First build question

[mraymond77]

EDIT: this question answered, but there's more questions below

I'm sure you guys don't get sick of these questions huh? but I suppose they can help others looking for similar help. I tried to search for it but I didn't even know which keywords to use.

I'm just confused about the schematic/layout for the princeton reverb. I'm coming up on the last stretch of wiring the board to the sockets/pots/power. Up until now I've ignored it, but now I gotta know. In some areas of the amp, it shows a wire leading off and then terminates in a box that has a letter in it like D, B, or X etc. I cannot for the life of me figure what the hell those boxes are supposed to represent.

[ThermionicScott]

Those letters in boxes represent power supply nodes. They just did that to eliminate some of the crossed lines on the schematic. (B is the cap-can terminal with the square, D is the terminal with no symbol next to it.)

Hope this helps,
- Scott

[telex76]

Scott S is right of course, but if you didn't understand, 2 points with the same letter should be wired together on the back of the board.

[JohnnyCrash]

If you look at the layout, you'll see a corresponding letter. This means that "D" in one location on the board needs a wire/jumper to attach to the other "D" on the board.

[muchxs]

Connect the dots.

[mraymond77]

I see. I guess the weber layout confused me because some letters that dont have partners such as Y. but on the fender diagram there are partners. well, I checked and I do have all those wired up correctly, so another question for ya. Must I put a grounding wire across the top of my board (the one that looks like a handrail)? I wanted to just ground all those points by wiring it to the bare ground wire I soldered across the backs of all my pots. but that may cause noise I'm guessing?

[mraymond77]

well I turned it on for the first time. fortunately sound come through the speaker, but not much of it. even cranked to 10 it wasn't that loud and had a nasty distortion. what could cause low volume? also how many mA should I bias a princeton reverb to?

[mraymond77]

I think we all love pictures, so heres some pictures.
http://www.flickr.com/photos/49163479@N05/?saved=1
Looking at these pictures, I think I didn't ground my speaker jacks and rca jacks properly. I didn't string them up and wire it to my ground point. Could that be a cause for Noise, low volume, and lack of tremolo? I sure hope so. I'm a bit concerned about my bias circuit. I just fashioned it out of some spare board I had and screws. I didnt have eyelets at my disposal, so it's really just wires twisted together. I figure it should still work, but I wonder if its a problem.

[ThermionicScott]

First off, I think you should pat yourself on the back. We're not always lucky enough to get sound at our first powerup!

What are you getting for your bias voltage? Overbiased tubes will have a pretty ugly distortion even at low volume levels. While you're in there, what are you getting for the other power supply voltages?

One thing I would do is find a way to wire 1-ohm resistors from each 6V6 cathode to ground (instead of connecting each cathode directly to ground.) When you measure the voltage across that, it will also tell you how much current is flowing through each tube. Multiply that by the plate voltage, and you'll get each tube's plate dissipation (well, plate and screen, but close enough). Most of us would like to see that number under about 10 watts.

- Scott

[muchxs]

Originally Posted by mraymond77

I see. I guess the weber layout confused me because some letters that dont have partners such as Y. but on the fender diagram there are partners. well, I checked and I do have all those wired up correctly,

Amp building 102: Don't always trust the layout or the schematic. For example the Fender 5F1 layout has been around for 50-some years and there's still a wire missing. There are countless entities inhabiting Cyberspace who build virtual amps, they're pretty pictures of amps that should work in theory... if said entities weren't weak on theory!

Originally Posted by mraymond77

so another question for ya. Must I put a grounding wire across the top of my board (the one that looks like a handrail)? I wanted to just ground all those points by wiring it to the bare ground wire I soldered across the backs of all my pots. but that may cause noise I'm guessing?

One ground buss should be adequate. Multiple ground busses can act like old fashioned "rabbit ears" antennas and pick up interferance.

Make sure you ground buss is really grounded. Solder a wire to one end of it, solder a ring terminal to the other end of the wire. Scuff off a spot on the chassiis and tie your ring terminal down to it with an 8-32 or 10-32 machine screw with toothed washers. Double nut it so it can't get loose.

...which I see you attempted to do. The ground point is over by the cap can, right? Soldered or bolted? Soldered doesn 't work well on aluminum unless you put a lot of heat to it. Use a soldering gun on the high range. If you used the same pencil type iron as you used to assemble your board that might not have been enough heat.

...you also might want to isolate your preamp ground from your power supply ground. Your filter caps are going "burp, burp, burp" (only faster! ) and dumping ripple into the ground. Your power supply ground point may have noise on it you don't want on your preamp ground.

There are two philosophies, one is to star ground everything. That means pick a ground point, it's the only ground point in the amp and all grounds go to that via long wires. You can go semi-star ground or buss ground using two ground points, one for the preamp and the other for the power amp/power supply.

In theory ground is ground and it's all supposed to be the same ground. One side of the chassis is supposed to be exactly the same as the other so in theory you could drop a ground anywhere. Look at any '60s or '70s Fender, there are grounds everywhere. You frequently won't see a lot of ground points in something more sophisticated.

A solid ground eliminates a lot of noise. A poor ground is the opposite, your amp will be noisy.

[muchxs]

Originally Posted by mraymond77

I'm a bit concerned about my bias circuit. I just fashioned it out of some spare board I had and screws. I didnt have eyelets at my disposal, so it's really just wires twisted together. I figure it should still work, but I wonder if its a problem.

Ghetto bias circuit:

If those connections aren't soldered they should be. Cadmium plated machine screws aren't the best conductor and they take a lot of heat if you attempt to solder to them. Good hardwares stores still sell copper tacks or better yet, forked brass rivets. Fastenal gan get you forked brass rivets. You could of course ping Turretboards.com

http://www.turretboards.com/

and get the real thing, eyelets, turrets. staking tools or fully assembled solder ready turretboards. But... if you're into Steam Punk improvised circuits built right now from locally available material brass tacks will do.

[mraymond77]

Originally Posted by Scott S

First off, I think you should pat yourself on the back. We're not always lucky enough to get sound at our first powerup!

I'm glad it at least made sound, haha.

Originally Posted by Scott S

What are you getting for your bias voltage? Overbiased tubes will have a pretty ugly distortion even at low volume levels. While you're in there, what are you getting for the other power supply voltages?
- Scott

I checked my bias with a the eurotube bias probe cheap version, I got the 6v6s to be at 19.5mA each, which should be ok I guess. should I do the other method you mentioned to get the plate dissipation?

sorry about my lack of knowledge here, To get some other power voltage readings what pins should I probe? this is the cheap multimeter I have. http://www.smcelectronics.com/PICTURES/DVM1-L.JPG
which setting should I use? sorry, so many questions!!

Originally Posted by muchxs

...which I see you attempted to do. The ground point is over by the cap can, right? Soldered or bolted? Soldered doesn 't work well on aluminum unless you put a lot of heat to it. Use a soldering gun on the high range. If you used the same pencil type iron as you used to assemble your board that might not have been enough heat.

Yeah that one's bolted. I bolted the ground wire from the power cord the the chassis with a loop of the wire poking up and I grounded everything by twisting and soldering it to that wire. I don't know if that was a good idea or not.

Originally Posted by muchxs

Ghetto bias circuit:

If those connections aren't soldered they should be. Cadmium plated machine screws aren't the best conductor and they take a lot of heat if you attempt to solder to them.

Yeah the wires that are twisted up are soldered. I found out the hard way that those screws won't take solder very well, so they act more like points to be twisted around. I guess it works, so I'm not too worried about it anymore.

I guess my biggest problems are the low volume, and tremolo.
when I turn the tremolo speed up, it starts out with a fast "b,b,b,b,b" sound and as I turn it up higher the "b,b,b,b" gets even faster. when I turn up tremolo intensity, I just get a deep bass-y sound that gets a bit louder as I turn it up. neither seem to effect my guitar signal

Reverb works great, and so do bass and treble knobs.

[mraymond77]

Alright I went in and measured some voltages. on the power transformer, I got 387 on the yellow wires, and 327 on the red wires.
On my cap can, I get 382 for the square, 374 for the D, 290 for the Circle, and 227 on the last one.
each respectively %10 less than stated on the schematic. I went through several points in the amp and anywhere that it tells voltage on the schematic, I measured my own and wrote it down. pretty much all of the measurements are about %90 of what is stated on the schematic for their respective points, give or take a percentile or two. it says on the schematic that measurements can be within a %20 difference range, so I dont know if its ok, or if my transformer is weak?

The only measurement I took that was inconsistent with the others was on V4 pin 1. I came up with 203 V which is only 78% of the stated 260V. The voltage before the 220k resistor matches the measurement at the cap can D at 374, but after the resistor its lower than I think it should be. bad resistor? I don't know how big of a deal it is in the first place. Can anyone give some insight?

[Blue Whale]

Howdy mraymond77

You'll be asking where are all the usual experts when you need them? In lieu of that here's my advice #:o)

Originally Posted by mraymond77

I checked my bias ... I got the 6v6s to be at 19.5mA each ...
... ...
I guess my biggest problems are the low volume, and tremolo.

when I turn the tremolo speed up, it starts out with a fast "b,b,b,b,b" sound and as I turn it up higher the "b,b,b,b" gets even faster. when I turn up tremolo intensity, I just get a deep bass-y sound that gets a bit louder as I turn it up. neither seem to effect my guitar signal

Reverb works great, and so do bass and treble knobs.

I wouldn't get too concerned with the mA draw by the 6V6GTs at this stage, best to iron out your real issue with the tremolo. But I'd be wanting a draw of say 24mAs each. As an aside I am happiest measuring mA across the output transformer windings, some consider a little dangerous but it's quick, effective and accurate.

Out of interest, as I see you seem to have installed a bias-pot to tweak the bias; What bias voltage are you getting between the two 220K resistors that connect Pin5s of the 6V6GTs, with the tremolo set to minimum?

Originally Posted by mraymond77

Alright I went in and measured some voltages. ... %90 of what is stated on the schematic ... ?

The only measurement I took that was inconsistent with the others was on V4 pin 1. I came up with 203 V which is only 78% of the stated 260V. The voltage before the 220k resistor matches the measurement at the cap can D at 374, but after the resistor its lower than I think it should be. bad resistor? I don't know how big of a deal it is in the first place. Can anyone give some insight?

OK then the tremolo. It's a simple tremolo circuit based upon V4, so check the associated wiring again to make sure. Check that a lead hasn't perhaps been misplaced under the board for starters.

Make absolutely certain that the wiring is correct before looking for faulty components.

[ThermionicScott]

Those voltages are a little low, but the amp should work fine and deliver a good majority of the rated power. Is this a Weber kit where the PT has 120V and 125V primaries? What does your wall voltage read? If you wired up the 125V primary and you've only got 122V coming out of the wall, all of your voltages will be proportionately lower. Is your 5U4 old and tired?

What bias voltage do you see on the grids (pin #5) of the 6V6's? If you're running a hot bias, that will bring all the voltages down.

- Scott

[mraymond77]

Originally Posted by Blue Whale

Out of interest, as I see you seem to have installed a bias-pot to tweak the bias; What bias voltage are you getting between the two 220K resistors that connect Pin5s of the 6V6GTs, with the tremolo set to minimum?

Yup, I put in a bias pot.
I get -28V on either side of the resistors, and -34 before the resistors

Originally Posted by Blue Whale

OK then the tremolo. It's a simple tremolo circuit based upon V4, so check the associated wiring again to make sure. Check that a lead hasn't perhaps been misplaced under the board for starters.

Make absolutely certain that the wiring is correct before looking for faulty components.

my v4 tremolo wiring looks to be correct, except for the wire that connects to pin one. on the layout, it goes from the eyelet that is a junction between the 220k and 1m resistors and connects to the eyelet directly to the right of it that is at the end of a .02 cap then goes to pin one. I have it the other way around. from the .02 cap to the left where the 220k and 1m resistors are and then to pin 1. could this be a problem? As I stared at it I thought it might not make a difference, but I'm probably wrong.

Originally Posted by Scott S

Those voltages are a little low, but the amp should work fine and deliver a good majority of the rated power. Is this a Weber kit where the PT has 120V and 125V primaries? What does your wall voltage read? If you wired up the 125V primary and you've only got 122V coming out of the wall, all of your voltages will be proportionately lower. Is your 5U4 old and tired?

What bias voltage do you see on the grids (pin #5) of the 6V6's? If you're running a hot bias, that will bring all the voltages down.
- Scott

My wall socket reads at 118 V. I didnt get any particular kit, I just got all the parts separately. The PT I bought was this one
http://www.tubesandmore.com/scripts/...item=P-TF22772
maybe its a cheap-o tarnsformer. I hope I don't have a bum 5u4! Its a brand new JJ just got it from eurotubes.

the voltages I got on pin 5 were both about -28v.

thanks you guys rock! great to have some advice on where to check

[Blue Whale]

Originally Posted by mraymond77

... -34 before the resistors ... except for the wire that connects to pin one ... 5u4! ...

All that looks fine and for what it's worth the HT voltages don't look too low to me for a Princeton. Should sound nice at that.

Did you double check the under board wiring, easy enough to stick a meter on for continuity and check;
- that V4 Pin2 goes the the 1M resistor on the far side of the board
- that Speed-pot takes lead goes to junction of the .1uF&.2uF caps
- and that the Intensity-pot joins at the other .1uF on that side of the board

I'll think on about your issue later ... in the meantime, this will probably seem too obvious but, have you tried a different 12AX7/7025 in V4? Just that a dodgy V4 would account for both tremolo & vol (re V4 also phase inverter) issues, otherwise can merely suggest rechecking all V4 connections, correct, good earths, and voltages ... certainly seems an issue surrounding V4.

[ThermionicScott]

Originally Posted by mraymond77

The PT I bought was this one
http://www.tubesandmore.com/scripts/...item=P-TF22772
maybe its a cheap-o tarnsformer. I hope I don't have a bum 5u4! Its a brand new JJ just got it from eurotubes.

the voltages I got on pin 5 were both about -28v.

thanks you guys rock! great to have some advice on where to check

Ah, that explains it! The PR schematic calls for a 340-0-340 secondary, and you've got a 325-0-325 transformer, so even if your wall voltage is bang-on 117V, your B+ will be lower than on the schematic. So your transformer and rectifier tube are just fine.

Personally, I think the PR runs excessively-high voltages on the output tubes for the power it gets from them.

- Scott