Electrical drafting is primarily done on a computer today, with software such as EAGLE or KiCAD. This wasn’t the case back when tube radios ruled the airwaves, though – schematics were drawn up by engineering draftsmen by hand. And as with any process with a human element, they didn’t always get it right.
I’m working on a 1934 Philco 66. It came to me in excellent original condition with little evidence of having been service, and throughout the process, I’d been relying on the schematics to guide me in the right direction. Unfortunately, along with a laundry list of other issues, my reliance on the schematic to be “the truth” led me around in circles longer than I needed to be to resolve a power supply problem.
Below is a schematic snippet of the power supply and audio sections of the 1934 Philco 66, with the RF chain to the left of the #75 Detector/1st Amplifier tube hidden for simplicity’s sake.
In green, I’ve highlighted the path B+ (high voltage) is supposed to flow from the rectifier cathode to the plate of the first audio amplifier. It’s a very straightforward path…if the draftsman had indicated that tube was supposed to be connected to the power supply. In red, I’ve indicated a missing connection symbol. Without it, there was no power being supplied to the first tube in the audio amplifier stage and the audio signal was being killed at that point before it could make it to the final output amplifier. Using an alligator clip, I restored that connection to test, and the radio sprang to life making noise on the next power-up.
The second filter capacitor should have been connected to both B+ and to the plate path for the #75 tube, rather than just the plate path. (Incidentally, the two capacitors are both at the same potential, so under the correct connection scheme could have been replaced with a single capacitor of a larger value.)
It’s not done yet, but I’m inclined to believe the final wiring issue has been corrected, and it’s on to performance.
I’ve had this radio on my bench for a little while, and she’s finally back up and running – and it plays great! It’s a 1938 Philco 38-C-12, special edition to commemorate the crowning of King George IV and Queen Elizabeth.
Since we don’t have a King and Queen of the United States, it’s fairly obvious this radio isn’t from around here. This particular model was made in Canada and brought to the U.S. sometime later, and was actually rediscovered in Florida. I can only assume a retiree seeking warmer weather brought it with them sometime in the last 75 years, and that’s how it traveled the long distance itself.
Period Canadian radios came with a Ontario Hydroelectric Power Commission approval stamp, which makes it easy to tell their origin.
The power transformer also gives it away – the 25Hz transformers used in some parts of Canada at the time are considerably larger than the 60Hz transformers found on most American radios. (You can use a transformer rated for a lower frequency, as the greater amount of metal makes it less likely to saturate, but you generally can’t use a transformer rated for a higher frequency on a lower one.)
This radio has seen a little bit of service in the past – both can capacitors have been removed; one was cut open and used to hold its replacement in a partial restuff and the other was replaced below the chassis. All in all, though, the radio came to me in very good near-original condition. This radio uses five tubes 6A7 78 75 41 84 – which is a little different from the typical tube line-up, but allows a smaller power transformer to be used as the rectifier can take advantage of the same 6.3V windings for the rest of the tubes, rather than needing a dedicated 5V winding. Its schematic is the same as the American Philco 38-12.
Capacitor replacement was uneventful on this radio, but I also had to replace the tuning capacitor mounting gaskets. These isolate the frame of the tuning gang from the chassis to keep it from shorting out. Over time they shrink and harden. Renovated Radios has many types of reproduction chassis gaskets. The new ones have restored the right tuner height and isolation. This part was pretty labor intensive, but needed to be done for best performance.
You can see in the next shot, the braided ground strap from the tuning gang ready to be tacked back to the RF ground. Desoldering braid works perfectly for this application.
On top of all these problems, the dial pointer shaft was seized up. I removed the shaft, cleaned with 99% isopropyl rubbing alcohol, re-applied lubrication, re-mounted the shaft and restrung the dial cord. This one is very easy – spring mounts on the gang itself, and 1 1/2 turns around the tuning shaft for tension.
As you can see in this shot…the reproduction gaskets don’t fit 100% the same way the originals did. They work, though, and this part of the radio isn’t visible while it’s in the case. So it’s time to put it all back together and get the shields on:
Back in the case:
Fully serviced, this radio will continue playing for many years!
Feel free to leave comments and questions.
I’ve been offline for a bit as I’ve been too busy at my career to do much on the side. My workload has died down a bit and I’m back at it. Currently on my bench is a Philco 38-C-12 “Coronation” model. It’s a Canadian model, with a 25-60Hz power transformer, but other than that it’s identical to the US model 38-12 code 121.
The tube line-up is 6A7 78 75 41 84. This was on the more economical side of price, and only one of the two IF transformers is located above the chassis and properly shielded. The other IF transformer is unshielded below the chassis and has some very specific lead dress instructions for professional service.
Again hinting at the economy nature of this radio, there are only a handful of capacitors that are immediately suspect. The unshielded IF transformer is visible at the bottom center of the radio, mounted perpendicular to the tube sockets.
The tuner on this model is nearly seized. It’s uncommon for them to be this badly stopped up, but not unheard of. I’ll be replacing this radio’s bad paper and electrolytic capacitors and cleaning and re-string the dial and tuner. Stay tuned, I’ll also have some more about exactly which coronation they’re talking about.
I had an interesting call the other day with a gentleman about a radio he’s working on, among other topics:
That’s a Philco 46-420. They’re nice little bakelite radios with 6 tubes designed to receive the AM broadcast band. He’d come across some unlabeled wiring while repairing and had dealt with it but we were talking about what it’s purpose was.
I generally work on pre-WW2 radios so haven’t run into this particular arrangement personally, but I’ve read a few different articles by other collectors on this topic and recognized it immediately. The coil, wound 8 turns around the capacitor and connected at one end to the chassis, is a type of wave trap designed to cancel out the inductance of the old capacitor. This helps to prevent interference – both received, picked up through the cap as if it were an antenna, and radiated interference from the signal passing through the cap. Philco used these capacitor wave traps in most of their radios from 1946 and on. There’s an article at the Philco Repair Bench describing one style; this is a slightly variation with the same effect.
Modern caps are constructed out of metalized polymer films that have very little inductance, but these older capacitors were just concentrically coiled metal foil sheets with a lot of natural inductance.
Modern caps don’t have that physical property, so it’s safe to replace the wrapped capacitor with any modern replacement and either shove the new cap through the coil, or remove the coil entirely.
Thanks to Bob from Old Tyme Radio for these photos of his project, and for distracting me from being snowed in for a bit!
I’m always taking mail from readers with interesting anecdotes, photos and questions so feel free to send them over either as comments or through the e-mail address I’ve posted in my Repair Services page.
In “House”, Season 8 Episode 5 (aired 11/7), we can see that the good Doctor has a 1937 Philco 37-620 Radiobar in his office. Unclear whether or not it has the original glassware. I’d love to have one of these in my collection, but they’re quite rare and expensive.
Philcoradio.com has some more about the history:
This Philco Radiobar sold for $252.50 in 1937 dollars, around $3800 in today’s money. This was a high end luxury for the wealthy to have in their homes, but out of reach of most consumers of the time.
I thought I’d start the weekend off with some more photos of butchered antique radios for your viewing
misery pleasure. This is the second-round photo roundup. Check out the first set of ruined antiques here!
An aspiring artist thought this 1940s Philco radio would look better painted in a motif reminiscent of Starry Night. I don’t really agree.
Somewhat similar, a dealer is selling a Zenith tombstone radio that’s been decoupaged with magazine clippings. This was almost an interesting work of art, but because the magazine clippings aren’t from the correct period, it’s just tacky.
This late ’20s lowboy radio was stripped down into an end table. Cleanly done but it would’ve been more interesting with the internals, even non-working.
From Craigslist, someone turned what I suspect is a late ’30s RCA into a bar with a modern stereo built in. Turning radios into bars seems to be a popular thing to do with them.
Radio bar conversions have been going on for a very long time – almost as long as radios have been around – and some can be very interesting. It’s just that many are done without respect for what the radio used to be – and without regard for the shape of the cabinet. Most upright radios don’t have a flat inside space to place anything, making shelving difficult – and ensuring that it’s going to look ugly no matter where it’s stored.
Most similar-looking Post-War consoles with a record player are reasonably suitable for conversions. This one has been adapted into a cigar bar:
That’s not too bad, but radios with more square space inside are even better:
I’ll be converting one in this style to a bar myself, soon:
Back in the 1930s, radiobars were intricate pieces of high-end furniture in custom made cabinets for the wealthy and were produced by several major brands. This 1937 Philco radiobar has great folding out sides and mirrored backing, with period glassware:
They came in a few cabinet styles:
There were even models produced into the ’40s and ’50s, like this Porto-Baradio mantle-top bar:
If you’re looking for an antique radio bar, you might be better off shelling out for an authentic one rather than a conversion.
And finally, leaving you with one that looks deceptively like a ruined antique but is in fact very special:
While it might look at first glance like a 1930s RCA radio that’s been painted black and had 1970s chair rails stuck on the ends, this is in fact an original by famed industrial designer and RCA contributor John Vassos and is worth thousands. Its style is the sort of thing that could be easily overlooked, too!