I have a set that uses a 2BU2 as its HV rectifier, and, unlike most tube TV sets, the tube is not in a metal cage (the bottom is in a plastic holder and the top is open).

The old tube, which likely came with the set (Zenith, 72-09 date code) has a warning that the tube has integral X-ray protection, and to replace with a tube "of the same type".

I got a new tube, which has a "2BU2" near the bottom (probably the original mark) and "2BU2/2AS2A/2AH2" in yellow ink higher up, but a different warning: "high voltage may produce harmful x-rays unless tube is shielded".

I guess, for now, that I'll stick with the original tube, but one would think that X-ray absorning glass would have been made a specification of the tube type, no?

If not, how would one ask for a 2BU2 with X-ray absorbing glass?

Curious.

The GE versions says it has integral shielding. The RCA versions says it minimizes x-rays but it talks about the need for shielding.

Both are rated to produce 0.5 mR/hr

http://www.pmillett.com/tubedata/HB-3/Receiving_Tubes_Part_1/2BU2.PDF

http://www.mif.pg.gda.pl/homepages/frank/sheets/123/2/2BU2.pdf

I think they all might have integral shielding, but might require additional shielding under some conditions.

The 0.5mR/hr is measured at 4" from the tube. 1/R**2 is going to reduce this to nearly unmeasurable levels at normal viewing distances.

John

Thanks a bunch.

I've got the original tube in there, for now.

If the horizontal foldover is from the old 2BU2, and the new one fixes it, I may switch, since it will be watched very little, and the set operates with HV well below the design maximums.

Anybody got a NOS GE 2BU2A? Check the box for the little white patent number label that leads you to the patent GE got for the lead silicate glass they used. No other tube manufacturer licensed the patent, 3854964.

Hence, you had RCA and others making an electrically equivalent tube with less X-ray protection and with a nice disclaimer.

When I worked at Cain Electronics selling both RCA and GE tubes, we quickly figured out why the RCA tubes didn't sell. It took confirmation from the GE folks as to why.

Cheers,

A good read, gemane to my above post:

http://tinyurl.com/videokarma

Cheers,

Yes, I think that's is the most informative I've seen. I was aware of the issue GE had, but there were some details I never knew until now.

That's a very good article. Thanks for finding it. It also seems to confirm though that 0.5mR/hr measured at 2"-4" is insignificant at 78".

John

Anybody got a NOS GE 2BU2A? Check the box for the little white patent number label that leads you to the patent GE got for the lead silicate glass they used. No other tube manufacturer licensed the patent, 3854964.

Hence, you had RCA and others making an electrically equivalent tube with less X-ray protection and with a nice disclaimer.

When I worked at Cain Electronics selling both RCA and GE tubes, we quickly figured out why the RCA tubes didn't sell. It took confirmation from the GE folks as to why.

Cheers,

BINGO!

The replacement tube is branded Sylvania (yellow paint), but was possibly a rebadging of the tube, since there is a separate silvery "2BU2 USA" mark near the bottom.

The original is branded Zenith, but has "188-5" next to the date code. 188-5 is the EIA code for GE Owensboro.

Interesting article. It reminded me of the 3DR3 tube that has lead shielding to block x-rays.
http://farm5.static.flickr.com/4026/4391448402_b4ef2cb91d.jpg

Interesting article. It reminded me of the 3DR3 tube that has lead shielding to block x-rays.


Don't forget the 3DS3 as well - it's the "preferred" type by my GE Tube manual. Probably higher current or HV rating. The rubberized lead shielding allowed the HV rectifier to be used without a cage in GE KE chassis sets and a few Sears-Simpson badged GEs as well. Your 3DR3 was probably used in Sears' 17 inch Color sets, as was the GEs. 3DS3 was used in the 19KD/KE chassis.

Cheers,

Let me correct myself - it's actually a rubberized coating that protects the ferrite shielding around the tube. US Patent 3725718 (http://www.freepatentsonline.com/3725718.pdf) is germane. Stackpole patent, no doubt licensed by GE. I can't find the patent number anywhere on either of my tubes or boxes.


Cheers,

Cool. Thanks for the correction.