Ampeg SVT IIP Preamp.

[steve-soar]

Hi Bass chatters. I have an Ampeg SVT IIP preamp that has served me well in the past, but it has developed a fault. Playing through it before into my power amp, then into my cab, it started to loose gain and start sounding scratchy. I swapped basses, still the same problem. I swapped preamps, then no problem. I have discounted basses, leads and the power amp, so the problem lays with the Ampeg
As I say, it started to loose volume,ie gain strength. As well as getting quieter,then getting louder, then starting to sound scratchy.

Any ideas as to what could be the problem?

Thanks in advance
Steve.

[Beedster]

Tube(s) need replacing

[ahpook]

[quote name='Beedster' timestamp='1407700360' post='2523188']
Tube(s) need replacing
[/quote]

Deffo the first thing to check - how long have the vales been in ?

[steve-soar]

1836. Yeah, try replacing glass then will report back.

[Ghost_Bass]

[quote name='Beedster' timestamp='1407700360' post='2523188']
Tube(s) need replacing
[/quote]

Yep! Sounds like this.

[mikeydee]

Dont know that exact model but my first check would be any signal interrupting jacks like send and return loop, headphones jack or similar. When the fault is there is it effected by tapping the aforementioned jack sockets. If so then they need replacement or may respond to a bit of cleaning or repeated in and out therapy.

Also I have worked on a couple of ampegs this year with bad solder joints from the factory. This can give the same symptoms as the amps warm up the joints go bad.

[Subthumper]

I would recommend a full service as these do suffer from solder joints going bad on all the front panel connections to pots and switches. If I remember correctly it's a ballache to change the valves too. If your not sure what your doing get it to a proper tech, it is valve so watch out for nasty voltages lurking in the filter caps. None of it is particularly difficult, it just needs a lot of care and much dismantling. Good pre amp when working.