[Amps] Swan Mark 1

[Steven Katz]

I'm very familiar with the Mark I.  It's not as good as the Mark II.  :)



Two potential issues:



3-400Zs haven't been manufactured in over 40 years.  3-500Zs are a direct replacement, however they are "taller" and the Mark I usually requires mechanical modification to accommodate the extra tube height.  Also, while the 3-400Z was a "zero bias" tube at 3000V (for AB2), the 3-500Z really isn't and normally needs a bit of cathode bias to bring the idling current down to something reasonable.  (They'll "run" at zero bias, but dissipate a lot of power under zero-signal conditions, creating heat etc.)



The other issue is the Mark I has the power supply in the same enclosure as the tubes.  The tubes get very hot (of course) and make the transformer hotter, so they are prone to failure.  I've replaced power transformers in several Mark I's over the decades - some didn't last more than a few years (back in the early 70s) before they gave up, if they were used a lot.  The Mark II doesn't have this issue, as its power supply is separate and has its own cooling system.



But should be a good candidate for a monoband amp.



73



Steve WB2WIK



-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of mike stokes
Sent: Tuesday, June 11, 2013 8:48 PM
To: Amps
Subject: [Amps] Swan Mark 1



Hello

I have an oppertunity to pick up a Swan Mark 1 amp which uses a pair of 3-400s.  10M-80M with no tuned input.  I thouhgt it might be a good choice to convert to either single band 6 Meters or 160 Meters.



Any thoughts are appreciated.



--

Mike Stokes

KK9V

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