Early Pignose 7-100 hissing

[datru]

Hi. A friend gave me his early Pignose 7-100 amp (from the 1970's). It has a pretty good hiss especially at full volume. The guitar tone throughout the amp is good, just the hiss in the background. The same hiss using battery power or the AC adaptor. I know this is a shot in the dark, but can anyone help with a diagnosis?

 

With amp at full volume and a guitar plugged in, the noise disappears if I turn the guitar volume to zero. Anything more than that and the hiss is there. I've tried cleaning the volume pot too.

 

Someone told they thought it could be the capacitors. I'm wondering about the germanium transistors.

 

Any ideas?

[onelife]

does the hiss go away when you turn the amplifier volume down?

[datru]

does the hiss go away when you turn the amplifier volume down?

 

Yes, it goes away at low volume.

[Mr.Grumpy]

I spent some time looking these up on the web. Yes, the early versions did use germanium transistors: two in the preamp and two in the transformer-coupled push-pull power section. The only control is the volume control, and that's right on the input!

 

All I can suggest is that maybe that the first transistor (Q1) is noisy, try to find the closest "cross" you can, install it and see if that fixes it. Since the amp uses voltage-divider biasing, a "close enough" (in gain, Hfe) Germanium replacement transistor should work. Also, the 1 nF capacitor on the input is there to drain off any RF or other random high frequencies like HISS. Make sure that capacitor is present and connected. Maybe someone removed it trying to make the amp sound brighter.

 

This appears to be the schematic for the Ge transistor version, since they are all PNP type.

 

[ATTACH=CONFIG]n31908489[/ATTACH]

This image was stolen from this thread at music electronics forum. I might have some helpful info for you, I skimmed the thread but didn't read all of it.

 

http://music-electronics-forum.com/t8790/

[datru]

Thanks! I'll give it a try.

[WRGKMC]

My buddy has a pignose and his hisses the same way when cranked. Its simply the ambient noise the preamp produces with the preamp fully cranked.

 

The amp is low wattage. They were designed to jam along with an acoustic guitar player on battery. They get noisier as the batteries get weaker too and you're simply tempted to drive it that hard and hear the hiss.

 

Its no different then most SS amps fully cranked, its just a higher wattage amp has more headroom and you wouldn't need to drive it that hard.

[datru]

My buddy has a pignose and his hisses the same way when cranked. Its simply the ambient noise the preamp produces with the preamp fully cranked.

 

The amp is low wattage. They were designed to jam along with an acoustic guitar player on battery. They get noisier as the batteries get weaker too and you're simply tempted to drive it that hard and hear the hiss.

 

Its no different then most SS amps fully cranked, its just a higher wattage amp has more headroom and you wouldn't need to drive it that hard.

 

Perhaps, but my friend who owned the amp swears it used to be quiet, and compared to the same model from the 1980's it is noisy at volume.