[ARC5] 1625 question

[Kenneth G. Gordon]

Ron:

What Robert is telling you is absolutely correct, of course.

I believe that the "voltage rating" for those sorts of tubes had something to do with the 
possibility of arcing over under certain conditions, most of which conditions were never 
clearly stated.

It has also been clearly discovered that any plate voltage to an 807/1625 much greater than 
about 750....coupled with some other factors....resulted in relatively quick deterioration of 
the tubes, mostly caused by issues with the screen-grids.

These factors are, among others, why I have always regarded the "maximum plate 
dissipation rating" as the single most important characteristice of our tubes. Exceeding that 
results in quick or quicker deterioration of the tube in question.

Ken W7EKB

On 6 Feb 2018 at 0:43, Robert Downs via ARC5 wrote:

>     The absolute max rated voltage given in the tube manuals is the DC output voltage of 
>     the power supply.  And includes a safety factor plus assumes that at that voltage, the 
>     peak voltage on the plates is going to be 1500 volts.  So operating the tubes with 1000 
>     VDC on the plates depends upon "using" some or most of that safety factor. 
>      
>     Robert Downs - Houston
>     WA5CAB
>      
>     Sent: Tuesday, 6 February 2018 12:07 PM
>     To: ARC5 at mailman.qth.net
>     Subject: [ARC5] 1625 question
>      
>     I am reading some old surplus manuals and find that they like to use the 1625/807 as a power 
>     amplifier ( typical ARC-5 parallel style ) and suggest that one could run up to 1000 volts on the 
>     plate. Every listing I can find shows a absolute maximum plate voltage for the 1625 of 750 volts. 
>     Yes, the operating plate voltage will depend upon class of service and therefor duty cycle but 
>     isn´t absolute maximum absolute maximum? Now I can remember pushing the stated maximums 
>     a bit and I even have a friend who admits running a tube in a coffee can full of water to get a few 
>     more watts out of it.  But none of it was "published" that I know of. What am I missing?
>      
>     Ron K3PID



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