The Amp Garage

Count me in for one set. Thanks

Sorry I posted to an old message by mistake.

It was the raw switch mod that I tweaked by using a DPDT switch. The ground of the presence pot was lifted when it was supposed to stay ground at all times. I should have just grounded the presence pot directly but I tried to accomplish the same with the switch and keeping it connected to ground wit...

I am not sure exactly, I just relayed what I was told by UA. I was able to find out what was causing the oscillation and I fixed it this evening :D One of the switches was bad and it caused a grounding issue. I replaced the switch and the oscillation was gone! Thank you to everyone that assisted wit...

What does the input of the Ox look like? Does the load impedance, even though 8R, have a large capacitave reactance, rather than inductive or resistive? I am not sure as UA does not disclose that info. It only shows that the ground input goes to ground across a 10k resister and the tip goes to reac...

I am using a 56k resistor for the negative feedback since I am using the 8ohm tap. I also have the ability to switch the negative feedback to 20k for more of a JTM45 sound. I am not using a 5k resister on lug 3 to ground on the presence pot rather lug 3 is connected to the 56k resistor.

I just tested the 47uf 500v cap across the first filter cap and it is still doing the same. I replaced the rectifier tube and power tubes and it still occurs as well. Thanks

The amp is a 5f6A bassman that I recently built from Rob Robinette's layout with some of his recommended mods. The amp has four F&T 22uf 500v caps for the power filtering. Is there a way to test to see if the B+1 caps are not working correctly? Or do you recommend I use a different type of filter ca...

I used the 4 ohm tap and set the attenuator to 4 ohms as well and its is still doing the same. Is it possible that the Output transformer is not working correctly even if it sounds good through a regular speaker? Very strange.

Yes the amp and the Ox are both set to 8 ohms. I changed tubes and had the same result. I will try to use a different tap of the output transformer (4ohm) to see if get the same result. What is strange is the amp works correctly when connected to a speaker directly. Not sure why the Ox is causing th...

I was able to record what is happening in the amp which I have not found with any other amp when using an attenuator. The clip is at https://youtu.be/B04BjqXIs0Y. Any thoughts on what is happening or help would be appreciated.

Has anyone experienced power tubes pulsing and making an audible sound when the output is plugged into a UA Ox attenuator? The amp works fine when plugged into a speaker cabinet. I have tried two separate Ox attenuators and speaker cables and the same issue. I have multiple amps that work with the O...

I would like one!