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7199 vs. 6GH8A

thevic24

thevic24

deep in sound thought
Whats going on fellas??


Do any of you have listening time with, both, 7199's and 6GH8A driver tubes?

I have a dyna 70 with a new, upgraded 7199 driver board and am wondering what thoughts you may have between the 2 driver tubes.

I have the adapter sockets and a friend of mine(an AK member) has a box full of NOS Sylvania and RCA 6GH8A's.

The 6GH8A's he has are all NITB NOS and made in the US. Any ideas as to who may have made them for Sylvania and RCA?

Of course I got a few sets(one of each brand) to try out but Iam wondering what other think. The Sylvania 7199's I have are NOS and have about 20 hours on them and I know they should most likely last longer than me.:D

What are your thoughts and opinions on the 6Gh8A's compaired to the 7199's?


-Vic
 
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I have a stromberg carslon that i did the same thing with. I didn't check to see if they biased correctly, but the 6gh8a sounded good. They were different, but I am not sure I would say better.

I'll give it a critical listen a little later today with my cornwalls hooked up and see if I can dicern the difference.
Mark
 
Hmm...:scratch2:

You say bias correctly, do you mean the drivers or the output tubes?

From what I hear, with the adapters, they are a "drop in" replacement for the Dynaco's and others.:scratch2:


-Vic
 
Ah yes, I thought about that.

I find my self liking the sound of the 7199 so I am going to keep the circuit the way it is. I have adapter sockets that just plug in so I can switch between eather tube.

But as we all know, some day there will be no more 7199's left and this will be the only option for the stock circuit.:thumbsdn:


-Vic
 
Biasing..........
I was told by some of our resident experts here to check the bias if I changed to the 6gh8a or the 6u8a. I assumed it would be the output tubes.

Didn't ask the question further.

BTW - I have all three tubes and I am going to go give them a listen now. I'll let you know in a bit.
Mark
 
Since the driver's phase splitter is cap-coupled to the output tubes there should be no effect on the output stage's bias. He may have meant circuit changes to the driver stage that would affect that tube's operating parameters.
 
Jcricket said:
Biasing..........
I was told by some of our resident experts here to check the bias if I changed to the 6gh8a or the 6u8a. I assumed it would be the output tubes.

Didn't ask the question further.

BTW - I have all three tubes and I am going to go give them a listen now. I'll let you know in a bit.
Mark
Click to expand...

I will do the same with the RCA and Sylvania 6GH8A's I have when I get back home.

-Vic
 
Well I have had some time to play with the driver tubes(7199 and 6GH8A) in my "stock" Will Vincent ST70.

Here is some info on the amp so you know what Iam playing with-
All new internal wiring, components, sockets, and a new upgraded 7199 driver board.
Iam using a NOS Philips "fat boy" GZ34 and a quad of EH fat bottle 6CA7's, all that I got from Jim McShane.

The 7199's that Will sent with the amp are NOS Sylvania. The 6GH8A's are a set of NOS RCA and a set of NOS Japan made 6GH8A's.
The Japan made tubes have no markings other than "made in Japan". They have larger plates then the RCA's do.

For the life of me, I could not tell the difference between the 7199's and the RCA 6GH8A's. To me, they sounded the same and would make(IMO) a great replacement to keep the same, stock sound.

The unmarked Japan tubes came with the adapters that I bought. I was totally blown away by the difference these tubes made!

Imaging between these and the 7199's were about the same but the sound stage improved 10 fold. They have a much better, open and detailed upper end with an excellent, fluid mid range. The depth of the sound improved 10 fold as well.

These 6gh8a's made a night and day difference in this amp. I can honestly say that the imaging, sound stage and depth now compare nicely to my Latino ST120.
Now dont get me wrong, the ST120 still dose everything better and in triode there is no contest.
But those 2 little driver tubes made a word of difference to me. I would never have thought that swapping 2 tubes could make that much of a difference!

I payed under $40 for the adapters with the tubes, IMO worth every penny.

So if any of you guys that are running 7199 driver tubes are looking for an outstanding replacement, Ive found one IMO.:yes::music:

I got them off the bay so I wont post the sellers name here but I will be glad to give it to you, just shoot me a pm.:thmbsp:


-Vic
 
Jcricket said:
Biasing..........
I was told by some of our resident experts here to check the bias if I changed to the 6gh8a or the 6u8a. I assumed it would be the output tubes.

Didn't ask the question further.

BTW - I have all three tubes and I am going to go give them a listen now. I'll let you know in a bit.
Mark
Click to expand...

Ah,

there was no affect on the output tubes bias between the 2 tube types.

-Vic
 
The pentode and triode in the 7199 or 6GH8) are direct-coupled - so the operating point of the pentode also sets the operating point for the triode phase inverter. The phase inverter really should be about 1/4 of the supply voltage (75-100V or so) on the cathode. Much higher and distortion goes up and it is risking the heater-cathode insulation (HUMMM...). Much lower and distortion goes up as well. I think the different sound of different tubes in this position can be explained by how they happen to bias in the circuit. Ideally you would add a 1 Meg or so pot to each to set the screen voltage on the pentode to adjust to the sweet spot.
 
I was hoping to get the name of the vendor Vic mentions in this post to get the adapter's and tubes. If anyone knows, could they please PM who that is if they even are still out there.

I looked on eBay myself, but only found Taiwan places to buy from. Thanks all!
 
Tom Bavis said:
The pentode and triode in the 7199 or 6GH8) are direct-coupled - so the operating point of the pentode also sets the operating point for the triode phase inverter. The phase inverter really should be about 1/4 of the supply voltage (75-100V or so) on the cathode. Much higher and distortion goes up and it is risking the heater-cathode insulation (HUMMM...). Much lower and distortion goes up as well. I think the different sound of different tubes in this position can be explained by how they happen to bias in the circuit. Ideally you would add a 1 Meg or so pot to each to set the screen voltage on the pentode to adjust to the sweet spot.
Click to expand...

If I use any pentode up front as a VA, i always use a pot to find the sweet spot. Pentodes can sound outstanding if you make them happy, or they can sound pretty bad. I guess they are persnickity. I love the sound of a good 7199, but there are a lot of tubes in that family and I agree that some can beat it.
 
Hi I have a heathkit AA-201 se 6bq5 amp i am in the process of recaping. it uses 7199's but i did not get any with the amp. so i did the 6GH8A swap.
i rewired the tube socket to accept them.

6bq5's bios is right on.

i still have not stuffed the can cap yet and has a slight hum in both channels but this amp blows me away.
if 7199 sounded better i don't want to know what i am missing at up to $100 each for nos i will keep these. for the $2.99 each shipped i will live with it lol.

they are GE nos grey plate i got off ebay.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=161036072374


i think i will order some more.


Don
 
Last edited:
Has anyone ever a full examination of all the common driver / splitter tubes available using the St-70?
 
jaymanaa said:
If I use any pentode up front as a VA, i always use a pot to find the sweet spot. Pentodes can sound outstanding if you make them happy, or they can sound pretty bad. I guess they are persnickity. I love the sound of a good 7199, but there are a lot of tubes in that family and I agree that some can beat it.
Click to expand...

jay, could explain using a pot for the sweet spot? is it a perminent thing?
on which tubes? on what pins?
thanks.
 
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