[Amps] Tube Voltage ratings Question

[rlm]

On Wednesday, October 29, 2003, at 07:45  PM, John wrote:

> I have a question to the tubers out there. What determines the Anode 
> voltage rating on a tube ??

***  Tarot cards?  Ouija board?
It's less than what burns holes in the anode using AØ emission,  
However, for SSB, a bit more potential can usually be used.  For 
example, the 811A is rated at 1250V - but, as Art Collins realized, 
1800V is ok for SSB as long as AØ is avoided.  [can be avoided by 
tuning up with high-speed dits or a repetitive pulse]  As a rule of 
thumb, for SSB. one can double the V-rating for AM.  However, more V 
means more gain, and since every tube made has feedback-C, one should 
try to reduce VHF amplification in HF applications by lowering the 
parallel-equivalent R of the VHF suppressor in the anode circuit.  The 
tradeoff of doing this is c, 2% less P-out at 28MHz.

later




>  For instance ....I have a amp with 3-500z in it.... the
> space between the anode and grid wire cage is very small ...Yet is has 
> a
> high rating for maximum plate volts..... My SB-200 with 572B has a huge
> space between the plate to grid....But it has a much less voltage 
> rating of
> 2750 V ...I know current and anode dissipation play into this. But 
> could the
> 572 B's run on higher voltage as long as the total plate dissipation 
> is in
> spec ?? because with all that space it looks like there would be no 
> flash
> over problems or is there more to it ???
>
> thanks John,
>
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Rich Measures, AG6K, 805.386.3734.  www.somis.org/