The Amp Garage

Thanks for everyone's help.

One last question. Do I need to adjust the bias or PI trimmer every time I replace one of the tubes?

Yes, it dropped down to 451VDC

With no signal injected measuring V4 and V5 pin3 I get 456V.

0.65*30/456 = 0.04276A, so with a 1R current sense resistor I would set the bias to 42.7 mV.

I am learning as we go so I will spell things out so I have a reference when I need to come back to this. I have moved the signal cable from the front high input jack to the loop input jack on the rear. The layout diagram shows power amp in. I injected 400Hz at 1.5Vrms which gave me a plate voltage ...

martin manning wrote: ↑Sat Mar 02, 2024 7:36 pm You need to connect the DMM from one cathode pin to the other, and read DC mV. What are you setting to 34V? Do you mean 34 mV?

Typo on my part. I corrected it to mV. I set the power tube bias to 34mV. Should I bump it up around 36-40mV?

When I connect the DMM probe from V4 pin8 and the second probe to V5 pin 8 I can now zero it. I assume from here I just need to do slight adjustment by ear to get it slightly out of phase? Would that result in a + or - voltage reading on the meter? Does this procedure need to be redone whenever a tu...

I gave the Ampeg procedure a try. I set the power tube bias to 34mV. Both tubes were showing 34mV on the DMM. I injected a 400Hz signal at 1.5 Vrms into the high input jack I adjusted the master volume for an output of 18Vrms at the 8 ohm dummy load Using a DMM I connected the black probe to the cha...

Thanks Ian.

If the method I outlined is one correct way to do it but my readings are not correct I need to fix the problem. I am indifferent to which method I use. I just want to get in range so I can fine tune by ear.

I recently assembled a Ceriatone HRM Bluesmaster 50. It is up and running, quiet and all the controls are working. What I am having a problem with is adjusting the PI trimmer. This is the process I am following to adjust the PI trimmer: Inject a 1khz signal into the return jack of the loop and adjus...

I am also considering building a Bluesmaster using an AA PCB. Has anyone documented the layout and changes needed to the PCB?

What are the dimensions of the chassis?

Thanks for the response Dan. For the shielded wire connections is it correct to connect the outside mesh shield on one end but not the other? In my schematic it has the shielded cable running from drive pot to the send jack but the mesh shield is only connected to the pot. I will check the capacitan...

This is my first go at building a Dumblelator using a prefabricated PCB board. I am at the stage or wiring everything up. My apologies if my questions are basic. What size/gauge wire should I use? On hand I have 22AWG, 24AWG 300v and 20AWG 600v stranded wire. I also have 22AWG 2 conductor 600v shiel...

I should have mentioned I was planning to install the transformer inside the chassis. The transformer is a Triad R-30X. I would need to find a cover for the transformer I was looking at to mount it on the outside.

I am looking into building a Dumblelator clone and I was wondering if mounting a transformer to the rear wall of a rack 1U chassis would be a problem? Are there certain considerations to take into account mounting it this way?