The AM Forum

A friend gave me this nice ol' WL-5736 tube.  It was used in the Westinghouse MW-2 transmitter and what else?
W2PFY has some pictures of his MW-2 on picasa.

The plate is rated 2.5KW and the full ratings apply to 60MC. Grid driven and grounded grid conditions are given in the data sheet.

The tube has a few neat features to look at, like bolted-on element supports, and in some pictures can be seen the little 'Yy" pattern in the glass on the side above each pin. I don't know if these are manufacturing marks or subtle ornamentation on the part of the tool maker responsible for the glass part of the envelope. Anyway the tube is an example of American craftsmanship and industrial art. I have not tried anything with it but was told it is good. Of course it has been sitting for many years.

The data sheet also says the class B grid driven service provides an 800W carrier. The point is that it is a good QRO AM tube whether in an amplifier or a transmitter and if it is good, and not abused, it could last another lifetime.  I am not sure when or how I might use it but it's almost like a cake that looks too good to eat.

more. The middle picture shows the "Yy" pattern in the glass and also what looks like the getter. What else might it be?

The pins are possibly silver plated, now black.. it looks like they have not seen a socket but who knows. The PDF is the data sheet. It would be great to locate a socket for it but that's not so likely today.  The file 0744 is the EIA registration data and more comprehensive than the other data sheet in some ways. It's dated march 30, 1949.

I don't know if they even used a socket, Patrick. I had a couple of MW-2 rf deck carcasses I stripped down and the bottom pins were coupled with fly leads and fittings with crossbolts. The anode fixture provided a stable mount. I have 2; one is possibly good, the other has an open filament.   

Here is a similar tube.  A Federal Telephone and Radio Corp. 7C23.  It looks pretty rugged, rated at 1500 W out, but seems like it would be good for more.

73,  Jack, W9GT

Yes, and just look at what it takes to light the filament... 6.0v @ 60AMPS! Class C PA specs shows approx. output at 3200 watts. Now, if we can just figure out how to modulate it!???

At any rate, some pretty serious service requirements.

Is that a corona ring on that tube? Yow.. Some of the old tubes ran many KV.



It's definitely a candidate for soft start on the filament. It would be an interesting experiment to use it but, considering the rarity vs. the effort to build a home for it, the prospect is not so practical. The MW-2 uses a pair of 833s for modulation. Possibly red-hot 833s. I may test it. Probably it will need gettering assuming it still has a vacuum.

Pat,

You could always drive it with that 5D21 you helped me identify:

http://frank.pocnet.net/sheets/201/5/5D21.pdf

Phil - AC0oB

Those Yy patterns appear to be similar location and reason stress lines, perhaps even partial cracks from the glass cooling process.  Interesting with magnification.

Yeah if it weren't for the huge filament requirement it would make a great display lamp, exceedingly retro, --really steampunk in some circles.

yes an old post that I missed?  Hello Pat and all, I don't know how I missed all of this thread? Yes having a getter in the tube was a real surprise to me! I have over ten spares and only one has a getter in it. I think that one is an RCA? I never had one with gas in the tube but I have had shorts that are probably a filament that broke loose and is stuck up in the envelope where it cannot be seen. Those filaments are the hair pin type that are I believe officially call a "catenary" design as opposed  to the spiral types. The tubes can be rebuilt and there was a place in Brocton, MA that would rebuild them for $750.00. The last two I got on ePay cost me $30.00 each and are NOS so I won't be needing any rebuilding for awhile if ever?  Yours is a newer model with that type of radiator. Earlier models had a rolled copper anode with the cooling fins inside just like yours. There was an earlier model that was exactly like the WL-5736 called WL-473 and they were found in the Westinghouse 3 and 5 kw FM transmitters back in the late 40's and fifties. I had been looking for one of those for about ten years and finally one came up on Epay. A couple of the pins are broken off but surprisingly, the filament is good and it does light up?? The glass on this one looks as if it had never been rebuilt and I'll take a picture of it later and put int on here. Right now I need to go out and get something dead to eat so I'll catch up later.........73 Terry.  

I'm glad the topic and tube are still interesting. I think I have since given it to someone who likes and builds/repairs their stuff that uses old tubes of that type, but it is an amazing construction.