> From: docdc@ix.netcom.com (Dale Harper)
> Subject: [AMPS] 30L-1
To: <amps@contesting.com>
> Date: Mon, 14 Jul 97 02:22:37 +0000
Hi Dale,
> about the 30L-1. It holds 1800 volts, and tunes very easily, and seems
> to run cooler than I have been led to believe it should (Something
> about cooking eggs on top of it...)
I've never heard of a heat problem with the 30L1, it's only a 260
watt dissipation set of tubes. Frying eggs on the outside is a
subjective statement anyway, what really matters is the temperature
of components INSIDE the case. And you can bet Collins did their
homework on that subject.
>I assume it works well from the
> contacts I have made. I would like to know what you think of the amp,
> what you would change about the amp, and any quirks about it that I
> should be aware of. It has been stored in it's original carton since
> about 1961.
Sound like you got a nice gift, if you want to pass it along keep me
in mind. ;-)
The grid circuit is not of Collin's engineering skill levels. If you
run the calculations on feedback, including phase, you'll see the
feedback system contributes to instability. You can measure this with
a network analyzer, or other more simple test equipment like a
MFJ-259 and an oscilloscope or RF voltmeter. I think if you
follow Collin's rules the PA will work just fine, although a
simple cathode feedback resistor would have been much better.
They did have some stability mods, and I think they mainly concerned
15 and ten meters. 811A's have a lot of internal feedback capacitance
(from the anode to the cathode) and they really need neutralized on
ten and fifteen meters, but with proper tuning and a long input cable
they got away without it.
Heathkit and others neutralized their 811 amplifiers, and so does
Ameritron.
But the bottom line is if the PA works and gives you no problems,
just leave it alone. There is no point hacking up something that is
working. Only the people at Collins knew why they made the design
choices they did.
73, Tom W8JI
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