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-   -   8156 Beam Pentode Compactron (http://www.diyaudio.com/forums/tubes-valves/203505-8156-beam-pentode-compactron.html)

Einric 31st December 2011 02:30 PM

8156 Beam Pentode Compactron
 
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

Einric 31st December 2011 02:36 PM

So I have found the datasheet.

Can anyone give me a hand deciphering it?

GloBug 31st December 2011 02:44 PM

Compactron Tubes: A Junkbox Guide

Einric 31st December 2011 03:55 PM

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

Eli Duttman 31st December 2011 06:08 PM

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.

Einric 31st December 2011 07:11 PM

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?

Eli Duttman 31st December 2011 09:18 PM

Quote:

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.

Einric 31st December 2011 10:22 PM

All of the tubes are NOS.
I do not have any tube testing gear.
I might dig through the pile of dusty test equipment upstairs that is leather bound.
Maybe I'll find some sort of tube gear up there.

Thank You

Einric 18th January 2012 02:31 PM

After looking at a bunch of designs I wonder if these tubes would be suitable for a phono stage?
It would be pretty cool to find a tube that could be run off batteries and used for a totally power noise free RIAA amp.

ryuji 18th January 2012 02:50 PM

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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