The Amp Garage

7025, just as Fender designed. Google says this... Low Noise & Hum: The 7025 was originally designed as a heavy-duty, low-noise version of the 12AX7 with improved shielding and microphonics control, making it ideal for the sensitive first-gain stage of guitar and hifi amplifiers Thanks again for th...

I have a Dumble #183 in front of me and the complaint with it is the first 12AX7 is a bit microphonic. That is to say it has a high pitched ring when you tap it. So far I have tried a few valves, I tried a EH 12AX7 which initially was quite good, but I decided to test it by inputting a 100hz signal ...

RG answers questions on the technical forum, you could him about it all.

Thanks so much for your help.

I did clean all of the earth connections previously and it didn’t help but as we know you have to try it.

I’ll give that a try and get back to you both. It’s now on the bench.

some new speakers worth trying w. trainwrecks: - blackback g12m 55hz: darker than the greenback RI, flatter response - v-type ceramic and neo: smoother, darker (the neo is a bit crisper and more articulate than the ceramic model) - g12m creamback 65w: less treble than greenback RI - g10 greenback: ...

I was given a Rose Morris built Vox AC-30TBR to fix. This amp had faults in the vib/trem channel, the TB channel and the reverb/amp is noisy. Of course the rail voltage and the bias are insane, now the amp works fine apart from the reverb. The reverb works but it’s noisy and even noisy when it’s swi...

I would say the first thing to do is make sure both the B+ and bias supply ripple voltages are low (all-new filter caps), and that the output tubes are well matched. You can adjust the bias level to keep the output tubes safe, and when this bias modulating system is working it sounds very good. IIR...

I find it so strange that the thump is quieter with the P.I. removed. That's a direct consequence of that strange PI input signal, which should not be there. As this signal gets amplified by the PI, producing opposite phase PI plate signals, it gets processed like a normal (guitar) signal without c...

Put the tremolo tube on a separate power supply node. Connect a 1K to the screen node and then a 40µF cap from the 1K to ground. Use this new node to supply the tremolo circuit. Does that help the thumping? Thanks for your suggestion, I did try it and it didn’t get rid of the thumping. The output w...

IDK if this has been solved, but thumping seems to be either LFO signal leakage into the signal path, or by other reports badly miss-matched output tubes. I put a simulation together to see what the waveforms should look like and to investigate the effect of the GNFB. The traces below are with zero...

Tried to use Grok to assist my son with a school project and Grok made impressive drawings and videos, but they were rubbish. I persisted with it for about two weeks and I had to abandon it. I tried Gemini and it doesn’t do drawing which was helpful as I didn’t waste time. I didn’t have Claude at t...

I recently used ChatGPT in live chat mode, using the desktop app, which can see your screen when you ask it to (automatically shoots a screenshot--you just say, "look at my screen"), in order to get up to speed quickly with Blender 3D. It was an amazing experience, like having an expert human on th...

We often get ourselves deep into looking for perfection out of a item of old gear which was back then like anything else, meaning it was not designed to be perfect, it was designed for a price point that it could be competitively sold at. Agreed, but I wonder why the thumping is quieter when the P....

The Tremolux tremolo effect is created by modulating the power tubes' bias voltage. The intensity pot controls how much modulation occurs. You usually can eliminate the thumping by just turning the intensity down. In some cases, putting a diode across the outer lugs of the intensity pot will elimin...

Tried to use Grok to assist my son with a school project and Grok made impressive drawings and videos, but they were rubbish. I persisted with it for about two weeks and I had to abandon it. I tried Gemini and it doesn’t do drawing which was helpful as I didn’t waste time. I didn’t have Claude at th...