6JC6 triode strapped?

[Bing Yang]

Hi,

I found the 6JC6 tube mentioned in Peter Millett's page. This is a frame grid pentode for IF amplification. When triode strapped, it has good gain. The 3 V version 3JC6 was sold at AES at only 0.50 per unit. However, I could not find any one discussed about this tube for audio use. Can this tube be used to drive a 2A3 SET? What would be the down side?

BY

[Miles Prower]

Originally posted by Bing Yang
I found the 6JC6 tube mentioned in Peter Millett's page. This is a frame grid pentode for IF amplification. When triode strapped, it has good gain. The 3 V version 3JC6 was sold at AES at only 0.50 per unit. However, I could not find any one discussed about this tube for audio use. Can this tube be used to drive a 2A3 SET? What would be the down side?

I got a bunch of those, which isn't surprising since just about every colour TV back in "the day" used them. From the characteristics, it looks like it'll make a pretty decent audio voltage amp. Don't have any data concerning trioded characteristics.

So far as using it to drive a 2A3, your best bet for that would be to use it as the CF in a Kimmel Mu Stage. Given the high Vhk rating (200V) the high g(m) (15mA/V) it would work just fine for that. Unless you're contemplating driving the 2A3 into Class AB2. For that, you'd be better off going with a MOSFET driver.

[Bing Yang]

Thanks for the reply. I actually think about using it as the driver tube together with a MOSFET CCS at anode. Will it sound good?

[Miles Prower]

Originally posted by Bing Yang
Thanks for the reply. I actually think about using it as the driver tube together with a MOSFET CCS at anode. Will it sound good?

In a case like that, I'd prefer a CCS made from cascoded BJTs. The Pd rating for the 6JC6 is just 2500mW, and that'll mean a very small Id for that MOSFET. That'll cost you a whole bunch of g(m) there (unless you use the MOSFET as the top of a Kimmel). Without that g(m), the performance of your CCS will leave a lot to be desired.

[Bing Yang]

I bought some 3JC6A from Antique Audio Supply during sale last year. I finally got around to put it together as the driver for my 2A3 SET. I connected the heater in series so that I can use the existing 6 volt filament supply. The tube is triode strapped. As I don't know the correct way to triode strap this tube, I simply copied how Marantz 5 did. I connected plate, screen, and suppressor altogether. The supply voltage is 281V. The load resistor is 20K Ohm. The cathode resistor is 100 Ohm. I tried four tubes from ECG and Zenith. They all have plate voltage from 97 - 120 V and cathode voltage from 0.8 - 0.9 V. The tube should be pretty linear at this bias point.

Compared with my previous driver, EH 6C45pi, the gain is about the same. The sound of the amp is good. I think 3JC6A actually has more ambient details. However, I cannot tell the differences without side to side comparison. I am very happy considering that this tube was on sale at 50 cents each. I also bought Sylvania brand. I have to check and see whether there is any sound difference among different brands.