[AMPS] Technical Question #1
Fri, 22 May 98 05:01:54 -0800
>> Date: Thu, 21 May 1998 10:04:11 -0500
>> From: Jon Ogden <firstname.lastname@example.org>
>> 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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