20 Watt Marshall makes no sound

[Keyboy]

Need your help. I built out a Marshall 20 watt, PA, 1917 model. I have the original schematic and my layout attached below.

So far what I built:
•   should be a straight copy of the circuit except I did use U.S.-style input jacks.
•   has Heyboer power and output transformers. I called the guys there, explained what I was doing and they recommended DE2116CT, HTS-7363-1 (output) and PT-290-50, HT6179 (power).

What happened?
•   I went through start up and the spec power measurements seem ok (spec in black type and the actuals in blue type.)
•   No sound whatsoever. No hum, distortion, feedback, squeak, buzz – nothing.
•   I took the circuit apart and put it back together, double checked everything – same result.

Thanks for your thoughts and questions!

[Dave]

If the power tubes have all the proper connections and voltages, there are operational tubes present, and there is a speaker connected, they should make some kind of sound even if the preamp section has wiring issues. A zero-sound condition, like you describe, tells me that you have to power tubes hooked up wrong. How about some pictures of your amp's guts?


Dave

[AlNewman]

No noise whatsoever would indicate a problem with the speaker connections, at least if your voltages at the tubes all make sense.  Pictures of your build would be most beneficial at this point. 

[Dave]

What he said. Wait, what I said. Wait, what we both said.

[Latole]

No noise whatsoever would indicate a problem with the speaker connections, at least if your voltages at the tubes all make sense.  Pictures of your build would be most beneficial at this point.

Dave is right.. it could be many things other than the speaker. 

[tubenit]

When you safely check the voltages of the plate resistors on V2 (the phase invertor tube) does the speaker make any noise at all?


With respect, Tubenit

[Keyboy]

Thanks for the responses. Per suggestions, I have attached two views of the chassis.

[Keyboy]

Apologies, here is the second view.

[Latole]

I don't like many solders on turrets board

[johnnyreece]

I can't really see what's going on with your output jack, but it looks like it may have issues.  You might want to be sure it's not shorting there.

[AlNewman]

Dave is right.. it could be many things other than the speaker.

Yes, but if the voltages are good, and the OT is properly hooked up there should probably be a hiss at the very least.  Tubenit's right, try checking voltages at the pi, and also the power tubes.  any noise?

The output jack looks a little mangled, is it possible the switch isn't opening when the jack is plugged in?

[Latole]

I often fix amps where voltages are all good and amp not working.

Most of the time on new build ; it is mistake on wiring or bad solder

[Keyboy]

She works! A spanky 20 watts! I want to thank the good folks who helped me track down the issue, which was the bad output jack. AlNewman, johnnyreece and Dave - appreciate you. Latole, I hear ya about the solders. My first pass at a new amp is not pretty, I'm just trying to understand the circuit and get it working. What was photographed will be a rebuilt via a new board with most new components, wiring etc. so I can make it nice and safe. Tubenit thanks for looking out!

Pretty good mood now! Cheers to you, Glenn

[Latole]

Congratulations on your work.

If I were you, I'd think about redoing the solders.
A poorly made solders can work for a while but fail in X weeks, months or even years.

And it's possible that when that happens, you'll be searching a lot, having forgotten about the solders.

[tubenit]

When you safely check the voltages of the plate resistors on V2 (the phase invertor tube) does the speaker make any noise at all?

When I suggested doing this, my reasoning was to attempt to isolate where the breakdown in the signal was to the speaker. Let's say there is NO sound thru the speaker.  Yet when you check the voltages on the LTPI plates it does make a noise thru the speaker then it means the problem may likely be in the preamp where the signal is not passing thru. Checking voltages on the LTPI plates can make a popping noise.


If you checked the LTPI plate voltages and there is no noise, then I'd look between the LTPI and the speaker jack. And in your case, it was the speaker jack as the issue. And that would have been the next thing I would've checked if no noise on the LTPI plates.


One can also trouble shoot by using insulated alligator clips safely and bypass gain stages as an example. Let's say you have 3 gain stages going into the LTPI but no sound.  Let's say you bypass stage 2 and then have sound, then you'd look for the problem to be between gain stage 1 and gain stage 3.   I hope this makes sense.


Just future FYI for your amp building.   With respect, Tubenit

[Keyboy]

Thanks Tubenit. Makes sense. I didn't mention that I did check the LTPI plate voltages as you recommended, and, as suspected, there was no sound. That helped motivate me to find the faulty jack. Thanks again!