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Scott 299b tubes

Rmac587

Rmac587

AK Subscriber
Subscriber
Hi Ya'll,
I also have a wonderful Scott 299b with a tube complement of four 12ax7, two 7189, two 6u8/6gh8, and a 5ar4.

I cannot afford to retube this whole unit, but if I were to partially retube this, where would the bang for the buck come? I'm new to tubes, and have all the fanaticism of the recently converted. They are wonderful....
 
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You need to have the tubes checked and replace all that are bad. You also will need to bias your ampifier and adjust per specification. If tubes are good and amp is adjust correct, that is all you need to do. Anything less and it is a waste of effort.
 
Great amplifiers! I really enjoy mine. I presume you have four 7189 tubes, correct (there are two per side)? Secondly, is the amplifier working and what do you think of the sound to this point?
Dave
 
Hi Stout and Dave,
I absolutely love this amplifier so far. I bought it from a local a AKer who had it restored at NOS valves about five years ago. It does have 4 -7189. The seller was too-notch and I think it was biased correctly, but I should check it since the move and the hours I've put on it.

Just curious if I can get a bit more out of this superb amp.

Thanks!
 
I agree with Stout--after 5 years you'll need to check and maybe re-set the output tube bias per the service bulletin, available in the AK database. If it's off much, this will help the sound. As far as tube rolling goes, what sources are you listening to? Are you using the phono section (eg. with a turntable)? Can you share the brands of tubes you have installed now? Finally, what does the "a bit more" you're looking for mean?
Dave
 
Craig does great work. He built my 299C and it has been a solid performer for several years now. Craig offers a modification to bias each output tube independently per each pair. There is a good chance yours has this feature and there is a special bias procedure for this, Craig can send you instructions if you ask. I would first get all the tubes checked to make sure they are up to specification. Once you know all the tubes are good, then you can start to think about rolling a few options. You may find out one or more of the tubes are weak and just fixing that will bring your amp to a new level.
 
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Hi Stout,
I just finished biasing per Craig's instructions moments before I saw your response! I was a bit nervous to be sure.

For step one Craig said to put the meter to the lowest DC voltage setting "preferably 1-2 VDC" and adjust D.C. BALANCE to "lowest possible reading or zero." I set both to zero. It originally read .06. When I went past a zero it began to read "negative" so I just stayed at zero.

Note: my Multimeter only goes down to a 20 VDC setting then it goes to milivolts. I used 20.

For step 2, I dialed in the DC at .25 for each channel. It calls for .275, but Craig's instructions said if I don't play it loud (past five) then the lower setting would extend the tube life.

I also checked the tube complement. The four 7189 and four 12aX7's are Telefunken, the rectifier and two 6UG's are Scott's. I really need to pull them and find a place to test them. My son worked in a mom-and-pop electronic store a couple of years ago right around the corner, but they closed after more than 60 years in business. They had all kinds of testers.

Sounds seems a little mellower, which I kind of needed. The Klipsch Forte I I'm running can be very sharp on the high-end with some recordings.

I hope to God I got this right and don't somehow destroy my amp. I really appreciate you guys chiming in and helping me, so much.
Peace, Rob
 
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Post above edited for voice recognition typos.
Note documentation that came with this unit!
 

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Cool documentation! Love the old stuff that you are sometimes lucky to get when acquiring one of these great old units.

Congrats on the bias adjustment. You have a marvelous tube complement--it's hard to beat the Telefunkens. Checking them all is a good idea, but a tube checker won't necessarily tell you all you need to know about the (7189) output tubes. Sound and power testing in the amplifier is the best way to check output tubes, but if it's sounding good and it's beyond your skill/comfort level to do, I'd just listen and enjoy!

If you want to try different tubes, the output tubes would be a first target but be advised the Telefunken's are hard to beat if operating properly and I wouldn't even try to roll something different in the front end (12AX7's) unless they test weak--just my 2 cents. If you change the output tubes, you'll need to re-bias.

One other thought: the Scott label 6u8's (you said 6UG, but I'm presuming 6U8?) you have as driver/phase splitters are interesting. The 299B schematic calls for the 6BL8 tube and both my 299B's had 6BL8's. The 6U8/6GH8 can be a sub for the 6BL8, but there may be subtle differences. Good NOS 6BL8's are not expensive and it may be interesting to try a couple and listen.
Enjoy!
Dave
 
gadget73 said:
Where are you located? Someone may be nearby that has a tube tester.
Click to expand...
Hi Gadget,
I just remembered that myteenager has contacts with the So Cal Antique Radio Society (SCARS). I went it their site and think I found a local!
 
Hi Dave,
You're right, I think the splitters are 6gh8, but the lettering is mostly worn off. It's hard to tell. They are marked as Scott and "Made in Holland." Amperex maybe?
 
Probably Amperex. They'd have been made in a Phillips factory and sold in the US under the Amperex brand.
 
Did you get the tubes checked out? You have some good tubes for sure. If all those telefunkin tubes test good I would not expect you could find a better sounding set of tubes? If all the telefunkin tubes are original you may want to save the hours on them and use something cheaper in their place?
 
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Sorry for the delay guys, was out of town. Step them yet Block, but I like the idea of testing them and them switching out if they are all good. I'd rather keep them reserved for really critical listening.
 
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