No sound after upgrade install [solved]

[Paul Birkeland]

Is the 680 Ohm resistor on the A side touching anything other than the terminals it's connected to?

It may be hitting the pin that has the 220 Ohm carbon comp attached to it, which would short the input to that channel and throw the bias way off on the output section.

-PB

[fullheadofnothing]

I'm having a bit of trouble following this thread. The funky voltages posted seem to be on the A side, but it's the left channel that is being listed as not working. I know I often suffer from the brainrot caused by flipping a chassis and flopping channels, but the B side would be the left channel. Could you please post a full list of voltages for all terminals called out in the manual? Also, were any of the standard tests to confirm channels performed, i.e. swapping tubes, switching cables, et cetera?

[mcwhart]

Checked the 680 ohm transistor to be sure it was not touching anything other than terminals.

Switched tubes, wires, etc., no change:  low level hum in both channels, not affected by volume, sound from right channel only.

Voltages are as follows:

Terminal      Voltage

1                  204
2                  0
3                  0
4                  409
5                  204
6, 16            389, 390
7, 17             both 0
8, 18             both 0
9, 19             .016, .050
10, 20           both 410
11, 21           354, 355
12, 22           both 0
13, 23           both 0
14, 24           both 0
15, 25           18.2, 17.36
A1, B1           .016, .049
A2, B2           367, 369
A3, B3           18.2, 17.4
A4, B4           both 0
A5, B5           70.7, 60.5
A6, B6           2.29, 2.31
A7, B7          -3.73, -3.71
A8,B8            2.23, 2.22
C1                -3.84
C2                 3.28
C3                 alternates between 0 and .046
C4                -3.84
C5                 2.46

C4S MEASUREMENTS:

0A                 70.1
0B                 59.3
10                 412
20                 412


Tubes still light up, as do all 4 LEDs.

Is there any other information I can provide?  I am at a loss for what to do at this point.

Thank You

[mcwhart]

Hello again, wondering if anyone has other ideas about this situation with my amp?  I am not sure whether to keep trying to fix it or to send it in for repair.  I have tried all that has been suggested and still can not get it to work properly.  Thank you

[Paul Birkeland]

Your voltages all look perfect (now), so there is a next step we can work on.  What is the lowest AC voltage range that your meter has?

[mcwhart]

I believe it is 200 mV.  The meter is a Radio Shack #2200820 22-Range Digital Multimeter.

Thanks

[Paul Birkeland]

Alright,

What you want to do is download or obtain a 60Hz test tone.  This will let us play AC through your amp and you can use your meter to measure it as it passes through each stage.

The first step is to play the tone into your SEX amp, then measure the AC voltage between ground and each lug on the volume control (turn it all the way up).

After getting these numbers, we can move on with testing other points in the circuit.  To perform the measurements on the pot, the amp can be off, but for the other points we may look at, it will need to be on.

-PB

[mcwhart]

OK.  Thanks.

Here are my readings, volume all the way up, amp off, 60 Hz test tone playing through inputs:

Going from left to right side of chassis, or from A side to B side:

Bottom lugs:  .4 mV, 347 mV, 348 mV

Top lugs:       .6 mV, 434 mV, 434 mV.

[Paul Birkeland]

Alright, this means that you have sound passing through your RCA jacks and out your level control, so we can rule those out.

The next spot to measure this AC voltage will be A1/B1.

-PB

[mcwhart]

I am assuming with power on, right?

With power on, and no 60 Hz signal, I get around 19 mV at A1 and around 50 mV at B1.

Thanks

[fullheadofnothing]

You need the power on and the 60Hz signal. PB is having you trace the signal through the circuit step by step to find out where it is dropping off.

[mcwhart]

Oh, OK, thanks.

With 60Hz tone I am getting about 15mV on A1 and about 29mV on B1.

[Paul Birkeland]

Alright, well, the signal is dead there...

What do you get at 19 and 9?

[mcwhart]

At 19 I get -12.3 V, at 9 I get -4.2 V.

[Grainger49]

If you get a negative voltage you are measuring DC.  The signal is AC.

Check the setting on your meter and make all the measurements again.