Gates BC-1H

AM Radio discussion. Directional arrays are FUN!
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HadYourPhil
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Gates BC-1H

Post by HadYourPhil »

I have crossed paths with two of these. One in FL that never gave me any trouble. One in Wisconsin that is kicking my butt. When an attempt is made to give it high voltage, the OL relays chatter away and it will not stay on. I've swapped tubes and checked the audio driver board. While I found that the output audio driver diodes were both bad, changing them made no difference.

When I hit HV on, the Mod Plate Current meter takes off, resulting in an immediate overload. The PA plate current meter barely registers, FWIW.

Like I said, the one BC-1H in F-L-A was trouble proof despite living in a swamp. A bit hard on modulator tubes but then I wasn't letting it loaf. This one will live out its days in a backup mode but it needs to behave better first!
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RGORJANCE
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Re: Gates BC-1H

Post by RGORJANCE »

Well, I don't happen to have the schematic in my files, so I have to do some guessing. Check grid bias on modulator tubes. I don't remember the layout, but you also might want to look at the coupling capacitors going into the grid of the mod tubes. If there is a high positive voltage at the griid, it will really overdrive the tubes. Check the solid state audio drive. Look at mod xfmr and mod reactor for possible shorts, but I think that world result in an HV overload.

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Deep Thought
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Re: Gates BC-1H

Post by Deep Thought »

You might want to pull the plate caps off of all four of the mod/final tubes and see if you still get an overload. If you do, the modulation transformer or choke may be shorted to the frame.
Mark Mueller • Mueller Broadcast Design • La Grange, IL • http://www.muellerbroadcastdesign.com
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Dale H. Cook
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Re: Gates BC-1H

Post by Dale H. Cook »

I will second Mark. It has been decades since I worked on an H, but I worked on a T and a G for a number of years after that and, IIRC, the design for the 833 tubes was pretty much the same in the H as in the T (which was the first version of that general design in the '50s) and the G (which followed the T and preceded the H in the '60s). You need to figure out where the current is going that it doesn't belong. If Mark's suggestion (the most likely scenario) doesn't pan out get back to us and well look somewhere else.
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HadYourPhil
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Re: Gates BC-1H

Post by HadYourPhil »

Thanks guys! I'll try the "plate unplug" trick tomorrow. The audio driver board's voltages are off also. This poor beast has been hacked by a few which just adds to the fun. It can be a bit confusing as to what the ground reference for the audio board is, IIRC.

Nice chat with RGORJANCE Sunday night! He gave me the tips mentioned above. With any luck I'll have some time to look things over tomorrow.
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Dale H. Cook
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Re: Gates BC-1H

Post by Dale H. Cook »

HadYourPhil wrote: Mon Sep 13, 2021 6:58 pm This poor beast has been hacked by a few which just adds to the fun.
In that case you need to unhack it if you want it to run correctly. I seriously doubt that any station engineer who hacked that transmitter had the qualifications of those who designed it.
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Re: Gates BC-1H

Post by HadYourPhil »

Today was productive as a shorted zener was discovered (100v, 50w). A new one will be ordered tonight..
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