Silvertone 1471 rehab

[Jazz P Bass]

Was C2 replaced.
Check the tone control side of C2 for any Volts dc.
There should be none.
The same goes for C1.
No Vdc on the grid of V1, pin #2.

[Brianr0131]

Update. I shortened the OT leads and double checked everything I decided to replace the 2 100K ohm resistors that run from pins 1 and 6 of 12ax7 over to the 6v6.

There is a very slight (put your ear near speaker and you can hear it) signal coming through the amp when I play some guitar loops. Here are the issues I am seeing.

1. voltage non-existant at pins 1 and 6 on 12ax7 (should be 100v each) this was not a problem before.

2. not getting the voltage drop at the last filter cap junction. I get 270v cap 1 250v cap 2 and somewhere around 220v on cap 3. The last voltage should be about 145 on schematic. I was getting voltages that were on target before these changes.

Where could my issues be now?

Tubes are all in

Yes tubes in.

Voltage at pin 1 12ax7 negative 0.1 with voltage meter set to DC 200

R12 reading Seems low 86K this is while connected. I'm not sure if I should lift leg from pin 4 to get accurate reading.


Thanks again for the help. I really appreciate it.

[Brianr0131]

Was C2 replaced.
Check the tone control side of C2 for any Volts dc.
There should be none.
The same goes for C1.
No Vdc on the grid of V1, pin #2.

Yes I replaced all Caps. I see negative .1 on pin 1 12ax7 0V DC on tone side of C1 and C2. Pin 2 12ax7 reads - .05 V DC (negative)

[Tom Phillips]

I see negative .1 on pin 1 12ax7 (negative)

Pin 1 is the plate and should have more like 100V on it with respect to chassis ground. There should be a plate resistor connected to pin 1. What is the voltage on the other side of that resistor? If it is 100+V then the resistor is open. If there is no voltage there then you should trace the line back to the poser supply and measure the voltage there. Use the schematic and mark the voltage readings you take. This sounds like something was mis-connected when you did your rebuild.
Tom

[Tom Phillips]

...I decided to replace the 2 100K ohm resistors that run from pins 1 and 6 of 12ax7 over to the 6v6.

There is a very slight (put your ear near speaker and you can hear it) signal coming through the amp when I play some guitar loops. Here are the issues I am seeing.

1. voltage non-existant at pins 1 and 6 on 12ax7 (should be 100v each) this was not a problem before.

2. not getting the voltage drop at the last filter cap junction. I get 270v cap 1 250v cap 2 and somewhere around 220v on cap 3. The last voltage should be about 145 on schematic. I was getting voltages that were on target before these changes.

Where could my issues be now?

....

Reading this again it appears that you lost plate voltage after you replaced the 100k Ohm plate resistors. I'm guessing that both new resistors are bad (unlikely) or something is hooked up incorrectly (More likely). Other clues are that you are not seeing any voltage drop across the resistors in the power supply. This is another indication that no current is being drawn by the 12AX7. I.e. something is not hooked up correctly.
Tom

[Brianr0131]

Thanks Tom. I will try resoldering the new joints although I tested for conductance and they all seem good. I am starting to think there's a problem with the 12ax7 socket. some of the lugs move quite a bit. I think I'll replace it if resoldering doesn't work.

[Tom Phillips]

I am starting to think there's a problem with the 12ax7 socket. some of the lugs move quite a bit...

That is normal. The lugs "float" within the socket body.

[Brianr0131]

ok good to know. I tested conductance from lug side through to the pin socket side and all seemed well but I thought the "swing" could have been causing intermittent problems.


Thanks