SB200 tube selection

[wa3dsp]

Now that my Ranger project is done I am off on an SB200 project. I posted this on the QRZ amplifier forum but I thought this might be a different audience. Perhaps someone here might have some input.

I have an SB200 that I got from an estate. I am overhauling it completely with Harbach and other mods. My dilemma is the output tubes. The ones that came with it look pretty cooked, one plate cap has fallen off. The were Celtrons. It looks like the only 572's that are available now are the Chinese variety and I suspect they are all the same. RF parts bought the Taylor name and puts that on the Chinese tubes along with there fairly good warranty but in the end they are probably the same tubes as you would buy directly.

I question whether these Chinese tubes are well suited for horizontal operation as is the case in the SB200. Does Svetlana still make 572's? They actually spec'ed them for horizontal operation. I have not seen that spec on the Chinese clones.

The other option is a completely different tube like the Russian GI-7B. I see a lot of web pages out there on conversions but most are dated and many now have bad links. I also question the availability of this tube in the future as it is no longer being produced. It appears to be a tough tube though with the drawback that it is not instant on requiring a 90 second filament heat time. I would like to find someone who is actually using two of these tubes in an SB200 and who has perhaps documented there modifications. There is one mod out there called SB200 sleeper that takes it way beyond where I want to go. I don't care if it has 600 or 800 watts output because as we all know there is not a bit of difference at the receive end only in your electric bill and wear on your equipment.

So interest in comments on this. What others have used in their SB200 and what your experiences have been. I see horror stories of smoked amplifiers using some of these tubes. I do intend to put in a series resistor and fuse in the high voltage and any other protection I can.

73 Doug WA3DSP

[W7TFO]

There is a lot more to tube sourcing than hoping to find plenty of new ones from some importer.

There are NOS examples of US-made ones out there, but you have to be patient, have a bit of money, and search-savy.  Above all, you can't be lazy in your pursuit.

Get on the internet, and beat the bushes.  Look into auctions, lists, forums, anywhere they may be lurking.  Don't be afraid to buy into unknowns from time to time, but try to get a 'return if bad' policy if needed.

Best sellers about the head & shoulders about how to properly pack & ship old tubes, as many are destroyed in transit.  Hand-to-hand transport is best, but that costs more...

Over the years, I have used this tact to secure many tubes for my future projects, with an overall investment below market value.

73DG

[Pete, WA2CWA]

I have read on some of the e-mail type reflectors that there has been good success with the Taylor 572B's in the SB-200/201. Plus, RF Parts has a good exchange policy if you get a bad one. I should change out mine; they have been in my SB-200 since 1969. What are you going to drive the SB-200 with?

[K6IC]

Doug,

RF Parts does offer Svetlana 572s as singles and Matched Pairs:

http://www.rfparts.com/572bmp-svet-select.html

These tubes probably need a slight change to the Bias setting,  as believe their gain is a bit different --  they used to have an Application Note on their site for this change to the FL-2100 series Amps.

These tubes are not dirt cheap,  BUT,  they are there,  FWIW.  GL, Vic

[DMOD]

I have two 572 Tubes in my Dentron DTR-1200L that are horizontally positioned and they are the originals with fairly high gain.

The tubes are marked "Dentron" but info has it they are really Cetron Tubes marked with the Dentron logo.

Phil - AC0OB

[KM1H]

Since I converted scores of SB-200/201's to 6M, and still do, I got a bit of experience with Chinese 572B's. The ones Ive had the most trouble with and have heard the same from others is Taylors. Pentas were always good to me but unless the customer demands Taylors I buy Shugan direct from China off Fleabay, havent had a bad one yet and they even run cool in a Clipperton L at 1100W on 10M and as an AM linear on lower bands. All 572B's come from the same factory altho Ive heard rumors one of the other factories is restarting a 572B line that they dropped to concentrate on audiofool tubes....lots more profits

Carl

[Pete, WA2CWA]

And, from the RF Parts web site, under Taylor 572B: "High-mu power triode for use in Class AB2, Class B, Class C RF, and audio amplifiers. The modern TAYLOR 572B is virtually an exact copy (both mechanical & electrical) of the original Cetron 572B/T160L tube. TAYLOR is the preferred choice for FL2100, SB200/SB201, 10-160L, 30L1, etc. Base indexed and internal structure aligned and supported for both horizontal and vertical operation."

[Knightt150]

Douge: I have a nice FL2100B amp I have had bad luck with the Chinese and Svetlana tubes these tubes do not work well in a horizontal instulation (poor internal support). The TAYLOR 572B's have good internal support. and will last a long time.

John W9BFO