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Old 6th December 2005, 08:17 PM   #1
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Default EF86 penthode

Hi everyone,

I found a good tube amplifier project in an old electronics magazine;it uses a EF86 penthode and a couple of EL34 tubes in push pull as output stage.
Trying to build it I came across a problem with the EF86 tubes that are quite difficult to find,so I'm wondering if there is any current production vacuum tube that I can use in place of :Could anyone help/advice me on this?

Any useful reply will be very appreciated!

Thanks very much

Sincerely
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Old 6th December 2005, 08:52 PM   #2
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If you wish, there are several european distributors you could check out. I normally order from Ask Jan First and even shipping is very affordable
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Old 7th December 2005, 12:26 AM   #3
rdf is offline rdf  Canada
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Available, if not exactly dirt cheap:

http://www.tubedepot.com/so-ef86.html
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Old 7th December 2005, 10:22 AM   #4
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Thanks for your kind replies.

But really I would replace the EF86 tube with a current production equivalent tube;Do you know someone?
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Old 7th December 2005, 10:47 AM   #5
SY is offline SY  United States
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The Svetlana is the only current production EF86 I'm aware of. Small signal pentodes as production items are rare birds these days, since the guitar market doesn't use them much. But NOS are plentiful, and a little bit of looking turned up lots of candidates at $15 or less. If you're worried about the future, in a decent circuit where care is taken to avoid turn-on and turn-off trauma, three or four spares will last you a lifetime.
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Old 7th December 2005, 11:32 AM   #6
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Quote:
If you're worried about the future, in a decent circuit where care is taken to avoid turn-on and turn-off trauma, three or four spares will last you a lifetime.
SY, I know opinions differ a lot on this issue, but would you care to expose your vision of a decent circuit? Does this apply for both signal and power tubes? Or should we better start (another) new thread to discuss it?

Thanks, many thanks

Erik
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Old 7th December 2005, 01:09 PM   #7
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i could not find the EF86 in india so am looking at a ckt using 6SL6 and 6SN7 instead but that is being discussed on another thread.

BTW what is this talk about a "decent ckt"? Are the ckts now available on the net not decent?

I found a bunch of ckts published on the net. see post 8 and 10 in the link below. which would be classifed as "not decent"?

EL34 schematic confusion

I'm not questioning anyone here all I am afraid of is getting tubes and OPTs for a ckt that is not good.
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Old 7th December 2005, 05:01 PM   #8
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Erik, I was really referring to taking care that the heater shock on turn-on is limited and that the circuit doesn't expose the tube to too high a voltage before warmup. Those are pretty easy objectives to achieve, though through dint of extraordinary effort, some intrepid souls have managed to avoid achieving them....

The heater issue is discussed in great length in Morgan Jones's book with some excellent examples.
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Old 7th December 2005, 05:38 PM   #9
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Hi SY

Thanks for your reply. I recently got Morgan Jones Valve amplifiers as a graduation gift and (re)read most of it.

The lovely Lm317:
- Reduces the frightening inrush current,
- seems to be good for the sound, ie, some people who compared an (indirect) heated valve feeded both from a voltage source and from a current source, prefer the current source,
- a simple CCS, sufficient to get your feet wet on this terrain.

Erik
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