Joe, that sounds extremely modified!
Glen, K9STH is a competent technician and I would trust his work, but if he
bought the amp already modified and didn't personally use it, then who
knows-? Did Glen say it worked okay when he had it?
A vacuum variable in place of the original? Holy cow. Not really needed
for the 3kV or less the Mark I provides for the 3-400/3-500's (whatever).
That one is surprising. Sounds like possibly somebody wanted to turn this
into a higher frequency amplifier. Is the original bandswitch there? Is
the plate tank inductor original (to cover 80 meters)? Obviously, with a
vacuum variable in place of the original, the front panel markings for plate
tuning will be meaningless, and the knob will spin around a lot more than
360 degrees....might make going from 10m to 80m a rather interesting band
change.
WB2WIK/6
"If everything seems under control, you're just not going fast enough." -
Mario Andretti
> -----Original Message-----
> From: Joseph DiPietro [SMTP:n2uf@joeham.net]
> Sent: Friday, August 23, 2002 10:45 AM
> To: amps@contesting.com
> Subject: [Amps] Boat Anchor
>
> Hi All,
>
>
>
> I am new both to this list and to HF amps, so go easy on me please!
>
>
>
> I have acquired a 1960's vintage Swan Mark I amplifier. The amp was
> extensively modified prior to the mid-1970's including a complete
> rebuilding
> of the rf-deck. The person I bought it from told me he never used the
> amp,
> and it had sat in storage for at least ten years.
>
>
>
> A DC check of the HVPS showed at least one of the old (date-coded 1966)
> electrolytic caps as bad. So I replaced all of the caps, as well as the
> equalizing resistors and rectifier diodes.
>
>
>
> Before powering up the amp I would like recommendations as-to what else I
> should do. As I said, the rf-deck bears little resemblance to the
> original
> Mark I. The 3-400Z's have been replaced by 3-500Z's. A "penthouse" has
> been added to the top of the cabinet to increase the clearance (for the
> taller tubes, of course). Parasitic suppressors and heat-sunk anode
> connectors have been added (yes, those silver-plated bands wrapped around
> composition resistors that Mr. Measures loves so much). The tuning cap
> has
> been replaced with a Jennings Vacuum variable and the coil and loading cap
> do not seem to be original (I can't tell for sure since I have never seen
> the insides of an unmodified Swan Mark I).
>
>
>
> I don't know who did the modifications, but someone went to a lot of work.
> There is a metal tag on the front panel proclaiming "Big Momma I Linear
> Amp" and it is signed "K9STH/WA4MLI/WA5STI". I contacted STH/MLI/STI to
> get some history on the modifications. He claims that he bought the amp
> already (rf) modified in the mid 70's. He says he added the "penthouse"
> and
> then sold the amp after having it less than one year.
>
>
>
> So experts, what should I do with this boat-anchor? Keep in mind that I
> am
> on a somewhat limited budget. New caps, diodes and resistors have cost me
> less than $30 so far, and I can't afford to spend a great deal more, (no
> vacuum relays in the budget!). This is my first HF amp. I hope to drive
> it
> with an Icom IC-751 into a G5RV antenna tuned with a very large military
> surplus (Collins) tuner.
>
>
>
> If it would help I can take some pictures of the beast and email them to
> the
> inquisitive. (Olympus C2100, 2.1 megapixels, 10to1 optical zoom, I like
> it
> very much, thank you).
>
>
>
> Thanks
>
>
>
> Joe DiPietro
>
> N2UF@joeham.net
>
>
>
>
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