$vboptions[bbtitle]

SE KT66 Amp Build

ejb222
February 28th, 2011, 02:22 PM
I'm finally going to take on my first amp build. It's going to be simple, so no worries, but has anyone ever built a Champ style amp with KT66 instead. I can find more complex SE KT66 schematics with tone stacks and parallel power tubes...but I'm looking for 1xKT66, 1x12AX7 with a volume control only.

Can I use the champ schematic as a baseline???

Any help willl be much appreciated.

big-daddy-59
February 28th, 2011, 03:15 PM
okay, here's what you do: start with a weber 5f1a kit to get the larger cabinet with a 10" speaker. make the following substitutions, 1-use the red secondary windings of the power transformer and substitute a 5AR4 for the rectifier tube. 2-change R11 on the weber 5f1 schematic to 27k ohms @2 watts to get the preamp voltages down to the correct territory for a tweed champ. 3-substitute R8 on the same schematic with a 270 ohm 10 watt part and the accompanying C6 capacitor to 25u 50volt. Use the WSE15 output transformer. Plug in a KT66 and enjoy.

Cliff Schecht
February 28th, 2011, 06:40 PM
That's a simple-minded method of doing this. What you are worried about with the KT66 is giving it enough voltage to put out a decent amount of power. You also have to consider that the screens will need to be dropped to 300V or whatever and so the dropping resistor after B1+ will be larger than your standard champ. You'll probably end up with a larger screen protecting resistor as well. Also you need to calculate the different bias and what your drive requirements are to get full power out (i.e. how much output the second stage has), as well as how much more voltage you need to overdrive stuff. There are many schematics out there using 6L6's in a Champ circuit and so you can easily reference those. Just do some Googling to get started and please ask questions if you get lost or confused!

big-daddy-59
February 28th, 2011, 09:04 PM
@ Cliff- first I recommend that he use the higher output of 2 secondary windings on the power transformer plus the use of a different rectifier with much less internal resistance than the stock 5y3 normally found in a champ. This gets the B+ up over 400v, enough to drive a 6L6GC or KT66. The 10k dropping resistor between the plate and screens is sufficient. And I have figured the value for the cathode bias resistor, which by the way is different than that for a 6L6GC. I've built a 5f2a using this setup and it's fine. Are you speaking from experience or just speculating?

ejb222
March 2nd, 2011, 03:17 AM
Thanks guys...I'm not going to buy the kit from weber...I have a cabinet ready to go and it calls for a 8" speaker at most. Looks like I've go my research ahead of me. But I guess I'll just keep plugging away. Thanks again.

big-daddy-59
March 2nd, 2011, 04:23 AM
Didn't know you already had a cabinet. One of the reasons I recommended the weber kit is because of the cabinet, it's well made and professional looking,something that someone with limited experience in woodworking would appreciate. That said, Weber does offer their kits without the cabinet, and even if you go with someone else's kit or source the parts yourself,you can still use the weber schematic to refer to the changes I suggested.

TubbyTone
March 2nd, 2011, 11:27 AM
I'm finally going to take on my first amp build. It's going to be simple, so no worries, but has anyone ever built a Champ style amp with KT66 instead. I can find more complex SE KT66 schematics with tone stacks and parallel power tubes...but I'm looking for 1xKT66, 1x12AX7 with a volume control only.

Can I use the champ schematic as a baseline???

Any help willl be much appreciated.

here's the lay out I used, I just pulled out the tone section. It works just fine and lots of volume. but, don't tell on me. also I used Hammond Transformers but, I'm just around the corner from Guelph, Ontario so tons of cheap Hammond iron around here. hope this helps you out, cheers

ejb222
March 2nd, 2011, 02:39 PM
here's the lay out I used, I just pulled out the tone section. It works just fine and lots of volume. but, don't tell on me. also I used Hammond Transformers but, I'm just around the corner from Guelph, Ontario so tons of cheap Hammond iron around here. hope this helps you out, cheers


Sweet! Thanks. I probably should have just stuck with the plain champ for my first time...but thanks for the schematic! Big help!

I was looking at a Hammond 270ex PT...I think that should do well...what did you use for choke and OT?

TubbyTone
March 4th, 2011, 01:14 PM
Cool, I used a 270 EX PT, a 125 ESE OT, & A 153 L choke CHEERS

ejb222
March 13th, 2011, 11:02 PM
Ok so this has evolved a bit after some research and considerations. This project has now become a SE 2x 6V6 in parallel with 6SL7 preamp.

My question is if the Hammond 270ex is still a good fit for this design? With both the preamp and output tubs at max 300v plate ratings i really only need about 220V RMS for this...so is this over kill? I'm was looking on the Hammond site and still like this PT, but is the 2nd fil wiring of 6.3v @ 4a good enough for the 6V6GT the needs 6.3v @ 4.5a? I know tubes are pretty forgiving except for heater elements:)

My other question..I am using Duncans Amp Tool to design my Power Supply how do I find a PT's "source resistacnce"?

Thanks for the help, yall
Cheers

celeste
March 14th, 2011, 06:32 PM
...... I'm was looking on the Hammond site and still like this PT, but is the 2nd fil wiring of 6.3v @ 4a good enough for the 6V6GT the needs 6.3v @ 4.5a? I know tubes are pretty forgiving except for heater elements:)

My other question..I am using Duncans Amp Tool to design my Power Supply how do I find a PT's "source resistacnce"?

Thanks for the help, yall
Cheers

6V6 heater is rated at .45a, not 4.5a, so the heater winding will be fine.

One finds source resistance by measuring the secondary HV winding with an ohmmeter and record the reading, measure the primary winding with the ohmmeter and multiply that by the voltage ratio of the primary:HV windings, then add that to the reading from the HV winding

laird
March 16th, 2011, 12:56 PM
The B+ voltages from the 270EX will be higher (probably around 375v straight out of a SS rectifier), but IMO that's a good thing. 144ma of current capability is great. This gives you some room to add another filtering stage, which makes for a huge improvement in hum on single-ended amps. Stick a 40uf cap and a 100-ohm 10W (just to be safe) resistor before your B+ reaches the OT, then follow with the typical cap / choke / cap /resistor / cap arrangement. B+ at the power tubes should be around 360v, perfect for 6V6GTs. Adjust the final power resistor as necessary (4.7K, 10k, 22k?) to get your preamp B+ down under 300V.

A 6SL7 pre into parallel SE 6V6GTs is gonna be sick!

-Laird

ejb222
March 16th, 2011, 05:10 PM
Thanks...I hope it sounds sick...time will tell.

Im a first timer so Ive been researching enough to make my eyes bleed. Still working out small details that are harder to find...

i.e. The 6SL7s heater is 6.3V @ .3 ... Will the 270ex 6.3V @ .4a need to be adjusted accordingly? The 6V6 requires 6.3V @ .45a which a poster above said was ok...

I noticed that alot of amps run higher voltages into these tubes than the spec sheets suggest...is there a absolute tolerance? I hope not by trial and error!!!!

And has anyone used Edcor GSXE series OTs? I think the 3.5k ohm 15 watt OT is what I might pickup...reviews?????

celeste
March 16th, 2011, 06:38 PM
.....
I noticed that alot of amps run higher voltages into these tubes than the spec sheets suggest...is there a absolute tolerance? I hope not by trial and error!!!!

And has anyone used Edcor GSXE series OTs? I think the 3.5k ohm 15 watt OT is what I might pickup...reviews?????

The anode voltage rating is not B+, but Vak, the voltage between the anode and cathode, so the actual voltage is lower then you think. Also, the spec's were made to ensure long life, generally that is not much of a consideration, so as long as you do not get arcing at max signal, you are ok.

Edcor GSXE OT's are very nice, and a huge bang for the buck. They are all made to order, so expect a few weeks for delivery.

ejb222
March 17th, 2011, 03:24 AM
So I've been trying to figure out the Duncan PSUD2 program.
Here is a screen capture of what I've got so far. Please let me know if I"m way off.
This is planned with Hammond 270EX 275-0-275 secondary 144mA. I tried my best to figure out the source impedance...not sure if I"m close.

But anyway I need 360V for parallel 6V6 plates and 300V for 6SL7....so am I to be looking at the RMS column at V(C1) etc?

There are no real instructions for this and I am a noob...so please have mercy...but I need your input and instruction.

Thanks!

Cliff Schecht
March 17th, 2011, 04:17 AM
Instead of the 5k load resistor, I like to use the built in current sink. You can change this by right clicking and changing the type to a current sink. Then you just add up the total quiescent (no signal) as well as the full power current draw (it's alright to estimate these numbers!) and setup the current sink to have a stepped response. Setup the sim times so that at the quiescent state the output voltage has enough time to settle to it's final value before you step up the current. This will show you how much voltage you can expect to drop at full load. You can get even more accurate by adding a current sink after the rectifier (acts like the KT66 plate), after the first dropper (KT66 screens) and after the last dropping resistor (all preamp stages) and stepping the current in each of these at the same time so that you can see the voltage drop at each stage at the quiescent current and max current draw. Let me know if any of this needs to be clarified.

ejb222
March 17th, 2011, 09:59 AM
Instead of the 5k load resistor, I like to use the built in current sink. You can change this by right clicking and changing the type to a current sink. Then you just add up the total quiescent (no signal) as well as the full power current draw (it's alright to estimate these numbers!) and setup the current sink to have a stepped response. Setup the sim times so that at the quiescent state the output voltage has enough time to settle to it's final value before you step up the current. This will show you how much voltage you can expect to drop at full load. You can get even more accurate by adding a current sink after the rectifier (acts like the KT66 plate), after the first dropper (KT66 screens) and after the last dropping resistor (all preamp stages) and stepping the current in each of these at the same time so that you can see the voltage drop at each stage at the quiescent current and max current draw. Let me know if any of this needs to be clarified.

Actually, I was hoping at least to learn how to read the results before I did anymore with this program. That way I know what I'm doing :razz: I'll try what you spoke of and see what I come up with. I've also read on some sites that it is best to start with a 10uf cap for a cleaner filter(but that may follow a choke)...but I've noticed that the way I have it set up above, it looks cleaner at with a 47uf or 100uf cap to start. This is why i second guess my effort....I was hoping someone would tear it apart so I would learn something :grin:

tubeswell
March 17th, 2011, 12:51 PM
For 2 x 6V6 in SE parallel, your choke in a whole-of-supply CLC filter should be rated at 120mA minimum to ensure reliability (altho' 100mA may work, but don't blame me if it doesn't). Your OT reflected load should be around 3k5 to 4k. FWIW

ejb222
March 17th, 2011, 02:32 PM
For 2 x 6V6 in SE parallel, your choke in a whole-of-supply CLC filter should be rated at 120mA minimum to ensure reliability (altho' 100mA may work, but don't blame me if it doesn't). Your OT reflected load should be around 3k5 to 4k. FWIW

Yeah I calculated the impedance to be about 3700ohms I think I'm going to pickup the Edcor GXSE15-8-3.5k should work nice with a 12"weber alnicoS...but I was playing through a Reverberocket II last night with a new Celestion that sounded like a million bucks!

Anyway, I should have full schematic up later for all to tear apart. Working on some final details :)

tubeswell
March 17th, 2011, 02:50 PM
If you get a 8k PR Z OT with a couple of taps (say 16R and 8R) on the secondary winding, you can use your (say 8R) speaker in either tap depending on whether you want to run 1 or 2 x 6V6s. (You would also set up the 6V6s with something like a 470R cathode resistor and a 2nd switchable 470R in parallel with that to get the 'right' amount of bias). What's more (if your PT is rated for 2 6V6s) you could also run 1 x 6L6 instead. (But if you were thinking to run 1 x KT88 in SE with a choke in a CLC supply filter, you would want the choke DC current rating to be about 200mA)

laird
March 17th, 2011, 04:24 PM
The 6SL7s heater is 6.3V @ .3 ... Will the 270ex 6.3V @ .4a need to be adjusted accordingly? The 6V6 requires 6.3V @ .45a which a poster above said was ok...

Your heater current will be...
6SL7: 0.3A
6V6: 0.45A
6V6: 0.45A
Total: 1.2A

The 270EX can do 4A on the 6.3V tap, so there's no worry about stressing the PT that way, even with different tubes. With 144ma available on the HT you could even swap in 6L6s or EL34s if you want to get crazy. :twisted:


I noticed that alot of amps run higher voltages into these tubes than the spec sheets suggest...is there a absolute tolerance? I hope not by trial and error!!!!

Heheh, well it depends largely on the tubes. A lot of old USA tubes can tolerate running into the 420-430v range pretty consistently, but most new-production tubes will die quickly under the stress. One exception is JJ's 6V6S, but it's kind of a weird tube - sort of a hybrid between a 6V6 and a 6L6. Anyways, any 6V6 (even cheap new ones) should run fine at 360-375v for a long time.


And has anyone used Edcor GSXE series OTs? I think the 3.5k ohm 15 watt OT is what I might pickup...reviews?????
Excellent transformers! They'd be a bargain at twice the price, really. I have two GXSEs in a hifi amp and a GXPP in an EL34 amp and they sound fantastic. They have a lot more iron in their core than many equivalently rated OTs and can handle lots of power.

Edcor's power transformers are very good too. Their XPWR009-120 is equivalent to the 270EX but with 175ma on the HT. Cheaper than the 270EX to boot.

-Laird

ejb222
March 19th, 2011, 03:06 PM
So here is schematic Version 1.0. I know that V2 is not correct...but the program I used didn't have 6SL7 tubes...so I used 12AX7...pardon the terminal numbers etc

Please let me know what you think. I'm still in the process of messing around with my PSU design...so that's to come.

So please feel free to tear it apart....the more I learn the better.

Thanks, your guys have been a big help.

celeste
March 19th, 2011, 07:29 PM
The grid stoppers on the 6V6's might be to small. If you can generate enough signal to overdrive them, you risk blocking distortion, I usually start at 5.6K and go up from there.

tubeswell
March 20th, 2011, 04:50 AM
You may want to play around with different tone stack designs - that one in the schematic could be a bit lossy with all those resistances in parallel. Whereas the 'early tweed Princetons (5b2 and 5c2) with octal pre-amp tubes just used the typical Princeton tone stack that they kept in the later amps.

ejb222
March 22nd, 2011, 05:07 PM
The other thing I think I made a mistake is that I should be running 360V to the OT to feed the 6V6 plates and running the 6V6 screens at 285V(?) or can I run these higher too? can anyone confirm or correct me if I'm wrong?

learning curve :)

edit: did a a little digging and someone helped answer my question...I can run the screen voltage pretty close to the plate voltage. which helped me realize that my OT actually looks to be in the 5500ohm range with 360V plate voltage.

EW57
March 29th, 2011, 07:40 PM
similar to this?
http://angela.com/angelasupersingle-ended6v6guitarampproject.aspx

bwacke
April 2nd, 2011, 05:26 PM
ejb222,

'Didn't see anyone comment on these two things:

1) R1 is going to give you trouble as drawn. It does nothing if the J1 is grounded to the chassis. It (R1) needs to be moved past the junction of R2 and R3 so it acts as a grid leak bias resistor for the tube and covers both inputs.

2) The Angela schematic shows a single, common 250 ohm cathode resistor for BOTH 6V6's. You show 240K resistor for EACH tube. Assuming you mean 240 Ohm, It would be preferable to tie the cathodes together and use a 10 watter in the 250 Ohm range. Otherwise, you may get some screwy signal problems between cathodes on the tubes as the parts age.

Just a thought...

Bob

tubeswell
April 2nd, 2011, 06:10 PM
ejb222,...

2) The Angela schematic shows a single, common 250 ohm cathode resistor for BOTH 6V6's. You show 240K resistor for EACH tube. Assuming you mean 240 Ohm, It would be preferable to tie the cathodes together and use a 10 watter in the 250 Ohm range. Otherwise, you may get some screwy signal problems between cathodes on the tubes as the parts age.

Another way would be to tie the 6V6 cathodes together and have 2 x 470R 5W cathode resistors in parallel, but with a SPST on one of them, so that you can either run one 6V6 or 1 6L6/KT66 or 2 x 6V6s. I did this with a parallel SE amp recently.

http://music-electronics-forum.com/attachments/12712d1297150735-super-se-ac4-v4-.pdf

ejb222
April 7th, 2011, 02:19 AM
similar to this?
http://angela.com/angelasupersingle-ended6v6guitarampproject.aspx

I guess no idea is original anymore...I figured there were similar amps already made. I just wanted something a little different than a 12AX7-el84 amp.

ejb222
April 7th, 2011, 02:32 AM
Thought I'd post some pics of the tubes I've acquired for this project.

ejb222
April 7th, 2011, 02:36 AM
any help?

ejb222
April 7th, 2011, 02:56 AM
ejb222,

'Didn't see anyone comment on these two things:

1) R1 is going to give you trouble as drawn. It does nothing if the J1 is grounded to the chassis. It (R1) needs to be moved past the junction of R2 and R3 so it acts as a grid leak bias resistor for the tube and covers both inputs.

2) The Angela schematic shows a single, common 250 ohm cathode resistor for BOTH 6V6's. You show 240K resistor for EACH tube. Assuming you mean 240 Ohm, It would be preferable to tie the cathodes together and use a 10 watter in the 250 Ohm range. Otherwise, you may get some screwy signal problems between cathodes on the tubes as the parts age.

Just a thought...

Bob

Thanks for the heads up...here is the revision...any other thoughts?

laird
April 7th, 2011, 04:02 PM
Thanks for the heads up...here is the revision...any other thoughts?

What you've got there is awful close to the 6G10 Harvard (tube swap aside). The operating points should be good for the 6SL7 triodes. With 25uf bypass caps on both gain stages and a tweed tone control, I'd expect it to be very boomy, bass-heavy. I'd probably start somewhere around 1-5uf on the bypass caps to tame the bass. The octal preamp will be thick enough on its own. :grin:

With R18 at 22K you're looking at a pretty high negative feedback ratio of 1:8.33... It may sound a bit lifeless. If it does, try less negative feedback, maybe a 39K if you want it cleaner or 47K if you want some more grit.

-Laird

ejb222
April 7th, 2011, 04:18 PM
What you've got there is awful close to the 6G10 Harvard (tube swap aside). The operating points should be good for the 6SL7 triodes. With 25uf bypass caps on both gain stages and a tweed tone control, I'd expect it to be very boomy, bass-heavy. I'd probably start somewhere around 1-5uf on the bypass caps to tame the bass. The octal preamp will be thick enough on its own. :grin:

With R18 at 22K you're looking at a pretty high negative feedback ratio of 1:8.33... It may sound a bit lifeless. If it does, try less negative feedback, maybe a 39K if you want it cleaner or 47K if you want some more grit.

-Laird

Thanks for the suggestions...some of these resistors and bypass caps I'm planning on tweeking during the build...hoping to learn how the different values change the sound for the first time in real life...:grin:

Biggest concern for me is making sure I build the Power Supply correctly.:roll:

laird
April 7th, 2011, 06:13 PM
Oops, didn't look at the power supply design! The XPWR009-120's high-voltage secondary has a center-tap, so you don't need a bridge rectifier, just a simple full-wave built from 2 diodes. According to the diagram online, the 6.3V doesn't have a center tap, but don't be surprised if it comes with one.

Try something like the design attached, give or take any value adjustments you may want. For parallel SE I might go 100uf on the first cap with a 2.5-5 henry choke... or put another 40uf cap and 100-ohm 10W resistor before B+1 for some extreme filtration. It'll drop the B+ a few more volts (maybe 10?).

-Laird

Cliff Schecht
April 7th, 2011, 07:47 PM
any help?

Where are you confused? All you are looking at is voltage over time. If you want to get more accurate add up all of the plate currents and put in a constant current sink that has a stepped value. The initial value is what the amp will draw at idle, the stepped value is what the amp will draw at full power. We can help you quickly figure out some numbers to see how much you will sag under full load conditions, amongst other things this program can display. Because you are using solid state diodes the transformer winding resistance isn't very important here, it's only important for tube rectifiers which have a minimum resistance per winding that you must meet to prevent arcing the tube rectifier.

ejb222
April 8th, 2011, 09:41 PM
Where are you confused? All you are looking at is voltage over time. If you want to get more accurate add up all of the plate currents and put in a constant current sink that has a stepped value. The initial value is what the amp will draw at idle, the stepped value is what the amp will draw at full power. We can help you quickly figure out some numbers to see how much you will sag under full load conditions, amongst other things this program can display. Because you are using solid state diodes the transformer winding resistance isn't very important here, it's only important for tube rectifiers which have a minimum resistance per winding that you must meet to prevent arcing the tube rectifier.

Im sorry if I seem a little slow...but I'm just want to make sure I don't make any major mistakes. I was using a resistive load on the PSUD to get the correct currant from the PT...I calculated 275V/175ma= 15.7kohm. So I assumed the load resistor should be 15.7k and then adjust my RC filter stages to achieve the correct B+ voltages. Not exactly sure how to use the constant currant.

laird
April 11th, 2011, 05:39 PM
PSU Designer is a great tool, but it does have a bit of a learning curve.
Let's start at the PT specs... if you edit the transformer properties and click the "..." button next to RMS V, you'll get the option to enter the PT's secondary ratings (275v, .175a)... stick with the 5% regulation figure. PSUD will calculate the off-load voltage and source impedance for you. For the XPWR009-120, it'll come out to 288.75V and 78.57 ohms.

Next comes your first filter cap. Choose whatever you want, but change the resistance to .01 ohms - 2 is way too high. Then build out your LC/RC filters however you want the power supply designed. Once that's done, it's time to start adding current taps.

Pick the point where the output transformer connects to B+ (usually at the first filter cap). right-click on the RC filter to the RIGHT of it and insert a current tap. Set the current to your intended idle plate dissipation. Let's say 70ma for the plates of the two 6V6s. Repeat this step for every node where you're taking B+ current, estimating the current draw for each step. Screen current, phase inverter, preamp, etc.

ejb222
April 12th, 2011, 07:31 PM
PSU Designer is a great tool, but it does have a bit of a learning curve.
Let's start at the PT specs... if you edit the transformer properties and click the "..." button next to RMS V, you'll get the option to enter the PT's secondary ratings (275v, .175a)... stick with the 5% regulation figure. PSUD will calculate the off-load voltage and source impedance for you. For the XPWR009-120, it'll come out to 288.75V and 78.57 ohms.

Next comes your first filter cap. Choose whatever you want, but change the resistance to .01 ohms - 2 is way too high. Then build out your LC/RC filters however you want the power supply designed. Once that's done, it's time to start adding current taps.

Pick the point where the output transformer connects to B+ (usually at the first filter cap). right-click on the RC filter to the RIGHT of it and insert a current tap. Set the current to your intended idle plate dissipation. Let's say 70ma for the plates of the two 6V6s. Repeat this step for every node where you're taking B+ current, estimating the current draw for each step. Screen current, phase inverter, preamp, etc.

Awesome! I basically came up with what you had...earlier. I used 100u cap for C1 to keep it clean and 20u for the other 2. I'm basically right at where I need to be 370v, 352, 300. With 70ma, 12ma, 5ma currant taps. Fullwave rectifier....big help!

Just to be clear, the currant taps in PSUD used like this are simulating the B+ currant drawn by each component... Tube plates and screens etc.

ejb222
April 12th, 2011, 11:10 PM
Thought Id post the print screen just in case i did mess it up :)

Plus my Ted Weber Speaker came today...I'm pumped. 12" Signature ceramic 25w

laird
April 13th, 2011, 02:29 PM
Awesome! I basically came up with what you had...earlier. I used 100u cap for C1 to keep it clean and 20u for the other 2. I'm basically right at where I need to be 370v, 352, 300. With 70ma, 12ma, 5ma currant taps. Fullwave rectifier....big help!

Just to be clear, the currant taps in PSUD used like this are simulating the B+ currant drawn by each component... Tube plates and screens etc.

Yep, you got it!

Wanna see something really cool? Add an RC filter before the first current tap, with a 150 ohm resistor and a 100uf cap - the AC ripple at the OT drops from 5.3v to 0.4v... on a push-pull amp, this ripple isn't too important, but on a single-ended amp this makes a huge improvement on the amp's noise floor.

-Laird

ejb222
April 13th, 2011, 04:27 PM
That's cool. I may try to mess around with that. I have an extra 47uf cap I could use instead of 2x 100uf...wonder how much it will reduce ripple.

ejb222
April 19th, 2011, 10:25 AM
Cut and drilled the eyelet board. Dry mounted some components to check for size and fit. That and I'm getting anxious to put this together. The PT and OT should arrive this week. Once that happens the chassis will be drilled and the real work begins to put this all together.

Grounding: Star Grounding VS Buss Wire Grounding anyone's $.02 or experiences? I dig the grounding instructions on Hoffmans site.

EDIT: Orange Drops VS Mallory caps?
removed duplicate photo

laird
April 20th, 2011, 02:36 PM
BAH! Ground wherever.

just kidding :)

100% star grounding is ideal, though in many cases it's not practical. I usually group my grounds into clusters based on their position in the signal chain (one for input jacks and first stage, one for 2nd-stage and tone stack, one for PI and NFB, etc) and then star-ground those clusters. If I have to do a bus, the bus is star-grounded with the power tubes, filter caps and PT. Just try to avoid creating ground loops.

Orange drops come in three flavors: 715P, 716P, and 225P. The first two are polypropylene film and are known for having a sharper, possibly harsher sound to them. Most places that sell "Orange drops" are selling you 715Ps. The 716Ps have a higher spec for pulse currents and some people say they sound more "airy".

The 225P is a mylar/polyester film cap, like the Mallory 150s. These tend to sound slightly warmer or rounder.

Depending on your sonic preference you may want to use one type more than the other. I find myself preferring the 225Ps or Mallory 150s for coupling caps, but I lean toward a thick vintage sound. For a more modern type amp like a JCM2000, or possibly even a Vox, the 715P or 716P may be a better fit.

-Laird

ejb222
April 20th, 2011, 03:53 PM
Yeah think im gonna go with the Mallorys.

Do you usually raise the 10w resistors off the board? I imagine it could get a bit warm.

ejb222
April 25th, 2011, 10:15 AM
Made a little more progress this weekend. The PT and OT came in and so I drilled the chassis and checked for fit. I did make my first mistake so far...well first that I know of :) the far right input jack hole was drilled to large so a couple washers are holding it in place for now...may figure out a more secure option later.

But its a start and I'm a rookie :)

ejb222
May 1st, 2011, 01:52 AM
Please help...first power up is not going well. I checked to make sure Ive got mains power correct. HV secondary reads correct 275v not soldered to my board. And the filament supply checks to be good and lamp stays on. But when everything is hooked up, I blow a fuse in 3 seconds. Any help would be appreciated. Meanwhile...time to test everything again :)

Keyser Soze
May 1st, 2011, 10:08 AM
Please help...first power up is not going well. I checked to make sure Ive got mains power correct. HV secondary reads correct 275v not soldered to my board. And the filament supply checks to be good and lamp stays on. But when everything is hooked up, I blow a fuse in 3 seconds. Any help would be appreciated. Meanwhile...time to test everything again :)

Most likely culprit is something that shouldn't be going to ground is going to ground.

Take a break for a day then go back and re-check all of your wiring. I like to use a layout diagram and mark out every connection with a highlighter as I visually inspect it. Don't forget to check the underside of the board for flying leads and loose bits. Also remember that any metal board mounting screws/standoffs are in continuity with ground.

ejb222
May 1st, 2011, 11:25 PM
Fixed the fuse issue. The OT bolts were too long and must have been contacting the underside if the eyelet board. Amp turns on now and stays on. Played for a little bit through my new Weber Sig 12" ceramic. It seems to distort early and I get squealing when I turn the tone pot up to around 1/2 way. Also if I tap the chassis I can hear it through the speaker. I switched out the preamp tube and still had the same issue for both the high and low jack. Didn't get to switch out the power tubes yet. It got late an I'm tired. but so far not too shabby :)

emu!
May 3rd, 2011, 11:08 AM
Bad self-grounding input jacks can cause squealing. Insert a dummy guitar cable into the open jack(s) and see if the squeal stops.

laird
May 4th, 2011, 03:44 PM
In case all the tubes turn out fine... Sometimes a component other than a tube can be mechanically microphonic. Usually it's something early in the signal path like the (hopefully shielded) input wire or caps/resistors connected to V1.

Also make sure your input signal never comes within close proximity of the output transformer or any of its leads. The high-impedance input acts as an inductor (particularly on high frequencies), causing a feedback loop across the circuit that varies with the tone knobs. Not like I've ever done that myself or anything. :)

-Laird

ejb222
May 4th, 2011, 07:00 PM
Thanks Laird...
I have a pretty good sound so far...but it definitely squeals as the amp is turned up and the tone is turned up. I checked voltages and I read 360VDC at C1, 350vdc at C2, 345vdc at C3, and, 325vdc at C4. But I have C2 running to the OT then to pin 3 of the 6v6s...voltage at pin 3 on each 6v6 is 330vdc and voltage at pin 4 on each is coming from C3 and measures 345vdc at the pins. My hunch is this is not good.?????

And another newbie question should I hear any noise from the speaker while checking voltages even if both pots are turned down?

ejb222
May 5th, 2011, 10:20 AM
Some pics

Keyser Soze
May 5th, 2011, 12:02 PM
...

And another newbie question should I hear any noise from the speaker while checking voltages even if both pots are turned down?

You might hear something if the power tubes are present and you are contacting their grids (since you might be introducing a very weak signal.)

But otherwise no, you really shouldn't be hearing anything. Re-check your output transformer secondary connections.

Also, try disconnecting the negative feedback and see if that changes anything.

printer2
May 5th, 2011, 08:13 PM
Bad self-grounding input jacks can cause squealing. Insert a dummy guitar cable into the open jack(s) and see if the squeal stops.

Any idea why? I have an amp that works fine now until I unplug the guitar cable and it breaks into oscillation. Plug the guitar in again and it is fine.

printer2
May 5th, 2011, 08:17 PM
You might hear something if the power tubes are present and you are contacting their grids (since you might be introducing a very weak signal.)

But otherwise no, you really shouldn't be hearing anything. Re-check your output transformer secondary connections.

Also, try disconnecting the negative feedback and see if that changes anything.

You will hear a small tick or pop. Depending on how much noise is picked up from your leads you may introduce a little on the grids. In both cases it should not be very loud.

printer2
May 5th, 2011, 08:29 PM
Thanks Laird...
I have a pretty good sound so far...but it definitely squeals as the amp is turned up and the tone is turned up. I checked voltages and I read 360VDC at C1, 350vdc at C2, 345vdc at C3, and, 325vdc at C4. But I have C2 running to the OT then to pin 3 of the 6v6s...voltage at pin 3 on each 6v6 is 330vdc and voltage at pin 4 on each is coming from C3 and measures 345vdc at the pins. My hunch is this is not good.?????

And another newbie question should I hear any noise from the speaker while checking voltages even if both pots are turned down?

Had my amp break into oscillation-distortion-squealing when both the volume and the tone pots are at maximum. A fine fellow at AX84.com suggested I drop my supply voltage on my preamp tube. Dropped it down from 245V to 150V and my squealing is now gone. I used a compactron as my tube (two pentodes in one tube, 12T10), so my problem may not be the same as yours but it is worth a look.

laird
May 6th, 2011, 04:11 PM
I checked voltages and I read 360VDC at C1, 350vdc at C2, 345vdc at C3, and, 325vdc at C4. But I have C2 running to the OT then to pin 3 of the 6v6s...voltage at pin 3 on each 6v6 is 330vdc and voltage at pin 4 on each is coming from C3 and measures 345vdc at the pins. My hunch is this is not good.?????

The voltage at pin 3 doesn't surprise me too much - Most Champs see about 10v dropped across their OTs with one 6V6; having two in parallel would presumably cause around a 20v drop. I am surprised by the small voltage drop at the screen. Try increasing that resistor between C2 and C3 to 2.2k or maybe even 4.7k, as long as it's enough to put the screen a few volts under the plate. The preamp feed could benefit from shedding those volts as well.

Another option would be to run separate screen grid resistors to each tube (1K I'd guess?) from C3; this would give the two tubes a little independence from each other, which may slightly thicken the tone or round off some of the edginess when overdriven.

-Laird

ejb222
June 13th, 2011, 02:02 PM
Ok...so I'm one problem away from finishing this thing. I still have squeal but I've pretty much isolated it. The input jack hovers over the signal wire that comes out of the second preamp stage cap and connects to the 1.5K grid resistors on the 6V6s. If I set the volume and tone to just about "squeal" level and hover a wooden dowel between the jack and the line...squealing occurs. I may move the jack, but would prefer not to...and as far as shielding the signal wire...it's on the underside of my board and that would be a pain to remove...

any suggestions?

I've adjusted some of the cathode bypass caps and i get some killer tones with the Tele plugged in. Can't really get it too far above 5 yet...but sounds awesome. This amp especially loves the neck/bridge tone.

MikeMurray
June 13th, 2011, 02:15 PM
I really think it's worth shielding it man :) Reduces noise, and it completely checks that off the troubleshooting list.

laird
June 13th, 2011, 05:07 PM
Yeah, shield the signal wire or (and?) relocate the run. Any sort of signal from later in the amp (including the OT wires out to the speaker) can cause feedback if it runs too close to the input.

-Laird