----- Original Message -----
From: "John T. M. Lyles" <jtml@lanl.gov>
To: <mark@sandlabs.com>; <amps@contesting.com>
Sent: Wednesday, November 13, 2002 4:14 PM
Subject: [Amps] 8877 dissp
> Yes, as pointed out by others, plate dissipation is only that
> electrode dissipation. And for 70% efficient amp in class B or C for
> FM service, it is only 1100 watts or so. But that leaves little
> margin for error, mistuning, VSWR effects. I would not be running a
> single 8877/3CX1500A7 at 2600 watts output anywhere except maybe
> pulsed or SSB. The transmitter I worked on the design of with Bill
> Harness years ago was 1750 output max, at 88-108.
>
All considered, when an amplifier has good protections (fast) with reflected
power, plate and grid current, the actual risks for mistuning errors and
errors in general is quite limited.
I'm talking in practice since my company produces FM amplifiers using a
selected version of the 8877 (YC236).
The point to care with I think is slightly different, stated that with
proper cooling a 2KW output power is conservative, and that the difference
from 2.5 and 2 KW is less than one dB, there's no reason to increase
complexity, costs (blower and extras) and to reduce the lifetime of a tube
amplifier for such a marginal power increment.
Talking about SSB, of course things are different in terms of duty cycle and
dissipation, but I'm afraid that IMD (linearity) won't be so excellent when
pushing the output at 2.6 KW.
If my memory doesn't fail, over 1,5/2 KW an 8877 at 4KV is already beyond
the compression point.
73,
Mauri I4JMY
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