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Tonight I began work on The Philco model 66B which I recently bought. Right off to bat I encountered a problem the likes of which I have never encountered before. The knobs, which are the correct originals WOULD NOT COME OFF ! I pulled and pulled by hand. No luck. I carefully put some penetrating oil down onto the shaft and left it to trickle into the joint between the knob and shaft. Still would not come off by hand !. Finally I very carefully took a piece of steel and laid it on the front of the cabinet and used a screwdriver and a pair of long needle nosed pliers to actually pry them loose. I hated to get that forceful, but there really was no other way. I finally got the knobs off. I won't vouch for whether I damaged the controls. The band switch may have suffered, but I'll find out for sure eventually. Oh, well, nothing for it. The knobs had to come off. After removing them, and examining the knobs and the shafts, I am convinced they were actually glued on. I'm not sure why, maybe to keep some child from pulling them loose, but it sure made a devil of a job for me. Perhaps that was the reason the radio was retired, and put away. Also, after examining the chassis, I am convinced that, other than the addition of the phono input, and replacement of tubes, no other work was done to this set. Anyway, here are some pictures of the chassis...
[Image: https://64.media.tumblr.com/0390135bf507...67fd5a.jpg]
[Image: https://64.media.tumblr.com/b3015c5437f5...0f1033.jpg]
[Image: https://64.media.tumblr.com/ff3747e7c7e2...760d58.jpg]
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This evening I tackled the tone control. It is an interesting little gadget, with a steel frame formed into a box at one side, and a 2 position switch with a 1/4" shaft which rotates a brass sliding contact onto and off of an insulated contact. The shaft and slider are grounded to the chassis, naturally. In the box there are two condensers, a 0.02 mfd and a o.002 mfd. They both connect to a lead going to the audio output tube. The other lead of the 0.002 mfd is directly grounded to the case of the little metal box part of the steel frame. The 0.02 mfd condenser's other lead is connected to the insulated contact, so that the slide contact connects it to ground or disconnects it, depending on position. Very interesting and simple design. I like it.
I melted the tar from the box housing the two condensers, and replaced them. I lubricated the shaft, and re-peened the end of the shaft that secures the brass sliding contact. The unit now functions well again. I then wired it back into the receiver.
(This post was last modified: 10-24-2021, 07:43 PM by mikethedruid.)
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Mike
Next time you deal with these tone ctl thingies from Philco, unless you love melting the tar  - you simply unbend the rear wide wall of the box, simply pull out the whole thing (the tar in the fishpaper), bend the wall back, put the news fishpaper insert, and then arrange and pot the caps after you wire them to the contacts.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Yes, Morzh, but I LOVE to make a little tray out of tinfoil and melt the tar. "Nothin' says lovin' like somethin' in the oven." LOL ! Besides, this way I don't risk bending the metal, and it's just about as easy.
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I love the smell of napalm in the morning. It smells like victory.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Tonight I replaced the two hard to get to .05 MFD condensers under that "component bridge" just behind the tone control. The job was a bit of a bear. I had to label and remove the wires from the side of the bridge nearest the tone control so I could tip up the bridge to get at where the condensers connected. Now that they are replaced things should go more smoothly.For those who want to follow along here is a link to the service information in the archive here... https://philcoradio.com/library/download...l.%201.pdf
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I remember that.
But the worst for me was trying to take apart fully frozen band switch.
And it is not a wafer type but two co-axial cylinders.
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Fortunately the same oil that I used to loosen the knobs seeped back into the band switch and has freed it up pretty well too. Luckily also, the wiring is all cloth covered and in very good shape, so I won't have to replace much; only 1 run so far. I really don't want to have to take all the wires off that band switch, label them all, and then put them back, and it looks like I won't have to. I WILL have to replace all the resistors though... they all seem to have drifted quite badly. Of course, all the paper condensers too, and the electrolytics. Fortunately both electrolytics are original, and are the kind that are pretty easy to rebuild.
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Last night and tonight I have begun more under chassis work, this time replacing condensers and resistors on the component bridge and elsewhere. Most of this has been pretty straight forward, but I did run into one discrepancy, part 27, a0.1 MFD condenser, was missing in my set, just not there, period...
picture as radio was received...
[Image: https://64.media.tumblr.com/d97adc5636a6...82bac6.jpg]
Here is the parts layout from the literature...
[Image: https://64.media.tumblr.com/90fd41632d26...0dc18a.jpg]
And this is where it goes in the circuit...
[Image: https://64.media.tumblr.com/85e5fa67f02e...9b5fd9.jpg]
At any rate, I have installed it per the schematic and parts diagram...
[Image: https://64.media.tumblr.com/2095fff8abaf...3d9df4.jpg]
I find this very interesting that on an apparently unmolested chassis there are these discrepancies. I looked in the notes on revisions in Rider's, nothing. It's not the first time I've found such things. ( Remember the two 100 MMF condensers supposed to be inside the second IF transformer can on that 38-10? )
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Tonight I finished up the under chassis work except for the electrolytic condensers. I replaced one bakelite block with a 3 position terminal strip because the safety condensers I use would not have fit in the bakelite block. I sometimes wonder why Philco used the dang things anyway. Other manufacturers like RCA did not. I really think it was to make it harder for the home repair guy to fix the sets, and to encourage them to just take it to the Philco service guy if the problem was anything more than tubes.
[Image: https://64.media.tumblr.com/22c1e374db1d...266a52.jpg]
[Image: https://64.media.tumblr.com/e5156c61e070...6cad9b.jpg]
[Image: https://64.media.tumblr.com/657f8edb11df...5722dd.jpg]
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HELP, PLEASE ! Well, things are to the point of testing now, and I have run into a problem right off to bat. It centers around the type 75 tube and the 2nd detector circuit....
[Image: https://64.media.tumblr.com/cb2ba248f2a4...fa99da.jpg]
If I feed an audio signal into the 42 output tube either directly to the control grid through a .01 condenser, or feed that signal in to the plate of the first AF, the 75, I get the sound loud and clear through the speaker. If I try feeding the signal in to the control grid of the 75, I get almost nothing. This is the pinout of the 75, followed by the voltages on the pins.
[Image: https://64.media.tumblr.com/97dcf3bb5f0a...d60a22.jpg]
Between 1 and 6 I have heater voltage just fine. K is +0.8 mv. GT is -1.6 v. PD1 is -520 mv. PD2 is -520 mv. PT is -550 mv.
Looking at the schematic, I should think the plate on the 75 should be strongly positive to work, but it is not connected to B+ in any way that I can see. Is there a dot missing on the schematic? What am I missing?
The plate voltages on the other tubes seem fine. The bias voltages coming from R44 are -1.85 V and -22.08V to ground.
(This post was last modified: 10-28-2021, 09:37 PM by mikethedruid.)
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Did you find it? I DID ! There IS a mistake in the schematic ! A dot is missing showing the connection of the wire running from R28 to 1/2 of C50 to the B+ the "white wire" to the speaker, the 42 output tube, and through various transformers to other tubes. I made the connection and BINGO ! Man does this radio work well on just my short test antenna ! I'm not even going to fool with the compensating condensers on the back of the chassis. It works too well as it is, and I learned a long time ago, "If it ain't broke, don't fix it !"
[Image: https://64.media.tumblr.com/5508e135e754...497888.jpg]
Next will come the cabinet, which is really very good, just a cleaning with GOJO should do the job, perhaps a single coat of tung oil just to refresh things and hide the scratches. Sadly the grill cloth is badly deteriorated near the top. It was hard to tell until the speaker came out. Then it became pretty apparent. Oh well, I'll find a suitable replacement. Too bad though, that metallic diamond original was really nice.
(This post was last modified: 10-28-2021, 11:33 PM by mikethedruid.)
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This dot is a well-known problem in Philco docs for more than one radio. I mean, if you rewire the radio, leaving a tube without the plate power should make one curious 
People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
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Yup, this is why when I draw a schematic I use a little half loop to indicate NO CONNECTION, as well as a dot to indicate CONNECTION. Yes, it is a tiny bit slower, and is a "belt and suspenders" approach, but it makes things absolutely clear. In all my years of working in the electronics field, nobody ever complained about my schematics because of that. I learned this method in the first electronics book I ever bought, The Complete Radio Book by Yates and Pacent (1922).
https://archive.org/details/TheCompleteRadioBook
This is where I first learned to read and draw schematics, and learned the names of the various parts. It is why I still call a condenser a "condenser" and not a "capacitor."
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Sometimes you just can't win for trying. I began to notice a strange distortion to the sound from the radio on my bench, and looked at the speaker. Along the outer edge it was developing a crack in the cone. Not really surprising. The cone was 86 years old. the fragility of the paper cones at that age is normal. This is not the first one I have had to re-cone. Fortunately there is a PERFECT replacement available from eBay : https://www.ebay.com/itm/333909714338?ss...2749.l2649
Here are pictures of the work in progress. I am waiting until the glue dries well before I do the final glue in of the cone to the basket...
[Image: https://64.media.tumblr.com/e17f1bb98f05...2b6a11.jpg]
[Image: https://64.media.tumblr.com/382a9c7258c6...466b3d.jpg]
[Image: https://64.media.tumblr.com/b70869dcbbe7...d58ba0.jpg]
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