6F8G tubes?

[Cryok95]

Hi all, was wondering if it is possible to place a 6F8G tube with an appropriate adapter in place of the input 12au7 tube in the crack.

I know it is possible to roll a 6sn7 there but was wondering of the 6F8G since I read that they are identical.

 

[Paul Birkeland]

The 6F8 will operate in the circuit with an adapter (or a socket change + plate cap wire).
-PB

 

[nick-seattle]

You will be very pleasantly surprised by the sound of 6F8G from Ken-Rad and Sylvania VT-99. These are definitely worth spending money on adapters.

 

[Wizzie]

the e80cc and 12BH7 needed a R1 resisitor mod the have it run optimally.

Do you know if there is any mods needed to optimise the 6F8G for BHC +SB?

 

[Chris65]

8)

 

[Wizzie]

Looks cool Chris65

can you comment on the sound quality and also did you make any changes for the 6f8g?

 

[Tom-s]

For me the 6f8G is a step-up from the average 12au7 and a side step (different flavor) compared to a good 12au7.
I'm using the Tung Sol round plate version and i like it a lot. 
Overall the mids aren't as forward as with most 12au7's, bass is different (deeper?), soundstage is bigger.
Big downside is that mine are microphonic .

 

[lth1]

I believe that the adapter is the problem, not the tube.

 

[Tom-s]

It's hard for me to differentiate the tube from the adapter. In case of one tube, it's only microphonic when completely warm > 1 hour.
Do you think it could be the adapter heating up and starting the microphonics?

One some other tubes it makes no unwanted noise.

 

[Wizzie]

Does the 6f8g require any hardware changes

 

[Chris65]

Can you comment on the sound quality and also did you make any changes for the 6f8g?

I would just echo Tom-s comments. A different flavour compared to a good 12AU7/ECC82.
No changes - only the adapter (machined teflon) in a stock Crack with Speedball (well, there are film output caps & a Tocos Japan volume pot).

 

[mcandmar]

I'm my limited experience with 6F8G tubes they did tend to be more microphonic than the smaller glass octal tubes.  I would almost say as a general rule the bigger the glass, the more microphonic the tube will tend to be.

 

[InnerTube]

8)

This photo is a bit confusing to me.  The 6f8g or 6c8g (with adapter)  is my very favorite tube in the Crack, however, I am using it as a power tube - a replacement for the 6080, etc.  It is a much cooler tube than the 6080 and sounds just great.  If you can afford the Tung Sol, you will not be sorry.

Great listening, JS

 

[Paul Birkeland]

The 6f8g or 6c8g (with adapter)  is my very favorite tube in the Crack, however, I am using it as a power tube - a replacement for the 6080, etc.

That's a great way to destroy the tube, at minimum, and maybe the amp while you're at it.  This is not a suitable replacement for the 6080 for a very, very wide variety of reasons.  Doing this will leave the amp distorting terribly until the grids of the 6F8 burn up from being positively biased, or maybe it will burn up from exceeding the plate dissipation rating.  It's just hard to tell which will happen first!

 

[Doc B]

To further PBs comment - 6F8G is rated for 9mA maximum plate current. The 6080 is drawing about 3 times that in the Crack.

 

[attmci]

To further PBs comment - 6F8G is rated for 9mA maximum plate current. The 6080 is drawing about 3 times that in the Crack.

A lot of ppl have no idea what they are doing.................

 

[InnerTube]

I realize now that I am doing the wrong thing with the 6F8G tube.  I am an old man and sometimes get things a bit confused although my hearing is good.  I have been using the 6F8G and the 6C8G this way for about 6 months and sometimes have left it on for weeks at a time.  I have experience no distortion - in fact quite the opposite.  I have many 6080 and 6SA7 tubes and have experienced better sound with the 6f than any of these tubes.  I will quite using it in this manner as I do not wish to damage the tubes or the amp.  Thanks for the helpful information, JS