Model 84, code 121 question(s) - Printable Version
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Model 84, code 121 question(s) - NostalgiaRadioTime - 06-03-2014
Found a nice, unmolested example of the 1934 cabinet design at the WARCI meet Sunday, and have a few questions with regards to the electronic restoration. First, for reference, here's a link to the PDF file schematic from Nostalgia Air. I've ordered "good" copies from Chuck: http://www.nostalgiaair.org/PagesByModel/875/M0013875.pdf
My first concern is this wire that is either cut or more likely broken off. It's attached to the OSC coil (I pointed to the lead the end of the wire is soldered to) You can see the broken end in the upper right hand corner of the pic:
Here is the broken off end, which appears MAY have come from the off/on/volume control? :
Here is a full view of the bottom of the chassis, pointing to the broken wire:
I'm hoping this set won't have the same OSC coil nightmares as the model 89's do. As with that set, if anyone has any info on the 84 as far as which terminals on the coil are the primary and secondary windings and (hopefully I won't need it) the number of turns of wire for each and direction to wind?
The other question concerns the electrolytic can containing an 8 mfd and a 10 mfd:
It appears to me that the terminal on top directly under the large resistor is the ground. There's green paint next to the terminal. Is that correct? Also, it appears to be a 'floating ground', as it's only grounded within the can itself, and not on the chassis (as there is a cardboard ring around the outside of the can). Is that the true ground, where everything on that terminal would be connected to the negative end of the replacement electrolytics?
Sorry for the dumb questions. Until I get a better, readable schematic, I'm at a loss, but I know there are some very knowledgeable and helpful Phorum members who I'm sure have tackled one of these small cathedrals at some point. Thanks!
RE: Model 84, code 121 question(s) - morzh - 06-03-2014
The wire is not cut, it is a makeshift capacitor and used for finetuning. It was probably wrapped around that other wire. I would not touch it just yet.
As for the cap, your GND and the rect. negative should buzz as 325 ohm. Both caps' negatives are connected to the Negative and NOT to the GND (this is one pin for both caps). You can veify the negative pin by seeing which one is 325 ohms to GND (chassis).
RE: Model 84, code 121 question(s) - NostalgiaRadioTime - 06-03-2014
Thanks very much!! That makes perfect sense.
RE: Model 84, code 121 question(s) - morzh - 06-03-2014
The best way is always to trace wires using the sch.
RE: Model 84, code 121 question(s) - OldRestorer - 06-04-2014
Whats a schematic?
It's like a road map right? Is there a GPS for radio repair?
RE: Model 84, code 121 question(s) - morzh - 06-04-2014
Greg
Now that I took another look at the wire, may be it is indeed is a broken wire and not a makeshift cap.
But the only one that comes to volume pot is the one from antenna coil (#2) which is on the right of the coil you are pointing to.
You need to trace it.
From what I can see it is the one going to the Cathode of Det-Osc tube 77.
And it also goes to Volume Pot through the cap #3.
RE: Model 84, code 121 question(s) - Steve Davis - 06-04-2014
It looks to me like it should be twisted around the lead to the volume control pot. Look at number 3 on the parts list, it says, "capacity obtained by twisting two leads together".
Steve
RE: Model 84, code 121 question(s) - morzh - 06-04-2014
So then it was a twisted makeshift cap.
What I do not get, if it is attached to the osc coil, this cap is not connected to it.....
Oh, wait. As I remember now, one pin on the coil is in fact free of the coil wires and serves as just a holder for that mica cap and 6Kohm resistor, so this is why.....
OK, good then.
RE: Model 84, code 121 question(s) - Steve Davis - 06-04-2014
Actually, it is not the oscillator coil, it is the antenna transformer that cap number 3 couples directly to. It also couples to the oscillator coil through a capacitor and resistor.
Steve