Antique Tube Box Art
I took a gamble on a box-lot of parts from Craigslist, and it turned out to be an excellent find. One of the things I found was a collection of tubes in their original boxes from 1926.
That doesn’t happen often. The art is in great shape. Back in the ’20s tube box art was a lot more eye-catching than when tube industrialization had completed by the ’30s and this is just one of the examples.
The RCA UX-201A was one of the first mass-produced vacuum tubes released to the public and was in common usage through the ’20s. Back then, companies were able to copyright the number sequence so many tubes had different first numbers and prefixes…Cunningham made a CX-301A, Arcturus had a 401A, Montgomery Ward licensed RCA’s number and called in an AX-301A…you get the idea.
1936 Grunow 566 Repair Finished! [Part 2]
I started this radio a few days ago in Part 1. I left off with the radio up on the bench ready for service. It had a lot of issues with the power supply – and as I discovered while working, some shipping damage: the volume control wires, and one wire from the power switch, had snapped. There was a fair amount of bad workmanship in the radio everywhere which contributed to that happening…you can’t expect much from a 50-year-old cold solder joint after all. I repaired it back to schematic along the way.
You can see some of the damage here where a 150 Ohm flex resistor broke. This could have been shipping or age but the combination sure didn’t help it.
I went to the Mike and Key Electronics Show and Flea Market today down in Puyallup to replenish my stock of parts and hopefully find some new ones…actually, I’m pretty disappointed. I had a very long list of parts I was hoping to find, the sort of things that are in everyone with a real workshop’s stockpiles. Quite a few had some elsewhere, or didn’t think to bring any, but I ended up not finding anything. I did pretty well though getting four front end sets (6A7 6D6 75) and four of each #41 and #42 output tubes, as well as a bunch more of various numbers mostly from $1 working-pulls bins. I don’t have any photos inside, but here’s one of the line to get in.
I pulled out quite a bit from the radio.
And for the first power-up.
I wish I could say it worked at this point, but it didn’t. I took the tubes out to test and found a 6A7 that tested just marginal but with no other issues. This really should not have been a show-stopping issue, but it seems it was as when I replaced it with one of the tubes I’d picked up earlier in the morning it fired right up.
Another shot for fun of the bottom:
At one point in the radio’s past, the IF transformers were replaced with service parts – in this case with Meissner universal coils. They work just fine and I’d really like to know what happened to the radio to need both replaced. It’s the first radio I’ve worked on which was in the shop so many times for what looks like major surgery.
Time for an IF alignment. I decided to broadly tune these for a little better fidelity at the expense of some selectivity which was going to be bad anyway. I tuned the secondaries to 465kHz and the primaries to 455kHz. This should give about 10kHz of bandwidth to pass as much of the signal as possible.
With that, I reassembled it and took some photos in front of a makeshift backdrop made out of cardboard boxes.
This one came out with an interesting camera glitch, but it’s below the radio itself so I’m leaving it.
This one needed some interesting troubleshooting to get it to work but most of the issues were things I spotted while looking it over initially, so I didn’t waste a lot of time on it. The radio has a really big speaker and is very powerful and sounds as good as it can sound so I’m glad I broadly tuned the IFs. This was a fun project with the bit of detective work involved in fixing mistakes.
Next Project: 1936 Grunow 566 Radio Repair [Part 1]
I’m off to a good start for my March projects, fixing up the Grunow 588. Next up is my Grunow 566 from the year before, from 1936. I picked this one up from eBay in shockingly good original condition – it looks almost brand new. Digging into it, though, it turns out I have a bit of work ahead of me. Someone’s been in this one – several times – and has made several modifications of somewhat questionable workmanship, to put it nicely.
This one is an even simpler radio than the model 588; it’s still a superhet but this model has no AGC (automatic gain control) on the front end. The tube line-up is 6A7 6D6 76 41 80. Most of the other radios I’ve serviced have a #75 in the 3rd position (a double-diode + triode tube); the #76 is a single triode only. The lack of the two diodes accounts for the lack of AGC. This does make it a simpler circuit to work on, though, as there are several fewer capacitors and resistors that would otherwise be on the AGC line.
The chassis is very clean and both tubes that need shields have the originals present. Finding missing tube shields is a real pain. The chassis tags are in good shape too, this was the only model to use the chassis 5-S:
Pulling the chassis out, it’s easy to see what I mean about it being messed with before. The electrolytic cap which usually clamps to the top of the chassis is missing to the left of the front coil:
There’s also something about that speaker…it’s been replaced! The original, correct, speaker for this model is an electrodynamic speaker with a field coil. Field coil speakers were used before materials science advanced to the point of giving us reliable and powerful permanent magnets, where the magnetic field for the speaker was powered by a high voltage passing through a large coil. Electrodynamic speakers required four wires to operate (two for the field coil, two for the voice coil). This one only has two!
Someone replaced the speaker with a rather large permanent magnet speaker. The original speaker had a hum-reduction coil which doesn’t exist on this speaker, so it’s been eliminated as well. Granted, this one might actually sound a little better than original, but it’s a big change. Swapping a field coil speaker for a permanent magnet speaker also leaves the issue of the field coil, which is a part of the power supply circuit and is necessary for the radio to work.
The previous owner replaced the field coil with what looks to be a much-too-small resistor in its place:
I’ll have to check the tube datasheets to see what kind of current they’re drawing, but that may need to be replaced for safety and reliability. Even worse than these mods, though, is what happened with the power supply. Parts failed a lot back then, it was just a fact of life. When the filter caps died the first time, the external filter was replaced with one under the chassis:
When this cap failed, it was replaced by two more caps – put in the circuit across the old caps, without removing them.
When one of those caps started failing, it was replaced by another also just tacked in across the failed point. And arriving with one end broken off.
I’m somewhat curious what “Semi-Polarized” means, but suspect it’s just a quirk of older manufacturing methods. Regardless, though: this radio which is supposed to have only two electrolytic filter capacitors currently has five installed. I’ll be cutting them all out and sanity checking the entire power supply.
The age of the parts used in these repairs leads me to believe it was modified like this sometime in the late 1940s up through the ’50s, which makes it somewhat authentic if not original. I’m going to fix it up as well as can be but don’t plan on reversing the speaker-swap and we’ll see how it goes. Stay tuned!
1937 Grunow 588 Radio Repair
I finally had a free day with no major commitments and was able to finally get some work done on my projects! It’s been a productive day.
I picked up this nice example of a Grunow 588 “Teledial” radio from the General Household Utilities Co. a few weeks ago and finally got a chance to work on it after a busy month. It’s a nice little five-tube radio that shares a lot in common with the Grunow 589s I’ve serviced in the past. It has a very nice original finish, original knobs, pointer and dial cover in good condition although covered in bits of packing material.
The Grunow 588 uses Chassis 5-W, which is also shared by Grunow 583, 585, and 586 radios. The tubes are 6A7 6D6 75 41 80. Nostalgia Air has the schematic for free from Rider’s 9-2.
The labels are in good condition for the most part:
The radio has all the tubes and shields intact. I tested the tubes and found 4/5 of them to be good, and the #75 tube had a good triode section but one marginal and one weak diode. I grabbed a NOS #75 from my stock but am keeping the used one as it probably has enough life left to be a bench sub.
The chassis is a little dirty but has been stored well for the most part, not much rust and no evidence of critters.
It’s been repaired a few times in the past. There are some ’40s, ’50s, ’60s and a ’90s capacitor present and a few different style resistors.
I tested the coils and found everything to be good, fortunately, so it was right onto replacing caps and checking resistors. Most of the resistors needed replaced as did all the caps.
I replaced all the paper and wax capacitors, and the 8×8 electrolytic with two 10uF discrete caps. I also eliminated the bias cell and associated 1M resistor and replaced them both with a single 10M resistor to provide bias. Bias cells were only needed for a couple of years, it wasn’t long before engineers figured out how to eliminate them.
Now, time to reassemble:
Back upside down for some final voltage checks from the bottom:
Now, time for alignment! For IF, I used the signal generator at 465KHz; for the oscillator adjustments I used known frequency stations at either end of the dial as it’s a bit faster that way. It was fairly out of alignment – I’d say I probably doubled the gain through the IF, and the RF was way off: 880 was coming in about 930! I was using a shorter antenna so didn’t pick much up on shortwave, but that’s to be expected.
Now, to put it all back in the cabinet!
This one was fun. These Grunow radios are easy to work on, have straightforward but well built circuit designs, and come in interesting styles. This Teledial table radio is unique for the era and it looks great on my shelf.
Feel free to write in or leave comments with questions!
First Look: 1937 Grunow 588 Radio Repair Project
Keeping my word about actually trying to accomplish projects in March, I started tearing into the 1937 Grunow 588. It’s vastly similar to the Grunow 589s that I’ve repaired in the past, the main difference being that it’s a table model radio and not a large console.
It’s also a five-tube radio with the line-up 6A7 6D6 75 41 80.
The chassis stickers are in great shape. It’s always nice to find them in good condition. I also like how on this model, the antenna and oscillator trimmers are on the side near the transformer (for adjusting the alignment) – on the 589, they’re up in the front partially under the dial face which is more difficult to access.
The chassis is pretty clean, just a little surface rust on the transformer and the tube shields with the rest in good shape.
The underside shows evidence of having been worked on a few times. There are some of the original Grunow caps, and several ’40s, ’50s replacements, a ’60s or ’70s replacement and one from the ’90s. Other than needing to verify the wiring to ensure past repairs were correct, it’s nearly the same radio as the others and should be an afternoon’s project at most, maybe two if I take my time on it. I’ll be getting started on that in the next few days.
March Projects
February was a pretty slow month for projects, about the only one I managed to accomplish was fixing the Firestone car radio. March should be a bit more productive, though. I have a list of a few projects I’m planning to try and complete.
First up, a pair of Grunow radios that are vastly similar to the pair of 589s that I’ve fixed in the past – a Grunow 566 and a Grunow 588. The 588 even has a Teledial.
I’ll probably also start working on a a Jewel radio that was a Christmas gift:
I also have a kit amplifier left mid-project, I’ve mounted the iron and hardware but none of the connections or components yet. (It’s a stereo amplifier with a 6SN7 dual triode driving a pair of 6V6 in push-pull for each channel, and should sound pretty good when complete.)
Plus other projects that seem interesting along the way. Stay tuned!
What’s been your most difficult challenge at work, and how did you overcome it? [Crazy Boat Connections]
I was swapping war stories with another technology professional the other day and we got to talking about our “best problem” scenarios. I happen to have an interesting story from my days as IT Manager of the Las Vegas Casino Lines, and how I solved a vexing issue with our shipboard Internet connection that had been around for a year and was costing the company money every time the ship sailed.
The Las Vegas Casino Lines were, as the name implies, a gaming establishment that operated out past the International Boundary out of Port Canaveral, FL. They went out of business a few years ago (spurring my move to Seattle), but while they were in business had a fairly sophisticated network on- and off-shore to allow tracking systems, cash- and game-management systems, security, navigation and communications to all continue without interruption even when the ship was out at sea.
This WWAN connection was provided by a Verizon Wireless air card and an external antenna. The only trouble was, every time the ship was out, it would randomly lose connection. Without a connection, patrons couldn’t withdraw cash from the onboard ATM, charge gaming credits to their credit cards, or do anything really. If you had money, you could keep playing, but if not you got to enjoy a 4-hour smoke-filled boat ride.
The ship’s antenna for the WWAN connection is circled in red above. The perspective makes the antenna appear a lot bigger, but it really was only a six-foot fiberglass antenna mounted on the railing. The antenna is on the right side of the ship (facing forward) near the bow on the middle deck. I rode along with the ship for a few days while monitoring the connection signal and started to work out a pattern of when the signal dropped off: only when the ship faced certain directions, and more on the return leg of the journey than on the outbound leg.
I had a hunch: the signal is clearly dropping when we face certain directions. What are we connecting to? I visited the FCC’s web site and pulled the listing of fixed cellular transmitters along the Space Coast from our route, and eliminated towers that didn’t belong to Verizon; then plotted the tower locations on the map along with our ship’s turn area and boundary markers. Then, I rode along again and took a GPS track of our ship’s position, which I annotated with comments about signal connectivity.
As it turns out, we lost connectivity when we were on the margins between cell towers, and when we were facing the wrong direction. With the ship traveling north, the antenna was attempting to transmit through the (grounded metal) superstructure of the ship itself to reach the tower. Combined with the fact that microwaves don’t travel as well through salty humid air over the ocean as on land, and it’s a perfect recipe for signal loss. The shipfitters had installed the antenna in a poor location for our application. It was an easy fix, after that: one of the crew helped me run new coax to relocate the antenna to the top of the ship’s tower.
The signal was completely lost at this point – I’d overlooked a small issue. Adding 250 feet of additional coax cabling had introduced a lot more cable loss into the system, so now we needed an amplifier to get the signal out of the ship. Finally, though, the amplifier was installed and the system worked perfectly. Patrons could now charge gambling expenses to their credit cards while out in the middle of the ocean, and everyone was happy.