Trouble with Fender Champ 5F1 clone.

[Phil_S]

Phil, I took a look at his OT (PTF 22905) over on AES and it shows Red and Blue on the primary and Black and Yellow on the secondary with Black being the ground.

Pictures can be deceiving. I would never have guessed the 4th lead was black. Instinct told me the yellow is the +, as it is one of the standard colors (yellow, green, white, sometimes orange). So, fortunately, the suggestion I made was the right one. Hopefully, he'll get it running.

[joebob]

I didn't think that wire from the OT was black, my old eyes must be really bad. Thanks for re-stating what I said. That looks like the only problem left to fix, since Travis moved the shorted pins, 3 & 4.

Dave

[Travis]

On your 6v6 pins 3 & 4 seem to be shorted, power off and unplug and then spread the pins further apart. On your OT you have 4 wires coming out of the chassis; the red goes to B+ that is normal; the blue goes to pin 3 that looks normal (except it appears shorted to pin 4). The other 2 wires; yellow and brown/blue don't look right. One should go to the speaker jack lets say the yellow one, then the other one, brown/blue should be grounded, you have them shorted going to the same tie point. Take the brown/blue go to ground with it; then take a wire from the yellow wire and 22k tie point to the speaker.
Dave

I saw the short on pin 3 and 4, fixed it. Now I'm looking at the other OT wires. The black wire is going to the speaker Ground, the red to B+, the blue to pin3 and yellow is tied to the 22k resistor and legged off to the speaker. What are you talking about with the brown/blue that needs to be taken off and grounded? I think your talking about the wire that's tied to the 22k and goes to the speaker.

I think you are close to solving the problem. Look at the OT wires.
The red and blue look like they are done right.
It looks to me that the yellow and the 4th wire (brown/blue?) are soldered together on the terminal strip between the 12AX7 and the 6V6. That's not right. This is what Dave is talking about. Maybe I can say it a little different from Dave....

One wire goes to the negative feedback loop (the 22K resistor), and to the tip of the speaker jack. I think you've already picked the yellow for this. (I can't see your speaker jack, or maybe you just wired it directly and that's OK.) Your take-off point for the speaker is at that terminal strip where the yellow wire meets the 22K resistor.

Clip or desolder the brown/blue. This goes to the sleeve of the speaker jack or the other terminal of the speaker if you are not using a jack. It also needs to be grounded. To reduce the possibility of noise, route the brown/blue around the other side of the 6V6 socket. You may want to lift the filament supply off the chassis floor to keep it away from that speaker wire.

Once you do this, you should be getting sound from your speaker, provided nothing else is wrong (didn't see anything) and nothing was damaged (I don't think this happened).

Expect voltages to change. Give us new readings on the 6V6 and the 12AX7. You can skip the filament readings.

For a first effort, you have done well. Stick with it and we will get your problem solved. You might get lucky here, but, judging from the picture, I'm expecting hum or noise. This is not hard to fix. I mention this to help set expectations.

Let me understand: Are you saying to put a ground on the speaker to the chassis, run the yellow wire to the other speaker term, run the black wire to the speaker term ground side and run the 22k loop to the pos term on the speaker?

If this is correct I tried this config and Im not getting sound. My voltages are:
6V6:
pin3=454
pin4=437
pin5=316
pin8=381

12ax7:
pin1=264
pin2=0
pin3=2
pin6=398
pin7=0
pin8=361

[Phil_S]

I'm not clear from the pictures what you've done. I think you got it. Maybe this explains it? (jpg below) If this is what you've done, then it's right.

Assuming the speaker is now done right, you are carrying B+ voltage to pin 8 of the 12AX7. This is the grid and should be almost zero volts.

You have B+ voltage on the cathode of the 6V6 (pin eight) and it should be about -15VDC.

I suspect this is one problem, not two.

Look at the junction of the 470 ohm, the 25uf, the 1500 ohm, and the 220K ohm. This is next to the ground connection for the second black filter cap. Is there a short somewhere in vicinity of that terminal? Is that terminal grounded? It needs to be grounded. If a ground needs to be made, join it to the filter cap ground buss. All this is hard to see, maybe a picture from the other side?

[Travis]

We have VICTORY!!!!!!!!! I was missing that ground!!!!! We are in business. By the way i also built the guitar from scratch too! Custom man! The way I roll.

6v6:

pin3=400
pin4=375
pin5=.01
pin8=23

12ax7:

pin1=208
pin3=1.64
pin6=204
pin8=1.65

[Cygnus X1]

We have a winner!



Nice guitar also!
I too have a home made guitar, a BC Rich bich clone.
Made of oak, of all things.

[sliberty]

Travis,
Congratulations! The first one can be a challenge, but it can also be the most satisfying. So how does she sound? If you have a way of recording a clip, post it for all to hear.
Steve

[Phil_S]

We have VICTORY!!!!!!!!! I was missing that ground!!!!! We are in business.
6v6:
pin3=400
pin4=375
pin5=.01
pin8=23

12ax7:
pin1=208
pin3=1.64
pin6=204
pin8=1.65

Excellent news. Those voltages are more like it. How does it sound? In particular, I'm wondering if hum is excessive. Your ground scheme is willy-nilly. There actually is a science to it, but sometimes you just get lucky. My first Champ has a willy-nilly ground scheme that works.

[labb]

Phil, or someone, take a look at his biasing on the 6V6. If he is using the 470 ohm cathode resistor , I think that he is at about 18 watt dissapation. Some one check me here:

Va = 400
Vc = 23
Rc = 470 ohm per original schematic
Vs -.005 (guess)

400 -23= 377

23/470 = .0489-.005=.0439

.0439 x 377 = 18.4 watts pretty hot.

I am a rookie at this so I may have missed something.

[Travis]

We have VICTORY!!!!!!!!! I was missing that ground!!!!! We are in business.
6v6:
pin3=400
pin4=375
pin5=.01
pin8=23

12ax7:
pin1=208
pin3=1.64
pin6=204
pin8=1.65

Excellent news. Those voltages are more like it. How does it sound? In particular, I'm wondering if hum is excessive. Your ground scheme is willy-nilly. There actually is a science to it, but sometimes you just get lucky. My first Champ has a willy-nilly ground scheme that works.

I'll record the amp tones tonight. There is very little hum all through the volume but when you get to 90%+ volume it is noisy but I think its normal for peging out the volume.

[Phil_S]

Phil, or someone, take a look at his biasing on the 6V6. If he is using the 470 ohm cathode resistor , I think that he is at about 18 watt dissapation. Some one check me here:
Va = 400
Vc = 23
Rc = 470 ohm per original schematic
Vs -.005 (guess)
400 -23= 377
23/470 = .0489-.005=.0439
.0439 x 377 = 18.4 watts pretty hot.
I am a rookie at this so I may have missed something.

Yup, that's right. In the heat of the moment of success, I didn't think to look at the numbers. That 6V6 is going to melt quickly. It is drawing close to 44mA according to your calc. That tube may have seen a bit of abuse in testing, and may never be right, it just might be one that's significantly different from average, or it might be the amp.

As far as noise, fixing this might fix the noise. If not, there are other things that can be done. First things, first. Address the bias issue.

One thing to do is see if another 6V6 behaves the same way. If it does, you'd know for sure it's the circuit. If that tube stays in there, change the cathode resistor from 470 to 1K or 1500, whatever it takes to get it closer to 5W.

There is something going on here with voltage running higher than expected. The PT 325-0-325 should push out about 360VDC through a 5Y3. However, 400 is just over +10% so is probably within reason, though clearly not right for this amp.

[labb]

Correction,,I slipped a number on the calculator..It should be 16.5 watts which is still too high...As for the higher voltages, he is running a Hammond 290---I think. That is going to make his voltages higher. I am surprised that his filliment voltages are not above 7 volt AC.

[labb]

And the Pmax should be 14 x .9 = 12.6 Watt , S.E. amp. Dang, it is tough getting old..Just can't get it right the first time.

[labb]

And the Pmax should be 14 x .9 = 12.6 Watt , S.E. amp. Dang, it is tough getting old..Just can't get it right the first time.

[Phil_S]

It is the 44mA that concerns me most. That balls to the wall kind of current flowing through the tube is going to cook it pretty quickly. Easiest way to address this is to increase the cathode R, at least double and probably 3x stock value. Adjusting plate voltage is probably an exercise in futility.