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...

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.

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.

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! :D

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

Looks like a HV rectifier. Here's the diagram of it...
http://www.nostalgiaair.org/tubes/3dr3.htm

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?

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.

The -11 had a 1v2 focus tube, the -15 used a #113397 selenium rectifier

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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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. :eek: :twak:

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?! :D

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? :scratch2:

I have moved this portion of the thread dealing with just HV tubes off to a new thread.

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? :scratch2:

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.

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?

Interesting what you say about no reports of repairmen with cancer.....I've heard that some broadcast engineers who were exposed to transmitter radiation (AKA Microwaves) had LOTS of health problems as they were literally being cooked from the inside out.

There's story, which may just be urban legend, of an engineer who worked at the Empire State Building transmitter in the early/mid 50's who seemed to age 30 years over the course of a single year and died. His wife sued someone over his early death...don't know anymore of the details....does anyone?

Then again, there are the Darwin Award winners such as the night watchman who was stationed out in some frozen tundra and noticed that when he passed in front of a microwave link antenna that he felt warmer.....so he pulls up a chair and starts sucking a bottle of booze inside out----he passes out and his crusty carcass is found the next morning! Please pass the BBQ sauce, YUM!

Anthony

I will try to remember to take the camera home tonightand see if I can get in to where the set with the lead shielded tube is...there has been recently more TV's acquired than I have been able to find really good spaces for so they have piled up in the garage. The set is a 25V" rectangular G.E.
So far as I know, have never seen any other brand of set with this tube.


Consumer reports must have included tubes with leaded glass in their write up of lead shielded tubes...most color sets using tube HV rects used the regular old 3AT2 or 3A3C.

Then again, there are the Darwin Award winners such as the night watchman who was stationed out in some frozen tundra and noticed that when he passed in front of a microwave link antenna that he felt warmer.....so he pulls up a chair and starts sucking a bottle of booze inside out----he passes out and his crusty carcass is found the next morning! Please pass the BBQ sauce, YUM!

Anthony

My father knew someone who walked in front of a high powered radar dish and got blasted with a few megawatts of microwave. DEW line maybe. His internal organs got cooked enough to cause death in a few weeks. :(

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Actually, I talked to an older TV guy who said he knew of no cancer cases w.r.t. color TV.

Realize, it's not just color sets that do it, though they got the attention. Typically, anything above 16kv absolute potential was considered to be good for it.

From what I understand, even color sets are at the low low low end of the spectrum - low energy and it can't go far anyway. I'd be more worried about zapping yourself :)

BTW, I *think* NTE still sells those solid state HV rect plug ins, and at least that cuts 2 sources out of it...

IIRC, the metal shield can around the tubes itself is beyond sufficient for shielding.

I've seen dark 6BK4s and a few dark 3A3s. Never saw a 2AV2 or such, though. I don't think dark = wasted, but it's a good sign the tube's been around the block a few times...

Hey, anyone remember all the fun 'fixes' that happened in the 70's and the fun failures of them?

I knew a TV repairman who had a heart attack and died after lifting one of the giant, real wood, consoles from back in the 1960s/1970s. Of course, he smoked and was very overweight. I wonder if this had anything to do with it? HM? I also have never heard of any issue with TV repairmen getting cancer or other illnesses from the radiation from TVs.

Remember B&W TVs do not have a metal shadow mask, the X-ray risk from these is much less if, it even exists, than from the color TV sets.

I have about 3 types of tubes that are HV regulators for tube type color TVs. They all look like a 6BK4, but they have different pin-outs and are not interchangable.

Have a Conrac b/w monitor which uses a 6BK4....was from a TV station and included features like this that were absent in consumer b/w sets. There is no shielding at all around the 6BK4 so I figure the HV is low enough where x-rays aren't a concern.

Guys, is there any market for these tubes you mention? I have a lot of them, and would be delighted to make someone a package deal on them all.

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The Magnavox T931 chassis I have uses the 6BK4B -
don't know how long-lasting they are, but would be happy to get a spare or two.

I remember the Xray scare when I was at Motorola - don't recall which tube it was (I worked on B&W design), but I do recall that the xrays were internally shielded by the electrodes if they were straight - but some tubes were manufactured with the electrodes crooked, and xrays could escape from the tube (at the bottom, I think). In the Magnavox t931 chassis, the tube is installed with the bottom toward the back of the set, and that side of the shield box is open - the 5 other sides are solid. (1967 model, 25AFP22 rectangular CRT, would be called 23V today).

HV regulation was abandoned in later color sets when it was discovered that the sweep current could be made to track the high voltage variation with beam current- so on bright pictures, the HV drooped, which would have increased the size, but the sweep B+ also drooped and the size remained constant. Part of the internal factory design specs was the maximum percentage of size variation with brightness that was allowed. Regulated sets had no HV droop, but then the sweep current had to be maintained constant under varying beam current loads - probably easier in sets where the video b+ comes off the line instead of the flyback like later transistor sets.

I am presently working on a Sears 12" color hybrid set from 1971. This set was made in Japan. On it, the high voltage regulation is accomplished by regulating the screen grid supply to the horizontal output tube. 1/2 of an 8FQ7 is used. I had not seen a design like this before.

After replacing a defective 1 meg resistor, the circuit is working, but some blooming is occurring on bright pictures. The high voltage at minimum brightness is within the Sams listed specification.

I plan to replace the 3AT2 high voltage rectifier to see if this reduces the blooming.

Guys, is there any market for these tubes you mention? I have a lot of them, and would be delighted to make someone a package deal on them all.

I think I might have heard of these tubes being used in some sort of exotic audio amps. Can't remember any details though.

Hey - an output device for electrostatic speakers ;)

BTW - the 6BK4, etc have a mu of 2000. Was this the highest of any 'conventional' (if you can call a beam triode that!) tube out there?