We picked this up a couple months ago so she could have a radio for herself that had a bit of color to it. It's AM only which makes it relatively breathable in the chassis, looks to be our first permanent magnet speaker, and there are some good options for how to mount an aux input and switch.
I figured I'd see what it needed for capacitors and resistors tonight since this will be the next project. It's not bad, again, I think thanks to the simplicity of having only one band to listen on, but I do have a question. In the photo below, circled on the right side are two 4.3k ohm resistors in parallel that are a bit beefier than most of the others in the radio. This is supposed to be R3 according the to schematic I downloaded and it calls for a 2.2k. Testing in-circuit yields 2.9k, so its out of spec either way.
The documentation I was able to find online was all of two pages, the first was the schematic itself and the second was the alignment procedure. No parts list. To my surprise, the schematic and parts list were glued inside the top of the cabinet. On this parts list, the capacitors are numbered according to their identity on the schematic in the cabinet, but diverges from the numbered parts on the schematic I downloaded - no biggie. The resistors, though - no numbers, just values and wattages. Interestingly, while the schematic in the radio agrees with the schematic I downloaded that the resistor in this location should be a 2.2k ohm, it doesn't list a 2.2k ohm in the parts list, instead, a duplicate of the 22k ohm exists, despite there only being one 22k ohm resistor in the radio, so it seems clear that this is a misprint on this part list label.
All that is to say, I don't have a good indicator for what the wattage of the 2.2k ohm R3 is supposed to be, and the parts that are in place are sized such that they could be a 2W, but there is only one other resistor in the radio that is bigger than 1/2 W - the 1k ohm between the two electrolytics. Would it make sense to need a 2W resistor all this way over in the RF section? Further, though perhaps less important, does this seem like it would be a later modification? Aside from the power cord, I'm not sure if there's any indication that this radio has been worked on so it seems strange it might have come this way from the factory. Would there be any advantage to doing the two resistors in parallel as it is right now, or should I simply go with a single 2.2k ohm?
There are only two other resistors that need changing, one, circled in the photo all the way to the left, actually physically is broken - maybe exploded? It was supposed to be 150 ohms, tested at 8, and it's right where power comes into the rectifier. The other gave such a flaky reading I did snip one lead to test it out-of-circuit and it was still way off: supposed to be 6.8M ohm, tested really low before drifting upward and settling in around 2.2M.
As for capacitors, two electrolytics to replace the dual can, 8 paper to be replaced, one mica being left alone and two small, ceramic dog bone-looking ones which I think, based on my reading, should be treated like micas and only replaced if we chase a problem down to them. Almost all pretty accessible to swap out. Definitely some different philosophies from the Philco and RCA I've worked on as far as wiring to ground.
On a separate note, I think I figured out why my IG-102 signal generator wasn't producing a signal. It has a 12AT7 tube with the very pretty white film at the top of the tube. The other tube in there, a 6AN8, has normal coloration and does glow when powered on; the 12AT7 does not glow. There's also a 20-20 dual electrolytic can in there, so I figure I may as well replace that with new electrolytics when I order. Most everything else is ceramic and looks sound. Wish I would have checked the tubes visually before I ordered this last time.
Roy;
It looks like someone didn't have a 2.2 K 1/2 Watt resistor, so they decided to use two 4.3 K 2 Watt ones in parallel that they had laying around. Why the original would have failed is a mystery as there isn't much voltage, or current draw on that grid, the higher Wattage ones would be found either in the power supply, or as the cathode resistor on the 35L6 tube, R13, R12, and R11. These sets are better then average, they have a tuner RF amplifier stage, so whilst somewhat simpler then a set with shortwave bands it does have an extra coil, and section in the tuning cap, just no switching.
Regards
Arran
+1 on Arran's comments. Frankly, I am surprised that there is a resistor there at all. I am also surprised at the 22K resistor between the first grid (oscillator) and cathode of the 12SA7 Pentagrid Convertor. The 2.2K resistor is between the secondary of the RF transformer and the signal grid of the 12SA7. it is also a tuned circuit, the RF section for the Pentagrid Convertor. Yes, I agree that it should be a 2.2K 1/2 W resistor. I can't see this resistor burning out as it carries RF signal at practically no current. It is between one leg of the transformer secondary (bottom of pic, rear apron of chassis) and the grid. The other leg of the secondary doesn't even go to ground, it goes to AVC. If there was an overcurrent condition, the coil would have blown to the middle of next week, not the resistor(s).
From the pic, it looks like it was a factory install, that they likely ran out of the correct resistor. This looks like an early post war or 1942 set (before manufacturing switched to war production) In either case, the manufacturer (either Arvin or Detrola, both rather small companies) was likely facing a parts shortage. I suggest that after recapping if it works, consider not messing with it, or to be pure, replace it, your choice.
"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis
I have a Plaskon Version in Ivory of this radio, plays pretty well, made by Arvin for Sears, 1955 listed as year offered on Rdaio Museum. This set went for 29.95 in the Sears Catalog. Does yours have a small 3 gang tuning condenser? Paul
Silvertone was not making any tube radios in 2014. I know that for a fact.
Maybe in 1995...the latest.
The resistors according to the sch is a 2.2K for R3 between the RF xfmr and the ctl grid, and 22K between the 1st grid and the K.
Now, as for the 2.2K resistor.
While not show in the app schematics (like the Radiomuseum reference design), the 2.2K resistor is useful for mostly this reason:
12SA7 is a different type of pentagrid.
It has the Grid 2 connected to SG and uses those as the osc plate.
There is a strong coupling between these and the Control grid, which they envelope.
So, the tube is not very stable around its own frequency and might oscillate around it with that second unintended oscillator, so the two might fight each other.
There are other things too due to very high gain at high frequencies (newer better tube), and since the Plate resistance is so high (1M) and the CG input impedance is super-high, a 2.2K resistor will not attenuate the intended signal much while, by forming a small low-pass with the CG capacitance it will attenuate unneeded VHF and will prevent the oscillations due to that 1st grid and SG enveloping the CG.
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.
2014 is the model, not the year. The ultimate question about resistor R3 was regarding the wattage. I was pretty comfortable with the resistance being 2.2K ohms as all schematics agreed, and the two 4.3K resistors mathematically are pretty darn close. The consensus seems to be 1/2 W is appropriate here.
Paul,
I'll check when I get to peek at it next. I think it might be a three-gang tuner.
Yes, I know. intentionally did not put the smiling face after it. I was wondering how many people would correct me.
The 2.2K resistor will not conduct any appreciable current and so can be any wattage whatsoever; I use minimum mostly 1W resistors, as the size / leads make it more convenient to work with vs 1/4W.
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.
Mike;
Are those 1 Watt ones the Vishay ones that are the same size as a 1/2 Watt carbon resistor, I think that Bob Andersen was using those in his TV sets as they had a reddish brown paintjob? I do know that they are the better ones to use if you want to replicate a Dogbone style resistor, as they would be more heat tolerant and less likely to fail inside the reproduction casing.
Anyhow I had one of these Silvertones years ago, also brown Bakelite, they were sold through Simpson's, Eaton's arch rival in the catalog business, back in the mid 1950s. The cabinet on mine was broken, but it did perform well, though I think it was missing the knobs. I eventually parted it out as it was not worth trying to restore, I still have the dial stashed away, likely the IF cans too, and the speaker was used in something else that I fixed up. I agree that the U.S ones were made by Arvin, but I'm not sure if Arvin had a branch plant in Canada or not at that time, or if they were made under license, or imported directly from Arvin in the U.S.
Regards
Arran
You mean those newer type that has reddish-brown paint but are of a size of 1/4W? No I do not use those much. Size matters so I try to use a larger body ones.
And, I simply do not do resistor replicas. To me using plastic is...questionable. And I tried to get the ceramic tube cut for me, but it fizzled.
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.
Mike;
I have never used them either, I have a large number of wire wounds, and metal oxide power resistors, but if they were rated at 1 Watt then using one in a 1/2 Watt application does not seem unreasonable. Ceramic tubing should be easy to cut, I don't have any on hand, but I do have a wet saw for cutting tiles.
Regards
Arran
A tile is a thicker thing and takes coarser-toothed blade (you are talking about a curcular one, right?).
I can see pieces of this tube flying around when that blade touches it.
I think it should be fine, kinda like hacksaw-type, diamond-coated cutter.
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.
Mike;
The tile cutter has a diamond blade, there aren't really any teeth to it, though obviously the diamonds act as an abrasive, which is why the water. I heard they won't cut glass tile but I've never confirmed that, I may try cutting a bottle and see.
Regards
Arran
Okay, getting a little bit ahead of myself here but, aside from polishing up the cabinet, there's one other non-electronic piece to this radio that I need some guidance on. The dial pointer is curved and I'm tempted to find a way to replace or straighten it - of course this assumes that it was originally straight which I personally would assume.
It seems to be a neon reddish, strong, translucent plastic strand, almost like 3D printer filament, I think. Here's a photo from an eBay listing for the exact dial from a sister model, but it too is curved.
My suspicion is that if there is a light that illuminates the dial, that this would also catch that light in a vibrant fashion. Paul, maybe you can confirm or deny this. Is your dial pointer similarly curved? I haven't opened it back up to check on the tuning condenser yet, but should be able to soon.
Obviously, the curved pointer can just stay as part of the radio and be adjusted to indicate properly, but I figured I'd sample the wisdom here on this point before I made a decision.
so I try to use a larger body ones.![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
