Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Jonas on February 25, 2026, 08:35:49 am

Title: 6GH8A any good?
Post by: Jonas on February 25, 2026, 08:35:49 am

I have a small collection of random tubes, one of which the 6GH8A. This is a 9 pin preamp with a pentode and triode section. 

https://frank.pocnet.net/sheets/135/6/6GH8A.pdf

Would this make for a good preamp? A couple ideas would be pentode -> triode cathode follower, pentode -> triode plate, OR triode plate -> pentode...

What are your thoughts?

Title: Re: 6GH8A any good?
Post by: johnnyreece on February 25, 2026, 09:21:07 am

My notes say it's in several old Univox amps.  Good replacement for a 7199 (with different pinout!), and much cheaper/easier to find. 

Title: Re: 6GH8A any good?
Post by: astronomicum on February 25, 2026, 09:25:31 am

Quote from: johnnyreece on February 25, 2026, 09:21:07 am

My notes say it's in several old Univox amps.

I am not aware of any and would be very interested in knowing which ones?

Title: Re: 6GH8A any good?
Post by: johnnyreece on February 25, 2026, 09:40:02 am

Quote from: astronomicum on February 25, 2026, 09:25:31 am

Quote from: johnnyreece on February 25, 2026, 09:21:07 am

My notes say it's in several old Univox amps.

I am not aware of any and would be very interested in knowing which ones?

Good call!  Looks like my notes were mistaken.  Univox used the similar-but-different 6AN8.  My apologies! 

Title: Re: 6GH8A any good?
Post by: kagliostro on March 04, 2026, 05:19:30 am

However the 6GH8A is considered a feasible/good substitute for the 7199 tube (with different pinout)

So to use it you can look to schematics that uses the 7199 tube


Franco

Title: Re: 6GH8A any good?
Post by: passaloutre on March 04, 2026, 11:00:51 am

I used the 6AN8 recently in a Kay 720 build (https://el34world.com/Forum/index.php?topic=33360.0). It's (the 6AN8) is very similar to the 6GH8, except that the 6AN8 has less gain (af=21) in the triode than the 6GH8 (af=46). Since I used the triode as a cathodyne splitter (gain=1), these two tubes would be sensibly equivalent in this circuit (except for the pinout), as the pentode sections have the same specs. I quite like the tone of this amp, which I attribute to the pentode-triode phase inverter and I plan to use it again.

Title: Re: 6GH8A any good?
Post by: Jonas on April 05, 2026, 05:00:08 pm

Hello!!! I put together a simple 1 knob "booster" project for guitar using one 6GH8A pentode-triode (sorry for the poorly drawn hand schematic...). I have voltages recorded on the schematic.
The component values were based off TIMBO's Bluezmeister schematic reverb driver for my project starting point. The booster sounds pretty good, but looking for your advice on which values I could / should adjust (and why).

Thanks!!