>
>
>
>On Mon, 5 Apr 1999 04:39:27 -0800 Rich Measures <measures@vc.net> writes:
>>>
>>Ä Most of the people I knew in CA, NV and AZ who initially purchased
>>one-tube and two-tube Viewstar amplifiers experienced intermittent
>>output-bandswitch arcing problems and returned the ampifiers to
>>dealers
>>for repair. Within months, no dealer in CA, NV and AZ was carrying
>>Viewstar amplifiers. It is my opinion that reports of bandswitch
>>arcing
>>can not be overcome by marketing. . . Since the output bandswitch
>>had
>>a breakdown potential much greater than the anode supply V, there
>>should
>>have been no arcing problems from the HF potential present.
>>. Not long after "Parasitics Revisited" appeared in the September and
>>
>>October, 1990 issues of *QST* magazine, I received a telephone call
>>from
>>QST-staffer James "Rus" Healy. Rus told me that he had just received
>>a
>>telephone call from one of the designers who had been involved with
>>the
>>Viewstar amplifier. Rus said that this designer described mysterious
>>problems with an under-development amplifier that sounded to Rus like
>>the
>>problems might be VHF-related. Rus said he recommended that this
>>person
>>telephone me - which he eventually did. We talked, however, my guess,
>>
>>based on subsequent events, is that he balked. .
>>- Free, unsolicited advice from yours truly: When a tube
>>manufacturer gives ratings for Amplifier or Oscillator Service, it's nothing
to
>>sneeze at.
>>- cheers
>>
>>
>>Rich...
>
>Well I cant speak for the initial Viewstars. Maybe reducing the HV was
>their way to do a fix.
? Reducing the supply of HV always reduces amplification. Less
amplification ususally means less chance of oscillation.
>However when B&W bought the rights to the 2500A I did a bit of work on them.
>
>And yes, the first units I saw had some funny looking stuff in the
>suppressor area that was Rich's magic fix.
? Mr. F. E. Handy recommended damping VHF parasitics with
resistance-wire in 1926.
? In *Proceedings of the Institute of Radio Engineers*, September, 1935,
in"PARASITES AND INSTABILITY IN RADIO TRANSMITTERS"
by G. W. FYLER, General Electric Company, Schenectady, New York, Mr.
Fyler concluded:
" If necessary, the plate or grid parasitic circuits should be damped
with resistance."
? Dittrich, H. F.; *Tubes for R. F. Heating*;
N.V. Phillips Gloeilaampenfabrieeken--Eindhoven, the Netherlands. Section
5.8, 'Parasitic Suppression Circuits' begins on page 96. There's also
some articles in QST, such as Oct., 1988, March 1989 and Sept./Oct.,
1990.
> They were the first thing that was thrown away.
>
>No voodoo at all, no mysterious VHF gremlins.
? Higher VHF Q (less VHF-resistance) dampens VHF parasites better?
>
>Just a slight readjustment of the PI-L, changing a few caps, and
>selecting the proper resistors for the original suppressors.
>
? Naturally, the details of these proper changes were omitted because
they are apparently too esoteric for us non-"experts" to understand.
- cheers, Carl.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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