5F1 Champ DIY: No sound (Tube/Transformer)

[MWJB]

"Pins 2 and 8 were 375V to ground." Confirm that you really mean pins 4 & 6?

If you're not getting significant voltage at pin 8 of the rectifier then it doesn't matter what happensat the 6V6 & 12AX7 as they are downstream of the rectifier, take them out for now & go back to them when the rectifier is sorted - solve the rectifier issue first.

The 375VAC leads from the PT go to pins 4 & 6 of the rectifier. Yellow 5V wires go to pins 2 & 8, pin 8 is then wired to first filter cap. Double check this.

What happened when you put in the 5AR4/GZ34?

Have you corrected the wiring at the PT centre tap, volume pot, speaker jack? Can you post pics of the tube sockets, shot from above?

[adammerah]

Alright here is some evidence.

I checked for continuity from pin 8 (5V 2A) of 5y3gt to the filter caps and there is a solid connection, but the wrong voltage when the amp is turned on. The first node at the filter caps was 1.2V and kept cycling very slowly from 0 to 1.2V over minutes. Pins 2 and 8 were 375V to ground.

On the 6V6 Pin 3 is 1.2 and over time increased to 1.213, pin 4 is 1.19, pin 5 is 3.38 and pin 8 is 0V.

On the 12ax7 pin 1 is 1.18V, pin 2 is .389 (and at input 2 it is .379 while input one is 0 and i had a jack plugged into input 1), pin 3 is .007V, pin 6 is 1.17, and the node between the .02 caps and 100k resistors is 1.19V.

I really have no idea what is going on right now. Voltages are increasing then decreasing, is the 375V lead from the PT supposed to be connected with the filter caps? and if not then how is the filter caps supposed to recieve 340V from a 5V 2a pin?

thanks mwjb

[adammerah]

1.09 was the voltage for the node from pin8 to the filter caps on the 5AR4 when i subbed it in and then it started to decrease and cycle again. What does this indicate, PT problems-issues--broken?

I did mean pins 4 and 6. the PT center tap was shrink wrapped (red-yel), volume pot is grounded and the OT leads are wired in.

[adammerah]

kitf

[adammerah]

dsgdfzs

[MWJB]

"the PT center tap was shrink wrapped (red-yel)" If you have used a typical Fender Champ style PT then the red/yellow wire should be grounded.

[adammerah]

youre the man. haha. i dont quite have sound yet (even with the guitar plugged) but there is feed going into the speaker and noise being output.

I turned it on and was measuring some voltages and the power tube socket started to smoke somewhere. There might be a short cause the tube was very very hot for being on 2 min. if that makes sense. i am still worried that the tube might be fried.

can you identify any problem areas that could be causing this? i am going to check the connections and for any loose metal

[MWJB]

I still don't understand your heater wiring, refer to my earlier post on the subject. If one of the wires to your 6V6 is grounded, why does the grounde wire go to 4 & 5 of the 12AX7. Remove the heater wires and start again.

"I turned it on and was measuring some voltages and the power tube socket started to smoke somewhere." So what were the voltages? Check for shorts around the socket after rewiring heaters. If you suspect the 6V6 as bad then throw it away and get another, tubes are cheap, transformers are expensive...what fuse do you have at the PT primaries, it seems to be taking an awful lot of abuse?

[MWJB]

looking at the pic of your preamp tube wiring & speaker jack, there is a bit of wire from the yellow OT secondatry/NFB loop that is perilously close to where the grounded barrel of the speaker jack will sit - clip off the excess wire.

[adammerah]

hey MWJB sorry its been so long, I have been swept up in work.

I pulled the amp out yesterday and the buzzing/screeching was still going. if i havent described it, the amp turns on, then there is the ambient amplified speaker noise then all of a sudden goes eeeeeeeeeeeeeeeee!!!

the volume knob has (very little) control over it, and i unplugged the speaker jack from the circuit and then the volume pot started to buzz with the same frequency as the noise did.

is this possible? could a bad pot create noise? the frequency increases and decreases at different rates as i move the volume control up and down (alot of control). is this my problem? i still dont get any sound from the input jacks (with guitar plugged in). please respond.

thanks

[MWJB]

You haven't mentioned any buzzing/screeching before.

You do not say which of my many recommenations that you have followed? Have you worked through them all?

Whate are your voltages at pins 3, 4 & 8 of the 6V6 & at pin 1, 3, 6 & 8 of the 12AX7.

Have you grounded the amp as I described?

Post new pics of the chassis (tube sockets & underside of control panel), I want to see what you have done before we go any further.

[adammerah]

hey sorry, i must have said something on another forum.

But yea, now i have ambient sound but HARDCORE screeching once the tubes warm up. I grounded the Red-Yel centre tap?? and that helped alot. The fliter cap section looks good (in terms of voltages). i will get you the voltages for the 12ax7 and 6v6, the PT runs a little hot at around 390V but its within tolerance.

i have grounded the amp in a better scheme. And when I was testing voltages i picked up a radio frequency so i know that the amp works to some degree (before the amp warmed up and the screeching started).

i think the problem is the volume pot because i did heat the pot up for a while when i was soldering grounds (and could have broken it) and due to the frequency changes when i move the knob around. i could record the sound to explain what i mean if that helps.

let me know if you think this is possible.

i will get some pictures and voltages for you. thanks

adam

[MWJB]

If you suspect the pot, then change the pot. You definitely have the LH tab of the pot connected to ground?

If so, I would swap the black & yellow speaker wires around, leave the NFB wire from the 22K resistor (red/red/or) where it is (spkr jack tip).

[mazzas]

What, if any, resolution has there been to this? I am troubleshooting a similar problem and could benefit from what you've found.

[MWJB]

Your problems may have a different cause? Please describe them fully. Please post dc voltages for pins 3, 4, 8 of the 6V6, pins 1, 6, 3, 8 of the 12AX7 and post some pics.