2
\$\begingroup\$

I am very inexperienced.

I am a HAM, I just got a HA-10 amplifier that has been modified. The half wave tubes were replaced with a string of Z5U .01 ceramic caps in parallel with 1M ohm resistors and unknown diodes, four sets on each side. Please see the pictures and schematic.

There is no visible identification on the diodes, the caps are Z5U .01 2K. The string is off a 3500 volt transformer that powers this string to the transmitter tubes 4 of 811a's. I want to replace it with new parts because the wires have black dust on them, I am guessing from running to warm. It is a 1 kW amplifier. Can anyone PLEASE help me and explain what this genius did maybe 50 years ago?

I want to build a nice little board with the proper diodes/diode and caps to replace this cardboard setup. I have wiring diagrams and some specifications. I do not have the knowledge at this level.

Any comments or suggestions are appreciated. I have a drawer of 25amp 50 volt full wave rectifiers and would love to use them. I am not sure how I would without it being partly guessed.

Correct, I looked with magnifying glass and bright light. If it is there it has long burnt out of eyesight range. You should be able to zoom in on the photo, I may have made it too small, but the only thing I could get was numbers on the caps, and a guess on the code of the resistors because the colors are not according to text book. The two tubes that were replaced were 866a half wave. I will send specs in a few minutes. Thanks, I hoped to just buy the same and rebuild the existing setup.

enter image description here

enter image description here


Correct, I looked with magnifying glass and bright light. If it is there it has long burnt out of eyesight range. You should be able to zoom in on the photo, I may have made it too small, but the only thing I could get was numbers on the caps, and a guess on the code of the resistors because the colors are not according to text book. The two tubes that were replaced were 866a half wave. I will send specs in a few minutes. Thanks, I hoped to just buy the same and rebuild the existing setup.

\$\endgroup\$
2
  • \$\begingroup\$ Are you sure there is no marking on those diodes? \$\endgroup\$ Commented Apr 8, 2018 at 20:05
  • \$\begingroup\$ FIY, there is a HAM Radio Stack Exchange. It would probably be a better place to post questions about equipment than here. \$\endgroup\$
    – AlmostDone
    Commented Apr 8, 2018 at 20:35

2 Answers 2

3
\$\begingroup\$

The Heathkit Warrior HA10 kW amplifier power supply used a transformer with a 3400V center tapped secondary, followed by two 866 mercury half-wave rectifiers connected in a full wave center tapped configuration. Each rectifier had 1700V on its anode.

Many owners of this and similar equipment replaced the 866s with silicon diodes when the 1kV diodes became readily available at low cost. The method used was to string multiple diodes in series, each shunted by a 500k-1M resistor in parallel with a 0.01uF ceramic disc capacitor, usually Z5U dielectric.

Most likely, what you have are 1kV, 1A diodes, such as 1N4007. Better replacements are available today, but you would be safe using this same diode in that configuration for the HA10.

Before you replace the diodes, I suggest you replace the filter capacitors and test the choke for shorts.

\$\endgroup\$
5
  • 1
    \$\begingroup\$ Probably not 1kV inverse rated diodes. There are far too many of them for that. \$\endgroup\$
    – JRE
    Commented Apr 8, 2018 at 20:37
  • \$\begingroup\$ THANK YOU!, I can at least pull it apart now and check each item. This makes sense, the tube replacement was about 50 dollars per tube with a solid state/plug in replacement. If you look a the photo, you have described it perfectly. The wires on the diodes are covered with black dust/hot wiring. I want to go best. I will check each of the stages before powering up. Again, thanks for the direction. \$\endgroup\$ Commented Apr 8, 2018 at 20:46
  • 1
    \$\begingroup\$ Four diodes for each leg? Not unreasonable for 1700V rms. Peak voltage would be 2380V; 4 in series is less than 2X. \$\endgroup\$
    – AlmostDone
    Commented Apr 8, 2018 at 20:47
  • \$\begingroup\$ I count 14 diodes. \$\endgroup\$
    – JRE
    Commented Apr 8, 2018 at 21:06
  • 1
    \$\begingroup\$ "...and unknown diodes, four sets on each side. " I was going by what you wrote above but must have misread it. Still, I would recreate it with a string of 4 (certainly no less than 3!) of the 1kV diodes. \$\endgroup\$
    – AlmostDone
    Commented Apr 8, 2018 at 21:10
0
\$\begingroup\$

866a is mercury vapor tube rectifier with high power efficiency, its voltage drop is just 15V. Replacing with silicon diodes just get the same efficiency.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.