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Author Topic: HL-2200 /SB-220 single 3-500z tube mod.  (Read 1642 times)
WA2JJH
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Posts: 523


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« on: March 28, 2006, 11:13:12 AM »

My old 3-500's are going south. My filiment transformer
starts to smoke after a while. I guess I have some shorted laminations.

  I really do not need 1500W out. My pre WW-1 building could never support max input anyway.

  Seems like the new zinc carbon fiber 3-500Z's are far more efficiant than my old Eimacs(they must be 15 years old or more.

  I was thinking of ordering a new diode voltage multiplier, new filter caps and meter board w/5w bias zener. A new filiment X-former too.

   I would also like to buy a N.I.B. single 3-500Z.
I can deal with 700W out. That is really all my old building wiring can handle.

  I am sure I am missing a few details to convert this old work horse to a single 3-500z. I also wanted to go with a resistor beard(lots of 2W resistors in parallel.

  I had an SB-230(single 8873) that used a resistor beard and did not have a tuned L/C network per band.
The GLA-1000 has the same type of non reactive input.

  I would think since I would only need 50W out of my 150W kenwood TS-950SDX to drive the GG signal tube to 700W, I would make amatuer specs for spec purity.

  Am I missing engineering details? I would use the excellent ATU in the TS-950SDX for extra matching/filter problems.

  All advice will be a learning experience. So blast away. You will not hurt my feelings/ego!

  TNX DE WA2JJH
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WB6BYU
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Posts: 18457




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« Reply #1 on: March 28, 2006, 01:29:20 PM »

If you use the same plate voltage at half the current as
the original two tubes, that doubles the plate impedance.
You will have to modify the output networks to match this
new impedance to 50 ohms.

Not that it can't be done, of course, but for an optimal
match this will require changing coil taps and making
sure the variable capacitors will tune to the necessary
values on each band.  You'll have to decide whether you
would rather rework the output networks or stick a second
tube in the amp and just run it at reduce output.
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