08-19-2009, 09:37 AM
I'm new here, so hi everyone!
Longish post, and covers more than just electronics, but I didn't want to break it up:
I am really a tube guitar amp guy, so I know very little about tube radios, except what I can figure out on the fly, or transfer from my knowledge of working on tube guitar amp circuits, or my long-ago Marine Corps avionics days. But I recently became fascinated by the idea of getting an old tube radio in a wooden cabinet to tinker with.
I found a 42-321 at an "antique mall" for a decent price with a tag that said it worked. I figured what the heck.
It was in pretty good shape overall. The cabinet had apparently been stripped down to bare wood and veneer, as it was bare and the trim was no longer painted. One small patch of veneer toward the back had chipped off, but nothing major. Still had both its knobs. Grill cloth was adequate (but more on that later). Looking in the back, arial was intact, chassis was just dusty as all getup, and from what I could see the speaker was intact. Someone had put a new cord on it at some point (brown, non-polarized, lamp cord). The one cap visible was clearly old, if not original.
Operating under the (I know, foolish) assumption that SOMEONE had turned it on already, in order to decide it was working, I very carefully did the same. Worked fine with a slight hum and a little unsteadiness (as compared to its newly restored state now).
Pulling the chassis revealed that the caps were all old/original. I suspect that someone, probably a long time ago, might have done some work on this. Obviously, the cord was newer, though maybe not too new as it was non-polarized. All the caps were the old dingy yellow, wax covered monstrosities, and were all marked Philco. Wiring was obviously old, but was a mixed bag in terms of insulation. In the end, there was only one length that was the old rubber type with the insulation crumbling off that needed replacing. The rest was either cloth, or some other old but intact type.
So I found the schematic and layout at Nostalgia Air and started studying the thing. Ordered a new set of caps from Antique Audio and replaced the old ones. Used the same values for all. Basically, I used the technique of cutting out the old ones, but leaving their leads to form a loop to solder the new, much smaller replacements in. I figured this would be minimally invasive to the rest of the componants/wiring. Replaced the dual filter cap with a pair of 22mf electrolytics I had on hand. Then I added a fuse and put in a new polarized cord with the hot wire running directly to the fuse first, then to the one/off switch, as I should be. Other than replacing one bit of crmbling wire, I left the rest of the electronics as is.
On to the cabinet: I wanted to keep it simple, and as the wood on this thing had really nice grain, I just wanted to emphasize it a bit. So I put a couple coats of natural (tint-wise) Danish oil on it. It looks really nice and was exactly the effect I was looking for. For the grill - well the old one was odd. Somebody had taken a hard painting canvas, cut it to size, pasted the grill cloth onto the front, then pasted that into position within the cabinet. It did the job of keeping the grill cloth taught and in place, but it also (obviously) blocked the speaker! (the only sound would come out the back side of the cabinet) Clearly a cosmetic fix. So I had ordered some Philco diamond pattern grill cloth (the wrong year for this, but I liked it and am not the Smithsonian). Using that same hard frame, I cut out out in the middle so the speaker would not be blocked, and mounted the new cloth on it. Worked well. I was going to get some
dark brown paint at re-paint the trim, but I couldn't find a brown dark enough by itself and got bored with the idea for now. Cabinet looks great either way - so maybe eventually.
So I vacuumed all the dust off of everything, sealed it all back up, and fired it up. It plays beautifully. (sounds a lot better than the solid state radio that I've been using for AM). Nice warm, slightly compressed, tube sound. Love it. Looks killer too. Alignment seems pretty good. A station I know to be at 610 comes up around 625-30 on the dial. Reception is good all up and down the range. I see no reason to screw around with that any (especially since I don't have a sig gen and don't really know how anyway!).
As I said, I think it migt have been worked on in the past. Evidence: the apparently newer cord, the lack of consistent rubber wiring, the obvious cosmetic alterations, 100% intact speaker. But it also was either old or original, as evidenced by the old Philco labelled caps. However, I find it hard to believe that caps from 1942 (or possibly earlier) were intact with no sign of leakage and still operated within the circuit. But what do I know about these things? An equally likely possibility is that someone found it original and tried to fix it up minimally for sale.
A couple of questions came up during the rebuild:
1). Inside the chassis, right in the middle, there is what appears to be a big cap, that has a wire wrapped around it for a few turns. The layout calls it a condenser and choke assembly. No values for either the cap or coil are marked on the schematic. (On the schematic, it's a cap, leading to a coil, leading to ground) I presume that the cap part is marked on its case. I assume it's just what it appears to be - a cap wrpped by wire. I didn't touch it for now, but maybe since it's probably an old cap I should. Could I just slide out the cap, install a new one in its place with the same value, maybe just setting it inside the coils (since the new cap will be smaller)... Or maybe get a new cap, wrap a few turns of wire around it, and use that... Or maybe just leave it alone, since it's all working fine for now. Any thoughts?
2). On the top of the chassis there is another mystery (to me) cap. .0015mf 600v. On the schematic, it runs from one end of the arial transformer to ground. Physically, it runs from one lug of what must be that transformer to a tab on the tuning cap, that is effectively the chassis. I have a .001 630v on hand. I'm not sure if this cap is performing some sort of tuning function, or just blocking something, so I wonder if .001 is close enough for these purposes, or if I should hunt up a .0015?
3). The old filter cap was marked as a 20-20 on the schematic. The one I removed was a much bigger 50-30, or something like that. I knoew I had a pair of 22's sitting around, so I just planned on using those and didn't order anything different (didn't see the values of the original until I pulled it). I used the 22's and there is no hum. So I assume that's adequate filtering and the bigger cap was either a later over-rated replacement, or whatever Philco had on hand when it was built. Sounds like I'm good to go with the 22's right?
4). I have a set of Philco decals from Antique Audio. They look to be a water slide type like for model airplanes. (true?) Does anyone know if I can simply apply these over the danish oil finished wood, or if I need to do something further if I want to use them. I know water slides can be picky about surfaces. I can do an experiment with an unneeded decal if it comes to it, but if anyone knows offhand from experience...
5). Did these things have an open back, or some sort of harboard covering? Mine has no back, and the few pics I've seen of others, when they show the back, have no back. Just curious.
Anyway, a great experience with a gret result. Love the radio. I put on a ballgame and it was like a sound from my distant youth. Not sure how often they go this easy...
Maybe when I figure out how, I'll get a pic or two up here.
Andre
Longish post, and covers more than just electronics, but I didn't want to break it up:
I am really a tube guitar amp guy, so I know very little about tube radios, except what I can figure out on the fly, or transfer from my knowledge of working on tube guitar amp circuits, or my long-ago Marine Corps avionics days. But I recently became fascinated by the idea of getting an old tube radio in a wooden cabinet to tinker with.
I found a 42-321 at an "antique mall" for a decent price with a tag that said it worked. I figured what the heck.
It was in pretty good shape overall. The cabinet had apparently been stripped down to bare wood and veneer, as it was bare and the trim was no longer painted. One small patch of veneer toward the back had chipped off, but nothing major. Still had both its knobs. Grill cloth was adequate (but more on that later). Looking in the back, arial was intact, chassis was just dusty as all getup, and from what I could see the speaker was intact. Someone had put a new cord on it at some point (brown, non-polarized, lamp cord). The one cap visible was clearly old, if not original.
Operating under the (I know, foolish) assumption that SOMEONE had turned it on already, in order to decide it was working, I very carefully did the same. Worked fine with a slight hum and a little unsteadiness (as compared to its newly restored state now).
Pulling the chassis revealed that the caps were all old/original. I suspect that someone, probably a long time ago, might have done some work on this. Obviously, the cord was newer, though maybe not too new as it was non-polarized. All the caps were the old dingy yellow, wax covered monstrosities, and were all marked Philco. Wiring was obviously old, but was a mixed bag in terms of insulation. In the end, there was only one length that was the old rubber type with the insulation crumbling off that needed replacing. The rest was either cloth, or some other old but intact type.
So I found the schematic and layout at Nostalgia Air and started studying the thing. Ordered a new set of caps from Antique Audio and replaced the old ones. Used the same values for all. Basically, I used the technique of cutting out the old ones, but leaving their leads to form a loop to solder the new, much smaller replacements in. I figured this would be minimally invasive to the rest of the componants/wiring. Replaced the dual filter cap with a pair of 22mf electrolytics I had on hand. Then I added a fuse and put in a new polarized cord with the hot wire running directly to the fuse first, then to the one/off switch, as I should be. Other than replacing one bit of crmbling wire, I left the rest of the electronics as is.
On to the cabinet: I wanted to keep it simple, and as the wood on this thing had really nice grain, I just wanted to emphasize it a bit. So I put a couple coats of natural (tint-wise) Danish oil on it. It looks really nice and was exactly the effect I was looking for. For the grill - well the old one was odd. Somebody had taken a hard painting canvas, cut it to size, pasted the grill cloth onto the front, then pasted that into position within the cabinet. It did the job of keeping the grill cloth taught and in place, but it also (obviously) blocked the speaker! (the only sound would come out the back side of the cabinet) Clearly a cosmetic fix. So I had ordered some Philco diamond pattern grill cloth (the wrong year for this, but I liked it and am not the Smithsonian). Using that same hard frame, I cut out out in the middle so the speaker would not be blocked, and mounted the new cloth on it. Worked well. I was going to get some
dark brown paint at re-paint the trim, but I couldn't find a brown dark enough by itself and got bored with the idea for now. Cabinet looks great either way - so maybe eventually.
So I vacuumed all the dust off of everything, sealed it all back up, and fired it up. It plays beautifully. (sounds a lot better than the solid state radio that I've been using for AM). Nice warm, slightly compressed, tube sound. Love it. Looks killer too. Alignment seems pretty good. A station I know to be at 610 comes up around 625-30 on the dial. Reception is good all up and down the range. I see no reason to screw around with that any (especially since I don't have a sig gen and don't really know how anyway!).
As I said, I think it migt have been worked on in the past. Evidence: the apparently newer cord, the lack of consistent rubber wiring, the obvious cosmetic alterations, 100% intact speaker. But it also was either old or original, as evidenced by the old Philco labelled caps. However, I find it hard to believe that caps from 1942 (or possibly earlier) were intact with no sign of leakage and still operated within the circuit. But what do I know about these things? An equally likely possibility is that someone found it original and tried to fix it up minimally for sale.
A couple of questions came up during the rebuild:
1). Inside the chassis, right in the middle, there is what appears to be a big cap, that has a wire wrapped around it for a few turns. The layout calls it a condenser and choke assembly. No values for either the cap or coil are marked on the schematic. (On the schematic, it's a cap, leading to a coil, leading to ground) I presume that the cap part is marked on its case. I assume it's just what it appears to be - a cap wrpped by wire. I didn't touch it for now, but maybe since it's probably an old cap I should. Could I just slide out the cap, install a new one in its place with the same value, maybe just setting it inside the coils (since the new cap will be smaller)... Or maybe get a new cap, wrap a few turns of wire around it, and use that... Or maybe just leave it alone, since it's all working fine for now. Any thoughts?
2). On the top of the chassis there is another mystery (to me) cap. .0015mf 600v. On the schematic, it runs from one end of the arial transformer to ground. Physically, it runs from one lug of what must be that transformer to a tab on the tuning cap, that is effectively the chassis. I have a .001 630v on hand. I'm not sure if this cap is performing some sort of tuning function, or just blocking something, so I wonder if .001 is close enough for these purposes, or if I should hunt up a .0015?
3). The old filter cap was marked as a 20-20 on the schematic. The one I removed was a much bigger 50-30, or something like that. I knoew I had a pair of 22's sitting around, so I just planned on using those and didn't order anything different (didn't see the values of the original until I pulled it). I used the 22's and there is no hum. So I assume that's adequate filtering and the bigger cap was either a later over-rated replacement, or whatever Philco had on hand when it was built. Sounds like I'm good to go with the 22's right?
4). I have a set of Philco decals from Antique Audio. They look to be a water slide type like for model airplanes. (true?) Does anyone know if I can simply apply these over the danish oil finished wood, or if I need to do something further if I want to use them. I know water slides can be picky about surfaces. I can do an experiment with an unneeded decal if it comes to it, but if anyone knows offhand from experience...
5). Did these things have an open back, or some sort of harboard covering? Mine has no back, and the few pics I've seen of others, when they show the back, have no back. Just curious.
Anyway, a great experience with a gret result. Love the radio. I put on a ballgame and it was like a sound from my distant youth. Not sure how often they go this easy...
Maybe when I figure out how, I'll get a pic or two up here.
Andre
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