The Amp Garage

What was it that fixed the low frequency oscillation? On the reverb, a 100V drop across the reverb driver transformer primary red-blue is way out. Normally there is 3-4 mA flowing through a DC resistance of 1k or so, and a drop of 3-4 volts. The secondary green-black shouldn’t have any DC voltage o...

Ok so I got the low frequency oscillation out, amp is running fine with correct voltages. But I have no reverb. On my reverb transformer I have 465volt on the red primary and 355 on the blue wire…but I’m not showing any volts on the green wire which would normally drive the reverb tank input. When I...

I hear the low frequency oscillation start as soon as the plate current comes up. Maybe you have the OT primaries reversed and you have a positive feedback? I swapped the primaries still is drawing plate current, and dropping the plate voltage and it is lighting up the light bulb limiter. Also inte...

martin manning wrote: ↑Fri Mar 20, 2026 4:29 pm Video?

I don’t see anything wrong with what you describe above, unless you are seeing excessive current draw on your bias probe.

The video hopefully shows more of what is going on, thanks Martin

Hi, I decided to build a JM/wonderland using the Fairfield county PCB boards from Ryan @ “tone geek”. I’ve checked all my grounds and wiring. I did a smoke test without tubes, my voltages on pin 3 of all power tubes is 455, the pins 4 and 6 also show 455 on all power tubes. I’m reading -41 volts on ...

Hi, I was just wondering if anyone has a dumbleator chassis screen printed control panel or separate panel is fine. I know I can buy blank chassis but I was hoping someone is making or has something professional looking to sell? Thanks

-Tom

Excellent! Thank you… I was concerned just running the HT (345 volt) with those caps rated at 100vi thought the entire board needed reconfiguration for the higher voltage. Thanks again!

-Tom

Here is the rectifier/bias supply board and this is being built into Tony Albany’s layout for #183

I found the bias circuit in a Marshall layout deriving from the HT winding. What is over my head is how could I implement this into my layout. I am Using an Amplified Nation chassis and running the boards as per Martin Manning updated board files. Is there a layout anyone has one within these parame...

I’m wondering if I can use the 100volt primary and run that to my existing board, boards are made from Martin Manning file, could run the 100volt to the rectifier board, install eyelet to receive the 100 volt supply followed by a maybe 10meg resistor?

Hi, I am currently building a 50 watt #183 and I was wondering if I can use this transformer. (Hts-13237-ld APD-8023H)I have only built a #124 and used a 100 watt fender power transformer, which had the bias voltage supply and also had 6.3 heater voltage. This transformer has no bias supply and the ...

Hi, the rock jazz switch works well in both positions. But I can’t get a good PAB. Also you had mentioned the middle position of the rock jazz switch switch? I only have a on-on at the rock jazz switch, could this be the problem. Update I’m poking around and noticed my PAB relay isn’t switching (I’m...

Clean volume doesn’t have any effect on the “thin tone”. I also wanted to state that the rock/jazz switch works great, but if I try to engage the PAB via the Footswitch or the manual switch in the rear it has that lower volume thing tone.

Yes I am talking about the PAB, it sounds weak no matter what is on or off. I did notice I get a slight volume increase when adjusting the bass pot. When PAB is engaged the volume goes down, tone gets thin and the circuit gets some “white noise”. The The FET works really good I set the bias via the ...

Hi, everyone I have been playing my #124 for about a year now, I decided the FET boost on a Footswitch is ideal for me. Following Martin Mannings ODs eyelet board files (he did a great layout) I took my time and I feel like I followed everything exactly, but my preamp boost sounds thin and weak afte...