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8156 Beam Pentode Compactron

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I have found some GE 8156 Beam Pentode Compactron tubes in boxes new at my shop collecting dust.
My boss has given me permission to have them and I'm wondering if anyone has any information on them.
Pinout? Specifications? Documentation?

Thanks
 
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I did see that page and didn't quite understand the Low-Mu, Med-Mu & Hi-Mu stuff.
I can understand the idea of combining three tubes into one and I was wondering if you would be able to use this as a Push Pull Pull all in one tube? Or is that not possible/intended?

Thanks
 
The 8156 data sheet shows a single beam power tetrode contained in a 12 pin compactron package. Obviously, you can't build a PP amp solely with this type.

What catches my eye is the tough screen grid. While the type was clearly intended for RF service, it may be suitable for use in UL mode. The low B+ voltage limit suggests keeping the primary impedance of the O/P trafo low, due to step down ratio considerations. Perhaps Edcor's model CXPP25-MS-4K will do.
 
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Yes, it is an RF tube, I am an RF Technician and I have a lot of parts that are associated.
I just hate to see perfectly good classic parts go to waste and be thrown away.
I'd be interested to see what I could do with the Six of these tubes I have.
It makes sense that they would be designed with low voltage in mind.
These tubes probably came out of a remote site GE VHF radio (WAAAAAY before my time).
I will be heading into my shop later today to pick up a few things, I will grab the other few tubes I found and do some more investigation.

BTW what is the difference between SE and UL modes of operation?
 
BTW what is the difference between SE and UL modes of operation?

SE = single ended, as opposed to PP = push/pull. UL = ultra linear and it is a mode of operation where the screen grids are connected to taps on the O/P trafo primary. Tubes setup in UL mode exhibit behavior in between triode and full pentode mode. In fact, UL mode is a form of local NFB. UL mode can be used in both SE and PP amps.

IMO, practical considerations suggest you use PP pairs as "finals". You stated that you have 6 specimens. RES shows a $15 price for an 8156. So, you may be able to get the 2 pieces needed to make up a spare set. A PP pair of 8156s operating in UL mode and Class "AB1" should yield about 10 WPC. You will need reasonably efficient speakers whose sensitivity is in the mid 90s. I hope you have access to tube testing equipment. The specimens have to be matched, as closely as possible, for both gm and cathode current. "Fixed" bias, with individual "idle" current adjustments for each tube, seems correct, given that specimen matching will not be stellar. My guess is that -12 V. on g1 will be about right.

The B+ PSU is not especially difficult. SS full wave bridge rectify the O/P of a Triad N-77U isolation trafo and CLC filter. 250 WVDC caps. will provide a good margin of safety.
 
They are a bit excessive for a line stage. Keep in mind that those tubes will consume full filament power even when they are doing nothing. You ought to be looking for small signal tubes for doing any kind of phono or line stage. Take a look at any 6l6/6v6/807 circuit for inspiration. you will need to adjust the operating voltage/idle current but that only means drawing new load lines and adjusting the specified b+ and one or two resistors(or a trim pot if you choose to use fixed bias)

Those tubes consume about 4 watts a piece just to keep warm. you can use small signal pentodes that require 6.3V at 0.3A or dual triodes at similar requirements, there are even compactrons with three triodes stuffed in one envelope

SE operation would not necessarily require careful matching the tubes unless you run them in parallel as you can adjust bias independently if you choose to use a fixed bias.
 
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Looks about like a 6L6, except it'll keep on working up to 175MHz+ (better than 807). Transconductance I think is a little higher, so alter the bias accordingly. It should do well in 6L6 non-GC (i.e., the lower dissipation models, G, GA, etc.) circuits with little adjustment.

The screen isn't too impressive, I have some similarly sized sweeps (compactron, same bulb, 15 or 20W plate dissipation; not nearly as low inductance connections to the cathode or plate though!) which claim 3W or so. Sweeps of course were built for abuse; this tube was made for the somewhat more gentle environment of a more-or-less well-adjusted radio.

Tim
 
You should be able to get 20-25 watts/channel in PP mode with them. I used 6JN6 Compactrons in a little amp with 6U10's on the input driving them. 180 v on the screens to keep them happy. They sound great in triode mode.
 

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