[AMPS] Plate load charts

[Rich Measures]

>
>
>
>On Thu, 7 Jan 1999 03:56:41 -0800 Rich Measures <measures@vc.net> writes:

>>>Re:  SB-220  on 10 M.
>>>
>>>K4AB  damaged the bandswitch 
>>
>>Ä  Did he damage the bandswitch through error?
>
>Yeah, Heathkits....not voodoo.
>
Barring spilt coffee, the withstanding potential of the Heath SB-220 
bandswitch is slightly over 5000v.  On the SSB tap, tank piv is c. 2600v. 
 With deliberate mistuning, the tank piv has been measured with an 
oscilloscope at 3600v max.  
>>
>>>before the 10M contest
>>>so he bypassed the bandswitch, wiring the SB-220 tank
>>>circuit directly for 10M.   Output went from the usual 900W to 1200 W.
>>>
>>>Wonder what could be done to improve efficiency on 10M
>>>using the bandswitch?
>
>Exactly the point I was trying to make yesterday. It is not the SB-220
>tank coil that is at fault since I use the same 10M coil on 6M and it
>works just fine at 60+ % efficiency.
>Several times I have suggested that the SB-220 switch shorting scheme is
>the culprit behind blown switches , arcing Tune caps and parasitics have
>nothing to do with it IF the suppressors are not damaged. 

 However, in my opinion, most folks don't bother to measure Rsupp if they 
appear to be ok -- which is undoubtedly no substitute for an ohm meter.  

>The shorted turn effect of the switch coupled with stray C and L forms a
>tuned circuit at some VHF frequency. When condx are just right things go
>zap. Before they go zap this circuit is consuming power and reducing
>efficiency.  This power is normally shunted to ground thru the low
>impededence of the capacitors, until the right combination causes a high
>enough impedence to force a breakdown.
>
>Proof?  Simple, just put the amp on a spectrum analyzer sweeping  5-300
>Mhz and Peak Hold on. There will be just enough VHF energy getting thru
>the circuit at the antenna port to be seen on a sensitive analyzer, 

 The HF tank is a low pass filter.  

>or you could just use a sniffer probe. 

definitely mo' betta

>No need to run full power for the
>test, 500W or so in the CW position will be fine and save the switch
>while you vary the caps. 

Intermittent vhf parasites are seemingly triggered at the instant of a 
rapid change in anode current.  With a cw keyer sending 50wpm dits, 
damped ringing at c. 110MHz can be seen coming from the anode-resonant 
circuit in a SB-220 (principally C-anode and the conductor L to C-tune).  
Varying C-tune moves this resonance only a few percent since C-tune is in 
series with - and is much larger than the 2 x 5pF of C-anode.  //  The 
idea of being able to save the switch makes no sense to me since a vhf 
parasite can occur at the instant of bias switching to Rx or to Tx, with 
zero drive.  This can arc open contacts on the band switch.  For some 
mysterious reason, TL-922s seem to be more susceptible to sans-drive bias 
switching arcs.  
>.......
-  later



Rich...

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


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm