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1937 Grunow 588 Radio Repair

March 3, 2012 3 comments

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!

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First Look: 1937 Grunow 588 Radio Repair Project

March 2, 2012 Leave a comment

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 29, 2012 Leave a comment

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!

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