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Old 26th May 2020, 12:00 am   #1
Chris Wilson
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Join Date: Nov 2011
Location: Whitchurch, Shropshire, UK.
Posts: 581
Default Exotic home brew 2 metre amp puzzle

I couldn't resist this Ebay amp, the engineering in it piqued my interest as I could see it was a labour of love on a CNC machine. It was allegedly built by a now deceased German ham, and came with limited documentation, mainly CNC drawings. It uses a pair of Russian triodes G17B's. It has inbuilt HV and LV supplies. I am probably out of my depth without schematics as the stuff seems electronically all custom made, in regard to PCB's. I am well aware though of the respect over 2kV DC requires. I have built a 4kW 27MHz industrial band amp for running a glue dryer for work, that's 5kV and I am still here!

Here are my questions and a link at the end to a largish zip file of photos of this unusual beastie. Thanks.


My initial questions are, what sort of tank arrangement do you think he had in mind? If you look at the big silver plated coil, to the side are two brass probes with either sliders or connectors on them. The assembly these probes are on is on a slotted mount and will slide along the axis of the big coil. There's also a small variable air spaced cap buried in there. Elsewhere I see two feed throughs, probably for the filaments.

He seems to have made his own equivalent of a Bird Thruline line section (!) that even turns 90 degrees. I have the alloy covers for each "compartment" and each compartment has a drilled internally threaded hole in it to the outside, for something. I do not know how he might have envisaged getting a forward and reflected signal from these, I have a Bird Thruline section on a Henry wood drying amp I use for work, and of course it just uses Bird slugs. The holes in his 2 compartments are only about 8 or 10 mm though...

The separate exotic transformer and adjustable regulator assembly is (I think...) now defunct and he decided to subsequently fit the 12 v toroidal transformer and a hard to see rectifier and regulator PCB. There is certainly no where I can find internally for the separate transformer, mount and heat sink to fit now.

The main HV rectifier board has DL4KH etched on the copper. DL4KH is one Richard Joachim, and he does not appear to deceased. He has a Germany based VHF / UHF antenna company and one product is a sequencer. I think a variant of this sequencer may be what a small PCB behind the main rectifier board is. I a wondering if Richard Joachim is the chap who built the amp, his company would almost certainly have CNC stuff for alloy fabrication.

Finally the black finned heat sink with a TO3 type semiconductor on it is maybe a grid bias device? It is hard to second guess what the builder had in mind and the notes files is not very helpful, mainly CNC drawings. All the internal wiring is designed to be hidden in plastic trunking and of course he has made things so compact getting at stuff is not particularly easy!

I would very much welcome any comments. Right now I am wondering if using a GM3SEK Triode Board to control things might be easiest, rather than reverse engineering what is already there, electronically.

The photos are in a large zip file at http://www.chriswilson.tv/amp.zip
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Old 26th May 2020, 8:46 am   #2
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: Exotic home brew 2 metre amp puzzle

Looks like he made his own tuning capacitor and reduction drive.

I love the heat sensing bulb held in the outgoing air and the thermometer gauge in the front panel.

I wonder where that triple-wide meter unit came from?

The cross needle meter on the front is a Daiwa one

So is that a conduction cooled valve with a heatsink clamped on? Ah, no, it's a parallel pair.

Beautiful mechanically, but less elegant electrically. GM4JJJ had one he built (forget the callsign of the design) using a pair of 4CX250B in push-pull with a U-shaped line of flat plate (silver plated) as the resonator with a pair of discs as a bridging capacitor to resonate it. Coupling loop to the antenna. For 2 metres at high power, the reactances you need are getting a bit low for efficient realisation as a coil, and a line-over-ground can be made to use its surroundings rathe than fight them.

Spiffing, though!

David
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