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Candohm replacement
#1

Am working on a 42-322 (my first restoration, unfortunately I didn't realize this had the rubber wire issue until after I bought it and started reading this phorum, but what the heck...).  The candohm filament resistor (#46 in schmatic) is faulty although it seems to have failed in an unusual way.  The 40 ohm section reads 250 ohms while the 80 ohm section reads 84.  Thought these usually failed open or shorted to chassis.  Anyway, my plan is to drill out the candohm and replace with a terminal strip and some 5 watt wire wound power resistors.  Does that sound right to you folks or is there another approach that works better?
Thanks for the help!
Bob  
[Image: https://www.dropbox.com/s/ckazdphd7vfl59....jpg?raw=1]
[Image: https://www.dropbox.com/s/3pvuhfhf88u0e9....jpg?raw=1]
#2

Yor're right on target. Dress the sand resistors against the corner of the chassis for most heat dissipation and you will be all set! Can't go wrong with 20 watters, but do ade a fuse too.
#3

did you take the incandescent bulb out when measuring the forty ohm section? that can explain 250 ohms instead of a full open.
#4

Thanks codefox & morzh! Yes the bulb was out of the socket, but good point, I should check to be sure there isn't something else amiss causing that reading. I had recapped, rewired, etc. and started to power up with a dim bulb tester. The dial bulb blew and the dim bulb flickered and went dark so I shut down and am back to checking things. Learning as I go.
bob
#5

If the candohm is otherwise working I would leave it alone, the worse that is going to happen is it will open up and the radio will quit working as it is in series with the filament string.
Regards
Arran
#6

So the 40 ohm side is probably open or even worse intermittant. It'll keep blowing out those bulbs.[/align]
#7

Thanks Arran & Phlogiston. I'll go ahead and replace it, I just don't trust it.
bob
#8

Recapped a 42-322.  Part #43 was a multi-section 20, 20, 10 uF (red, yellow, green w/ black common wire) electrolytic cap. I wired the negative leads together as the black common and the positive leads to the red, yellow and green wires respectively.  Did I get the polarity right?

[Image: https://www.dropbox.com/s/siqnuvnlc3trnc....jpg?raw=1]
[Image: https://www.dropbox.com/s/ckazdphd7vfl59....jpg?raw=1]
[Image: https://www.dropbox.com/s/1dxql2due9iimy....jpg?raw=1]

Reason I ask is that I only measure -1vDC between the common lead and the point where I should see 100vDC.  Rectifier tube filaments glowing (don't have a tube tester), field coil measures ~500ohms, dim bulb power up went OK.  New 35Z3 on order but your thoughts on other next steps I should consider would be helpful.
Thanks!
Bob
#9

Your cap wiring is fine. You should check your B+ at a few other spots:

1) Cathode of the 35Z3
2) input side of the field coil
3) output side of the field coil.

Is your dial lamp working? If not, check that and the resistor (40 ohm) in parallel with it that goes to the plate of the 35Z3. Check for ~120VAC on the plate of the 35Z3.

Make sure you have connected your common B- to the proper point. This will have a floating chassis, so no DC between the chassis and B+ line.
#10

Thanks BrendaAnnD.

a) 35Z3 cathode is -1vDC
b) 35Z3 plate is 108vAC (line is 110vAC through isolation xfmr)
c) both in and out of field coil are -1vDC
d) B- common is same wire as original wire (but heat shrink covered to replace old rubber) and has continuity to other B- points
e) dial lamp is working (now that candohm was replaced with some power resistors http://philcoradio.com/phorum/showthread.php?tid=5697 )

Regards,
bob
#11

That sounds for sure like an open cathode on the 35Z3, or a tube that's REALLY flat.

Do you have a silicon diode you can temporarily sub across between plate and cathode of the 35Z3 (just for test purposes, don't leave it in.)? The band end of the diode would go to cathode. If you get voltages at that point, it would verify a dead tube.
#12

Good thought, thanks! Don't have one but easy to get.
cheers, Bob
#13

Been awhile but the rectifier tube arrived before I got the diode and that solved the B+ voltage problem. Still had no response at all except if I touched the output tube grid. Without a tube tester I swapped tubes to find the problem and finally get good broadcast volume on our local am stations. Lost my radio virginity to a 42-322 Icon_biggrin There does seem to be more hum between stations than there should, any thoughts on that? Need to see if SW comes in tonight.
Time to work on the cabinet too.




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