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CMC/Marconi BH-30 Owners?

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

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  1. VE9GFI

    VE9GFI Ham Member QRZ Page

    Hello all. I have one (picking it up next weekend). I have the manual, and I'll be interested in setting this up for amateur use too.

    I'll check back in when I open it up.

    Greg VE9GFI
  2. VA3DXV

    VA3DXV Ham Member QRZ Page

    I forgot that I posted this :) This amp is a true beast, you'll enjoy it.

    My tubes were indeed dead, but I eventually found a good pair of 1974 NOS tubes and it's making about 1000 watts running on 120v (about 2kv B+). Have yet to get 240 in the shack.

    I built a control box for it with a raspberry pi, a display and a relay board, wrote the program in Python. The box sits with the amp and I can control it over WiFi or from the box itself.

    Still searching for that stupid 26 pin Winchester MRAC connector though, so it's not really "in service" yet. Otherwise you have to reach inside the amp to change presets... No thanks!
    Last edited: Feb 3, 2020
  3. VE2GCE

    VE2GCE Ham Member QRZ Page

    Marconi was sold off and split off into two different companies around 1999-2000 with the new companies focusing on avionics and military equipment
    • CMC Electronics (formerly Esterline)
    • Ultra Electronics TCS

    I remember having Marconi consumer products (TVs and radios) in our house when I was a child.
    Marconi took the same path as Raytheon. Both companies started manufacturing consumer products, but then switched to the more lucrative military markets with much higher profit margins and less competitors.
  4. VE9GFI

    VE9GFI Ham Member QRZ Page

    So my dad is retired from CMC, from the Land Mobile division, where he worked for the commercial fishing industry in Nova Scotia. Interestingly, he didn't deal with this BH-30 equipment at all... different group. He dealt with radar, sonar, SSB, fish sounders, mapping systems, loran, gps, etc.

    Can you describe what how this 26 pin cable is used?

    There's a paragraph in the manual that talks about S301 and a selection of one of 12 channels by the CH25. I didn't pick up the amplifier yet, so I'm trying to piece this together without the benefit of having seen it yet. I'll pull down your project from git tomorrow and look at the code.

    By the way, my dad is retired from CMC but he didn't work on this equipment. But I'll ask him about the cable.

    Greg VE9GFI
  5. VA3DXV

    VA3DXV Ham Member QRZ Page

    So there's no band switch (well there is, but it's not directly switchable by you). There's 12 (16?) pre-set channels that can be set up in any one of the 10 frequency ranges listed. 2-22 MHz. You select which frequency range you want for each channel by wiring jumpers on one of the boards inside the front panel... this is what sets the actual band switch when you select a channel.

    Then to select what channel to operate, you short pins on the rear 26 pin connector, J301 - (J302/J303 will also control other remote accessories). Very hard to find connectors, but you'd connect this to a band decoder or a rotary switch in a box at the end of a cable, or whatever switching method you desire. This connector also has your PTT, ALC, and pretty sure it even has provisions to set it up with remote metering (haven't figured that one out yet but a BH-30 owner in VE2 land has done it).

    Selecting a channel on that connector moves a motorized rotary switch, S301. This then tells the band switch to move to the frequency range you selected for that channel (with the jumpers), and sets the Load/Tune controls to their last preset. S301 can be manually actuated, but it's internal and only accessible inside the top cover. There's also 6 antenna ports that this switch can be wired to, so you can assign a separate antenna to one or more channels.

    To adjust the actual amplifier tuning, you switch the amp to "Tune" mode, select the channel with J301 or S301, then Load/Tune it like you would any other amp. You can run it like this all the time but you have to change channels to change bands.

    In order to "save" or lock-in that channels current tuning, there's 2 servo control boards inside the front panel. One for the Load capacitor, one for the Tune capacitor. Both boards have pots corresponding to each channel. After you've done your Load/Tune routine, you switch the amp to "adjust" mode. Then adjust the corresponding pots on the control board until the light above the corresponding Load/Tune control lights up. Now it's locked in and you can switch to "operate", and switch between channels. It will always turn the Load/Tune back to the point you set it to for that channel. The Load/Tune servo boards are both identical, and can be swapped, but if you swap them you'll have to re-adjust.

    The amp requires a little tweaking in the tank circuit to get it to cover all HF amateur bands. The input tuning is "acceptable", but because it's set up for such a wide range, you don't get the best input swr. It's best to redo the input matching network, and adjust the taps on the tank coil, to optimize it for the amateur bands. I do not believe it will operate on 29 MHz without modification. Getting it to the bottom of 160 might also be an issue. I've heard there's a larger tank coil from Harris that will drop in but I'm not sure what the part # is or where to get it.

    I just set my channels up like a band switch with high/low presets for each band, and I tweak the load/tune manually if I move elsewhere in the band... Then again I'm not really using it often since I don't have the connector and can't change channels :) It might be more convenient to set it up differently.

    Hopefully that's to convoluted of an explanation!

    PS the J301 connector on the amp is Winchester MRAC26PJ6-N1 . I assume the corresponding mate is MRAC26S??-?? but not sure. There's a couple on ebay that look like they fit, but they're of course missing the gold contact pins. :mad:

    Brian VA3DXV
  6. VE9GFI

    VE9GFI Ham Member QRZ Page

    Hi Brian,

    OK, this is clear now.

    The manual that I have doesn't talk about the coil, or at least I can't find the section. The parts list shows the EF Johnson clips; Are the taps on the coil factory set, but as you suggest, perhaps should be modified?

    I still don't have the unit yet. We had an ice storm on Friday night and snow on Saturday, and cold on Sunday. We pushed it from Saturday and then Sunday, and then cancelled the pickup because we can't get a truck behind the house with the combo of ice and snow that is on the ground.

    The circuit boards show blank spots for additional potentiometers (looks like this could be a 18 channel unit, but only 12 are installed.) Since you have a RPi controlling part of your amplifier, have you considered putting a programmable voltage reference in place for each of the TUNE and LOAD circuits on one the channels? You could then adjust that unit during your setup, and then store the values in your Python code, and send the appropriate POT settings for each band. I.e. You would setup channel 12 as "fully automatic" and control the TUNE and LOAD positions by changing the reference voltage in code. Of course, I may be ahead of myself.

    Getting back to the tank coil. If it should be adjusted, can you explain how this should be done? It's been years since I've had tubes in the shack (Kenwood TS-820S.)


    Greg VE9GFI
  7. VA3DXV

    VA3DXV Ham Member QRZ Page

    Yes exactly. It's set up to be really broad. I'm far from an expert here and haven't done it with this one yet, but the method I've used for my homebrew amps is I put an antenna analyzer on the output of the tank circuit (accounting for the T/R relay by bypassing it or "keying it up"). Leave all power to the amp off but the tubes in place. Put a resistor from the plate of the tubes to ground that represents the output impedance of the tube at its operating voltage/current (I forget what value that would be for a pair of 3-500z I'm sure other folks potentially lurking would know). Then adjust the tank using the antenna analyzer or VNA. Same thing for the input side, leave power off but tubes in, put resistor from cathode to ground that represents the input impedance of the tubes and build your input network accordingly.

    I didn't think of doing it with the Pi, but I thought of replacing the boards entirely with an arduino set up... unfortunately I then remembered I don't know C# :confused: :) I don't think the Pi will read an analog signal but I'm sure you could build an ADC or something... that's actually a good way to do it, you could essentially have unlimited memories if you could get the Pi to control the band switch too. I wasn't sure how far I wanted to go so I copped out and found a lazier way... It's an excellent thought for the future though, there's so much potential there.

    Hopefully you can get some snow and ice cleared so you don't have to wait till spring! We got dumped on here over the weekend as well, probably not as bad as you guys but hey at least we aren't in VO1 land :)

    Hope you have lots of help! I unloaded mine from the back of my SUV by myself. It wasn't a wise decision I'll leave it at that! 3 fit guys could do it easy I think, one each on the side handles and one on the front/bottom handles, and a good dolly. Don't forget to pull the tubes.

  8. VE9GFI

    VE9GFI Ham Member QRZ Page

    OK - With the ice storm behind us, and COVID-19 restrictions lifting in New Brunswick, I was able to travel 20 minutes and pick up the CMC BH-30 amplifier. Getting it from basement to basement took 5 hours. Much of that was the prep time to cut a piece of 3/4 plywood for the base and bolt that onto a Princess Auto Dolly with four 3 inch wheels.

    Getting it down the stairs from the garage into the basement was easy because I used another 1/2" x 3 ft x 8 ft piece of plywood as a ramp and the handcart was lowered down slowly. Once I was at the bottom, I lifted the handcart and the BH30 stood up on it's new wheels.

    I spent the first day blowing out debris - mostly wings (no bodies??) and dust. By Tuesday night, I had validated the primary windings on the TB101 and removed and replaced the jumpers with white wire for the neutral side (as per the manual.) There were two solder joints that had become loose. The 3000V from the transformer to the voltage regulator and the jumper between both 50K ohmite resistors. I replaced the jumper and fixed those up.

    On Wednesday, I was able to insert the 20 AMP fuse (115VAC) F101 and remove the F102 fuse and I disconnected J101 for an initial power up. Having not seen smoke, I reconnected J101 to get the metering working and the PS indicated 2300 V (with no Tubes and 115 VAC input). The blowers came to life and the filament indicator came on too.

    My next step is to measure the voltages on the T102 transformer which supplies the rest of the unit. Its fuse was removed for the first set of tests.

  9. VE9GFI

    VE9GFI Ham Member QRZ Page

    I should mention that I was feeling good and I did screw in the F102 fuse to get the blowers going. Now I'm going to spend time validating the voltages in there and then focus on the Tubes section afterwards.
  10. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Ant or termite wings...

    Great thread! Great looking amp!

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