Silvertone SS XL 40 WITH LOUD HISS

[Joe49]

Seek advice on Sears (Silvertone) SS 40XL Model #257 14222000. I have worked on tube amps but not SS amps. Assuming loud hiss on both channels caused by failing transistors and will need to replace all. I will also need to replace the electrolytic caps including the filter cap can. Besides the hiss, the amp does amplify and I can hear that the reverb & tremolo are functioning. The schematic link on the previous discussion on this amp no longer works and can't find the schematic elsewhere. Any advice appreciated on finding the schematic, where to source correct replacement transistors and if I need to replace all the transistors. Thanks!

[phatt]

As the amp is working it's unlikely the hiss is failing transistors.
A fair bet those older circuits were noisy by design.
 I just found this schematic Sears 40 XL;
https://www.ssguitar.com/index.php?topic=4127.30  (post 38)

If that is your Schematic I can tell the circuit will be prone to Hiss as there is no inter-stage volume. The Volumes are before the first stage (passive) and wired backwards so even with the volume control off the rest of the circuit is wide open. = Hiss
So even if you replaced Everything that design will always be prone to hiss.
Phil.

[Joe49]

Thanks for the info on the amp design and link to the schematic. It's helpful. Unfortunately the hiss on the amp is extremely loud and overwhelms the guitar amplification. The amp is useless if I can't lower the hiss to an acceptable level. (Like several others, I bought this amp thinking it was the tube version. That was decades ago and it's been sitting in the basement gathering dust since.)

[Joe49]

Hi all,
Any second opinions on this Silvertone SS amp before I move on to other projects? Thanks.

[g1]

If the hiss is so loud that the amp in unusable, it is likely a noisy transistor is the cause.
If you understand the signal path, you can try a cap to ground at various points along the path to try to isolate the location.  Something like 0.1 or 0.47uF rated 100V or more should work.
If the cap to ground kills the hiss, you know the source is somewhere ahead of that in the signal path, so you move the cap further toward the input and try again.

[Joe49]

Thanks, I'll try this.   

[Loudthud]

I would suspect Q1. Any big negative Voltage hitting the input will slowly degrade Q1 (making it hiss) as it has no protection.

Always plug the guitar cord into the guitar first, then plug the other end into the amp. That loud buzz you hear when you do the opposite is what damages the input transistor.

[Joe49]

Thanks for the info on Q1 and how to use the amp. Appreciate it and will replace Q1 first to hear if there's any improvement.