----- Original Message -----
From: "Jerry Kaidor" <jerry@tr2.com>
To: <amps@contesting.com>
Sent: Saturday, June 16, 2012 12:16 AM
Subject: Re: [Amps] Alpha 78
> >
>>> Hi Guys,
>>>
>>> I've come upon a local Alpha 78...
>
> *** Another thing that tempts me is the Heathkit SB230. Another rare and
> valuable tube. I see them in working condition for about $400. Said to
> be an ideal platform for conversion to a dirt cheap GI-7B tube. It has
> the famous BeO block, which is said to be about 1000 times more poisonous
> than PCBs :).
>
> I find the idea of a small conduction cooled linear very appealing.
>
> - Jerry "dreamer" Kaidor, KF6VB
Sanding it and taking deep breaths could be a problem but OTOH there were
thousands of 8560A and 8072 amps in use by the commercial FM folks for
decades without problems.
The 3CX400U7, which often shows up even NIB for under $50, would be an
easier swap if youre a bit handy with tools.
Many years ago, out of desperation, I trimmed the anode cooler of a 8874,
sweated on a copper plate and used it as an 8873. Added a muffin fan on top
to suck out the heat thru the remaining fin area. That customer is still
running the same tube about 21 years later.
Ive often wanted to try a 8072 with a machined block to slide over the anode
and mate to the existing block. Or a 8121 with a muffin fan in place of the
heat sink. The 8072 is almost a freebie these days and the 8121 was used in
several commercial products long since scrapped. The rest of the work is
pretty straightforward to use a swamped grid tetrode. Add a filament xfmr,
develop a regulated 300V screen supply from the HV and add a -25 to -40V
regulated adjustable bias. Use a real meter that includes a screen current
position for tuning. BTW, it uses the stock socket, just rewire it.
Carl
KM1H
>
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