BC-1H1 Broadcast Transmitter Project

Discussion in 'Amateur Radio' started by WQ5Q, Feb 26, 2017.

  1. WQ5Q

    WQ5Q Member

    I recently brought home a 1974 Gates BC-1H1 acquired from a local ham friend and broadcast engineer. This 2 x 833 modulating 2 x 833 transmitter is the version with the solid state audio driver that replaced the 2 x 807 cathode follower driver. The transmitter was taken out of service fully operational last year.

    The transmitter is in really decent shape. Since getting it home I've thoroughly cleaned it and mounted casters. I've also taken a panel over to a local auto paint store to get a match so I can do some repainting of the more worn and scratched areas.

    The iron in this later model is not huge, but an advantage is I can pick up the plate transformer. The mod transformer is probably a replacement...it's a Peter Dahl and is comparatively "light."

    My plan (short version) is as follows:

    Stage 1:
    1. Clean up, paint, and mount heavy duty casters.
    2. Install 30 amp 240 vac service to ham shack. Install #10 4-cond. power cord and NEMA L14-30 plug to transmitter. This will provide both safety ground and a separate neutral for 120 vac where needed.
    3. Signal monitoring - will dedicate a Tek 465 100MHz scope I bought for this purpose.
    4. Power up and verify operational condition using a dummy load on original frequency.

    Stage 2:
    5. Set up T/R functionality and sequencing, including antenna switching, receiver muting, and HV on/off which only requires the operator to throw a single switch.
    6. Decide on a frequency determining unit for 160/80 meters (vfo, dds, signal generator, etc.), amplify and match feed to the 807 RF drivers.
    7. Reconfigure the RF tuning circuits in the IPA and Final for 160/80, including band changing methodology.
    8. Add outboard audio processing including limiting the audio to prevent over-modulation.

    Kelly WQ5Q
  2. WQ5Q

    WQ5Q Member

    Here are the pics.....first the iron:


    And the transmitter:

  3. W5HRO

    W5HRO Administrator

    Below is the schematic for the BC-1H. Any difference between a BC-1H and your BC-1H1 or are they both one in the same?

  4. WQ5Q

    WQ5Q Member

    The BC-1H1 has the solid state audio driver---this is what I have. I've heard these sound really good on the air. The BC-1H has the 807 cathode follower audio driver. I believe this is the only difference. My manual shows the BC-1H schematic but there is an additional schematic for the audio driver.

    Here's a pic I took of the audio driver in my transmitter. You can see the TIP54 power transistors heat sinked to the panel below the board.

  5. WD5JKO

    WD5JKO Member

    If the goal is to put this thing on 75m, consider getting a Retro-75 with the VFO option. This thing can put out over 3 watts if the modulation transformer is bypassed, and is a small, and stable transmitter. The RF output stage is class D, and is clean and efficient. Some form of matching network would be required to drive the two parallel connected beam power tubes (807's?).

  6. W5HRO

    W5HRO Administrator

    Here's a link below to some good info on that transmitter. Might want to get it now because Bill is dead. No telling how much longer the page will exist unless someone else is maintaining it like K5PRO. Bill was pretty cool unlike the other asshole moderators on AMfone. Looks like the transmitter is in Santa FE, NM at K5PRO or it was...


  7. W5HRO

    W5HRO Administrator

    Here are those pdf files from the page just in case.

    Attached Files:

  8. WQ5Q

    WQ5Q Member

    Jim, I had not considered that...thanks for the idea, I'll look into it. I have a "bread boarded" Franklin vfo on 160m that is incredibly stable considering it uses tubes. I need to put it into a cabinet with buffer, multiplier, and amp stages.

    Brian, I've seen this site before but had forgotten about it. Thanks for the reminder. I'm sorry to hear about Bill.

    The ham I got my transmitter from also gave me copies of the first two Electric Radio articles mentioned on K5PRO's website for converting these to the ham bands. On the BC-1H looks like they converted it to a PI network using one of the original coils and adding two vacuum variables. I would prefer to use a PI-L but have a lot to do before I start designing a new output network. I'm planning on converting to 160 and 80. Would like to also get it to 40m as well but don't know if that's feasible. I'm thinking I'll have to rearrange things to make the entire plate circuitry more compact to do this.
  9. WQ5Q

    WQ5Q Member

    Jim, I just checked the Small Wonder Labs website and it looks like they have been closed since 2013 due to his retirement.
  10. WD5JKO

    WD5JKO Member

  11. W5HRO

    W5HRO Administrator

    Man, that looks a bit messy and complicated. It will probably work though.

    Below is the audio driver module in my McMartin BA-1K. If I was smart I would probably just rebuild and use it, but I want tube drivers instead with the phase rotator in front of it. Like yours though it was designed for the typical 600-ohm line input so there is no speech amplifier.

  12. WQ5Q

    WQ5Q Member

    Jim, I'll certainly check out the Retro Yahoo Group. Sounds interesting. I've been away a few days camping in Quartzite, AZ. That is, if you consider using an RV to be "camping." :confused:

    Brian, the SS audio driver in this transmitter has a reputation for fidelity and being able to fully drive the 833's. That, I think, would be a tall order and supposedly Gates' engineers achieved it with this design. I think the reason it looks "messy" is that there were some repairs done during the 42 years of operation and they were probably in a hurry. I will eventually go through that and "clean it up."

    Well, on the McMartin I think you should get it going as-is before any major mods. That way you get to use it and see what you want to change after some experience with it. That's what I'm planning to do with the Gates. As you said, I will need to acquire some audio processing gear to feed it.
  13. WQ5Q

    WQ5Q Member

    Update on progress:

    I installed the heavy duty casters and they really make it easy to move the transmitter around. Of course, it's lighter at the moment with the rear door, a front panel, the side panels and the iron removed for cleaning and prep for painting.

    Yesterday, I put in a 30 amp circuit from my electrical box to the garage/ham shack where the transmitter will be located. The box is just on the other side of the wall so it's only about a 3 foot run of 10 gauge romex. I'm using a NEMA L14-30 plug and receptacle which is rated for 250 v 30 a and is locking. The power cord from the wall to the transmitter will be 10 gauge also. I bought enough to reach anywhere along the wall that the plug is on plus some extra. Should work FB. I'm also using 3 conductor plus the safety ground conductor throughout. I wanted to have 120 vac available without using the safety ground as the neutral. I did the same thing for my 4kV power supply for another project. This gives me the option to use 120 vac transformers, blowers, etc. down the line if needed.

    I've finished the general cleaning and I'm now prepping for painting. I took in a front panel to have a specialty paint store match it. I bought 4 rattle cans worth and some extra in a regular paint can. The bottom floor where all the iron sits badly needs repainting. And a few scratches here and there.

    Here's a view of the floor where the IPA power supply sits. There's some rust and discoloration. Plus it was pretty dirty when I took this picture.

  14. W5HRO

    W5HRO Administrator

    Any progress on this?
  15. WQ5Q

    WQ5Q Member

    Yes, I am currently taking vacation from retirement life 8) down in Rockport, Texas on the Texas coast for about a month. Before leaving I finished the painting of the cabinet and I did some terminal repairs to the HV supply plate choke. Here's the before pic:

    DSCN0518 (2).JPG

    I'll have to put up some after painting pics. The bottom floor that was so beat up and dis-colored looks almost like new. I sanded, primed, an then repainted it with two topcoats. All the scratches in the paint throughout the transmitter are now re-painted with matching paint.

    I also picked up the dummy load that goes with it that I hadn't picked up when I brought home the transmitter itself.

    As soon as I get back I'm going to start reassembly of the parts removed for cleaning and painting including the iron. Then it will be time to fire it up in stages and test on the original frequency into the dummy load.

    One thing I'm planning on doing when I mount the iron is to use those red stand-offs for the mod transformer and the mod reactor. I have a local surplus source for these and picked a few up on my last visit. I figured with modulation, the voltage gets pretty high between the positive peak and the transformer core and frame if it's grounded, so floating the core above ground would add some protection for these 1974 vintage transformers.
  16. W5HRO

    W5HRO Administrator

    You mean the red ones like these :mrgreen:



    I also added ceramic ones to the negative peak limiter resistor mounts.

  17. W5HRO

    W5HRO Administrator

    Also, does that transmitter have any ball gap (spark gap) on one side of the modulation transformer's primary to it's center tap? If not you should add one. You can get a lot built up via the mod reactor and you want it to dump across the gap when the HV turns off and not through the transformer and tubes.

    I don't think the Gates have it so add the gap like in the below if you can.
  18. WQ5Q

    WQ5Q Member

    No gaps anywhere. Thanks for the tip.
  19. W5HRO

    W5HRO Administrator

    BC transmitters were designed to be on 24/7, 365-days a year CCS and they were never designed for amateur radio use with short transmissions on the ham bands. They were turned on and left on so the HV was always there and not constantly being switched on and off. Well, using them modified with PTT for ham radio use changes the game a bit. Even a lot of the old BC transmitter techs would add spark gaps as a safety precaution just in case the load changed suddenly or if the power was interrupted inadvertently.
  20. WQ5Q

    WQ5Q Member

    It cooled off a bit here (down into the 90's :eek:) so I rolled the beast outside and installed the iron. I put the modulation transformer and mod reactor on the red glastic stand-offs for a little extra insurance since they are 42 years old.

    I thought about installing a gap on the secondary side of the mod transformer. I thought this was standard practice if you wanted a bit more protection of your mod iron. I've never seen the gap across half of the mod tranny on the primary side like the one you show above. Do you know of any references I could look at or commercial rigs that use this?
  21. W5HRO

    W5HRO Administrator

    Here's the one from my McMartin...

    The typical high power transmitters without the audio reactors would add a ball gap across the secondary when the DC was on it. The Johnson Desk KW, Collins KW-1, etc. However, when the DC is off and the one end has a cap to ground instead and uses the big reactor then you want the gap on the primary side instead on the end which is out-of-phase with the secondary. At the same time it wouldn’t hurt to use one on the other side of the primary too and then one on the secondary, but those are usually not necessary. The main thing is dealing with what gets kicked backed in the opposite phase from the reactor. That is what will protect the secondary more and the primary.

  22. WQ5Q

    WQ5Q Member

    Finished rewiring the HV stuff today. Progress!
  23. WQ5Q

    WQ5Q Member

    Ready to power up...slowly.:smile:
  24. W5HRO

    W5HRO Administrator

    Did it smoke :surprised: or did it work ;) ??
  25. WQ5Q

    WQ5Q Member

    Had forgotten a few misc. odds and ends on the transmitter I needed to "tidy up" today before power up. Finished that and did some ohm meter and low voltage checking to verify that the HV wiring was done right. Everything looked good.

    However, when I tried to start it up normally, the "power on" push button circuit is not engaging the mains contactor. I jumpered it and everything starts up. If I have time tomorrow I'll troubleshoot it...it has to be either a wiring issue or the switch itself. Shouldn't take long to figure out. I just ran out of time today.