Tube Stereo Radios

[Jeffhs]

Originally Posted by Kingfisher

Mine has a bad hum, part of the circuit board near the output tubes looked fried. I haven't used it in several years. This must have been one of the last tube models Arvin made since it was bought new in '68. Won't be finding any 50HK6 tubes at Rat Shack. They stopped selling that kind of stuff loooong ago. Arvin was known for wierd tube numbers, 50HK6, 20EZ7, etc. It's often a dead giveaway as to who actually made some store branded radios.

Some Zenith MJ-1035s used 50EH5s in the output stages, while others had 50C5s in the same position. Mine (an MJ-1035-1 from 1965) has 50EH5s as the output tubes, and has a couple of tubes with 19-volt filaments as well, wired in a series-parallel arrangement with a filament transformer. The tubes are wired in two separate strings, with the transformer feeding both. I'll have to look at the schematic to see how that's done, as before this one I had never seen any radios with two series string wired in parallel with a transformer. I guess Zenith did it that way because of the two 50-volt output tubes, which could be a series filament string by itself--50 volts x2 equals 100 volts, close to the line voltage. However, in my MJ1035-1, one 50EH5 is in one string while the other is in the second string. I don't know offhand what the combined filament voltages of both strings would be (probably well over 200 volts, since the MJ1035 series had either eleven or twelve tubes). Zenith may have had no recourse but to use series-parallel wiring and a 6.3-volt filament transformer. The downside is that the B+ for the tubes is still derived from the AC line (in fact, the radio chassis is directly connected to one side of the line, as attested to by a warning on the back cover), so the filament transformer will not provide any kind of isolation.

I agree that tubes are difficult to find these days, with everything being solid-state, surface-mount components and such. However, it is possible to find old tubes (even real oldies such as 01As, et al.) if you look around. John Kendall's Vintage Electronics (www.vintageelectronics.com) in suburban Baltimore has many vintage tubes currently for sale at dirt-cheap prices; I've purchased tubes on that site for my vintage sets that I might not have been able to find elsewhere. I don't know if John Kendall has 01As or anything older than the late '40s, but he does have tubes from the '50s to the end of the tube era.

One warning: While the price of the tubes on vintageelectronics.com may be low, the shipping charges, depending on where you live in relation to the Baltimore-Washington, D.C. area, could be quite high. I live in northeastern Ohio near Cleveland and found a shipping charge of something like $8 for my last order of tubes purchased from the site; the tubes themselves cost only about $2.25. This is shipping for tubes sent to Ohio; of course, shipping to other areas, especially to the West Coast, will be higher. Note as well that single tubes, even miniatures, will be shipped in large boxes, to survive the rigors of the USPS's automated sorting system. The reason tubes are not shipped in mailing envelopes, even padded ones, is precisely because of the automated sorting machinery. I was advised some time ago by an AK member that tubes sent in mailers would be crushed and/or smashed on their way through the sorting equipment, resulting in the customer receiving an envelope full of smashed glass and crushed metal.