Today I was eventually able to bring myself to tackle another radio, having recuperated after the AK808A restoration - this one seriously sucked me dry of energy. Plus the closing and new house dolores de cabeza.
I chose Kirk's 62 of all the nasties that seem to creep up on me when I am not looking, like those weeping angels from "Doctor Who".
Now first I thought the power xfmr was a gonner until I realized this radio has a fuse that is also 110V/125V selector! And the fuse was open.
Now that it is bridged with a piece of wire the primary seems to be no longer open.
Which does not in itself mean the transformer is good.
The Variac-assisted test tomorrow will tell.
Meantime I am trying to make sense of the schematic.
There are two mods described in Riders, and mine seems to be the third.
I have the one where the field coil is plugged into the positive leg for filtering, but the sch in Riders shows another choke and 8uF cap which are not there, that filter plate voltage to the detector.
The first resistor to the bias filter seems to be huge wire-wound 9kOhm instead of 5kOhm shown, and I think it did not degrade as it is a wire-wound. It is a rheostat but the way it is mount I doubt it was moved.
The values shown are questionable: the two mershons on the chassis' drawing are shown to be 8uF and in the sch they are 2 and 4uF respectively.
And of course Kirk did not give me the speaker. Which has the field and the tranny. And I do not seem to have a speaker that could substitute for it.
So in fact I do not even know if the speaker is in working condition.
Oh...and the volume regulator is 18K end-to-end and all versions say 3K......minor thing, just minor......
Kirk;
Give Mike the speaker, it's needed to repair your Jackson Bell. It looks like, according to the schematics posted on Nostalgia Air, that Kirk's 62 is the earlier version as the earlier version has the 2 and 4 uf caps, but it also shows an 8 uf between the chassis and the junction of a filter choke and a 500k ohm resistor. This is what you are dealing with I would guess, but wide variations in circuit design and parts values seem to be the norm with Jackson Bell products, maybe they had intermittent supplies of certain parts at the Gilfillan plant and had to redesign things accordingly? But 18K for the volume control seems rather off the beam, it seems to be in the cathode circuit of the three RF amplifier tubes in the front end, but also controls the input of the antenna circuit. It seems that they were in part using the RCA method of obtaining bias on the tubes by making the cathodes of each tube slightly positive with respect to ground, on the #45 tube they show a center tapped filament winding with a 2200 ohm resistor going to ground since it's directly heated, and in the case of the three RF amplifier tubes they were using a rheostat in the cathode circuits to control the volume. The 5k, 10K, 10K, and 10K resistors in series, with the .1 uf caps between, appears just to be a voltage divider in the B+ circuitry, why an 8K rheostat was added does not make sense unless the original 5K burned out and they just had an 8K rheo lying around? Is this 8K rheostat a rheostat or just a variable wire wound resistor?
Yes I am dealing with the version with output self-bias reistor 2.2K (which is at this point 3.8K and needs to get replaced), and 8uF which is nowhere to be found, and the resistor in question is a ceramic bobbin with wire wound around it (which at closer look is a cord with fine spiral wire around it, and then wound around the bobbin, I was wondering myself at first how 20 turns could produce 10K until I looked in a magnifying glass) and a sliding clamp contact.
(This post was last modified: 01-18-2015, 11:56 AM by morzh.)
OK, good news is, the transformer seems to work (I usually only check the rectifier's voltage A/A and the filament; the rest of the voltages are also filaments and have little chance of open): the A/A is about 700V at 110VAC Vin and the transformer kept running about 10 minutes did not get warm at all.
Filling up Mouser order. Kirk, I am ordering 24-karat Rose Gold-plated resistors to go with the Copper Mershons and those beautiful brass caps of theirs, so don't spend much on beer.
But we b**ched about it. You were entrusted with coming back to the store and producing the moldy pack to them and shame them publicly. But nooooooooooo, you were too eager to shun the confrontation. You'd rather we all leave with the notion that we drank moldy beer and no one got held responsible.
(01-18-2015, 08:00 PM)morzh Wrote: OK, good news is, the transformer seems to work (I usually only check the rectifier's voltage A/A and the filament; the rest of the voltages are also filaments and have little chance of open): the A/A is about 700V at 110VAC Vin and the transformer kept running about 10 minutes did not get warm at all.
Filling up Mouser order. Kirk, I am ordering 24-karat Rose Gold-plated resistors to go with the Copper Mershons and those beautiful brass caps of theirs, so don't spend much on beer.
Mike,
I can see that resistor you were talking about in one of Kirk's photos, it's definitely a replacement, it may still be functional if they put the slider in the right spot, but I don't think a 5K wire wound is a non standard size so you might as well pull it out and change it, save the adjustable for something else. How nice of Jackson Bell to mount half the resistors and bypass caps on that circuit board on one side, it brings back memories of my Rogers Ten-60. If Jackson-Bell was kinder then Rogers they will have added tie points on that circuit board, the Rogers had rows of drifting B.E.D code carbon comp resistors, with spade terminals, going through holes to act as tie points for the wiring. The missing 8 uf unit may have been an early dry electrolytic cap, the kind inside a rectangular cardboard box, even it it is missing I would assume that it is supposed to be there and order a replacement anyhow. What's inside that metal box on top of the chassis? A pair of bypass condensers?
If you want a set that gives that A.K 808A a serious run for it's money pick up a Rogers Ten-60, or equivalent, nice performing sets but a disaster in terms of mechanical layout, and rubber covered wire just for fun. Rogers was just like Grigsby Grunow in that regard, they were ahead of their time with the rubber/gutta percha wire, but you just have to work with it, or switch brands.
Regards
Arran
(This post was last modified: 01-18-2015, 11:05 PM by Arran.)
The top box content is described in the note on the p.3.
Two wires go in it and they are in good agreement with the sch, one going to the 2,200 Ohm output cathode bias resistor/filament winding centertap and the other is the detector cathode feedback bypass.
The 8uF was certainly not being used as otherwise there would be that extra filter choke that goes to it from the 2uF cap and Field coil connection, but instead the wire-wound big resistor (which we spoke about and which should be 5K ) and 500K detector plate load one both go to that connection of 2uF and field coil.
Given the fact they had so much deviation about the caps I will use 5uF plus 5uF i/o 2uF and 4uF.
I have tons of switch grade 10uF 450V that I use everywhere in series to make high voltage 5uF, so I only need to order one cap, 0.25uF for tone ctl, and this one has to be 630V. I have already build a kit in Mouser, today will add few things and order (I am out of popular values in film caps and resistors).
(This post was last modified: 01-19-2015, 11:03 AM by morzh.)
Mike;
I see, so the model 62 that Kirk has is the second series, which is somewhere between the first series model 62, and the third series Model 62, for which they didn't bother posting an actual schematic but posted that note on the third series schematic instead about the 1 uf and 2 uf paper caps in the tin box. I seem to remember that we may have discussed this before, maybe after Kirk fist got the radio and attempted to work on it. Why they could not have given each set a different model number defies logic, or even just a suffix like Model 62-B, or 62-C to avoid confusion? At least the successor company Packard Bell did this, there was a 46A and a 46B for example, maybe Herb Bell learned his lesson?
Regards
Arran
