Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: big-ez on October 17, 2021, 08:50:27 am

Title: Adding cathode follower to Thunderbolt/6420
Post by: big-ez on October 17, 2021, 08:50:27 am

I've built of clone of the Supro Thunderbolt (6420). Schematic here:

https://el34world.com/charts/Schematics/Files/Supro/Supro_6420tr_tbolt.pdf

I want to use the extra triode in V1 to put a cathode follower before the tone control. Is this schematic correct? Do I need a coupling cap where I wrote in the '??' to prevent DC from reaching the tone pot? If so, what value?

Title: Re: Adding cathode follower to Thunderbolt/6420
Post by: sluckey on October 17, 2021, 12:08:33 pm

The grid circuit of your CF is wrong and will not work. You do need a coupling cap where you indicated. Use same value as other coupling caps in the amp. Here's some good basics on cathode followers...

     http://www.valvewizard.co.uk/accf.html
     http://www.valvewizard.co.uk/dccf.html

BTW, I noticed you are currently posting about this amp using two accounts, big-ez and ampnewbie. Why?

Title: Re: Adding cathode follower to Thunderbolt/6420
Post by: ampnewbie on October 17, 2021, 12:29:45 pm

Yeah, the 2 accts is annoying. My phone auto logs me in as one and my PC as the other. Will fix.

Thanks for the advice, appreciate it!

Title: Re: Adding cathode follower to Thunderbolt/6420
Post by: sluckey on October 17, 2021, 01:21:52 pm

Quote from: ampnewbie on October 17, 2021, 12:29:45 pm

Yeah, the 2 accts is annoying. My phone auto logs me in as one and my PC as the other. Will fix.

That's an easy fix right here on the board. Just log in using the device that has the user name you DON'T want to use. Then log out. And immediately log back in, but use your preferred username/password ***AND*** check the box to keep you logged in forever. You don't even have to let your device "remember" your log in name/pword.