Friday, December 28, 2018

What's On The Workbench?

Had a couple of "small" projects I knocked out before going into my next "big" project.

The first was the installation of an LED light kit for my Yaesu rotor control head. The OEM incandescent bulb is a non-serviceable part, and one of the cottage-industry Ham guys came up with a  nice little PCB with three white LED's on it. Took about 30 minutes to install it, it's much brighter, and will probably never "burn out".

The second project was rebuilding my #2 Drake MS-4 speaker with AC4 power supply. The original speaker is old and dried-out, and the electrolytic capacitors and rectifier diodes in the power supply are old tech, and better modern components are available.

In the same space, you can now have capacitors with higher voltage ratings (good for reliability), and more capacitance (better filtering), with a higher temperature rating (better reliability again), and better manufacturing processes. The rectifiers also have higher voltage and current ratings, and their surge capability is far higher than the old type rectifiers the supply was manufactured with. And all the new components mount on a convenient PC Board.

The supply looked like it got into a bar fight at some point in it's life, but since this is an aluminum cover, I should be able to make most of the dents go away.

Pretty clean inside, though....

But, yow....I haven't seen rectifiers in a "Bullet Case" package since high-school! These are 1N3194's, rated at 400V and 750mA. The replacements are rated at 1000V and 1A, a nice upgrade.

So most of the old capacitors, and all of the rectifiers get removed. The two big can capacitors were left on 'for looks'.

Then the new PCB gets mounted, wired in, and a couple of cable ties added to keep the wiring neat.

And the speaker gets replaced.....

Testing revealed 790VDC no-load on the HV, and 275VDC on the B+. Bias (for the 6DQ5 final PA tubes) is adjustable from -25VDC to -65VDC, all well within specs.

So bolt it all back together, and put it back on the shelf next to the one I did a few weeks ago.

Yes, they're sitting quite differently. The one on the right has the "short feet" on the back of the enclosure, tilting the panel back slightly, while the one on the right has same size feet, making it sit level.

Next up on the project Heathkit AR-15, soon (actually already is) to be On The Bench.


  1. Neat, DRJIM!! I wish that I had half of your knowledge and skill in this sort of effort.

    1. I'm attempting to "Keep The Filaments Lit" in the hope that some youngsters might take an interest.

      And to make Analog Believers out of them....

  2. Amazing how much room you got back and the reliability went way up at the same time.
    I'm with LL, I wish I knew about a tenth of what you do. I'd be dangerous.....

    1. The power supply is around 40~50 years old. Components have improved tremendously since then. Since I rebuild my equipment to use, it would be silly not to take advantage of improvements.

  3. Replies
    1. Thank you, sir! It's a bit too cool in the garage this time of year, so I thought I'd get the electronics workbench going.

      Keeps me out of the bars, you know.......

  4. Fix it up! I love restoring stuff, btw.

  5. While I strongly agree that Tube equipment and Solid-State equipment sound different, this older late 1960's~1970's Solid-Sate gear can give anything a run for it's money.

    And both the older equipment types sound vastly better than today's over-processed digital "realism".


Keep it civil, please....

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