Peavey 5150 - lowering the noise

[HomespunEffects]

I’ve got to say I’m really happy that I didn’t pass on this Craigslist deal a while back. This 5150 has got to be my favorite amp. I don’t mind the shared EQ as it works well for both channels. However, the noise floor is really awful.

Has anyone had anything done to lower the hiss? I’m starting to look into this.

 

[MirrorProfiles]

I’ve got to say I’m really happy that I didn’t pass on this Craigslist deal a while back. This 5150 has got to be my favorite amp. I don’t mind the shared EQ as it works well for both channels. However, the noise floor is really awful.

Has anyone had anything done to lower the hiss? I’m starting to look into this.

Have you tried swapping preamp valves? that’ll give the most improvement with minimal work, with so much gain finding low noise valves will help a fair bit.

You could also try tinkering with the bias. Aside from that, I’m not sure it’s worth tinkering with the circuit too much. Maybe check the ribbon cables and PCB in case any wear on those is causing noise. If you have hum, it could mean it’s worth replacing the filter caps and that’ll help make it quieter too. Probably worth doing given the age and price point of these amps

 

[HomespunEffects]

I have a small stock of 12ax7s that I can swap in. I probably should look at the filter caps but all the 5150s are pretty noisy.

 

[joezlo]

Try a noise gate solo in the fx loop with it barely on.

That's what Ed did.

 

[likitlikeyoulikeit]

I always have loved my ISP Decimator G String II....it is a double gate..... flawless from day one.

 

[Humbug]

Iiirc the 5150 has a 68k grid stopper on the first stage. Swapping that out for a 33k (or tacking on a parallel 68k) will reduce hiss quite a bit. Might make the amp a little brighter, though.

 

[HomespunEffects]

Iiirc the 5150 has a 68k grid stopper on the first stage. Swapping that out for a 33k (or tacking on a parallel 68k) will reduce hiss quite a bit. Might make the amp a little brighter, though.

I’ll check the schematic. The grid stopper works with the capacitance of the tube to stop RF so adding an appropriate cap to ground would prevent any change in brightness, thanks. I did this with my Bassman and it does help with hiss at the first stage.

I do put a noise suppressor in the loop. Thanks all.