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Scott 299c 6u8 vs. 7199

allhartfidelity

allhartfidelity

More gear than sense
Scott 299C
Its been my understanding that to switch from a 6u8 to a 7199 there had to be a wiring change.
Info in attached pic seems to suggest either tube can be used, or perhaps there were variations of the amp?
While the 7199 seems to cost more, if i read this correct i can plink a 6u8 in there with no mods? If not, how do i determine which variation my amp is set up for?
Thank you for any assistance,
Charles20181228_113948.jpg

Question 2:

The headphone does not shut off the speakers which is well known. If i use a speaker switcher, and either turn them down or shut them off while phones are in use, does the amp still see the load needed?
 
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Which tube is currently in the amp now? That's the one it is wired for. To change one to the other does require a couple wire changes at the socket.

Between 1961-1964, they used both tubes but neither one is directly interchangeable.
 
Pinouts are definitely different.

The tubes are reasonably similar other than the wiring changes, but not identical. Might need to change the screen or cathode resistors to dial it in. If schematics exist for both tubes, go with those values.

amps want a load under any condition. Switch it to a dummy load if you don't want to listen through the speakers.
 
cademan said:
Which tube is currently in the amp now? That's the one it is wired for. To change one to the other does require a couple wire changes at the socket.

Between 1961-1964, they used both tubes but neither one is directly interchangeable.
Click to expand...
6u8 currently. As Craig at NOS jas done a rebuild on this, i had no question the correct tube was in, but have another scott with the 7199. Researching to change it over found the adapters and such, but when i came accross the note in the specs not really differentiating, i though maybe there was something i missed in that one could be used for the other but not the other way ect. So thought i would check.
 
604man said:
You can use a 7199 to 6u8A adapter , about 10 bucks,
I used two in a Seeburg stereo AY-160 works & sounds
good.
Click to expand...
With soooo many variations of the 6u8, does this adapter leave them all as options?
While i do see a 7199 to 6u8 does it make sense at all to go the other way ? Like a 6u8 back to a 7199?
Guess im curiouse as there is no markings on the amp, how one was ever to know what tube thier amp used
 
gadget73 said:
Pinouts are definitely different.

The tubes are reasonably similar other than the wiring changes, but not identical. Might need to change the screen or cathode resistors to dial it in. If schematics exist for both tubes, go with those values.

amps want a load under any condition. Switch it to a dummy load if you don't want to listen through the speakers.
Click to expand...
Oh, understood. Insert dummy load into the switcher on one side.
Are the "non inductive" loads i see the correct way to do that?
Tx
 
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allhartfidelity said:
This reads like...rocket science to me...
From my layman point of view, this seems high praise for the 6u8 having been deemed as a replacement. Great read, thank you for the information.
Click to expand...

7199 tube is used in a lot of audio gear , out of production, NOS quite expensive $60.00
and I have found the 6U8 a good substitute.
 
The 7199 was specifically designed for audio use. As far as I know it was the only triode/pentode that was intended for that task. There are a bunch of triode/pentode tubes out there though, tv sets used them pretty frequently as did amp makers that didn't want to use the 7199 for whatever reasons.
 
gadget73 said:
The 7199 was specifically designed for audio use. As far as I know it was the only triode/pentode that was intended for that task. There are a bunch of triode/pentode tubes out there though, tv sets used them pretty frequently as did amp makers that didn't want to use the 7199 for whatever reasons.
Click to expand...

That is exactly correct. Scott later stopped using the 7199 in their amplifiers, opting for the 6U8/6GH8. And yes, those later tubes were used in television, mostly color sets. I suspect the reason was to reduce the cost to HH Scott. They also went to the USA made General Electric 5AR4 in stead of Great Britain (or Holland) Mullard manufactured tubes. Close tolerances of the 7199 can also lead to some shorts in high hour versions. My understanding is that most if not all 7199 tubes were manufactured by either RCA or Sylvania. You may find other brands but if you look closely, they are probably rebranded.

(I tried to add some advertisements by RCA for the 7199 but was unsuccessful, sorry)
 
Just a few thoughts here...

When Kegger redid my Magnavox 8802 he redid the circuit from 6EU7 drivers for 6U8s as he liked them better and there are many plug in subs that are cheap, plentiful and sound good; he especially liked 6BL8s. So there are many options you can look into for the 6U8 that are simply plug and play.

Also, there are boards and mods out there that allow one to redo Dynaco ST-70s to use 6U8 variants rather than the stock 7199s, and they seem to be quite popular, as I guess 7199s are less common, more expensive and less reliable.

It seems what you are attempting to do might be viewed by some as a downgrade of some sort going to a more expensive tube which may result in negligible change, if any. Why don't you try rolling some 6U8 variants before dealing with switching pinouts? They are cheap tubes. Heck, I have bags of 6BL8s and 6GH8s here and would send you a couple if you wish?

Let me know!!

Here's a link to a thread on the ST70 swap from 7199 to 6GH8A you might find interesting, especially since you are looking going in the opposite direction.

http://audiokarma.org/forums/index....ard-modification-7199-to-6gh8a-how-to.723611/
 
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604man said:
7199 tube is used in a lot of audio gear , out of production, NOS quite expensive $60.00
and I have found the 6U8 a good substitute.
Click to expand...
Sounds like i should hang onto the 7199 i have, but then what good would they be? Tough choice. Image i get another Scott that uses it, (sold the other one already) but then wouldnt i prob want to change it to the 6u8... would be a tough choice.
 
Andyman said:
Just a few thoughts here...

When Kegger redid my Magnavox 8802 he redid the circuit from 6EU7 drivers for 6U8s as he liked them better and there are many plug in subs that are cheap, plentiful and sound good; he especially liked 6BL8s. So there are many options you can look into for the 6U8 that are simply plug and play.

Also, there are boards and mods out there that allow one to redo Dynaco ST-70s to use 6U8 variants rather than the stock 7199s, and they seem to be quite popular, as I guess 7199s are less common, more expensive and less reliable.

It seems what you are attempting to do might be viewed by some as a downgrade of some sort going to a more expensive tube which may result in negligible change, if any. Why don't you try rolling some 6U8 variants before dealing with switching pinouts? They are cheap tubes. Heck, I have bags of 6BL8s and 6GH8s here and would send you a couple if you wish?

Let me know!!

Here's a link to a thread on the ST70 swap from 7199 to 6GH8A you might find interesting, especially since you are looking going in the opposite direction.

http://audiokarma.org/forums/index....ard-modification-7199-to-6gh8a-how-to.723611/
Click to expand...
Intriguing thought to roll some variants. I would like to do that, searching "6u8 tube equivalent " does show a bunch, but given the actual voltages are more important then what one page says will "work", i do not posess the knowledge to know what tube is an actual variant for THIS amp. I see like 5 other tubes...the 2 you mention certainly seem like the real deals. I will check my stash and see if i have any, and if not maybe we can work something out.
Note: no, i dont wish to reinvent the wheel, as its clear much of this may have been hashed over already. To others in the post, i dont expect miracle nirvana nor do i chase the "bag" thinking Scott diddnt get it right. Im just learning through this process with "youall" help, the variarions of this tube placement and some of the "why" even.
While most of the technical stuff is over my head, it is not beyond my ability to learn, and i thank you all for the oportunity to do so, which you have provided unselfishly.
 
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