[AMPS] Bias for SB-220

[Rich Measures]

>€  How many peak volts on your 'scope?  With "normal" ALC indication,  my
>TS-440S overshoots to about 120v-p. into 50-ohms.  .
>
>I didn't measure it on my scope because I thought I needed a fast
>peak-reading or storage scope. 

€  A triggered scope with a vert.-deflection delay line will see the 
leading edge.  

> I have a peak-reading RF DVM now, but I think
>the minimum pulse width is 1ms. One of these days I'll see if my HP scope is
>fast enough to show it in the phosphor persistence.
>
>The test procedure you describe in a other post implies that you've tested
>the 440 only for SSB overshoot. Try it with CW. 

€  I did.  Running it in the ALC ok zone makes for a fast rise time.  
>
> While a sharp syllable might
>have a pretty fast rise time, I would bet that the CW waveform rises much
>faster, exacerbating the problem of slow rise time on the ALC. Also, QSK CW
>is likely to cause a stream of spikes, whereas SSB will probably cause
>spikes mostly when the VOX is initially tripped. 

€  I set my VOX fast to enough to drop at commas and periods because I 
want to hear comments.   I do not remain in a conversation with anyone 
who does not let the VOX drop at the end of sentences.  

>I found this to be true
>under contest battle conditions -- the 87A tripped much more often in CW
>contests than SSB contests. I'm sure when it did trip in SSB contests I was
>frantically bleating my call.
> 
€  3cx800a7s can be driven to full output with a lot less drive than is 
typically available.  One workaround is to add 50 ohms in series with 
each cathode of a pair.  This raises the driving Z from c.25-ohms to 
c.50-ohms - and it makes the cathodes virtually impossible to overdrive 
with typical transcievers.  An added benefit is that the cathode feedback 
resistors automatically balance the anode currents in unmatched tubes.  . 
 .  
>.......
>Well, another reason I replaced the 950 with a 1000mp is that the 950
>overloaded with strong adjacent signals during contests. I'm not sure that's
>exclusively an AGC problem, 

€  probably not.  It sounds like a vco  noise problem.  

>but I'm sure it's involved. I've always thought
>the IF filters on the 940 and 950 are not very good 

€  the measured shape factors are quite good.  
>......
-  cheers, Dick


Rich...

R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  


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