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Projects involving EF50 tubes?

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Emnitec

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Joined 2006
emnitec.com
#1
Hello all!

I'm all new here and rather new to the diy-community. My experience is building effectpedals so I have very little knowledge about tubes, but I'm in process of learning now..

So, I've found a whole box of different NOS tubes at my work and most of them I recognise from schematics I've seen, but then I have a great amount of EF50 tubes that I've never seen in any schematics?

Do u people know of any project(s) with this tube involved?? I would be glad if someone could direct me or tell me a little more of what this tube could be good for...

Thanks in advance!


/Emnitec
 
#3
The EF50 was a very common RF pentode, found especially in military equipment. I have never heard of its use in audio work and I don't know whether it's linear enough to do a reasonable job; so many RF pentodes aren't suitable for audio. It may even be remote cut-off, for all I know, which would make it unsuitable.

If it is applicable to audio, its use would be confined to small signal amplification, in either pentode or triode mode, or as a constant current source/sink. It's rather bulky and there are plenty of other popular tubes for these purposes, so that maybe why it's never applied to audio.
 
#6
....and the list is..:

Philips EF50 : 20 st
Philips miniwatt ECL11 : 8 st
Philips miniwatt 6V6GT : 11 st
Philips EF95 : 2 st
Philips 90AV : 2 st
Philips 866A DCG4/1000G: 7 st
Philips 5894 QQE06/40 : 3 st
Philips miniwatt EAA91 : 2 st
Ediswan D.L.S 15 : 2 st
Telefunken ECL11 : 4 st
Brimar 6V6GT : 6 st
General Elect. 6V6GT : 6 st
Zaerix EF50 : 1 st
Triotron 6AU6 : 6 st
Sylvania 6AU6WC : 1 st
LM Ericsson 5591/403B : 2 st
LM Ericsson 6J6 : 8 st
LM Ericsson 6761: 5
Lorenz ECC81 : 3 st
BRIMAR 807 : 4 st


All unopened....but there are some diodes and so that I'll probably never will use...



/Emnitec
 
#7
You could build a nice PP amp with the 807 as powertubes, and ecc81 as phasesplitter perhaps.

The 866A are mercuryrectifiers, contains mercury 🙂

If you dont want them I can buy some from you. Ive been looking for some of them for an amp im building
 
#11
Your 6V6GTs will make good output stages for modest power ~ 10watt in push-pull. A lot of guitar pratice amps use those.

The 6AU6 is a sharp cut-off RF pentode that is suitable for audio use. It can be used as a normal voltage amplifier in pentode mode, in triode mode with g2 and g3 strapped to plate, or in triode mode using g2 as anode and with g3 and plate grounded (small signals only). The 6AU6 is also good as a constant current source/sink,
 
#13
I was recently given what seems to be a piece of tube radio/radar gear possibly from the WWII era. Once I saw it I started getting ideas to build a cool studio pre-amp/compressor/distortion unit, either using some of the existing tubes, or just gut the whole thing and just use the case and cool-looking panel. It is half-gutted already with no controls left on the panel.

Firstly it has a number of EF50 tubes (RF Pentode in a screened can. Not sure of their condition, but they can be got on ebay). I know these are ancient and probably shouldn't be used for a new design, but it intrigues me to think how they might sound/perform with audio in a quirky way. Especially for an overdrive/distortion unit. It also has a few EA50 vacuum diodes in there which I think were used as demodulation diodes. So what would you guys think? Can the EF50 even be used properly for audio or is it just a no-no? If not then I'll just go for something more common and put new sockets in etc. And, could the EA50 diodes be used in any interesting way to manipulate/distort the audio? Probably not...

Just throwing the ideas out there without any experience with tubes this old. I might be trying to resurrect useless technology here! 😀... Just thought I'd bump this thread in case anyone has any ideas...
 
#15
My first valve guitar amp was fun.
I made all the classic valve mistakes.
Had long pcb tracks to input valves.
Placed pcb transformers too close to valves and they picked up hum.
Didn't elevate heaters to 45VDC or use a balancing network to the DC supply.
Didn't decouple each power supply to each valve and got feedback.
Placed output transformer too close to mains transformer.
Badly routed heater wires.
 
#16
General Guidance on Pentodes for audio.

Lookup their datsheets.
If they are described as "Sharp Cut-Off" then they are good for audio.

If they are described a "Remote-Cut-Off" then you might be able to use them in a compressor or something like that but they won't be good as audio amplifiers.

Cheers,
Ian
 
#18
r-type.org states the EF80 is a replacement for the EF91.
The EF91 entry at r-type.org has schematics using this tube in every stage of audio amps.
If you have a bunch of these tubes the possibilities for diy are awesome. Warm up the breadboard!
 
#19
I have used EF50's and EF54's (B9G Base) in small signal amplifier stages, but have found them to be rather microphonic. The Mullard EF37 or ME1400 (Octal base) is much preferred. The B9G base is available from China but I find the vintage type to be better - if you can find them! If you fancy using B9G based valves, why not try the EF55? Designed for video service but being a true pentode, really excellent trioded for SE use, and very cheap! I much prefer them to 6v6 or 6L6/807's. Run at around 45mA with 5K load they are excellent!

Regards.
 
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