Two 6J5 versus one 6SN7

[audiobliss]

Is there any advantage in using seperate 6J5s as input and driver, compared to one 6SN7, other than less crowding on one socket and maybe more tube rolling posibilities ?

AB.

[ray_moth]

In the case you mention, I doubt there is any difference. However, if you were looking for a matched pair of triodes, you would stand a better chance of finding them with two 6J5s than with a single 6SN7.

[sgerus]

If you have the space and the layout of the amp looks good, I think having 2 sockets is the way to go just for the flexibility…..

And, According to the Morgan Jones book “Valve Amplifiers 3rd edition, p189” the Pinnacle 6J5GT is one of the best “6sn7’s” you can get.

[jeapel]

hi
it s just to share my hum test with ac heater
with stereo preamp

-for the 6.3 vac heater with 6sn7

1-pin 7 to ground and pin 8 to 6.3vac
=> zero hum to right but hum to left
2-pin 8 to ground and pin 7 to 6.3vac
=> zero hum to left but hum to right
3-my final solution is:
pin 7 to 33ohm to ground
pin 8 to 33ohm to ground
=> low hum to both channel but not zero

if my test is right maybe avoid dual triode
and always ground one side heater
but wait for guru confirmation :-)

[audiobliss]

Originally posted by jeapel
hi
it s just to share my hum test with ac heater
with stereo preamp

-for the 6.3 vac heater with 6sn7

1-pin 7 to ground and pin 8 to 6.3vac
=> zero hum to right but hum to left
2-pin 8 to ground and pin 7 to 6.3vac
=> zero hum to left but hum to right
3-my final solution is:
pin 7 to 33ohm to ground
pin 8 to 33ohm to ground
=> low hum to both channel but not zero

if my test is right maybe avoid dual triode
and always ground one side heater
but wait for guru confirmation :-)

[audiobliss]

You had to complicate things.

[jeapel]

the hum was a problem in my 6sn7 preamp
i m not a tube expert but for me there was
a hum problem with dual triode for me it s
because in 6sn7 heaters are in series not
parallel

not easy ! forget about it

[kevinkr]

Originally posted by jeapel
the hum was a problem in my 6sn7 preamp
i m not a tube expert but for me there was
a hum problem with dual triode for me it s
because in 6sn7 heaters are in series not
parallel

not easy ! forget about it

This isn't the real cause.. Almost all 6SN7 I have ever seen except for a few of the very last coin base types have parallel filaments, and I have never had a hum problem with this type with ac heating in pre-amps or power amps. Undoubtedly an issue of execution.

IMO Using two 6J5 where a single 6SN7 will do is both a waste of space and a socket. It confers no real advantage I can see. Last time I was aware the 6J5 wasn't being made any more..

[jeapel]

6sn7EH electro harmonix = series heaters

execution problem very possible

[kevinkr]

Originally posted by jeapel
6sn7EH electro harmonix = series heaters

execution problem very possible

I guess that is an oddball design, I don't use them as my preferred Sylvania 6SN7 is readily available on eBay for no more money and to my ear sounds much better.

I've not had hum problems with the 6SN7EH either.

I have used 6SN7 in SRPP and conventional common cathode cathode follower and transformer coupled line stages as well as LTP and drivers in my power amplifiers and I have never had a problem with hum in any of my designs.

You may need to bias up the heater supply when using AC to something like 50Vdc to assure absolute silence.

Of the many people here I would say your experience with the 6SN7 is quite atypical and the problem points either to a defective tube (design) or something not quite right in your design. Do you have a scope, other test equipment - and how much analysis have you done?