[Heath] Results of experiment with reactivation of 5

[Kenneth G. Gordon]

On 8 Aug 2012 at 13:53, Chris Kepus wrote:

> Ken, 
> Thanks very much for this interesting, if not depressing, summary of your
> experiments with the Chinese tubes.

Yes. It most certainly WAS depressing to me to discover what I did. VERY, in fact! ;-(

>  No wonder you're headed towards the
> 4CX250Bs  (Lots of us will be interested in that one! :-))

Well, I will be discussing it when it occurs. I went to the metal shop today to get two small 
chassis ordered on which to mount the pair of 4CX250Bs..

> After reading your entire message, I wonder if you have incorporated any of
> the more credible mods in your SB-200's? Soft-start, "Measures" VHF
> parasitic suppressors, etc.? 

Well, according to Measures, followed by what I discovered, neither the SB-200 nor the SB-
220 NEED "soft-start" since that function was purposely built into the power transformers. I 
have replaced all my filter caps with 470 ufd jobs and have never had a problem that way.

I DID add a "soft-KEY", however, and parasitic suppressors designed and used by Carl 
KM1H. Those made a very big difference in how stable the amp was. I also got a bit more 
power output after I installed those.

I posted that info to the list some time back, and made photos available.

BTW, the "soft-key" wouldn't work properly until I replaced C-3, the 33 MFD 450 VDC filter 
cap for the bias line. Mine had so much leakage that the 60 Hz hum was biasing the "soft-
key" so that when I used that, final amp bias was too high, showing improper idle current. 
That took me quite a while to figure out.

Also, I am implementing Measures' HSS (HighSpeedSwitching) circuit for full-QSK with my 
SB-200. It works very well indeed with the SB-200.

Lastly, my SB-200 came with the input circuitry modified for much better (lower) SWR 
between the amp and the exciter.

Once I modify one of my SB-200s to the 2 ea 4CX250Bs, I think I will just use it from then on. 
;-)

vy 73,

Ken W7EKB