CMC/Marconi BH-30 Owners?

Discussion in 'Amateur Radio Amplifiers' started by VA3DXV, Jun 29, 2018.

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  1. VA3DXV

    VA3DXV Ham Member QRZ Page

    I recently obtained one of these beasts and I'm coming up mostly blank in my search for info. I'm interested in seeing how other hams have modified their units to be more "ham friendly". I'd like to get this thing on the air :)

    Thanks for any leads!
  2. WB1E

    WB1E Ham Member QRZ Page

    The only image I could dig up is this

    Well, like any other pair of 3-500z operating grounded grid (GG), should be fairly straight forward. Any idea of what the applied plate voltage (Va) is?

    Looks like a nice layout, plenty of space at least.

    KD2ACO likes this.
  3. VA3DXV

    VA3DXV Ham Member QRZ Page

    Yep all I could find was that page and an old post, a few old classifieds, and a couple of brief videos. Nothing really in depths. The amps got some potential. The RF deck and power supply is pretty straightforward (and built like a tank)... but the "channelized" bit is going to be a challenge perhaps.

    It's a fun project at least. I think I'll video my adventure and make a YouTube series out of it... here's part 1:

    WB1E and KD2ACO like this.
  4. W1QJ

    W1QJ Ham Member QRZ Page

    I had something very similar to that years ago and it was reportedly a ship amplifier that was channelized for Marine frequencies throughout the low band spectrum. Looks like you can re-tap the tank coil to move the sweet spots into the ham bands. Shouldn't take too much to get it to peak on the ham bands.
    WB1E likes this.
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Insatiable gear junkies are looking forward to your adventure! :p
    Last edited: Jul 7, 2018
    K3XR and WB1E like this.
  6. VA3DXV

    VA3DXV Ham Member QRZ Page

    Thanks :) Here's part 2

  7. VA3DXV

    VA3DXV Ham Member QRZ Page

    Well, unfortunately the project is on hold since it appears the tubes in it are dead (high SWR on input no matter the band, only about 80ma of idle plate current which doesn't change with RF level applied, and adjusting the load/tune has no effect on anything).

    Hopefully I can find an old pair of tubes that can be re-gettered at reasonable cost. New ones aren't in the cards.
  8. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    First, have you seen this?

    Second, I'm sure you're aware CMC is alive and well as a company in Saint-Laurent, PQ. I've visited them many times (late 70s to mid-80s) and the engineering department is loaded with hams. Most spoke English fine, a few didn't.

    Third, based on your description I doubt the tubes are bad! It sounds to me like there's a disconnect between the RF input port and the amplifier cathodes -- I don't have a schematic, but I'd bet somebody at CMC does. Could be something as simple as a T/R relay in the amplifier that's not keying properly or not making proper connection in the RF path.

    If it's drawing idling current, at least one tube is alive (maybe both). If it weren't so enormous and heavy, I'd ask you to ship it to me for debugging, and getting it going. That would be a truly fun project, as I've never seen one of these. But based on size and weight, shipping cost would be ridiculous.

    Try to find someone at CMC (there must have been 100 VE2's working there when I last visited) to help.
  9. VA3DXV

    VA3DXV Ham Member QRZ Page

    Thanks for the info, I've seen that site and a few other tidbits of info scattered around the web. Also discovered a few other owners in Canada and was in contact with one VE2. He's passed along a few other callsigns to contact but I haven't reached out to anyone else. I have the schematics, and ended up making good progress figuring out the control circuit myself after asking a few basic questions about it's operation.

    It's a pretty standard design RF wise, your basic grounded grid. The T/R relay triggers another one that switches bias on the filament center tap to a 4.7v 50w zener. Cathode is floating at +24v otherwise. After cleaning all the relays and switches and ensuring their operation, I thought the zener was bad but it tests ok. Though I haven't tested it under full current. Another thing is there's no grid current meter on this thing, so I can't see whats happening there. I considered getting rid of the zener. Been reading W8JI's site and a few others, and countless forums posts on the subject trying to figure out where to go next. Everything I've found seems to have indicated bad tubes though? I'm getting slight deflection on plate current (a needle width or two), as soon as I turn on the heaters without B+ turned on. Unsure though if that's just an inaccuracy in the metering circuit or if it indicates a tube short.

    Currently running it off 120v so I'm only getting 1900v on the plates. I guess I should figure out how to add a Ig meter and then I might try powering it up with only one tube at a time.

    CMC is still alive under a different name, mostly focused on avionics communications and navigation it seems. I didn't bother to contact them directly since I doubt I would get much response for info on a 40+ year old product. It would be incredible if they still had spare parts collecting dust in a warehouse somewhere :) I doubt the company would give me the time of day though... and I can only assume any leftover spares were probably gobbled up long ago by the VE2's who worked there and got their hands on surplus amps :)
    Last edited: Jul 20, 2018
  10. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, I'm sure "the company" would not go out of their way to help you (or me, or anyone with 40 year-old surplus gear), but there just may be hams there who would try.

    They're big enough, and were mostly in aerospace and avionics for decades, that they probably have very good archives in Document Control someplace -- although it's not unusual that records that old were never computerized and may be "paper" drawings and parts lists and stuff, archived almost anywhere including off-site.

    If you find any "old" hams (guys in their 60s-70s) who work there, I'd think they'd be the most likely ones to try to help.

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