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ambience exists 31st July 2008 04:44 PM

Put amp in chassis, then, right channel doesn't work!
I put my S-5 kit in a chassis made of an aluminum pan and when I flipped it on the right channel didn't work. I took a voltage measurement on the three OPT leads that go into the transformer and they all read OK, but there was zip coming out of the other side connected to the binding posts! What could be wrong here? When I touch the signal leads going into the PCB, there is no "buzz".
If anyone can help that would be great.



ambience exists 31st July 2008 05:10 PM

2 Attachment(s)
heres a picture

SY 31st July 2008 05:20 PM

"No sound" can come from anywhere in the circuit. I'd start comparing DC voltages between the channels right from the input stage on through to the output.

ambience exists 31st July 2008 06:11 PM

Is there any possibility of ruining a transformer? I had to desolder it from th e board and then re soldered it.

SY 31st July 2008 06:16 PM

Unlikely. Fortunately!

ambience exists 31st July 2008 07:33 PM

I have checked and checked the wiring inside the amp visually, cleaned up the wiring by re soldering some things, and just tested it again and still no sound.

I am not sure where to put my volt meter for tests though, could I have not put in a coupling cap right?

Tom Bavis 31st July 2008 09:09 PM

Did you check that the speaker terminals are isolated from chassis?

Measure the voltage to ground at all tube socket pins for both channels. Same or close on both channels? Good. If not, you have a clue where to look in the circuit. Clip one probe to the chassis, use only one hand for measurements. A shock from one arm to the other can be fatal!

If the voltages are correct, you have also narrowed the problem down. Look for a short to ground at input or output (the only places that DON'T have a DC voltage).

Jeb-D. 1st August 2008 01:01 AM

On their kit that I bought, the hole they supplied for you to connect the volume control shaft to ground, was actually connected to the inputs of one of the channels instead.

So, if the shaft of your pot is now grounded, and you still have that wire going from it to the board, make sure it's actually going to audio ground and not the hole that they supplied. Since how they had it would short out one of the inputs when you mount it in a grounded chassis.

If that is not it, check to make sure the speaker terminal is not shorted to ground. Although, keep in mind that if your audio ground is mains grounded as well, you will measure continuity because you will be measuring the DCR of the output transformer. But that continuity should not be less than the resistance of the output transformer secondary.

ambience exists 3rd August 2008 09:07 PM

I know that the speaker posts are isolated, because with my multi on AC, I measure signal all the way up until somewhere between the first tube grid and the OPT. There is no signal from the OPT! Help!

ambience exists 4th August 2008 04:18 PM

OK, I'm all set, it WAS the binding posts! It was touching the metal and was shorted. Just shows what a noob knows!

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