The Amp Garage

Cool, thanks Roe. So my to-do list is: 1) Replace 470R 1W carbon resistors on output tubes with ultra low noise Vishay metal films. (waiting on stock) 2) Swap reverb pot in and out wires 3) Add 10-22k resistors in series with reverb drive grids For the 'Miller Effect' caps (Cgk) I added to the first...

Here's the spectrum.
Reverb = 0 Reverb = 10

So this would be an addition to the original design, yeah? What value would you suggest? Also, I just discovered that if I have the reverb turned to maximum, the HF of the amp is rolled off. It sounds like it's creating a highly resonant low-pass filter. The difference is massive. Any ideas? Edit: f...

try and see if it helps. use 22k or higher values on each grid I'm a bit confused. There isn't current a series resistor feeding the parallel grids. The pairs of 470K resistors seem to just be isolating each channel output from the other's output. (But this is just a guess.) !reverb driver.jpg If y...

Roe wrote: ↑Wed Jan 22, 2025 2:40 pm..separating the two cathodes of the driver tube and installing seperate grid resistors on it is often enough

Ahh! I wasn't aware ofthe separate grid resistors mod. I added separate cathode to ground resistors+caps, but didn't know about this.

Thanks @lonote
Here's a rough video I filmed while documenting the reverb tank placement process: https://youtu.be/1gFeXflm-Pg?si=WMk6AdAzqxx8UI4I

Also, I realised the attachments didn't 'stick' to my previous post which was supposed to have photos, so I've corrected that.

Here are some photos of the finished areas.

Thanks Roe! I did manage to almost completely silence the reverb. I had the idea to shield the open side of the tank (foil wrapped around cardboard, contacting tank's bare metal), but also happened to discover that the position AND orientation makes a HUGE difference. I would never guessed that upsi...

So what do we think about changing the 6L6GC's G2 resistors (R60,61,64,65) for ultra low noise metal films?

Hey Roe, thanks for that. Forgive my ignorance, but what is SSS? And John Mayer in this context?

Also, at some point I'll share the audio files taken after each mod.

I made all the suggested changes (except the Miller effect caps), R126 (91K) - upgraded to Vishay metal film, R101+103 (8M2, channel mixer) - upgraded to Vishay metal film, R3+20 (1M, input bypass resistors) - upgraded to Vishay 3W metal film, R4+5+21+22 (68K, input grid resistors) - upgraded to 10K...

Thank you, sir!

Incidentally, increasing the reverb recovery cathode bypass cap from 22uF to 122uF (simple parallel test) seems to decrease LF hum, but increases white noise around 1kHz.
I'm going to swap the 1K5s for 2K4s now and record a new test.

Hey everyone! I'm doing the mods at the moment, taking a recording of the amp with a pre-recorded guitar loop between each component swap. I'm up to separating the reverb driver tube which has 2 stages in parallel. Current value of cathode bias resistor is 1.2k - should this be 600R on each triode o...

Yes, I'm figuring that a shallow cut with a circular saw (track saw, mitre saw, etc) should provide the required relief for the piping lip and 2 layers of Tolex.

As far as the caps, you should be able to just temp in a large bypass cap across each of those cathode resistors, with out removing anything, to see if it helps with your issue. Yes, good point, that would be an easy way to test quieting down the reverb send/receive. I'm hoping I can make a lot mor...