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1944 BC-610 E back home!

Discussion in 'Amplitude Modulation' started by N6YW, Jan 28, 2019.

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  1. HB9FWY

    HB9FWY Ham Member QRZ Page

    Just to let you know that there are quiet a few BC-610 running regularly in Europe. My dad HB9EPC and I HB9FWY own conjointly 7 BC-610 all in running order.
    We also have completely refurbished 2 WW2 Ho17 radio Shelter one of which is currently sitting on my CCKW truck (SCR-399). Had quiet a blast last June in Normandy commemorating the 75th D'Day commemorations. 400w AM usualy on 1615 Kc. Bets 73's.
     

    Attached Files:

    KE5YTV, W1BR and (deleted member) like this.
  2. K4KYV

    K4KYV Subscriber QRZ Page

    The metal (tantalum?) plate and no dedicated getter seems to be the culprit. Graphite anodes with a fired getter seem to be less vulnerable to on-the-shelf gassing. That half-dozen 211/VT4-Cs that I dug out of the ground under the collapsed floor at the OT's house up in Indiana, were all perfectly good except one, after I cleaned the corrosion off all the exposed metal parts (tube pins and metal base).
     
  3. N2DTS

    N2DTS Ham Member QRZ Page

    I have a bunch of 100TH and TL tubes and they all are good.
    I am surprised anything holds vacuum that long.
     
  4. W9BHI

    W9BHI Ham Member QRZ Page

    Gee Billy ain't that great that you start a post about your BC-610 that you are proud of and after a few relative posts, the notorious hijackers change it to something that they want to talk about?
    I see you interjected a post about leaving it on 40 meters.
    The next post was right back to the non BC-610 subject.
    That is just plain rude.
    You want to talk about something other than what the original poster started, START YOUR OWN THREAD.
    I am sure some people will agree.
     
    KE5YTV likes this.
  5. K4KYV

    K4KYV Subscriber QRZ Page

    One problem with the BC-610 is that the modulation transformer has too much step-down, limiting audio voltage swing to leave no positive peak headroom beyond 100%. This was probably intentional to make the unit foolproof to non-technical operators under battlefield conditions.

    My suggestion would be to re-wire the plate transformer primary so that in both Phone and CW modes, the +HV remains at the full 2500 volts, the normal CW plate voltage. Insert a 2000 ohm, 150 to 200 watt wirewound resistor in series with the B+ line, between the bottom end of the modulation transformer secondary and the +HV. By-pass this resistor with a 10 mfd (or more), 600v oil capacitor. This will drop the +HV to the RF final back to 2000 volts, but supply the full 2500 volts to the plates of the modulator tubes. The by-pass capacitor allows the full audio voltage swing to reach the final unimpeded, while dropping the DC plate voltage. The series resistor also works to a certain extent and for short durations as a current limiting resistor, in case the transmitter is fired up at full power with the plate tank off resonance.

    The bias to the 100THs will have to be slightly increased, but this should be within range of the the bias rheostat. Set the modulator resting plate current to run about 20% below normal,to keep the 100THs at normal plate dissipation when no modulation is present. This will allow up to 125% positive peak modulation capability.
     
  6. W2VW

    W2VW Ham Member QRZ Page

    Or find a different modulation transformer.

    I used a Thordarson T-11M78 on my BC-610F.

    Moved a lot of stuff around, replaced the final and modulators with tubes that were easy to find and could be shipped.

    Triode connected 813s for audio and an 833 for the final.

    The later plate transformer is easy to configure for several power levels too.

    That rig logged a lot of hours on the air including coast to coast AM on the top of 40 meters.

    Lugged it to Gaithersburg, '98 and set it up in the AM gathering area.

    Of course all the above is quite unnecessary if one is fine with less performance and can find tubes which ship and store poorly.
     
    W2NBC likes this.
  7. K9PHT

    K9PHT Ham Member QRZ Page

    Back in the late 50's I was Air Force stationed in Germany on a mtn Radar site called LANGERKOPF and of course when a Ham Radio guy comes in they usually get assigned as custodian of the MARS RADIO side. They had two 610E just siting there as they were recently replaced by the I model. These were being used by an ARMY guy for his daily radio net check-ins for their missions.

    SSB was just coming out so I grabbed one 610E and made into in a linear amplifier being driven by a SSB Radio. We had a 200 foot high very large beam antenna setup on it. I forget the model number now but it had 40-50 foot span on it... This was DL4IZ Langerkopf Germany... When you got on 20 meters and said HELLO WORLD you have latterly hundreds of DX guys trying to answer you haha...

    Ran that setup for four years of my Air Force assignment there... Never left the Radar site... I was in Ham Radio hog heaven hehe...

    [​IMG]
    Langerkopf Radar site Germany probably early 60s photo. Never confirmed by that is most likely me walking the road back to the barracks which I did every day... The MARS STATION was in the building you see next to the very high 20 meter Antenna setup... The other end of the building was the site library that had to listen to all of the radio squeeks and squawks reading their books haha...

    [​IMG]
    This is me yaking away to the states haha... That's the ELDICO S-LINE radios suppose to replace the Collins S-LINE.... Eldico was a piece of junk haha... BC610-E to the left there...

    I was DL4RO back then...

    Roy Ken
     
    Last edited: Jan 22, 2020
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  8. K4KYV

    K4KYV Subscriber QRZ Page

    Unfortunately, that happened to a lot of BC610s, and other heavy-metal AM rigs as well.

    I remember in the late 60s you could find 250THs for $5 each at hamfests, and 100THs for a buck apiece. They were sold cheap because "they don't make good linears".
     
    K5UJ likes this.
  9. K5UJ

    K5UJ Ham Member QRZ Page

    How hard is it to find non-stock mod. iron for 100TH modulators? I had some idea that they were real high Z so finding anything like a broadcash rig transformer was out of the question. Nevertheless, the 610 is a FB half gallon rig paired with a xtal mic like a D104. Add neg. cycle loading and away you go. I would probably still look for a reactor and keep current out of the mod. transformer secondary to reduce talk back.
     
  10. K4KYV

    K4KYV Subscriber QRZ Page

    Plus, the older open-frame transformers such as is the E model, could be disassembled, cross-laminated and used with a reactor for greatly improved low frequency response. Problems would be where to mount the reactor, and the lightweight driver transformer isn't the best of quality.
     

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