noise issues

[BaLLsAgNe]

i just retubed my ENGL SE (had stock tubes in). i put JJ KT77s in the power section, and the preamp section has a Tung Sol in V1, JJECC83S in V2 and V3, and 9th gen chinese in the last two spots. since ive done this my amp is much noisier when i have any remotely noticable gain on. would this be because of a bad tube (if so how would i check), or is it just from switching to high gain tubes (which a noise gate would fix?)?

[jpfamps]

The most likely cause is a noise valve (tube!). The most crucial valve for noice is the first one your guitar signal hits, which is almost certainly the one nearest the input jack. Try swapping this valve with other valves to se if you can rectify the problem.

Many valve vendors claim to select pre-amp valves for high/low gain etc. In practice the difference in gain bewteen these valve in a real circuit is marginal.

I don't think that a noise gate is the answer; you are simply traeting the symptom and not the cause.

[HTH AMPS]

I don't think that a noise gate is the answer; you are simply traeting the symptom and not the cause.

agreed - try unplugging/replugging the preamp valves, the contacts might be a bit dirty (amp off).

you could also try tapping the preamp valves lightly and see if one of them is microphonic - this will need to be done with the amp on of course.

I'd agree that the most likely culprit is the first (V1) preamp valve - you could try replacing this with one of the old preamp valves temporarily to see if the noise goes away.  In fact, I'd put all the old preamp valve back in the amp then replace them one at a time to isolate the 'bad' valve.

Lastly, I've only had one quad of those KT77s and one was bad right out of the box - made a loud hum and a fair bit of background noise.  Don't rule this out.  Oh, and did you get the KT77s rebiased when you put them in? - the amp may be running too hot (this would cause more hiss than a correctly-biased amp)

 :twisted:

[BaLLsAgNe]

thanks a lot guys.. when i get a chance ill replace all the preamp tubes with the stock ones and if the noise is still there ill try the power tubes. if the noise goes away ill try each preamp tube 1 by 1