I have read several threads here on the Zed regarding 572B's--and the final analysis is clear as mud. Some like Svetlana's, some generic Chinese tubes, etcetera.
Ultimately, I find that the selection has boiled down to NOS American made tubes, or the Chinese variety. I understand that the Taylor tube sold by RF Parts is a Chinese tube--but ultimately how well does it hold up? Especially for horizontal mounting (SB-200)--and how do these compare to the Chinese tubes sold on ePay that have the circle and bird logo?
All I know is that the Svetlana 572Bs are not identical replacements for any other manufacturer. They require significantly different bias voltages.
"Ham Radio does not abide by the 'Right Tool for the Job' rule. Quite the contrary.
It often gets the job done with things you wouldnt normally recognize as tools."
From what little I know, there can be problems and they're not necessarily limited to Chinese tubes. IMHO, the expert is Rich Measures, AG6K, although he's sometimes controversial. Let me suggest you look at his website : http://www.somis.org
Also do a google for "nearly perfect amplifier".
Short answer - some of these tubes seem to work sometimes and blow perfectly good amps other times, so YMMV. But Rich's page gives some hints for avoiding problems. I'ver known guys with AL-811?? Amps who have had good luck, and those who haven't. Personally, I've got a brand new set of 572-b's here I've been afraid to plug in.
[EDIT] Rich does sell stuff, but it looks like it's close to cost.
Last edited by k3wrv; 08-21-2008 at 11:17 PM.
hmm. i picked up an sb 200, with brand new chineese tubes in it. tuned input was well off, as was the power. the anode cap came away in my hand from one tube. i replaced the bad tube with another taylor/prc. its my understanding that this type of amp, does not need matched tubes (grounded grid?). anyhoo, tuned input now ok, and power out still fairly low? cut a long story short, i obtained used, but in good condx, usa manufactured tubes, from a gentleman in the south, who replaced these with a new set,with apparently very little gained.
the brand new chineese tubes on 10m cw gave about 300w, and the used usa manu tubes are showing about 500w at just under 500ma plate current. on 20m, its closer to 650w, so not bad for the old tubes.
i have to say, if i need replacement tubes for the sb200, or my trusty ts 830s, it will be anything i can find, except chineese.
may have to stock up though !!
regards, bob. ve3ptc/gm0ley
The Taylor brand tubes from RF Parts have a very good warranty, and they make good on it. I wouldn't hesitate to use them.
I have heard that the problems with the chinese tubes comes from the horizontal mounting. Well, the problem now is that all 572b's are made in china. I bought some from Epay and put them in my amp. I let it idle for several hours. Everything looked great so at lowest power from the exciter I keyed down...BANG!!!!...sizzle. I am still irritated by the whole incident. It happened two days ago. I ended up replacing two resistors and two small capacitors and the three diodes I added for meter protection, and, they did protect my meter, Thank God.
Before that I bought two NOS "Pride" tubes from RF Parts. One was DOA. I called them and they are sending me another one free of charge without me having to send the bad one back. Hopefully, I will finally have a spare set when that one arrives.
I would advise anyone to take any and all precautions before putting in any new 572b tubes. I am already afraid to try the tube coming from RF Parts, it's not even half way here yet.
With all we are hearing here and in the HF Amps forum, I am thinking really hard about converting my sb-200 over to the GI-7b tubes. Cheap, powerful, plentiful, and built like a tank...
I found a website once that actually detailed a ham doing that. Now I cannot find it. It's a shame that there is such an issue with these tubes. It's almost worth buying a junk amplifier to test the 572b's in first.
Just go to:
K4POZ and W4ZT created a socket for these tubes to help with conversions. Details of many conversions on the web site.
The GLA-1000 conversion is probably the best $$ return for the investment.