18Watt.com

You can calculate the bias at rob robinette tube bias calculator.
Select 6BQ5 tube
You have to extract the cathode voltage (11.3V) from the plate voltage (350V). This means 339.7V
Then all you need is the cathode resistor value and your cathode voltage and fill them in

Wow.. the amp has a cathode follower.. how does it sound? This is probably a gainy little animal..Can you post a clip?

Bieworm wrote: ↑

Fri 04/09/21 10:10 am

Wow.. the amp has a cathode follower.. how does it sound? This is probably a gainy little animal..Can you post a clip?

For my own edification, can you tell me what part(s) in the schematic that is?

As for your question, this is the first tube amp I've had so I don't have much for a frame of reference. It sounds fine to me, but again, little frame of reference. From what I understand, the Trinity siii version (this amp) is the least gainy of the 18 watt kits Trinity sells. I haven't gotten a lot of gain out of it at this point, but I also haven't cranked it up. Trinity has a voltage regulation module (VRM) which I have but haven't yet built or installed since the recommendation from Trinity is to build the amp stock first and make sure everything works. Since it does work, that's one of the things I will be doing next. At that point, I should be able to crank it up without complaints from the neighbors.

I will be glad to try and get a clip, but I'm not that great a player. It might take me a few weeks, so bear with me.

M.

The cathode follower is the 2nd half of V2. It drives the tone stack. A normal TMB tone stack will take a substantial part of the built up gain, but the cathode follower won't.
Usually the tone stack would come after the plate output of V2b ( pin 6).
But with a cathode follower the tone stack connects to the cathode side. This results in a higher gain preamp... to not get too technically...
But you can read about it here:
http://www.valvewizard.co.uk/accf.html

The DC-coupled cathode follower actually does two things:
1 - Yes, it acts as an impedance buffer, to match the high impedance of the output of the preceding preamp stage to the low impedance input of the TMB tone stack, thus reducing the insertion loss of the tone stack.
2- It asymmetrically "soft clips" the signal, for a warm, thick distortion. This is an important part of the "Marshall sound" of JTM45 and Plexi amps, carried over from the F*nder Tweed Bassman.