thing to start with is where the mains AC leads connect to the PT. Make a note of what tabs those mains wires are connected to so that when you have disconnected everything, you know to hook up those tabs to your mains voltage for testing VAC between the remaining tabs. But I wouldn't do this live test until you have disconnected the rest of the circuit from the PT and metered the other tabs with your R-meter for DC continuity (making a note of where the continuity is).

When you do eventually live test the PT, do so with a dimmer in series with the active/phase mains wire, and make sure the phase/active wire is properly fused with a 1A or 2A Slo-Blo fuse, and that the metal chassis you are testing the PT in, is properly earthed with a secure dedicated chassis connection to the mains earth ground. It also helps if you have a variac to gradually bring the mains voltage up to par. And make sure that there are no wires on any of the tabs which could short to each other, or short to the chassis ground.

The other junk affilliated with that part of the chassis can be discarded because its mainly old filter caps that are most likely past their use-by date. Some of the old resistors might still have a bit of life left in them. If you make a note of which tabs are connected to the rectifier diodes, that will give you a clue about the High-Tension winding.

And the main thing is be very careful what you are doing, and read up thoroughly on any stuff you don't feel confident about or don't understand.

An old fashioned 10 or 20 gang terminal block would be helpful. You strip the ends of the wires and screw them down on the block. Each wire would have and independent slot.

That way, the wires are not sticking up in the air where they are difficult to control and measure with your MM. You just press your probe to each screw on the terminal block.

I also concur with tubes as he recommended a Variac.

I would begin by guessing that A and F are the line in AC.

With a Variac, you could apply a safer low voltage - say 10 volts to begin and see what happens by testing the terminal points with your MM.

If no sparks, then crank it up a little at a time and take readings as you go.

Ultimately, with 115 volts (or 220 where you are, right?)

You want to see taps for 5V, 6.3V and 200 to 300V+ or so.

The idea is, of course to identify the leads.

The pics are a bit blurry, but the thing to start with is where the mains AC leads connect to the PT. Make a note of what tabs those mains wires are connected to so that when you have disconnected everything, you know to hook up those tabs to your mains voltage for testing VAC between the remaining tabs. But I wouldn't do this live test until you have disconnected the rest of the circuit from the PT and metered the other tabs with your R-meter for DC continuity (making a note of where the continuity is).

When you do eventually live test the PT, do so with a dimmer in series with the active/phase mains wire, and make sure the phase/active wire is properly fused with a 1A or 2A Slo-Blo fuse, and that the metal chassis you are testing the PT in, is properly earthed with a secure dedicated chassis connection to the mains earth ground. It also helps if you have a variac to gradually bring the mains voltage up to par. And make sure that there are no wires on any of the tabs which could short to each other, or short to the chassis ground.

The other junk affilliated with that part of the chassis can be discarded because its mainly old filter caps that are most likely past their use-by date. Some of the old resistors might still have a bit of life left in them. If you make a note of which tabs are connected to the rectifier diodes, that will give you a clue about the High-Tension winding.

And the main thing is be very careful what you are doing, and read up thoroughly on any stuff you don't feel confident about or don't understand.

when i striped all the junk of the trans, it turn's out to be 240vac in and 240vac out,

240VAC - so thats 0-240? or 120-0-120? or 240-0-240?

An old fashioned 10 or 20 gang terminal block would be helpful. You strip the ends of the wires and screw them down on the block. Each wire would have and independent slot.

That way, the wires are not sticking up in the air where they are difficult to control and measure with your MM. You just press your probe to each screw on the terminal block.

I also concur with tubes as he recommended a Variac.

I would begin by guessing that A and F are the line in AC.

With a Variac, you could apply a safer low voltage - say 10 volts to begin and see what happens by testing the terminal points with your MM.

If no sparks, then crank it up a little at a time and take readings as you go.

Ultimately, with 115 volts (or 220 where you are, right?)

You want to see taps for 5V, 6.3V and 200 to 300V+ or so.

The idea is, of course to identify the leads.

there is no circuit between A and F, i'd like a variac, but i have'nt got one, the AC voltage over here is 240v, thank's,

240VAC - so thats 0-240? or 120-0-120? or 240-0-240?

0 - 240

here's a pic,, the yellow wire's have no connection to each other or to the other wire's,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0109.jpg

That should be okay for ~340VDC (or maybe 320VDC) with a FW bridge rectifier for a low-powered SE amp. But you still need a 6.3VAC heater supply (Did you measure the VAC across the yellow wires?)

the yellow wire's have no continuity between each other or the other wire's, and were not used on the original radio set, i only want a low power amp 1 watt or less would be fine, i'll look for a transformer in my stash that can supply the 6.3vac heater supply,

i have a 5z4g rec tube i can use , for the dc supply, will it be ok,

just found out the 5z4g tube has a 5 volt heater,

You won't need a tube rectifier. Just use silicon diodes (1N4007) in a bridge. That'll get you around 320-340VDC, enough for a low-powered SE amp. Have you tried measuring for VAC across the yellow wires?

there is no voltage across the yellow wire's,

Ah well, it was worth checking I suppose. So you'll be wanting that other 6V PT then.

well i bit the bullet and bought an old used transformer so i can get on and make an amp, i can sort out the other transformer later on, this one is=

0 - 250vac input

output is
350 - 0 -350 vac
0 - 6.3 vac
0 - 6.3 vac
0 - 5 vac
0 - 4 vac
0 - 4 vac
and one terminal marked "screen" that's the earth connection, is'nt it,??

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0125.jpg

i've checked the output voltage's and they are what's marked on the transformer,
going to have a go at making the amp "printer2" suggested, only he said to use 2= 6AT6's instead of the 12AX7, no really sure how to go about doing that, ?

here's what i'v got at the moment,,
1 meg ohm on/off volume pot, 2= 6AT6, EL84, 6X4, and chassis,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0126.jpg

the output transformer read's , 1 + 3 = 1k ohm
2 + 4 = dead short,
which pair is the input to the transformer and which pair is the output to the speaker,??

Ah well, it was worth checking I suppose. So you'll be wanting that other 6V PT then.

yes i will,
really appreciate you taking the time to reply to my newbie question's,

Look at the pin outs on the 12AX7 and the pin outs on the 6AT6. (Google images.)

You have a grid (input), a cathode (bias) and a plate (anode).

The 6AT6 has one set of these.

The 12AX7 has two sets.

One 12AX7 is like two 6AT6.

The other pins are heaters and (6AT6) has diodes (you will not use these pins).

Google pin outs for 6AT6 and 12AX7 so you can see them.

thank's "hackworth1", had a look, i see what you mean, so 2= 6AT6's wired in series (less the diode connection's) will be equal to a 12AX7, think i'm learning a bit now,

well i bit the bullet and bought an old used transformer so i can get on and make an amp, i can sort out the other transformer later on, this one is=

0 - 250vac input

output is
... one terminal marked "screen" that's the earth connection, is'nt it,??

Usually. Check if for DC continuity to each of the other taps if you're in doubt. Sometimes the faraday shield will be connected to the case of the PT.



here's what i'v got at the moment,,
...2= 6AT6, EL84, 6X4, and chassis,

Get the datasheets:

http://scottbecker.net/tube/sheets/127/6/6AT6.pdf

http://scottbecker.net/tube/sheets/129/e/EL84.pdf

http://scottbecker.net/tube/sheets/127/6/6X4.pdf

Look at the heater current requirement for each one.

You'll see that the 6AT6 draws 300mA and contains 1 triode (the same specs as a single 12AX7 triode). Now if you got a 12AX7 instead, you get two such triodes in the one bottle, for the same total heater current! (So a 12AX7 is a 'more economical' tube that gives you more possibilities with your pre-amp - just sayin')

The EL84s may quite possibly be still useable if they've had an easy life in a radio (or they may not).

The 6x4 is a rectifier tube designed to use a 6.3VAC heater supply.


the output transformer read's , 1 + 3 = 1k ohm
2 + 4 = dead short,
which pair is the input to the transformer and which pair is the output to the speaker,??

When you say dead short, beware that some transformer windings have very low DC resistance that can read as a 'dead short' on your R-meter - when in fact they're not. The only way to be sure is to (carefully) put some VAC across 1 and 3 and (carefully) measure if there is any VAC across 2 and 4. The ratio of VAC between the two windings, when squared, is the impedance ratio. You multiply the impedance ratio by the speaker load in order to get the reflected load resistance for the output tubes.

Furthermore, you may find this useful for understanding some of the terminology

http://www.diystompboxes.com/pedals/tubedummy.html

Furthermore, you may find this useful for understanding some of the terminology

http://www.diystompboxes.com/pedals/tubedummy.html

thanks for that, good reading,,

as i have 2= 6.3 v supply's available from my power trans, can i supply the 2= 6AT6 valve's from one supply and the other EL84 and the 6X4 from the other 6.3 supply,?

Better to keep the 6x4 on a heater winding all of its own (which you should probably fuse).

In addition to fusing the heater winding, it would also pay to install a 1N4007 SS diode in series with each side of the HT winding and each of the 6x4's plates (banded end of the SS diode pointing to the 6x4 plate) to protect the HT winding.

(Note: 'HT winding' is not shorthand for 'heater' winding. HT = High Tension)

dedicated 6.3v supply for the rectifier, ok,

why do i need the diode's + the fuse on the 6X4,?

will be buying some new capacitor's for this build, can i use this type,
http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/capacitors1jpg2.jpg

or do i have to use this type, if so why, if both type's are the same spec,?
http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/capacitors1.jpg

SS diodes are a good backup feature in the event of the tube rectifier shorting. A shorted tube rectifier will dump high VAC onto the filter caps, which the latter are not designed to cope with, and they will short, which will create a continuous short to ground for the HT winding, which will be bad for the PT.

For a few cents worth of SS diodes, you can prevent that. The SS diodes 1/2-wave rectify the VAC coming off the HT winding before it hits the tube rectifier. Each diode only drops 0.6V, so the B+ supply doesn't 'notice' this in comparison the much higher voltage drop provided by the tube rectifier. You still get the same performance out of the tube rectifier. See the example schematic (the voltages won't necessarily correspond with your project, and you can get away with a 1A mains fuse)

http://farm9.staticflickr.com/8180/7979079987_39ff32f545_b.jpg

thank's again,^^^^

any thought's about the capacitor's, ??

well here's what i've figured out, probably lot's wrong with it, ie value's of resistor's and capacitor's, etc, if someone could correct the mistake's, i'd be greatfull, and how do you decide what capacitor's are what ie electrolitic, ceramic, etc,?.

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0127.jpg

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0128.jpg

after a lot more reading and asking question's, this is the No3 schematic, hope i'm getting somewhere near, anyone care to check it, i'd appreciate it,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0132.jpg

started putting a test bed board together, just to see if everything work's,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0133.jpg

When you say dead short, beware that some transformer windings have very low DC resistance that can read as a 'dead short' on your R-meter - when in fact they're not. The only way to be sure is to (carefully) put some VAC across 1 and 3 and (carefully) measure if there is any VAC across 2 and 4. The ratio of VAC between the two windings, when squared, is the impedance ratio. You multiply the impedance ratio by the speaker load in order to get the reflected load resistance for the output tubes.

found an old transformer out of a fluorescent light fitting that gave me 105vac using 240vac input, i put the 105vac onto the output transformer connection's No 1 + 3, the output voltage on terminal's 2 + 4 is 3vac, do these figure's sound ok,?

here's how i've done the calculation,
3 into 105 =35,
square root of 35 = 5.916, i've called it 6, so is that 6 to 1,?
6 x 8 (8 ohm speaker) = 48, so is that 48 ohm's,?

does that look ok,?

just wondering why do i need the reflected load resistance (what does that mean,?) of the output tube,? thank's,

Actually what you do is take the winding ratio and square it, so 35 x 35, this gives you the impedance ratio between the primary and the secondary. Then you multiply that by the load impedance, so 35 x 35 (1225) x 8 ohms = 9800 ohms. This is about twice as high as the EL84 likes. The solution, a 4 ohm speaker which would be 35 x 35 x 4 = 4900 ohms. Perfect.

Your schematic looks right. The small capacitors are signal capacitors, usually under 0.1uF, from 0.047uF to 22uF (although larger capacitors can be used) are used for cathode bypass, 5uF to 100uF are used for power supply filtering.

Capacitors come in different types, usually greater than 0.47uF are normally electrolytic. These are polarized and you have to put them in the circuit with the lead with the negative sign connected to the negative side of the circuit. Signal capacitors come in a lot of varieties, not sure if I would use a ceramic though (although there are some high quality ceramics), a general film capacitor with the proper voltage rating should work.

printer2, thank's very much for the explanation's, and oking my schematic, and also for correcting my math's,

how did you know the EL84 like's the 4900 ohm's, ?

I will be watching this thread very closely, as I to just bought an old radio with the same idea in mind. I have yet to pull it apart to see what's good and what's not but here are some pictures. Luckily mine has a useable PT and OT section, but I have not decided on trying to make it a stand alone unit or head.
Schematic for mine http://www.nostalgiaair.org/PagesByModel/092/M0015092.pdf

http://pdw2.homeserver.com/high/radio%201.jpg
http://pdw2.homeserver.com/high/radio%203.jpg
http://radioattic.com/old/sold_radios_2011/more/Chagnon_RCA_68R3_(1946)_more.jpg

Why not take the cover off so we can see what you got? Should be interesting. I'm game to help you assess it.

Would be best to begin your own thread on this site so your project and that of the OP don't get confounded.

This may sound pompous,but if people in general worked and cooperated like this, the world would be a different place to live in.

... here's my small stash of future hack's, ...,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0101.jpg

A friend of mine just gave me one of those red 'portable' phonograms - looks identical to the red one you have in your photo. Nice old piece of kit on the outside, but when I opened it up it turns out it was a mains-tranformerless circuit with a UL84 power tube and a UY85 rectifier - pretty much useless for a geetar amp conversion, and his dog has chewed through the mains chord so its not worth saving. Just sayin' because I'm curious about what you have there.

how did you know the EL84 like's the 4900 ohm's, ?


The 'formula' for determining optimum load resistance (Zout) for centre-biased Class A operation for a single-ended output tube is:

Zout = Va/(Pa/Va)

where:

Va = the plate idle voltage
Pa = the maximum rated plate dissipation of the tube

Say you had the EL84 set up to idle at 300V. An EL84 is rated for 12W maximum plate dissipation.

So: 300V/(12W/300V) = 7,500R

Now if that OT is 9k, then running the EL84 at 330 plate volts (on the high side for an EL84) would be about right - and provided that you biased the EL84 to dissipate 12W at idle, and not more, it should work okay depending on the actual tube you have.

Russian EL84M (6P14P-EB) would easily handle that. A NOS EL84 would probably handle that easily too. Some modern production EL84 might let you down.

thank's again,^^^^

any thought's about the capacitor's, ??

You'll want new electrolytic caps. Old e-caps have a useable life of about 10 years before the electrolyte compound dries up/becomes useless. So get some new 450V, 16 to 20uF filter caps and some 25V, 22 to 25uF caps for the bypass caps.

how did you know the EL84 like's the 4900 ohm's, ?

The datasheet says so, I am guessing your voltage will be on the lower side of 300V. First page, pentode operation Ra = 5.2k or 4.5k.

http://www.r-type.org/pdfs/el84.pdf


Oops, just looked up and saw your transformer voltage, running into 8 ohm with a 10k impedance might be better. Mind you I would probably throw in some good power supply filtering, namely some added resistance, and knock down the voltage along with cutting the hum. Since it is a SE amp you can use all the help you can get.

You'll want new electrolytic caps. Old e-caps have a useable life of about 10 years before the electrolyte compound dries up/becomes useless. So get some new 450V, 16 to 20uF filter caps and some 25V, 22 to 25uF caps for the bypass caps.

thank's, i've ordered some,

A friend of mine just gave me one of those red 'portable' phonograms - looks identical to the red one you have in your photo. Nice old piece of kit on the outside, but when I opened it up it turns out it was a mains-tranformerless circuit with a UL84 power tube and a UY85 rectifier - pretty much useless for a geetar amp conversion, and his dog has chewed through the mains chord so its not worth saving. Just sayin' because I'm curious about what you have there.

the red one is a reel to reel tape recorder, cant remember the name of it, it's in the loft, with the rest of them, till i've sorted this project out, then i'll gut it and see what i can make of it,

This may sound pompous,but if people in general worked and cooperated like this, the world would be a different place to live in.

yes, it's nice to be nice,,

and if it was'nt for the nice people on here i'd be still just sat looking at a pile of tube's, resistor's etc and wondering where do i start,

The datasheet says so, I am guessing your voltage will be on the lower side of 300V. First page, pentode operation Ra = 5.2k or 4.5k.

http://www.r-type.org/pdfs/el84.pdf


Oops, just looked up and saw your transformer voltage, running into 8 ohm with a 10k impedance might be better. Mind you I would probably throw in some good power supply filtering, namely some added resistance, and knock down the voltage along with cutting the hum. Since it is a SE amp you can use all the help you can get.

think i'll have to print out some datasheet's, thank's,
so it's back to an 8 ohm speaker then,?

you've lost me with the "10k impeadance", and the "added resistance to knock the voltage down" where and what would i put in my circuit,?

The 'formula' for determining optimum load resistance (Zout) for centre-biased Class A operation for a single-ended output tube is:

Zout = Va/(Pa/Va)

where:

Va = the plate idle voltage
Pa = the maximum rated plate dissipation of the tube

Say you had the EL84 set up to idle at 300V. An EL84 is rated for 12W maximum plate dissipation.

So: 300V/(12W/300V) = 7,500R

Now if that OT is 9k, then running the EL84 at 330 plate volts (on the high side for an EL84) would be about right - and provided that you biased the EL84 to dissipate 12W at idle, and not more, it should work okay depending on the actual tube you have.

Russian EL84M (6P14P-EB) would easily handle that. A NOS EL84 would probably handle that easily too. Some modern production EL84 might let you down.

the OT measure's 1k ohm not 9k ohm,

the OT measure's 1k ohm not 9k ohm,


To determine what reflected load you'll get from an OT, you need to determine its primary:secondary impedance ratio. Impedance is a measure of resistance to AC, so you cannot measure impedance by measuring the winding's DC resistance.

Fortunately we know that the impedance ratio is the square of the VAC ratio, and we can measure the VAC ratio with 2 VAC meters and a smallish VAC supply hooked up to the OTs secondary winding. If you don't have a variac you can use the 6.3VAC heater winding on your PT as a VAC supply thus:

http://farm9.staticflickr.com/8032/8058227336_aa652eba56_b.jpg

You really should use 2 meters for this to simultaneously check the accuracy of the VAC ratio being supplied to the secondary and the resulting VAC measured across the primary winding.

Be sure not to let any of the winding ends touch each other or anything else that is not insulated for this test. And be careful measuring the VAC across the OT primary because it will be in the vicinity of a hundred or more VAC.

Once you have measured the Pri:Sec VAC ratio, then square the result to get the VAC ratio, i.e.: e.g.: say we applied 6.3VAC to the OT secondary winding measured 199VAC across the OT primary winding (end to end), that would be a Pri:Sec VAC ratio of 31.62:1. So that is 36.62:1 x 31.62:1 = 1000:1 pri:sec impedance ratio.

Lastly to get the reflected load we would see at the OT primary when we hook a speaker up to the OT secondary, you multiply the OT impedance ratio by the impedance of the speaker load you are attaching, thus say we have an 8R speaker, that would be 8R x 1000:1 = 8000R or 8k load resistance that is seen by the output stage with an 8 ohm speaker through our example OT. Got it?

Hope tubeswell's explanation clears things up. Personally I do not think you need two meters as we only really need a ballpark figure as the speaker's impedance varies and tubes are fairly tolerant.

To answer your question on the voltage, if you put a resistor in series with the rectifier and the first capacitor there will be a voltage drop across the resistor. This will bring down the DC voltage developed across the capacitor and also help smooth out the DC (less hum).

^^^^^^^^^^
thank you,

tubeswell, yes i've got it, thank's,
this tube stuff is a lot more involved than i thought, but i'm getting my head round it, a bit at a time,

To answer your question on the voltage, if you put a resistor in series with the rectifier and the first capacitor there will be a voltage drop across the resistor. This will bring down the DC voltage developed across the capacitor and also help smooth out the DC (less hum).

would that be the same as a sag-resistor,? 1k 25 watt,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/KGrHqJoE8VkiIpgBPIVJDQoJQ60_35.jpg

well at least i've the main's indicator light working, lol,
i'm just waiting for my tag board to arrive, then i can start doing a bit more,



http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0135.jpg

drew a lay-out drawing, the dotted line's are wire's going under the tag board,, hope it's right,, ??

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0138.jpg

started mounting the component's, the copper wire is for all the earth connection's, would there be any point in just putting 100vac on to it when i've finished it, to see if everything's ok, ?,
i did'nt have a 20uf capacitor, so i doubled up two 10uf one's, is that ok,?,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0140.jpg

drew a lay-out drawing, the dotted line's are wire's going under the tag board,, hope it's right,, ??

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0138.jpg

Your layout doesn't seem to match the schematic you posted earlier (unless you changed the design since you drew the schematic?)


http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0132.jpg[/QUOTE]

i know i forgot to draw in the earth connection on the 10uf cap, but where do you think i've gone wrong,??, i did'nt mean to change anything from the original schematic,

Why have you got 22k in series with the coupling cap after V2?

Why have you split the resistors in the screen supply node (1k and 2k2?)?

Why have you got 22k in series with the coupling cap after V2?



i read that it will stop unwanted radio signal's etc, or is'nt it needed, ?

Why have you split the resistors in the screen supply node (1k and 2k2?)?

my mistake, i think it should be like this, or not, ??

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/lod1.jpg

i read that it will stop unwanted radio signal's etc, or is'nt it needed, ?

The way you have the 22k laid out on the board, it won't function optimally as a grid stopper. As a grid stopper, a resistor like that only works if you have the resistor attached right at the grid socket pin. The idea of a grid stopper is to put a resistance between any potential antenna and the signal grid. If you have some more antenna (i.e.: a resistor lead or connecting wire) between the resistor and the grid, then it undermines the purpose.

Also the way you have the 22k laid out on the board, it is acting as a voltage divider with the (330k) EL84 grid load resistor. This attenuates the signal slightly (i.e. 330k/(22k+330k) or 94% of maximum, which doesn't really do much in the way of attenuation (if you want attenuation that is).

If you don't want attenuation, but still want a grid stopper, then put the 22k (or whatever grid stopper size you want*) between the 330k and the grid pin.

* bearing in mind that as grid stopper resistance increases, it interacts with the inter-electrode capacitance of the tube to roll-off HF.

my mistake, i think it should be like this, or not, ??

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/lod1.jpg

Better if its not. Ideally you want the screen supply node decoupled (with a filter cap). That way its drawn on the layout you'll most likely get unwanted voltage changes causing oscillation in the power supply rail as the screen current changes.

right, i've got it with the 22k resistor, solder it to the pin, i understand about it cutting the HF,

not really sure what you mean by" screen supply decoupled with a filter cap", do i need a cap in series with the 1k resistor to the EL84 ,?

Each power rail supply node (each point where you take DC supply from for plates, plate resistors, and screens) needs a filter cap between the junction of that node and the ground return. This is known variously as 'filtering' or 'decoupling', because you are isolating each node of the DC supply from each other node of the DC supply with the capacitor, which 'shunts' (to ground) any AC that may otherwise appear on the power rail at that point. You don't want AC in the power rail because it causes unwanted hum and/or oscillation.

i think i've got it, like this, ?

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/decouple.jpg

is this looking any better,?,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/layout.jpg

Looks good to me. You are an artist.

Not necessary, but I would split the grounds. Split the bus. Send the first two filter caps to the PT side grounds. Send the rest to ground at the input end of the chassis.

Otherwise, I can't find any issues. (Though this is yours and Master tubeswell's baby.)

i think i've got it, like this, ?

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/decouple.jpg

You only need a cap at each point where the power supply DC voltage is different (i.e.: at the junction of each supply/dropping resistor, as each supply resistor defines a further drop in DC voltage). So you'd have a (reservoir) cap at the rectifier cathode, then a decoupling cap at the next supply node (i.e. after the first resistor or choke in the B+ rail), and then another decoupling cap at the next node (after the next supply/dropping resistor) and so on. You can have extra filter caps in parallel on each supply node if you want, but that just increases the decoupling capacitance at each node.

Your above schematic shows five filter caps all basically in parallel at the same voltage (because there are no dropping resistors in between any of them)

Looks good to me. You are an artist.

Not necessary, but I would split the grounds. Split the bus. Send the first two filter caps to the PT side grounds. Send the rest to ground at the input end of the chassis.

Otherwise, I can't find any issues. (Though this is yours and Master tubeswell's baby.)

would like to take credit for the drawing, but i cant, it's not by me,

the bus is the ground, thought a common earth point is the best type to use,?

and feel free to comment on anything you like, this is afterall an open forum, thank's,

I just got one of these that works and has an input phono jack and the am/fm/phono knob. It is a 1951 Sparton.
http://i690.photobucket.com/albums/vv263/SSGVABEACH/Radioold.jpg
http://i690.photobucket.com/albums/vv263/SSGVABEACH/insideoldradio.jpg

look's good, might work as it is for a guitar amp, but dont take my word for it, i know very little about all this tube stuff, you could start your own thread about converting it, and get some good advice on what to do with it,

made a bit more progress, just waiting for a few more resistor's i ordered to arrive, it's starting to get a bit cold now in the garage, 4 degree's last night, but i'm still enjoying it,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/DSCF0150.jpg

Garage Hermit, you've come a long way in a short time, and I'm quite impressed at your rate of progress. A tip of the hat to you, mate! :smile:

That said, beware of too-long wires. Two long wires run side by side act as a small value capacitor. Tubes (valves!) are willing to work happily at quite high frequencies, and at those high frequencies even that small amount of capacitance can be enough to send the signal to places where it shouldn't go. As a result, an otherwise sane and happy tube amp can go bonkers and oscillate, squeal, howl, pretend it's a radio transmitter, and so on.

One other thing, which is a matter of personal choice: I find I make fewer wiring mistakes if I use multiple colours of wire, and have some sort of mental scheme as to where I use them. For instance, black for ground, red for positive DC voltage, yellow for signals, or something like that.

-Gnobuddy

thank's "gnobuddy" , yes the long wire's might cause problem's, but it's just a prototype, as long as it does'nt blow up and it amplifie's the guitar sound i'll be pleased, i think i'll mount all the component's to the valve holder's etc and do away with the tag board, a lot simpler, yes, i'll have to buy a few different coloured coil's of wire, as you mentioned, easier to keep track of what's going where,

decided to mod it a bit, it looked like a rat's nest, so i un-soldered everything, re-positioned the tag board inside the chassis and re-positioned the valve's/tube's,

http://i81.photobucket.com/albums/j236/w124-2door/radio%20amps/amp1_zps8dc23e45.jpg