Quote:
Originally Posted by Tom Bavis
As far as tubes... I test 'em, replace weak ones, and if it doesn't make a noticeable difference, I put the weak one back...  I'd have a replacement set of tubes, but I wouldn't necessarily CHANGE any... Although I HAVE changed god tubes when they weren't the original brand and I had one that was.
17JK8 will cost you $1.80 at Antique Electronic Supply. If you're desperate, a 12DT8 would probably work, or a 17EW8... but it is an oddball tube, with two unequal triodes. And 50EH5 costs half of what a 50C5 costs...
If the cord clamp make you nervous, wrap the cord with Nomex or similar tough insulating material where it goes through it. |
Tom, you have a point as to replacing tubes. If they work, why replace them in the first place? My MJ1035 still has a few of its original tubes, which are still in good shape--even for being as old as the radio itself. It is for these reasons that I am going to put that re-tubing job I mentioned on the back burner until or unless a tube actually goes bad; in the meantime, I intend to enjoy listening to the radio on my favorite oldies stations (there are two in this area). There is no sense digging into the radio when it's working well. I admit, I've had bad luck with modifying anything, be it a radio or anything else, when it's working, even if its performance could stand improvement.
Thanks for the info on the tube substitutions and the line-cord antenna. I didn't realize that, in a pinch, the two tubes you mentioned as subs for the 17JK8 (the 12DT8 and 19EW8) would work, especially since the two substitutes have 12- and 19-volt filaments respectively. However, you did say that the 17JK8 is unusual in that it has two unequal (I read this as dissimilar) triodes, which tells me that a substitute for this tube would rarely work as well as the original. It's always better to replace tubes with the same ones which were originally supplied with the unit, anyway. Substitutions often work, but seldom as well as the tube for which the circuit was designed.
I did not realize, either, that a 50EH5 would actually cost less than a 50C5, at least at Antique Electronic Supply; I thought it would be vice-versa, since the 50C5 has been around at least since AC/DC radios used miniature tubes. In fact, until I got my MJ1035, I had never even heard of a 50EH5 tube and was, admittedly, surprised when I found two such tubes in my set (I had expected to find 50C5s). The Sams Photofact for my MJ1035 (set 715, folder 9) shows two 50C5s, one in each output stage; however, that particular Photofact is dated 4-65 and could well be for a later version of the radio, perhaps the MJ1035-W1. Mine is model MJ1035-1, which has the RCA phono input jacks on the rear panel; further, the original MJ1035 had the radio-phono switch near the jack panel at the top rear of the set, whereas the MJ1035-1 (and possibly the MJ1035-W1 as well) had the phonograph input switch as a fourth position on the band switch, with the RCA jacks for the phonograph input at the lower left-hand rear corner of the cabinet, below the FM antenna terminals, looking at the front of the radio.