CBS Rectifier Identification Help Needed

[bob p]

I've got a rectifier tube that I'm trying to identify. Unfortunately, all of the writing on the tube is long gone, and the only identifying marks that are left are on the base. I've tried the foggy breath trick, but none of the writing that used to be on the glass is readable.

I'm hoping that somebody might be able to help me ID the tube based on some high res photos:

High Res Photos

Can anyone tell me:

1. The tube ID number.

2. The maker of the tube. I'm guessing that its CBS by RCA. Did RCA ghost manufacture for CBS?

3. The era in which the tube was made. If anyone knows the history of which companies manufactured for CBS and when they did it, that would be helpful.

Thanks!

[Rob Mercure]

Hey Bob,

Unfortunately your images open to such a great size in my browser - Mozilla - that I can't view the tube in it's entirety and when I download the images only the first one seems to be stored such that the Windows Picture and Fax viewer allows viewing - perhaps if the individual shots were broken down into individual files?

But CBS, under their subsidiary Hytron, produced tubes until the late 1950s and perhaps into the 1960s so I suspect that this is a Hytron product. Secondly I suspect that it is a 5U4B or a 5AS4 which are essentially the same tube. No matter what it's one of the higher powered consumer rectifiers which will generally sub for each other. The only possible "ringer" would be a 3DG4 which can sub for the 5 V rectos with suitable dropping resistors - measure the cold heater resistance and post it and I'll check a few 5U4s and 3DG4s for reference.

If you choose to redo the pics an off white or beige background would probably help more with details.

Hope this helps.

Rob

[bob p]

Thanks for looking Rob. Sorry about the image size problem. I didn't even consider that potential problem, as my browser (Konqueror) automatically auto-sizes large photos to fit to the window size. I cropped those photos using Gimp on a linux box and saved them as jpegs with 100% resolution. I have no problems viewing them via XP using the photo slideshow feature. Since they've been passed back and forth across multiple machines via FTP and HTTP, you might want to check the file attributes to make sure that they're both READ and WRITE on your PC.

I've shot some more photos on a beige background for you. This time they're 640x480. I took two sets, one with and one without flash. Hopefully they'll work out better for you.

Low Res Photos

I was thinking that the scallopted top piece on the tube looked a lot like what I've seen on RCA tubes. I'm not sure if that's meaningful though. I don't know if this info helps, but I found the tube in an old TV repairman's tube caddy.

Regarding the heater cold resistance, I measured the Z across pins 2 and 8 at around 1.0 ohm, but the numbers were bouncing around between 1 and 2 and I'm not sure that I trust my multimeter to provide reliable readings at such low impedances.

I have no idea what this tube might be. I can tell that it looks like a twin diode / rectifier, but that's about all that I can say. It would be very helpful to know if it is/is not a 5AR4, 5U4, etc.

thanks again.

[Rob Mercure]

Hey Bob,

Well heater on pins 2 & 8 eliminate the 3DG4 but a quick cold resistance sampling of 6-7 5U4GA/B - 5AS4s gives me about 0.4 ohms on the average using a Fluke 75 series II DMM so your resistance reading seems a tad high. Perhaps you've got a 1 ohm 1% resistor you could use for reference to "calibrate" your DMM.

While I've probably got around 20 new and used 5U4/clones floating around here - maybe more still in equipment - I'm too lazy to pull out more than 1/2 dozen right now but I'll keep my eyes open in case I see something that truly matches. As is, other than the getter location, your tube very closely matches a RCA 5U4GB made during the 9th week of 1965 - In fact I'd call it a match if the heater resistance wasn't so far off. Now the 5AR4s that I've got - mostly all Mullard with a couple of 1960s Sylvanias (not including Chinese and JJs) - have about 1 ohm heater cold resistance but I've never seen one in the T-12 envelope your valve sems to be enclosed in - all the ones I've got/seen are in the T-9 bottle (although I seem to remember seeing a pic of one from the 1950s in some sort of ST bottle and perhaps some other large bottle).

I mentioned in one of your other tube related posts there are often other characters etched/screened on some tube envelopes and with octals sometimes screened/stamped on the base. You've probably already done so but if not you might want to look over the phenolic base and see if there are traces of any other characters that might help identify the tube - TungSol, for instance, always - as best I can tell - screened their mfg. number on their octal bases.

As is I'd probably feel comfortable using it in circuit as a 5U4GA - it's probably a GB which has 25% greater current capacity, etc., but it never hurts to be cautious.

Hope this helps

Rob

[bob p]

Hi Rob. Thanks again for your help.

I'm not convinced that we can place much faith in my heater resistance measurements, as I'm not measuring with a high precision instrument that I would consider accurate or precise at extreme readings. I was using a cheap DMM and the numbers were bouncing all over the place between 0.5 and 2 ohms.

I've tried using a less cheap DMM (Radio Shack digital, not quite so cheap, not necessarily a lot better). This one gave me steady reading of 0.9.

I don't really have a precision ohmmeter, but I'll see if I can have someone with a better measurement instrument take the measurements for me.


I'm wondering what made you think that the tube looked like an RCA. Was it the top plate or something else?

I've looked at the envelope and base again, under high magnification. There aren't any numbers etched on the bottle or screened on the base. The base only shows a couple of scratch marks where it looks like a tube-holder scratched the base. And the envelope has no traces of silkscreening, even with the humid breath test.

I appreciate your help with this -- this thing looks like it could be a decent functional tube, and it would be a shame to throw it overboard just because I can't determine what it is.

thanks again.

[Rob Mercure]

Hey Bob,

First off you should be able pull from circuit or otherwise find a few low value precision resistors to use as a calibration reference for your meter - you'll want this for measuring cathode current sense resistors and transistor emitter resistors. Secondly, not to be flip, I suggested the RCA tube due to it's overall "look" - the shape of the mica insulators/spacers, the type of ribbing in the plates, the size, location and style of the plate crimping slots, the curvature of the "dome" of the envelope top (there's got to be a great art/machining/drafting term that describes this - help me out folks) and - but not in this case - the location, dimensions, and "style" of the getter as well as the characteristic color of the getter "flash."

One thing that helps is this being a "consumer" electronics valve - even for lower powered (say, 5 KV or less and less than 1/2 amp continuous) military there are many strange and interesting variants that look like models for space craft. But once you've limited the field to "higher powered consumer" rectifiers you wind up mostly with variants of a few "historic" designs - such as the 80. So the 5U4, the 5AS4, the 3DG4, etc., "look alike" and it's a matter of sorting out from there. The T-12 envelope helps as that eliminates the 5Y3 variants due to size - an ST bottle would have suggested an earlier design which would have eliminated the 3DG4, for example.

I dunno, as I try to get more specific I feel like I'm losing "focus" - there really is no substitute for having the bottles in hand cuz there are lotsa little details that are hard to describe and that don't come across in photographs.

In any case unless you've got an open heater or an internal short you probably have "at least" a 5U4GA and probably a GB. Back in the "bad old days" of tube televisions this was the most common tube replaced and seein' as how lotsa folks left their television on continuously and that the 5U4GB was operating at maximum current draw in a color set it's amazing that these bottles survived as long in service as they did - service shops made sure that there were using the best rectifiers they could get to prevent "call backs."

Rob