This sounds correct. They are putting out about 1500 watts at 300ma.
Bumping to 400ma yields 1700+ watts delivered, but this is really pushing
them hard. The almost instantaneous increase in ambient shack temperature
was alarming and uncomfortable.
Keith
-----Original Message-----
From: Michael Tope [mailto:W4EF@dellroy.com]
Sent: Tuesday, August 16, 2005 2:10 AM
To: amps-bounces@contesting.com; keith@dutson.net
Cc: Amps
Subject: Re: [Amps] Grid Current Advice
If you assume an input impedance of 58 ohms (115 ohms/tube divided by 2 for
the pair) and 100 watts of drive power, that works out to around 76 volts
RMS grid-to-cathode potential. With a 40W maximum grid dissipation (2 x 20
watts/tube) this works out to a maximum grid current for a pair of 3-500ZGs
of 525mA. That seems a bit high to me, but it is consistent with the
guidelines for the Ameritron AL80B, for instance, which specifies a maximum
grid current for a single 3-500Z as 250mA.
http://www.ameritron.com/man/pdf/AL-80B.pdf
Personally, I don't think I would run a pair of 3-500ZGs much beyond 300 to
350 mA of grid current, just to be safe.
Mike, W4EF.........................
----- Original Message -----
From: <amps-bounces@contesting.com>
To: <keith@dutson.net>
Cc: "Amps" <amps@contesting.com>
Sent: Monday, August 15, 2005 7:52 PM
Subject: Re: [Amps] Grid Current Advice
There is no max grid-I rating. The max rated grid dissipation is 20w,
but several experimenters have found this to be somewhat conservative
-- probably because the grid is made from Mo, which melts at 2617ºC.
Figuring grid P --- According to "Care and Feeding ... ... ..." ,
grid-dissipation is approx. the indicated DC grid current multiplied by
the RMS grid to cathode potential.
cheers, Keith
.
On Aug 15, 2005, at 7:22 PM, Keith Dutson wrote:
> What is the maximum recommended grid current for a pair of Eimac 3-500G
> tubes? Thanks.
>
> 73, Keith NM5G
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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