JJ KT88s and other octals

[kevinkr]

Originally Posted by rknize

Hmmm...I didn't realize that little detail. Most of the tube vendors still refer to "Winged-C", built in St. Petersburg, as "SED". They make it a point to do so because of the confusion over the "Svetlana" brand in order to justify the higher price of them.

SED is the acronym for Svetlana Electron Devices which was a joint venture company out of Huntsville Alabama partnered with Svetlana located in St. Petersburg. The joint venture company went bankrupt sometime around 2000 - I no longer remember the exact date. SED tubes are not made in most cases by JSC Svetlana and you have to be careful to note that the tubes you purchase have the "Winged C" and not the S logo - please see here to clear up the confusion: Winged C Home Page

The real deal incidentally is available from Antique Electronic Supply.

I have no current affiliation with Svetlana or anyone else for that matter as a way of disclosure. Way back in the 1990s I did have a limited professional relationship with SED. (Designed a 300B PP amp which was in their design library and was also published in VTV issue 12)

[rknize]

They are available from TubeDepot, TheTubeStore, and Jim McShane as well. As I said, the big Saratov power tubes all seem to have the same or similar plate structure. The Winged-C tubes look quite different.

[audio845]

I wouldn't think of running a modern tube above ~500 volts. Certainly not 600 or 800. Even the best modern tubes aren't up to the standards of the originals.

One other point. The maximum grid leak listed on the original KT88 data sheet for fixed bias was 220K. You are playing with fire using the maximum allowed value. I would use 100K or maybe 180K.

I love the Genalex reissues, I get mine from Jim McShane as well.

Charlie

[Jim McShane]

Originally Posted by kevinkr

SED tubes are not made in most cases by JSC Svetlana

That is incorrect! SED tubes are the same as "winged C" tubes, and are made in St. Petersburg, Russia by JSC Svetlana. 100% of SED tubes are made by JSC Svetlana

"Svetlana" branded tubes are made in the Saratov plant owned by New Sensor - who went to bankruptcy court when the US importer when bankrupt - and won the right to use the "Svetlana" name in the US only.

In the USA SED tubes are the real deal, meaning made by the St. Petersburg plant. These tubes have the "winged c" logo which can only be applied to tubes made in St. Petersburg. Again in the USA only, "Svetlana" S-logo tubes are made by the New Sensor owned plant in Saratov.

Prior to the old US distributor's bankruptcy in the early 2000's there was none of this confusion.

The real deal incidentally is available from Antique Electronic Supply.

And other places as well - but the SED 6550C is gone, there has been no new stock arrivals since last spring. And the prices have gone through the roof - 50% plus increases on some tubes!

[kruesi]

Originally Posted by audio845

I wouldn't think of running a modern tube above ~500 volts. Certainly not 600 or 800. Even the best modern tubes aren't up to the standards of the originals.

One other point. The maximum grid leak listed on the original KT88 data sheet for fixed bias was 220K. You are playing with fire using the maximum allowed value. I would use 100K or maybe 180K.

I love the Genalex reissues, I get mine from Jim McShane as well.

Charlie

The thought of actually trying to run at 800V scares me to death, too. I'd think 550 or so should be OK on a part with published ratings of 800- but I hate to start depending on HOW MUCH I'm being lied to by the published specs..!

You'll find the schematic of this amp in the first post of this thread- I'm not using grid leak bias- just "grid stoppers" to help prevent oscillation. I'm using 2.2k in series with the control grid, and 1k for the screen grid stopper.

In my opinion, power output stages are a poor place to be using grid leak bias at all... But that's just me.

Everyone's experience points toward using Gold Lion. Though a bit more expensive than EH, better Quality Control is worth its weight in Gold (no pun intended). I've already seen fireworks from 2 sets of JJ KT88s - I want something that actually WORKS this time ;-)

Thanks again-

[rknize]

Originally Posted by kruesi

You'll find the schematic of this amp in the first post of this thread- I'm not using grid leak bias- just "grid stoppers" to help prevent oscillation. I'm using 2.2k in series with the control grid, and 1k for the screen grid stopper.

I think he was referring to the 220k grid leak resistors in your bias circuit. You probably want to drop these closer to 100k to keep better control of the grids in the event of some grid current flowing. This, of course, means you'd need to bump up those coupling caps.

[kruesi]

Hmmmm....


Audio845 - I got thinking about the grid leak thing...

Do you mean that my 220k dropping resistor to the negative grid bias supply may be too high?

Not that I'm using grid leak bias per se, -the thought was that the 220 k would present a minimal load to the audio being supplied from the previous stage.

Oops... I see in another window here that rknize has already replied to the affirmative.

Yeah... Good idea in any case. I'll drop these values.

Thanks.

[kevinkr]

Originally Posted by Jim McShane

That is incorrect! SED tubes are the same as "winged C" tubes, and are made in St. Petersburg, Russia by JSC Svetlana. 100% of SED tubes are made by JSC Svetlana

"Svetlana" branded tubes are made in the Saratov plant owned by New Sensor - who went to bankruptcy court when the US importer when bankrupt - and won the right to use the "Svetlana" name in the US only.

In the USA SED tubes are the real deal, meaning made by the St. Petersburg plant. These tubes have the "winged c" logo which can only be applied to tubes made in St. Petersburg. Again in the USA only, "Svetlana" S-logo tubes are made by the New Sensor owned plant in Saratov.

Prior to the old US distributor's bankruptcy in the early 2000's there was none of this confusion.



And other places as well - but the SED 6550C is gone, there has been no new stock arrivals since last spring. And the prices have gone through the roof - 50% plus increases on some tubes!

I guess I am confused because SED (Svetlana Electron Devices) was the name of the joint venture company, but I guess New Sensor did not get the rights to that name, along with Svetlana and the "S" logo? Sorry for inadvertently adding to the confusion, and it is confusing. Noted in checking the new sensor site that it now comes up under "www.svetlana.com" and all of the S branded tubes are not for sale to EU countries.

Unfortunate news about the 6550C, it was a good tube IMLE.

[rknize]

I think you are both right. Technically, SED doesn't exist anymore. However if you look at most retailers in the US, they use the term "SED" and "Winged-C" interchangeably. It's the brand "Svetlana" that is messed up and it's sad that New Sensor decided to be the bad guy and try to sell their own tubes using the Svetlana name. It's one thing to try to profit from recognizable names of dead companies (Mullard, Genelex, Tung-Sol). It's another to do it with existing companies. I hope we don't start seeing RCA and GE tubes.

TubeDepot doesn't even carry "Svetlana" branded tubes and I think it's a good idea not to.

[Jim McShane]

Originally Posted by rknize

Technically, SED doesn't exist anymore.

Not so - look here:

Welcome to SED-USA!

That is one of the current St. Petersburg tube distributors in the USA. It's a division of PM Components, a UK based distributor. They box tube in boxes that say "SED".

TubeDepot doesn't even carry "Svetlana" branded tubes and I think it's a good idea not to.

But you'll see the official "SED" logo on their site.