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  #1  
Old 02-28-2005, 10:52 PM
nasadowsk nasadowsk is offline
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Am I the only one here who finds the 6BK4 a creepy tube, though? I've heard the 'beer bottle' look on used ones is due to X ray bombardment. I've seen them in all sorts of stages of darkness, and it sure doesn't happen evenly...
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Old 02-28-2005, 11:01 PM
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Yeah, its dark & disturbed!

When I was working on the CTC-15, which is missing the hv door, I watched as the glow of the regulator changed with screen brightness. That was kinda strange to see.

Getting further off subject, I was just rooting through some old Admiral literature looking for info on that "Royal" in the other thread...found a manual for an Admiral color set that uses a 21AXP22 & it includes an xray warning stating that without the safety glass in place there are soft xrays present up to 9" from the face of the crt, but only at the center area. The glass should stop them. It said one should not spend more than, IIRC, 17 hours per week that close to an unshielded screen.
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Old 03-01-2005, 07:59 AM
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That may be true that more x-ray emission comes from the CRT's without built-in safety glass if the safety glass is not in front of the faceplate...seems like modern CRT's have leaded glass in the safety glass or faceplate to attenuate x-ray's more.
Found a GE set which has a lead shielded rectifier tube to reduce x-rays, it is in a HV enclosure like any other set...but, there is an HV regulator tube (not 6Bk4 but something else) sitting right out on the chassis with the usual type of shielding around it...don't get that.
Seems like the cheaper sets like Silvertone put less shielding around the 6Bk4.
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Old 03-01-2005, 12:55 PM
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Quote:
Originally Posted by Chad Hauris
Found a GE set which has a lead shielded rectifier tube to reduce x-rays, it is in a HV enclosure like any other set...
Must be like one of these... a 3DR3. Found this in a bunch of tubes I got from someone in town. Heavy little tube! You throw this baby at someone... they're goin down!
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Old 03-01-2005, 05:34 PM
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I've got a tube like that. I was thinking that it was a solid state replacement - I don't think there's actually a tube in there. Isn't a high voltage rectifier tube? Not sure though/can't remember.

-Ian
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Old 03-01-2005, 05:43 PM
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Looks like a HV rectifier. Here's the diagram of it...
http://www.nostalgiaair.org/tubes/3dr3.htm
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Old 03-01-2005, 08:53 PM
nasadowsk nasadowsk is offline
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The 6BK4 was pretty much the only HV regulator, IIRC. There's like one or two others. I think GE had a Compactron one. They all were probbably just repackaged versions of the same tube.

I remember seeing ads in old TV mags for a big recall on them in the 70's (Radiation scare!).

RCA had that pulse regulator setup, but it seems that shunt regs were common up until the end of the tube era (though I've seen tube set schematics with doublers and triplers, solid state). Didn't a few of RCA's portables have shunt regs too?

Oh yeah, didn't RCA flip flop between a solid state and tube focus rect? ISTR the CTC 16s have tubes (the 38/39ish I think did), but the 15 and 11 (?) didn't.

Interesting - the lead covered HV rect. I've seen 'em. I wonder how they got around HV arcing issues? Weren't later 6BK4s made of a thick leaded glass, too?
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Old 03-01-2005, 10:24 PM
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I believe that in the "C" verion of the 6BK4 they switched to leaded glass, to fend off the radiation scare. In a tube manual I have, it warns about always switching out this tube to the newer one to make the set safer.
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Old 03-02-2005, 12:09 AM
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Focus

The -11 had a 1v2 focus tube, the -15 used a #113397 selenium rectifier
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Old 03-02-2005, 07:20 AM
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None of the RCA series string portables used a 6BK4 regulator...the earlier ones like CTC-22 and CTC-36 used a 17KV6 or 22KV6 pulse regulator tube, and a 3A3 rectifier tube. The later ones like CTC-53 have no seperate regulator tube...it must somehow regulate the bias on the HO tube with zener diodes or something. These too used a 3A3 tube.
The very last portables used the bias regulation on the HO tube along with a solid state tripler and high focus voltage (all other RCA portables used a low focus voltage CRT). Would like to see one of these as the performance would probably be just as good as the XL-100 sets as opposed to the softer, dimmer picture of the low focus voltage tubes...have not actually come across one yet. These sets were styled a lot like the XL-100 models too.

There were some 19" RCA sets that used a transformer powered chassis like CTC-31 (that is, CTC-19, CTC-27 and CTC-50), these did use a 6BK4.

Some 16" portables like Sears and some others, usually Japanese makes, did use a 6BK4 with a series string chassis...the CRT and 6BK4 used a 6-volt filament transformer.
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Old 03-02-2005, 11:10 AM
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I think I had one of those RCAs when I was a kid. It looked very much like an XL-100, but was mostly tube. I remember it having the best picture of any tube set I had seen at the time. It looked very much like the picture on an XL-100. It had an odd intermittent fault that I could never find and I eventually parted it out.
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Old 03-02-2005, 12:07 PM
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Exclamation Maybe some shuffling around is in order here

Ya know guys, while this talk is all very interesting and informative, we've seemed to have hi-jacked Tim's thread on his very nice looking roundie.

Sorry about that, Tim. Don't want you to think we forgot about ya! It sure doesn't take much to steer away from the main topic, does it?!

Perhaps a higher-power can move this high-volatge tube stuff over to a high-voltage tube thread so we can continue our 24,000 volt conversation?
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Old 03-02-2005, 02:26 PM
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I have moved this portion of the thread dealing with just HV tubes off to a new thread.
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Old 03-02-2005, 02:54 PM
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Thanks, Chad. Now we can continue this without hoggin Tim's thread on his new find!

Back to the tubes... I too have wondered about those regulator tubes that darken with use. I've seen many. If it's been hit with heavy duty x-rays, this doesn't necessarily mean the tube has exhausted it's ability to do it's job well?

Stuff like this makes me also wonder just how badly we are being exposed to these rays as we're working on sets with the backs and covers off. We probably spend a fair amount of time back there with the set operating and checking for voltages, looking for intermittent connections, etc.

Concerning the above 3DR3 lead shielded tube, I found a comment about it in an old style bulletin board from 6 years ago. Here's what someone said...

3DR3 is a lead oxide shielded HV rectifier for a large old black and white
t.v. and it only is good for a max of about 40mA I'm pretty sure with peak
current of 120mA or so.


That I can think of, i've never seen a set with this tube. It would be interesting to find one with it.
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Old 03-02-2005, 03:36 PM
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A line I recall from an old Consumer Report's article on the subject read something like "most color televisions no longer contain these tubes and those that do have lead shielding to protect you" I think it was c.1972. For some reason I want to say those lead shielded tubes were used by GE. Guess it will take a look through the old photofacts to be certain. I've got some of those tubes on the shelf, I think there is more than one type with that design.

I haven't heard of a rash of old tv repairmen succumbing to cancer. But I don't think I would hang around the unshielded hv section of a 60s color set any longer than I had to. Where is that link to the fella who takes xray photos using an old tv?
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