>
>On Thu, 25 Sep 1997 19:29:17 +0200 (MET DST) Johnny Johansen
><johnnyj@stud.ntnu.no> writes:
>>
>>Hello all,
>>
>>I was wondering if anyone have some experience with three 3-500Z in
>>parallel??
>
>The Amp Supply LK-550 used 3 tubes. With a bit of rework it is a fairly
>decent amp.
>
>
>>Anything particular to be worried about?
>>
>>Have built an amp with two such tubes - grounded grid construction -
>>previously, without any problems at all....easy and reliable, but what
>>about adding one tube??..anyone?
>
>The primary concerns are getting enough air flow and a sufficiently low
>minimum C from the tune capacitor. ...
- With a 4kV supply, at 29MHz, for a tank Q of 12, a single 3-500Z needs
about 13 pF of C1 to tune the tank. Since one 3-500Z anode contributes
5pF, a minimum C of 13pF -5pF = 8pF.is indicated. ... With two 3-500Zs,
26pF would be needed at 29MHz. Subtracting 2*5 = 10pF for two anodes,
means that C1 needs a 16pF minimum. ... ... With three 3-500zs, 39pF
would be needed to tune the tank to 29MHz. Subtracting 3*5 = 15pF,
indicates that 39 -15 = 24pF would be needed. With four tubes in
parallel, a minimum C capability of 32 pF is indicated.
>A spit section air cap or a vacuum
>variable would do the job.
It looks to me like any capacitor that is capable of tuning one tube at
29MHz ought to capable of tuning three tubes at 29MHz.
>
>The CB crowd run 4, 6 and even more 3-500Z's on 27MHz !!!!!
Apparentl;y, at least some of the CB crowd knows about hamdom's old
wives' tale of not being able to tune a multi-tube amplifier at the high
end of HF.
Rich---
R. L. Measures, 805-386-3734, AG6K
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