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Old 8th December 2004, 06:54 AM   #1
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Default Single-end... which tube?

Hi guys and gals!
I have got a bunch of single-end transformers 9kohm/4ohm, i wonder which tube i can use with these, i was thinking of an EL34 at low voltage maybe?
as far as i know these transformers where once used with ECL86 or similar tubes, but i dont have any ECL86s 8-(

can i use EL34?
or should i get hold of some EL84 maybe?
recommendations please!! 8-)
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Old 8th December 2004, 07:23 AM   #2
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Of course you can use the EL34. It will work, but power will be low because of the high primary impedance (but distortion should also be low, as will be output impedance). You'd probably be looking at about 2W or so in triode mode... I haven't worked it out properly...
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Old 8th December 2004, 08:08 AM   #3
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By 'low voltage', what sort of B+ range were you looking at? Do you have the power supply already, or do you need to buy the parts? If it's the latter, buy what you need to build what you want.

9k:4 would make nice 211 OPT's, even at 600V or so. They look real purrrty all lit up too.
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Old 8th December 2004, 08:38 AM   #4
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hmm.. EL34 could work..ok, what is the recommended voltage in that case?
211, ain't that tube hard to find? as i recall it has four pin base and the anode at the top, but to me it looks like overkill for these small OPT:s...
Maybe one 832A or 829B? yep, prone to oscillate but they looks nice.
Would EL84 be a good choice if i could find a pair?
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Old 8th December 2004, 09:14 AM   #5
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oops... missed the 'low-voltage' bit. Yes, of course the EL34s will work. Working well and producing reasonable power output is a different matter altogether though.

The 211/VT-4C has a 4-pin base but no top-cap.
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Old 8th December 2004, 09:24 AM   #6
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If you are considering EL34s then why not have a look at triode connected 12E1s. Very cheap at the moment and do their thing at fairly low voltages. 9k is too high to get much power but it would probably sound nice.
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Old 8th December 2004, 09:26 AM   #7
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Quote:
Originally posted by Mr. Triatic
hmm.. EL34 could work..ok, what is the recommended voltage in that case?
To get reasonable power, you need to use a rather high idle voltage, because using the high primary Z OPT limits the current swing available, and allows greater voltage swing. You need to take advantage of the greater allowable voltage swing so you can get some reasonable power output... P = V x I

Quote:
Originally posted by Mr. Triatic
Would EL84 be a good choice if i could find a pair?
um.... no, well not with conventional thinking. Well, the same caveats would apply. (low power... etc) This is not to say it won't sound good. Commercial amps like the Decware Zen use high primary Z OPTs with the SV83 (similar to EL84) to good effect.

Quote:
Originally posted by Mr. Triatic
Maybe one 832A or 829B?
Sorry, I don't know those valves. Will check and see. Usually the primary Z is around 3-5 times rp for triodes... (Very rough approximation...), so you'd be probably 1.8-3K of rp. hmmm... maybe you could knock up an amp with a bunch of paralleled driver valves? Just for something different...

Quote:
Originally posted by Brett
They look real purrrty all lit up too.
Of course they do.... Nothing quite beats the look of a lit transmitter valve with that glowing filament...
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Old 8th December 2004, 09:32 AM   #8
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Quote:
Originally posted by martinab2
If you are considering EL34s then why not have a look at triode connected 12E1s.
12E1s? Cool! I have a personal belief that there are a bunch of happy diyers out there using 12E1s and not spreading the word so the price doesn't rise....

They're available from Retrovox for something like US$5 each.

That and the 807 are probably my picks if I was building a new amp now...

With about 400 ohm of rp in a 12E1 and a 9K, you have a 0.178 ohm ouput Z (well, the part from the output valve anyway), without negative feedback. At that kind of level, the secondary DC resistance becomes very significant.

However, unless you want to go out and buy new OPTs I don't think you could use the 12E1s because they'd need quite a bit of idle current, which may saturate the OPTs you have. How big are they?
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Old 8th December 2004, 09:48 AM   #9
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Quote:
However, unless you want to go out and buy new OPTs I don't think you could use the 12E1s because they'd need quite a bit of idle current, which may saturate the OPTs you have. How big are they?
You are right of course! I forgot that mine are running 140mA each - hot transformer time
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Old 8th December 2004, 09:55 AM   #10
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Martin, I forgot another great thing about 12E1s... cats love 'em. Well yours does anyway!
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