[Heath] Biasing in the SB-200

[Kenneth G. Gordon]

On 27 Sep 2011 at 20:20, Jerry Haigwood wrote:

> Ken,
> The Chinese Shuguang 572Bs are equivalent to the Cetron.

I agree, although, at least in MY SB-200, the Shuguang tubes need a 
bit less bias in order to draw 90 mA at idle. Mine draw 69 mA.

>  The
>  Svetlana 572Bs require different bias.

And, in my amp, they require neutralization, otherwise, they run 
away. When properly neutralized, they put out as much power as the 
Cetrons or Shuguangs, and are very reliable. However, Svetlana hasn't 
made any of those for at least 5 years.

>  I am currently running a pair of Taylor
> 572Bs which I believe are of Chinese manufacture - at least they have
> a small "PRC" printed on them. ;-)

Yes. I bought a pair of those some time ago too, and yes, as I 
understand it, they are specially selected Shuguang tubes.

>  I did not change the biasing and
> they are performing very well (600W output with 52W of drive).

I am getting the same output for the same drive as you are. I think 
they are good tubes. I run my TS-940 at 80 watts output for 750 watts 
out of the amp on 80 meters, but I normally keep it down to 600 
watts. The added 150 watts would never be noticeable on the receiving 
end, and the tubes last longer. 

>  The
> Shuguang 572Bs are of excellent quality better than I had anticipated
> from the Chinese.

I agree.

> A pair of tubes cost $59.95 and shipping $24.90. 
> They come with a 30 day money back guarantee and a 1 year warranty. 

I have had extremely good experiences with the company from whom I 
buy them off eBay. It is probably the same as the company you buy 
them from.

They honor the warranty and don't even ask questions. I had one tube 
I bought from them that I kept as a spare for over a year, then when 
I tried to use it, it had a grid to filament short. They took it back 
with no questions and sent me a new one, despite the fact that it was 
out of warranty.

> They are available on ebay.  I have a very nice Clipperton-L with the
> original Cetrons still in it.  It still makes 1100-1200W peak on SSB. 
> Whenever I decide to change tubes, I am buying 4 of the Shuguangs.  I
> enjoy watching your progress with the SB-200. I think I told you that
> I rebuilt my SB-200 a few months ago. 73, Jerry W5JH

Yes, you did, and I enjoyed reading what all you did to it. :-)

BTW, the only reason I am so, apparently, serious about the necessary 
bias voltage is that I am concerned about the linearity not being the 
best it can be if the biasing is wrong.

I tend to be a "belt and suspenders" type, I guess...

vy 73,

Ken W7EKB