[AMPS] Technical Question #1

Rich Measures measures@vc.net
Fri, 22 May 98 05:01:54 -0800

>> Date:          Thu, 21 May 1998 10:04:11 -0500
>> From:          Jon Ogden <jono@webspun.com>
>> Tom:  Did you say that you have seen parasitic oscillation damage of 
>> *ANY* kind in SB-220s?
>Yes. I certainly did say I saw what I thought was parasitic damage. I 
>was very clear in staing it was from what I beleived could have been 
>low frequency osscillations.
>> The reason is that while Tom may have never seen *VHF* oscillation 
>> damage, he may have seen damage due to oscillations at *HF*.  HF 
>> parasitic oscillations can occur in an amp that is not properly 
>> neutralized.  Especially the two tube variety.
>> So Tom, please clarify for all of us what you told Rich.
>I specifically told Rich that there were cases where the chokes and 
>capacitors on the grids looked like they were exposed to high 
>voltages. Many of those cases were in amps with long leads and poor 
>solder connections, and loose hardware. 
As I recall, he mentioned that, however, we were discussing bandswitch 
arcing -- like that shown in photographs A and B on page 33 of the Oct. 
1990 *QST* article, "Parasitics Revisited", which is why he called me.  
According to Mr. Paul Pagel, Ameritron customers whose bandswitches 
seemingly had failed quite similarly were telephoning Mr. Rauch and 
asking questions -- which I presumed were somewhat "unfriendly".  .  

>I told Rich I found several SB-220's I could make oscillate at lower 
>frequencies, with proper external loads. 
... which Rich believed was unsliced smoked-bologna because VLF is hardly 
likely to get past the SB-220's  1000pF DC blocking cap. and the 50uH 


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

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