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

    Today I noticed that the two Servo Amplifier Boards are missing. Not to panic! I confirmed that the previous owner didn't have them. I should mention that this AMP sat in his basement until he decided he wasn't going to set it up, and he gave it to me. Like a real piano, the moving part was my responsibility.

    Now for some history. I called my Dad yesterday to tell him that I picked up the amplifier. My Dad worked at Canadian Marconi for his entire career, in Nova Scotia. As we were talking, I asked him about Darrell Garland and "Lee". He laughed because Darrell was one of his first bosses and Lee was another senior tech in the Dartmouth office. Their names were printed on the front of the BH-30 Service Manual that came with this unit.

    Another neat thing is that the manual includes a two page diagram for a CH-150 connection to the Amplifier. This diagram is written very neatly on the back side of Canadian Marconi drafting paper, with an old "30 Simmond's Drive, Dartmouth NS" address. The 2nd page to that diagram is a connection to a MAC1000 Antenna Tuner. If someone knows what a MAC1000 is, please let me know.

    So why not panic about the missing boards?

    The missing boards seem fairly straight forward to etch and re-produce. The only issue I have is to confirm the pin placements for the component side of the board. I have noticed that this amplifier labels and counts by skipping the letter "I" and possibly "G" and "O". Thus the potentiometer wiper outputs labelled "B" through to "P", and skipping "G" and "I" would seem to be on trace numbers 2 through to 13. The card edge is labelled 1 to 22 on one side and A to Z on the other side. A,Z,1, and 22 are grounded. So the next trace on the edge is "B" and "2' on the flip side. So I just need to confirm that the labelling skips G, I, and O and then I can etch a board.

    Another peculiarity is that the programming board is already setup for HAM use, with "160 - but really 150m", "80m", "40m", "20m", "17m", and "15m" already setup. But the CMC CH-25 radio that came with the amplifier is a single channel (4755.0 kHz) unit. I'm trying to figure out if the AMP never came with the servo boards since it seems that it was potentially only used in a static setup (one channel), but the programming board is setup for ham and the channel "1" position is set to 2.0 to 2.25 MHz (what I called 150m) instead of the 4.5 to 6.5 MHz (where the 4755.0 kHz lies).

    If someone out there has the servo board, could you please take a photo of each side for me? I would like to confirm the outputs of each wiper to the edge of the board. In the meantime, I will trace it out by eye and compare back to the schematic and set up myself to create the two missing boards.
    KD2ACO likes this.
  2. K4AGO

    K4AGO Platinum Subscriber Platinum Subscriber QRZ Page

    I got a "No Results Found" error on the video. I am very interested in following your progress.

    It's a beautiful piece of equipment (and history.)

    I wish you great success in the restoration.
    VE9GFI likes this.
  3. VE9GFI

    VE9GFI Ham Member QRZ Page

    Ok - I just shot a YouTube video, hopefully the first of many.

    W1TRY likes this.
  4. VE9GFI

    VE9GFI Ham Member QRZ Page

    Sunday June 7th.

    I connected the CMC CH-25 tube radio that mates to the CMC BH-30 Linear Amplifier. A couple interesting observations:
    1. The CH-25 channel selector switch will cause the motor that drives the ceramic wafer switch (S901) to function. S901 is driven by B901 and is controlled by Relay K801 on the Relay PCB.
    2. Even with the CH-25 radio off, the channel selector switch will cause the BH-30 switch to function.
    3. The motor B901 only goes in one direction (clockwise), this is also evident from looking at the schematic, where you 'll see there is only one relay and the motor has only one input for that one direction.
    4. My BH-30 is rather loud when it goes back to position one. The relays chatter a lot. Going from 1 to 2 is silent, 2 to 3 is silent, but when it gets back to 1, there is a concert of relay clicks.

      Can someone comment if the relay chatter is is normal?

      I'll post a video.

    73 de Greg VE9GFI
  5. VE9GFI

    VE9GFI Ham Member QRZ Page

    The noise I heard is the Channel Selector switch which selects a channel between 1 and 18. When I move up through the channels, this knob turns clockwise one step. When I decrement a channel or wrap around from channel 6 back to 1 (on the CH-25), this knob continues in the clockwise direction but steps quickly and makes quite a chatter.

    When the channel selector moves (S301), the programming board is then connected to a new frequency range (one of ten) and the large ceramic switch (S901) turns clockwise and selects a new inductor setting.

    Whereas S901 has a motor, S301 has a solenoid to make it move.

  6. VE9GFI

    VE9GFI Ham Member QRZ Page

    Tuesday June 9th

    I mustered the courage to plug in the one 3-500Z tube that came with the amplifier. It came with only one tube because the other one was dropped or otherwise broken before I got this amplifier. That said, I have in my possession two matched 3-500ZGs from RF Parts. The boxes are on a shelf just behind my radios and they are eagerly waiting for an amplifier to live in.

    So tonight I decided that I had checked all the parts that can be checked. I popped in the tube into the socket that has the thermistor. When I applied filament, the tube glowed nicely from the bottom. I waited for about 5 minutes and then I turned on the HV switch. There was a brief flash, but not overly bright. No sounds per se, other than the roar of the fans. When I looked at the plate voltage, it was indicating 0 volts. and when I looed back at the HV switch, it was off.

    The 20 AMP fuse blew.

    I have since replaced the fuse, and removed the tube, and rechecked the filament and HV switches, and I'm back to where I was a few hours ago. The power supply is still producing 2700 VDC and the fans are still humming.

    So.... either this tube is bad, or I have shorted resistors, or capacitors. Or maybe I shouldn't turn it on with just one tube. Or perhaps my Type P NRN 20AMp fuse should be replaced with a slow blow. I'm not sure. Should a tube that hasn't seen any action in 10 years be brought back to life in some special way?

    Also, I didn't have any input or output RF cables connected. I would expect that no input would be OK. And I'm going to connect a large dummy load so as to prevent the proper impedance to the tubes, even though I wasn't driving them.

    If anyone has comments, I would sure love to hear them now.

  7. VE9GFI

    VE9GFI Ham Member QRZ Page

    Wednesday June 10

    I removed the parasitic coil and resistors that attach to the plate of each tube from the amplifier. These would be L204/R203 and L205/R204. Each resistor measured 47 ohms and 40 ohms each. With a nominal value of 50 ohms +-10%, this places the range at 45 to 55 ohms. So R204 is at the lower limit of 20%.

    I also checked the capacitors C210, C211, C206, C207 which all sit near the tubes and are all 1500 pF at 6KV. None were shorted with a low voltage DC test.

    I placed the one old 3-500Z into the socket with the thermistor and I turned on the filament switch. It glowed nicely. I proceeded to cook supper and chat with my wife. Some 2.5 hours later, I connected a cantenna to J304 (the RF output) and I turned on the HV switch. Essentially, this is the same test as yesterday, except that the plate of the 3-500 Z is disconnected. Nothing special happened. No fuses blew, and the HV plate voltage is indicated as 2700 VDC.

    At this point, can I assume that this old tube is gone gassy, and perhaps the rest of the amp is fine?

    When do I plug in my brand new 3-500ZGs?

    Greg VE9GFI
  8. VE9GFI

    VE9GFI Ham Member QRZ Page

    Thursday June 11

    I exchanged emails with "Claude". Part of my paralysis was that the 20 amp fuse blew when I turned on the HV. From the top of my eye (I was bent over), I did see a flash, but it wasn't like a flash bulb. What I suspect now is that the old tube was gassy. I discussed what I had done up to now, and most importantly I wanted to know if I could damage the new tubes if I popped the new ones in. I suspect now that my carefulness was actually placing the amp at risk because the gassy tube was conducting like a short, as evidenced by the F101 fuse. Claude said that I should put the new tubes in.

    I proceeded to remove the old tube - this will become an ornament at my operating position.

    I installed the brand new RF Parts 3-500ZGs and I repeated the filament test. I turned on the amplifier without the HV and both tubes glowed nicely.

    I turned off everything and then proceeded to reconnect the filament chokes. Once everything was tight again, I turned on the filament followed by HV.

    This time nothing flashed. The plate current was still 0 mA, so I depressed the Transmit button on the ALC board and I measured 0.11 (I presume 110 mA).

    With that, I decided that I should shut down everything and get some rest since it's about 11:40 pm local.

    My next step will be to remove the dummy load on the input and connect the CH-25. I already have a Cantenna on the output, so I'll see if I can whisper and get some amplification.

    W1TRY and KD2ACO like this.
  9. KB1MM

    KB1MM Ham Member QRZ Page

  10. VE9GFI

    VE9GFI Ham Member QRZ Page

    Monday June 15

    At lunch on Friday I hooked up the CH-25 radio and measured 15 watts when whistling loudly. Connected this to the BH-30. No output. I was going away for the weekend, so that was the totality of the tests on Friday.

    Supper on Monday. Opened the manual, and I'm getting ready to tune up the BH30 with a Yaesu this time. Flashback to Friday.... the CH-25 only has one channel, tuned at 4755 kHz. The BH-30 has a programming board setup for Channel 1 to tune to Range 1 (2.0 to 2.25 MHz). So using the CH-25 was a non-starter anyway.

    So, tonight's task is to setup the amplifier for 20 meters. I will set the CH25 to channel 4, because the Programming board is configured with Ch4 set to Range 7, which covers 10.0 to 15.0 MHz. Then I'll use a Yaesu rig for generating RF at 14.250 MHz.

    I followed the instructions on page 2-2.
    1. meshed the capacitors
    2. set the input power to 10 watts
    3. adjusted the tune control by dipping the plate current
    4. adjusted the load control by maxing the rf output
    5. increased the power slightly
    6. repeat 3 to 5
    40 w, 100, 200, 500, 600, ... , finally 1000 watts! Which surprises me since this is running from 115V. I'll mention that my meter is not a Bird 43 or a lab instrument.

    Now I need to complete my KiCad drawing of the two servo boards, and I will need to get the PTT and bandcontrol outputs from the Yaesu into the cable that goes from the CH25 to the BH30. I have the rats nest drawing and I'm part way through the tedious layout process.

    For now, I'm going to put little pencil marks on the tuning positions but the good news is that it tunes up.

    Last edited: Jun 16, 2020
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