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Author Topic: BC1-T mod transformer mounting position  (Read 3668 times)
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k4kyv
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Don
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« on: July 08, 2005, 04:09:44 PM »

I have finally replaced the clipleads and permanently wired in the modifications and mounted the components in my BC1-T.  I am ready to attach the side and back panels.  Perhaps some other BC1-T owners could answer a couple of questions for me.

Firstly, what kind of fasteners did the stock transmitter use to hold the panels in place?  Mine has threaded rods in the form of screws inserted into tapped holes in the cabinet frame, from the inside of the cabinet.  The panel slips in place by passing the mounting holes in the panels over the threaded body of the screws, and then fixing in place with a washer and nut.  What doesn't match up is that the screws are 6-32's, but the mounting holes are about a quarter inch in diameter.  I suspect some other mounting hardware was originally used, and that this is someone's JS arrangement after the originals were lost or damaged.  Years ago I worked at a BC station with a 1-T, but I don't recall this detail.

Secondly, the modulation transformer mounts on the floor of the cabinet on the right-hand side, as viewed from the front.  There are numerous mounting holes in the area, but the only four that I could find that would match those on the transformer, place the transformer in a position so that the righthand panel is less than 3/8" away from the paper on the transformer winding.  I am reluctant to attach the side panel this close to the transformer out of fear that the transformer could arc through the paper to the panel, and damage the transformer.  My question is, is this mounting position normal for the transmitter?

I recall while I worked at a broadcast station in the 60's that one of these transmitters blew a plate transformer because the plastic clamp holding the primary leads in place had broken or deteriorated, and the loose primary leads got too close to the winding and it did arc thru the paper to the wires.  I am afraid the same thing could happen with the mod transformer and side panel.

The solution I am using for now is to install some spacers that hold the panel in position with additional clearance.  The panel looks out of place sticking out from the side of the transmitter, but that beats replacing a modulation transformer.
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Don, K4KYV                                       AMI#5
Licensed since 1959 and not happy to be back on AM...    Never got off AM in the first place.

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w3jn
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« Reply #1 on: July 08, 2005, 06:17:54 PM »

Quote from: k4kyv
I have finally replaced the clipleads and permanently wired in the modifications ...


That's pretty poor practice, Don, replacing clip leads.  Now it'll never work again.
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W1GFH
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« Reply #2 on: July 08, 2005, 08:18:38 PM »

Quote from: k4kyv
There are numerous mounting holes in the area, but the only four that I could find that would match those on the transformer, place the transformer in a position so that the righthand panel is less than 3/8" away from the paper on the transformer winding.


Maybe drill new mounting holes an inch to the left of the old ones...?
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w3jn
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« Reply #3 on: July 09, 2005, 05:27:21 PM »

:lol:  :lol: Nice one, Joe!  For a second there I thought someone had hacked my account or I had double posted!
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W7IXZ
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« Reply #4 on: July 10, 2005, 11:35:33 PM »

Hey Don, My three BC-1T's are all a little bit different.  The one I have on 160 uses 6BG6 tubes instead of the 807's, the other two use 807's, and one other one I gave to N7QMM had 807's.  The one I have on 160 also had the complete CONELRAD change over kit in it, the large plate switching relay as well as the CONELRAD box containing the oscillator board, 807 driver board, and 1240 tank circuit.  Really a Rube Goldberg change over kit.....from the factory no less!  All of the BC-1T's had 10-24 or 10-32 screws inserted from the outside as the holes in the case were threaded.  My modulation transformer is mounted the same way yours is, but the original instruction book seems to have it at 90 degrees.  In other words, the iron core runs from front to back.  I do not have the sides on yet so will check that out too.  I know about the arc's!  Lost a plate transformer in a 50 KW Continental 317C1 because the ground strap for the frame was too close to the winding....blew across about two inches and punched a hole in the winding!  Kind of ruined my day.  Hope this helps.
By the way, I am running a 5 band Greg Labs processor and Sennheiser MD-421 Mic on mine.  Look for me on 1945.
Larry W7IXZ La Grande, OR.
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