Dual rec plate current draw

[Melvin1011]

Can anyone tell me how much plate current Mesa spec'd EL34's will draw in a dual rec ? I want to put some EL34's in mine, but don't want to pay twice as much for Mesa tubes. Lately I've been getting EL34's that are way too hot to run in these amps.

 

[Platypus]

From eurotubes:

These setting are in the "EL34" mode.

Rectifier mode in spongy setting = 44mA which is actually just getting out of crossover distortion and sounds very good.

Rectifier mode in bold setting = 50mA nice an aggressive with great dynamics.

Solid State mode in spongy setting = 78mA now this is getting some heat in the tubes and the dynamics are spectacular.

Solid State mode in bold setting = 88mA this is getting up to about 80% of max dissipation and will shorten the tube life about 10 to 15% and the tone will start to "brown" but it's a lovely sound!

I run JJ EL34L's in my dual rec and I love it. Takes all the crappy mushy farty sound out of it and tightens it right up.

 

[Melvin1011]

Those readings are for KT-88's running with the bias switch in the EL34 position. Those readings would be WAY to hot for EL34's.

 

[Platypus]

Those readings are for KT-88's running with the bias switch in the EL34 position. Those readings would be WAY to hot for EL34's.

Whoops, you're right.

 

[Dale B.]

Can anyone tell me how much plate current Mesa spec'd EL34's will draw in a dual rec ? I want to put some EL34's in mine, but don't want to pay twice as much for Mesa tubes. Lately I've been getting EL34's that are way too hot to run in these amps.

Well, if you're getting them from KCA NOS Tubes, Doug's Tubes or Eurotubes, you will want to look for a set that falls between 25 and 30 on their scale. I think they all grade their tubes with 400 volts on the plate. Ruby Tubes are pretty much the same as well. The Groove Tubes Hardness ratings you would want to look at are 4, 5 and 6, but GT is just about as much as Mesa.

All vendors use different kinds of grading systems, but the vast majority of the vendors that I use grade power tubes with 400 volts on the plate. A lot of vendors can supply you with power tubes that fall within the ranges specified for Mesa amplifiers.

In a Dual Recto, Mesa spec'd EL34's will draw around 25 mA (give a take a few). Even if they fall within Mesa's spec's, they can still be different due to there being 6 different grades within Mesa's grading. Figures may vary here and there due to component drift, tube drift and the current coming in from the wall.

Here is probably what you would see from the Highest Cathode Current reading to the lowest Cathode Current reading:

Bold/Silicon Diode - 25 mA - 445 to 455 volts on the plate
Spongy Silicon Diode - 17 to 20 mA - around 400 volts on the plate
Bold/Tube Rectifier - 12 to 15 mA - between 375 to 395 volts on the plate
Spongy/Tube Rectifier - 9 to 12 mA - between 350 to 375 volts on the plate

Those are just rough shot figures from the top of my head, but they're pretty close to what you would actually see if you had Mesa spec'd EL34's in your amp. I've looked at a ton of Rectos and how they react in their different modes in conjunction with the Cathode Current (Bias Current).

Dale

 

[Melvin1011]

Dale,
Thanks for the info!