Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: MarkT on April 30, 2024, 01:06:36 am

Title: 2-el84 cathode biased amp.
Post by: MarkT on April 30, 2024, 01:06:36 am

2-el84 cathode biased amp.
1 of the tubes is red-plating slightly. Can be seen with the room lights off.
I switched the tubes around and the red-plate occurs on only the one socket.
I'm thinking its a dirty/oxidy/loose socket or the 110 ohm grid resistor going bad. I'm going to clean the socket with a contact clean. Let it dry real good and go from there.
Cheers.
MarkT

Title: Re: 2-el84 cathode biased amp.
Post by: dtcurare on May 08, 2024, 10:16:15 am

I may have that on a new 18 tmb build.  Its V5 on mine.

Title: Re: 2-el84 cathode biased amp.
Post by: AmberB on May 08, 2024, 01:07:21 pm

My suggestion would be to use a common cathode resistor for both EL-84s.  That way, you know that you have a specific resistance for both tubes.

Title: Re: 2-el84 cathode biased amp.
Post by: passaloutre on May 08, 2024, 02:05:24 pm

What’s the measured dissipation?

Title: Re: 2-el84 cathode biased amp.
Post by: sluckey on May 08, 2024, 02:51:50 pm

Quote from: AmberB on May 08, 2024, 01:07:21 pm

My suggestion would be to use a common cathode resistor for both EL-84s.  That way, you know that you have a specific resistance for both tubes.

Did you mean to say "use a separate cathode resistor for each EL84?