Cathode Bias bros?

[Nigel]

.

[RockyStar]

You would have to be light on your feet not to...

[Nigel]

You would have to be light on your feet not to...

Skeletor says wat?

[harddriver]

I have a 5 watt single ended Cathode biased 1x12 combo amp that runs a single EL34 that I built a modded jose 2203 preamp circuit for it, it's a cool little practice amp but if cranked I think it loses some definition due to the cathode bias.

These days I generally like to bias most of amps to 50% dissipation but my 68 plexi variaced down to 85ACV I have the bias cranked up to about 70% but at a plate voltage of 350DCV on the plates.

[Nigel]

Ever tried a JJ KT77 in there?

If you get one with low current draw, and up the bias resistor, you'll get that bottom end, the definition and the grind, and it'll last a long time.

I use the lowest bias point specimens available from tube depot and they take the abuse all day long.

Bruce Zinky hipped me to low current (plate AND screen!) tubes being the most robust. High current draw tubes are weak and burn up fast...but you can market them, oh yes you can!

[Nigel]

Also thanks for the responses guys!

[harddriver]

Yeah I usually run lower current draw tubes in it. I bought a few different tubes for it all under 25-30 ma current draw or something like that so I guess I run it somewhat cool using the low current draw tubes. I can't remember if I tried a KT77 in there or not.

I have run a EI Magnoval 6ca7m EH6ca7 and both tended to get a little plate ring due to being mounted upside down and in a Combo amp.

I keep going back to the EH EL34 for something different I guess, I like it. It's a cool amp to jam through when I don't want to fire up the big boys, it was my first amp build project that I completed before I tackled my first plexi build. It's an old 75 watt Marshall Solid State combo 1x12 that used to have the 150watt Celestion Sidewinder speaker in it, I gutted the chassis and installed a PTP board, it's a 2203 circuit that also has a Jose Master. It's a little gained up from stock but nothing major, a three way bright cap switch on the preamp gain pot, Saturation switch ala Friedman on the JCM master pot, Jose master with 20V diodes oriented asymmetrically on an on/off switch and I'm running a Celestion G1265 speaker in it.