[Milsurplus] RBM HF Receiver Help Needed

[hwhall at compuserve.com]

Isn't C-517 one of those little trimmers that sometimes short out when the brass bit retaining the rotor fails?  I'd suspect that puppy first, from personal experience.
 

 Wayne
WB4OGM

 

-----Original Message-----
From: Joe Connor via Milsurplus <milsurplus at mailman.qth.net>
To: Milsurplus List <milsurplus at mailman.qth.net>; BoatAnchors QTH <boatanchors at mailman.qth.net>
Sent: Fri, Feb 3, 2017 9:46 pm
Subject: [Milsurplus] RBM HF Receiver Help Needed



I just finished my MF RBM receiver and it's working great. I just started the HF receiver and need some help. 


R-505 (the RF plate filter resistor) is smoking. I go to the plate of the RF tube and measure resistance. It's supposed to be 18.5K but I'm getting a dead short.


I disconnect the lead from R-505 that goes into T-502 (the RF assembly). Now I've got B+ on R-505. I disconnect the lead from T-502 to the plate of the first RF tube so that T-502 is completely out of the circuit, and test T-502: it reads a dead short, so it seems like the RF assembly is shorted. A likely suspect is C-518, a .02 paper cap that bypasses the RF plate, but that cap is inside T-502.


Does anyone know how to get into T-502 or how to drop the box? I just don't see any way to do it. 


Failing that, can I bypass the RF stage and, if so, how? Any other ideas of what might be shorted?


As always, thank you for your help.


http://www.virhistory.com/navy/rcvrs/ww2/rbm/RBM5_HF-schem.pdf



Joe Connor

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