Plate Voltage TC-50

[BoogieDawg]

Has anyone measured the plate voltage in EL34/6v6 and 6L6 bias modes. I am to lazy to pull the chassis and measure the voltages on the plates myself. With the plate voltages and a multimeter/bias probe with the use of my maximatcher I can figure a good range of natural current draw to try and source some good old NOS tubes that fall within that range. I really don't feel like pulling the chassis.

 

[BoogieDawg]

Ok folks I've pulled the chassis and took some measurements. In EL34/6V6 bias mode I'm getting 419V on the plates using Mesa branded Winged C's and Mesa branded Siemens EL34's. Both pairs of EL34's have a natural current draw of 38ma using my maximatcher. In 6L6 bias mode I'm getting 429V on the plates using a pair of Winged C 6L6's that have a natural current draw of 20ma as measured using my Maximatcher. Using a pair of Russian 6V6's @ 32ma I'm getting 411V. With a pair of JJ 6V6's @ 28ma I'm getting 417V. I've also measured the bias of each set of power tubes using a bias probe in the TC-50. And I'll tell you that the 6L6's and EL34's are on the cold side. But the 6V6's are smoking in this amp. Almost as hot as the coldest EL84's in my DC-3.

 

[mace]

So, those two sets are 6V6's are using 13.2 and 11.7 W (amps x volts)? From a quick google search, I found that 6V6s should be at around 9 W. Is that what you meant by they are running hot?

Your EL34s were 15.9 W and 6L6s were 8.6 W.

What class of amp is the TC-100 and TC-50?

 

[BoogieDawg]

I mean hot as in running above 70% max dissipation. I have a pair of GE 6V6GT that draw 25ma on my maximatcher and they are also hot in this amp running around 80% max dissipation. I'm guessing off the top of my head that a pair of 6V6GT that have a natural current draw of 20ma would get you around 70% max dissipation. But I don't have any that cold to test.

 

[domct203]

It would be interesting to see what Mesa branded 6V6’s run at in that amp.

 

[rrguitars]

Sorry but in laymen's terms what does all of this tell us?
Is there an article I can review to better understand the pros and cons of the info?

 

[domct203]

Research vacuum tube bias and idle plate current. Also research cross over distortion.

The above conversation refers to the idle plate current, or bias setting on vacuum tubes. A byproduct of power tubes is heat, the more power (current) you push through the tube the hotter it runs. If you run them too hot, you can exceed what the tube can dissipate as heat, damaging or destroying the tube(s). A common issue with running tubes too hot is ‘red-plating’, where the plates of the tubes actually get so hot the metal starts to glow red. This will destroy a vacuum tube quickly.

Running a tube too cold can result in a fizzy and stiff amp, with the tubes experiencing crossover distortion in the over lap between the ‘push’ and ‘pull’ of a class AB vacuum tube amp.

There is a sweet spot where the amp designers target for the best performance vs reliability. Since just about all of Mesa’s designs rely on preamp distortion, the power sections are designed to run clean, and bias will be on the conservative side, usually around 40-50% of maximum plate dissipation.