The Amp Garage

A quick update I did some tube swapping this morning and lowered the gain of the reverb recover (V3) and this seemed to really tame the reverb. I think before I was just swapping (V2) as I was thinking the send was too hot. The reverb is still very thick and chewy compared to a DRRI which is more li...

Based on your description the driver stage is distorting the input of the tank? A simple way to trim it is with a divider network made from a 470k resistor (signal) and 470k to ground. A 50% cut will give you a clue if it is the right idea. If you do a bounce test by turning the reverb up and bangi...

what is the reverb tank code? You bring up an interesting point. I believe this custom amp is usually paired with a short tank reverb. What I am using is the stock DRRI reverb tank (4AB3C1B ) and I’ve also tried an aftermarket “MOD” replacement. Both sound nearly identical. I’m wondering if the rev...

It seems unlikely that the reverb transformer is bad. More chassis photos from several angles, with sufficient resolution to read all component values, are required. I think up to 60% of their limit is more appropriate idling design max rated valve types such as 6L6GC in fixed bias. And given the 6...

I’ve got a custom built AB763 style amp which is a single channel w/reverb. No tremolo. The reverb does not sound as good as a stock deluxe reverb and I’ve never been happy with it. The amp is a beast and sounds incredible, I just keep the reverb very low or off. I would like some help to identify a...

To me this is how these amps sounds when they breakup. I notice the same thing when playing alone and it drove me to adding a bright cap switch and new tubes. I found when playing with a band I don't even notice the crackle. You should try another DRRI if possible just to make sure you're not fighti...

Read up on how to install your coupling caps the right way, as this must be right first before doing any further trouble shooting if getting this right does not cure your issue on its own. In general in terms of good signal flow wire layout, grid wires should be very short, as short as possible sin...

Crikey, it’s hard to do amp tech stuff in the absence of test kit :cry: Does the issue manifest if the amp is operated with the reverb driver tube in V2 removed (and reverb control turned to minimum)? With the reverb mix to 0 and/or v2 removed the problem almost goes away completely. The very stran...

Would manually dampening with a chopstick work to locate the problem leads? I was poking around inside of the amp today with a loop running and I couldn't find anything that I was able to manually dampen. I'm just not positive if a chopstick would work for oscillations that high. You're not trying ...

I hear trailing oscillation around 4.5 kHz in the second recording. Most likely a parasitic, and lead dress related. Maybe try moving the power tube grid leads, maybe even try twisting them together. Would manually dampening with a chopstick work to locate the problem leads? I was poking around ins...

I also only hear reverb on the video from today. In the second video the one from 'earlier' I can definitely hear some ring, but it almost seems to me like it's frequency dependent, and may just be that you've got the amp a bit too 'bright' and loud and it's feedback at that frequency because the r...

Here is a great demo video from today. You can hear the ring with the amp reverb turned to 0. Increasing the reverb exaggerates the ring. Sorry, I cannot hear any "ring" or odd sounds in this video. When you turn on the reverb briefly, I hear...reverb. Otherwise, I can't hear anything odd. (I'm lis...

Here are some pictures of the amp circuit: https://drive.google.com/file/d/1C16ah4_fSbNlcsOezeg4f1K56dJg70YA/view?usp=sharing https://drive.google.com/file/d/1BvZfqs6v4Vx9lmpqdzRh9NcAWVm6bHAy/view?usp=sharing https://drive.google.com/file/d/1BxCiHFDnGMwX3pRpKLu6ryLzyl1M9zz-/view?usp=sharing https://...

Here is the original video I posted on this forum a couple weeks back

https://drive.google.com/file/d/19UQnrT ... sp=sharing

Hello, I have posted about this previously in another channel but I have more information and hopefully will get more views here. I have a custom built AB763-ish circuit. This one is only one channel and does not have the vibrato circuit. v1: 12ax7 - pre-amp v2: 12at7 - reverb pre v3:12ax7 - reverb ...