Squealing Sovtek 7199s

[DizRotus]

As my first venture into tube gear I have restored a Dyna SCA 35 to drive Heresys.

Everything went well until I replaced two different brand 7199 tubes with Sovteks. Upon powering the unit, with the volume at zero, there is a squeal from the speakers that varies in pitch and volume and sounds like a doppler demo.

It lasts approximately three seconds and then everythingg is fine. If the unit is turned off then turned back on within a few minutes it does not happen again. After the unit has been off awhile the noise returns when first turned on.

I experimented by replacing a single Sovtek with one of the old 7199's. The squealing returned in both channels as long as at least one Sovtek was in either channel. What gives?

[lynnm]

Your description suggests that the SCA35,(nifty little beggar BTW - I had one once and still regret selling it)or the Sovteks may have a problem , DUH!!c>

What I am really suggesting is that perhaps the SCA was operating at the fine edge with its old tubes but when the Sov's are installed a parameter is changed that tips the SCA over the edge.

The behaviour you describe leads me to suspect that when the Sovteks are in place they are going into oscillation due an undersupply of voltage related to the tendency of capacitors to suck up all available D.C. until they are charged.

Other - more savvy tech types will likely have further input for you soon.

------------

It is meet to recall that the Great Green Heron rarely flies upside down in the moonlight - (Foo Ling ca.1900)

This message has been edited by lynnm on 08-02-2002 at 09:22 PM

[NOSValves]

I would start by testing voltage on the various pins on your 7199's with the old tubes and the new one's. It's possible that the Sovtek tubes are junk.

MDeneen I believe has expereince with those little jewels if you email him I'm sure he would help if he doesn't reply to this thread in the next day. He's pretty busy with work.

Craig

------------------

HH Scott 299 Amp

HH Scott LT-110B Tuner

HH Scott P-87 Turn Table

JVC JL-F50 Turn Table

Sony CDP-CA7ES CD Drive

1985 Walnut Heresey I W/Layne Audio Woofers

KSW-15 Subs>c>

[DizRotus]

lynnm, NOS440 & mdeneen,

Thanks for the input. To answer mdeneen's questions, yes I replaced parts, but no I did not change circuits (unless replacing the multi-stage electrolytic can capacitors is changing circuits. In any case, the oscillation problem manifested itself before I changed anything other than the Sovtek 7199 tubes. I was hoping that the new parts might solve the problem, but no such luck.

In the interest of full discloure, I bought the fibergalss cap and output boards sold on eBay by John Sullivan. I used his suggested parts list to replace the can capacitors. The output boards received all new coupling caps and resistors of the same value. Only the two ceramic disc capacitors on each output board were re-used. They tested OK, and I could not find modern equivalents. I also installed ceramic tube sockets.

I'd like to take the advice about measuring pin voltage, but, as a tube tyro, I'm not certain as to how to do it. I assume that the negative lead of the DMM is attached to the chassis and that the positve lead is sequentially touched to the pin terminals, with the DMM at the proper settings. If my assumption is incorrect, please let me know before I destroy the amp, the DMM or myself.

Has anyone had experience with the cap replacement sold by John Sullivan on eBay? If so, what are your opinions. Is there a better alterantive to forty-year-old can capacitors?

NOS440, someday I'd like to drive to Burton to check out your new La Scalas and that Camaro. Now that my kids are too old to get excited about a ride on the Huckleberry Railroad, I don't get up that way often, but I would make a special trip to meet you and get some expert tube advice.

Regards,

Diz

[Marvel]

You may find the parts you need for Dynacos at Triode Electronics:

http://store.yahoo.com/triodeel/index.html

I have an ST-70 that I STILL need to get upgraded. hey have replacement cap boards that will fit inside the ST-70 chassis, and other tube mods, mostly to replace the 7199 with a better tube. They also have the schematic on their site.

Marvel

This message has been edited by Marvel on 08-06-2002 at 05:49 PM

[NOSValves]

DizRotus,

I'l resurrect your lost thread sorry MDeneen and I both lost it LOL !!!

So your still getting this Oscilation at cold start !! This can be a bear and I'm not that versed in Dynaco gear. I still would think its the Sovtek tubes myself. There not exactly known for there quality although I've heard there getting better. Some of the Scott amps came equipted with 7199's and I've read many threads where they converted them to other tubes because of the pour available choices of 7199 these day's.

Where do you live must not be to far if you want to come for a visit. You better wait for a while I'm going to have to remodel my Basement(dungeon) just to make room for the Lascalas.

Craig

------------------

HH Scott 299 Amp

HH Scott LT-110B Tuner

HH Scott P-87 Turn Table

JVC JL-F50 Turn Table

Sony CDP-CA7ES CD Drive

1985 Walnut Heresey I W/Layne Audio Woofers

KSW-15 Subs>c>

[NOSValves]

Here's some snips of what people at the Scott forum have to say about Sovtek 7199's

"Hello all,

I have just completed a recap of my 222C. I still had a slight hum in one channel, and by tube swapping determined that I had a weak 7199 (Zenith). The other 7199 (RCA) was fine. I ordered a pair of Sovtek 7199s. When I replaced the Zenith with a new Sovtek, the hum was considerably louder. When I installed both Sovteks, both channels started to hum. I then ordered a NOS RCA to match my good tube. When I installed it, the hum disappeared. Although the RCA was more expensive ($28 from Brent Jessee Recording), there doesn't seem to be an alternative for my amp(other than the 6U8 mod I guess).

--Ken

And Another

Hello Everyone,

I recently purchased (2) Sovtek 7199's to use in a 299-C. The amplifier still contained the original 7199's, which were shot. After receiving the Sovtek's, I installed them in the 299-C. They worked beautifully for exactly one hour (no hum, hiss, or pops). After a period of one hour, the amplifier started to hum. 15 minutes later, the hum reached unbelievable levels

(1 volt peak-to-peak on the scope!). I couldn't believe it, it only took an hour for these tubes to turn microphonic. So, I sent them back and bought (2) Phillips 7199's instead (hopefully, these will NOT be microphonic). Anyone who was considering buying these tubes: DON'T! These are a waste of money, and they will cause you nothing but headaches. Best to stick to the original 7199's. (The original 7199 tube had a spiral heater that acted as an inductor, which in turn, would reject the 120 Hz common-mode signal). Anyone else have a bad experience with these?

Regards,

Ryan

So as you see this is why I suspect the tubes.

[DizRotus]

Many years have gone by. The esteemed mdeneen has retired, lynnm has passed to the listening room in the sky, Marvel is recently married and Craig now has sewer problems. The Sovtek 7199s were indeed the problem. Unless others have had more recent positive experiences with Sovtek, I'd avoid them.

It is fun to show the boxes with the hammer and sickle to friends.

[Groomlakearea51]

My experience with Sovteks.... If they were made after 2008 they are likely ok. Middle of the road, but OK. To get a good reviw of which Sovteds do (or don't do) start at tubedepot.com, etc.

[DizRotus]

Mine are pre 2008. Are Sovtek now called Svetlana or something like that?

[Guest " "]

. Are Sovtek now called Svetlana or something like that?

nope. Svetlana is a separate company. Mcinthosh power tubes are re-branded Svetlana tubes. Sovtek is a front runner tube comany as well. I would take a Sovtek tube over "NOS" tubes any day.