[morzh]

Well, I bought the first one. Risking $5.

[morzh]

Tonight I took apart the tuning cap gear, which worked fine, but I figured it would be all gunky inside, which it was.
It took me 5 minutes to remember how to get the gear back together, after I had cleaned and re-lubricated .
the whole thing.

Then I measured the Candohm, the 133/15 Ohm part. The 133 resistor alone should be dissipating 11-12W.
This is probably why this Candohm is bad. The 133 Ohm is 190 Ohm, and 15 Ohm is 109 Ohm.
I decided that I will use 8.3uF cap to sub for the resistor (did that in the past) and then use a resistor for the 15 Ohm. This will save me power dissipation, and I do not need the DC performance.

[Arran]

Mike;
The watch batteries will fit the original bias cell holder, if you choose one of the correct diameter. The positive of the watch/coin cell will fit flat against the edge of the cylindrical part of the bias cell holder (which is what Rogers and apparently this Philco 37-604 used) and the spring contact will press against the negative part at the center of the watch cell. again the Mallory bias cells had the polarity the opposite way around from a modern watch battery/cell so you would need to flip the connection to make it work. There is another type of bias cell holder that is made out of stiff piece of wire, and I'm not sure if those would fit a watch battery like the type the Rogers sets used with the cylinder, they look like a stupid design anyhow.
Here is some history behind the Mallory bias cells:
https://antiquewireless.org/wp-content/u...s_cell.pdf
Also here: https://antiqradio.com/post_mallory-bias-cells.html
Another method is to hollow out the old cell and use it as an adapter for the new watch battery, like they did on this thread, he used an LR44: https://www.vintage-radio.net/forum/show...?p=1386709
As I mentioned before Rogers and Canadian Marconi really took a shine to these infernal things, and I guess that the engineers behind the Philco 37-604 did as well, so radio collectors in Canada are quite familiar with them. When they go dead the radio basically stops working as well, I think that the cost savings in parts was not the motivation since you need the holder as well as the cell (something not mentioned in the advertising) as opposed to a resistor and bypass capacitor on the tube cathode.
Regards
Arran

[morzh]

Arran

Emptying the old cell is not a bad idea.
I have to see if the holder is strong enough to hold the new cell alone first.
In this thread they suggest a diode to drop 0.5V; I think it does not matter as the tube actually asks for 2V bias.

[Arran]

Mike;
  I don't think that the diode is really necessary either, I think it's theoretically more of a problem running the 6Q7 without any bias on the grid then fractions of a volt too much, most have a resistor between one end of the bias cell and ground as well I think. It's not uncommon to see 12SQ7s, 12AT6s, etc., run with no external at all, just a 10 meg resistor from the grid to ground, and the cathode tied to ground as well, millions of AC/DC sets were built that way. For years I was a bad boy and ran a Deforest Crosley "Elgar" without the bias cells, someone had soldered in some AAA cells under the chassis, which had failed and leaked, which were removed, and in my ignorance I shorted out the bias cells and ran it that way. Maybe the set would have worked or sounded better with them installed but it didn't kill the 6Q7M tube, schematic here:

https://pacifictv.ca/schematics/rogers13-71data.pdf

Regards
Arran

[morzh]

Arran

What you should've did was take a zinc and a copper round pieces, a piece of felt soaked in some diluted sulfuric acid and.. and...well, you know. It all could be wrapped in some black tape and potted with epoxy.

[Chas]

ebay has coin or button cell adapters, some hold two cells but one side can be jumped. The cell is less than a dollar and will last for years. LR-44 comes to mind. The lithium cell is 3 volts that maybe too high but they have a shelf life of at least 10 years, never, ever leak. The holder can be bus wired into the circuit even if it is for PC/surface mount. I did look for smaller cells but most of those holders are for several cells...

[morzh]

OK, coming back to my workaround for the shaft bushing.

So, since the 7mm bore / 9 mm OD bushing seems to not be in existence, I ordered 8mm bore / 10.6mm OD nylon bushing, which comes in qty of 10 for $5.

Now, thought I to myself, I need to diminish OD by 1.3mm (the original seems to be 9.3mm OD).
To do this I would have to cut a sector such that the outside lengthe would be 3.14 times that, which is about 4mm.

So, this is the bushing
   


This is the bushing with 4mm section cut out.
   


This is the bushing that now fits snug into the hole in the bracket.
   
   

An this is the shaft going through with good, not tight but properly restrained fit. Plus this nylon is more slippery than the original material.
   

[radiorich]

Hello morzh,
Nice job !
Can't wait to get my 3d printer because I could print the correct bushing .
I have been saving money to buy my new printer .

Sincerely Richard

[morzh]

Rich

Yeah, maybe, when I have 5 years remaining for me to live, I will buy me one and learn to program it (is it Autocad or Solidworks, or what input does it take?)
Then I will print one bushing and happily kick the bucket right after.
I'll be kicking that bucket all the way to the newly bought farm.

Seriously, I should learn it.

[RodB]

Mike - or you can wait for just a short time and have AI make one for you. Tada!!

[morzh]

Yeah yeah yeah. Eventually it will take over everything. Even making our children. It is AI. It is smarter and faster.



Aw'rite.

I am proceeding with the restoration.
Right now it is the recap.
What can I say....it is pretty tight in there.
I was able to restuff 3 backelites and two tubulars, plus some resistors.
I was in doubt about the 2x110pF block, but then I disconnected one cap and measured it; it was over 300pF, so, no, those inside were not micas.

The battery came out of its socket fairly easily. I wonder if I should try to fit LR44 there.

[morzh]

I restuffed all caps but the tin can, but delaying replacing them as there more work needs to be done under where they go.

First of, I need to clean the mushed wire insulation stuck to the chassis and things in it.

   

THis is how it looks. I do not think this was an animal activity, as there is no droppings and such, but also this is only near the candohm, which was supposed to be hot as heck. As I said, this will be replaced by a capacitor, and it just so happend I have exactly the value, 8.2uF film Solen caps (8.3uF was the calculated one). I stocked up on thos a few years ago as this seems to be the one often needed to replace the curtain burner wire or a candohm in these 5-tubers.

I also figured why the choke 32-7569 was burnt (and replaced by a large ceramic 2.2K resistance): the catalog gives this as a 10mA choke, and the calculated curren through it might be up to 12.8mA (and I am sure it was at least 10mA), so it would be used at its limits.
I want to reinstate the choke, so I will be buying one. Not necessarily the exact replacement, but I'd like it to be at least around 20H and a 1.5K or so, the rest will be compensated by an added resistance.

This radio is a handful.

PS. I was told "if you plug it, it will play". Not sure, but then the cord was cut.

[Arran]

"PS. I was told "if you plug it, it will play". Not sure, but then the cord was cut."
Mike;
That is like the often used phrase in used car ads, "Running when parked". I see similar stuff in ads, particularly in fleabay listings "Works, powers on but can't get any channels" or (if an older seller) "Everything lights up but doesn't work, must need a tube", why not just plead ignorance rather then confirming it? A newish one I ran into for sets that have been worked on but don't perform well "Just needs an alignment", then why didn't you align it then?
That bushing you had to replace, what did it have there originally, a rubber one?
Regards
Arran

[morzh]

Arran

No, it is some sort of fiber epoxy something. Brown-orange. Same exact shape.
It cannot be rubber: it would impede the shaft rotation. It needs to be solid non-friction material.
I think it is vulcanized fibre.
This is why I chose nylon.

   
   

As for the radio, well, I know the guy well, and I am sure he resold it for someone who told him that, plus it did not even matter, as I would never ever plug in and power up a radio I did not go over myself.
Plus the price was really good. Let's just say, my eye were open on this one.
It's like me buying Jeeps. I am a Jeep guy, and I know they are crappy cars, but I love them. So I fully ingone whatever the salesman tells me, I know it's crap, and I know I want it.