Zenith 5H40 chassis restoration.

[jaymanaa]

Hello all, I recently acquired this Zenith, and while restoration may not be the correct word, I would like to get it safely operating again (mostly for DXing fun). I found a ton of useful information here, http://www.transoceanic.nostalgiaair.org/h-500.htm , but being relatively new to radio repair I thought I might save myself some heartache by asking you fellows. As the pictures reveal, someone has made some "repairs" in the past. The multi can was replaced by a tubular lytic of all the wrongs values, and it looks like the two caps (one lytic and one film) with the green spaghetti on them were also replaced. My main question is this; On tube Hi-Fi gear, which is my main hobby, I normally just replace pretty much every cap, diode, and resistor. I have a feeling though, that the same approach here may affect the operation in a detrimental way, in regards to alignment. However, I also feel that a radio of this age, probably needs an alignment anyway, and I would have to send it to someone for that. I have a tone generator and scope but that's about it. The radio is in good cosmetic shape, so all it really needs is electronic work. Any ideas or advice on how to approach this would be very much appreciated. I re-capped a Zenith console from the 30s years ago, but it worked well enough in my upstairs room with it's built in wave magnet, that I didn't worry about alignment. I live outside Kansas City and my main goal is to listen to the Grand Ole Opry out of TN on Sunday nights. Thank you all very kindly in advance.

Edit- And the selinium rect. has also been replaced. I was wondering if I could use a single uf4007 diode there, or would I need to account for the increase in voltage due to the lower drop of a modern piece?

[jaymanaa]

Here's an interesting article. http://w3hwj.com/index_files/RBSelenium2.pdf

[Reece]

You'll want to replace the selenium with a silicon diode and put the 50-75 ohm resistor in series with it. Replace the electrolytics by disconnecting the original can and putting new ones which will be much smaller under the chassis. May need some terminal strips. The striped black plastic caps will be leaky and need to go, also. I would leave the resistors and mica caps alone. Transoceanics have a very complicated filament supply circuit that with resistors provides just the right voltage to each filament along with proper bias. You could check each resistor with your ohmmeter and if within 20% leave it.

These one-volt tubes have very delicate filaments. Once it's operating, never turn the set off and then back on quickly. Also never never yank a tube while it's operating and then plug the tube back in. The voltage can build up beyond what it is supposed to be and blow at least one tube when plugged back in.

Before tackling a TO for the first time I'd search on line for a while and read all I could about restoring your particular model. There is a lot of information out there.

[jaymanaa]

Thanks for the reply, I followed all the advice, and I'm glad I did. The power supply is all finished up and I have a good set of tubes all tested up for it. Just a couple questions now; I checked the power supply voltages and they look like they will be good once loaded with tubes. Is there a way to test filament voltages without tubes, or is it a leap of faith type thing? I was very lucky with this radio, as it hadn't been all hacked up. The couple repairs that I found, were good enough to fix up. I did mount a couple terminal strips for the new caps, and they fit quite nicely, I did remove the little plug deal for the 220 adapter to make a neater job of the recap, but I'm pretty sure I'll never move to Europe. Would it be a good idea to place a thin piece of sheet metal under the chassis where the battery would have been. They do mention putting one there when aligning the set, so my thinking is, it may improve overall performance. Thanks again, jay

[jaymanaa]

Oh, I am in the process of replacing the striped plastic caps with some orange drops. I'll check the resistors too, there aren't that many really.

[Reece]

I haven't done a 500, but did a 600, which is very similar. I did a lot of reading before tackling that one and I just very carefully marked off with a highlighter every change of component I made on a copy of the schematic. I let it sit for a day or two and then traced everything out again to be sure. The filaments are in series in these sets and I read that the voltage from the start of the series to the end should be within a certain range, seems like it was eight point something. I hooked my voltmeter to those points and plugged the radio into my variac and sneaked the voltage up. When the radio started playing I was happy to see my filament voltage was right on. The set I restored was for a friend. It played before restoration but I changed the caps and rectifier to keep it going right. It was beautiful cosmetically as it had sat in a closet for many years.