The Amp Garage

If the above advice doesn't fix it, you could consider reversing the OT primaries. I had a similar problem with a loud deep sound when the volume was raised and that solved it.

The sound I got was a bit different, so maybe you have a different problem.

Any ideas/experience? I'd really appreciate some advice.

I already checked the resistances. I don't think it's related to any of that because it happens with the bedroom setting especially (rheostat).

I just finished building an Airbrake copy. It sounds good on the first three settings, but after that it tends to add a buzzy fizzle sort of sound to notes. I've heard some people say that they experience this buzz and some say they don't get it at all with their airbrake... what gives? Is there a m...

Found some suitable screws, works well.

Does anyone have any experience gigging with an amp not in a cabinet? Is it too risky?

Right now I don't have any immediate plans to mount into a cabinet. What I don't understand is how the bolt is supposed to stay in place. The chassis only has four small holes for attaching the bottom plate: https://images.campyent.com/sites/default/files/uc_products/p-h1444-1053.png Do I need to at...

There isn't any difference in hiss with the guitar plugged in. The jack is also working correctly. I spent another hour rolling tubes and finally found a nice and quiet combination: Tesla 12ax7s in V1 and V2, with an American Amperex 7025 in V3. Putting the amp on its aluminium bottom cover also hel...

I'm using a variac to keep the voltage as close to 220V (the transformer primary voltage) as I can. Following the logic that hiss that increases with the volume control must be caused by circuitry before the volume control, I tried substituting some resistors in that area with 1W and 2W ones (includ...

NOS tubes seem to be quite hit and miss. My current production tung-sols and mullard 12ax7s are quieter than most of my NOS tubes!

What problems exactly did you run into with NOS power tubes?

It's crazy how picky this amp is when it comes to tubes! My mazda silver plates become microphonic and noisy in the trainwreck. Does anyone know a quantitative way to measure noise from an amp? I saw someone mentioning using a multimeter to measure output but I wasn't sure exactly what procedure to ...

Thanks a ton, M Fowler.

I tried swapping the OT primaries and the squeal is now totally gone. The noise is also noticeably lower.

What a great forum!

Hello. I recently completed my first Express build. Following the recommended start-up procedure, I measured all the voltages and found them to generally be satisfactory (though the power tube screen voltages were about 10V too high). However, the amp lets out a high pitched and deafening squeal whe...

What differences are there between a 47ohm and 100ohm artificial center tap? Even Chinese tube dealers here think Chinese tubes aren't very good! You can get an incredible range of 50s and 60s Chinese and Russian tubes though, generally they are considered to be pretty decent. I can't believe the pr...

Ok, thanks for the help guys. Why didnt they add any center tap to the schematic? Also, why use 100ohm resistors, I've heard of people using two 47ohm resistors instead. Sorry for the slow reply, the Chinese government blocks ampgarage! I have no idea why!! I can easily get some 1% metal film Chines...