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Old 20th April 2011, 03:17 PM   #1
mfaughn is offline mfaughn  United States
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Default Noob. Help PP EL34 / EF86 both as triode schem.

Hi,

I have iron from an HK TA260 (I think same as A500). 4.3K primaries, no screen taps. What to do with it? I am thinking PP EL34 triode strapped. I also have a lot of nice EF86 tubes and was thinking first stage with these also triode strapped. I will most likely drive it directly from strong sources (DAC, CD player).

This would be my first real build. I was hoping that a schematic for such a beast existed already. I'm not yet capable of understanding how to design/adapt an existing schematic that is "close" to what I'm looking for. I WANT TO LEARN*. If there is either a schematic of what I am describing or a person willing to talk me through modifying a "close" one I'd be grateful.

Of course if there is some compelling reason why I should not do this I'm all ears. I don't have the money right now to go and buy a bunch of stuff so I'm trying to mostly use tubes that I've got for this project -- right now that mostly consists of EL34, EF86, 12AU7, 12AX7 tubes.

I do also have some other iron but it is more obvious what to do with those (a set for RH84 and a set suitable for Mullard 5-20 or Dyna ST70). I might tackle the RH84 before this but I have more of a need for 15Wpc than I do 5Wpc right now speaker-wise.

Thanks for any consideration you can give.

-Michael

* on wanting to learn -- I find it is hard to find just the right material for reading that hits the mark for me. Is there perhaps any literature or tutorial that starts with a basic schematic(s) and steps you through what each component does (how and why)? seems to me that that would be pretty helpful.
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Old 20th April 2011, 03:51 PM   #2
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Consider Poindexter's 6GK5/EL34 Music machine. Two stage, no feedback, triode, CCS in the tail of the LTP, about 12-14W or so. I built one with Edcor Iron, and it surpassed my expectations.

No EF86's, but 6GK5's are less than $5/ea.......(you'll need 4 of them, single triodes, 7 pin mini's)

Or a Mullard 5-20 variant with EF86/KT88's triode like Sgregory's Opus or Tubemack's Soloist...

"Mullard 5-20 KT88 PP blocks!
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Last edited by boywonder; 20th April 2011 at 03:54 PM.
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Old 20th April 2011, 03:55 PM   #3
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Quote:
Originally Posted by mfaughn View Post
* on wanting to learn -- I find it is hard to find just the right material for reading that hits the mark for me. Is there perhaps any literature or tutorial that starts with a basic schematic(s) and steps you through what each component does (how and why)? seems to me that that would be pretty helpful.
loadmatch3-pp-triodes
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Old 20th April 2011, 05:39 PM   #4
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Another useful " bare bones " read. It's not just about guitar amps so don't be put off by the title.


http://www.freewebs.com/valvewizard/index.html
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Old 20th April 2011, 05:49 PM   #5
mfaughn is offline mfaughn  United States
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Thanks boywonder. I don't really want to get into semiconductors just now and the soloist seems to be unbuilt as of yet. I'd run across the music machine. I'd probably go with the tube rectified ps version as I have a couple of nice Mullard GZ-34 also (forgot to mention that). I may end up going that direction as NOS Mullard 6GK5 are indeed quite cheap.

I'm still curious about my original proposition. I really would like to use what I've got on hand....though I do have some heptal sockets...so, maybe...

-Michael
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Old 20th April 2011, 06:09 PM   #6
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by mfaughn View Post
Hi,


* on wanting to learn -- I find it is hard to find just the right material for reading that hits the mark for me. Is there perhaps any literature or tutorial that starts with a basic schematic(s) and steps you through what each component does (how and why)? seems to me that that would be pretty helpful.
Valve tube automatic grid bias for vintage radios

http://en.wikipedia.org/wiki/Valve_a...0%93_technical

http://my-bankruptcy-help.com/?b=Valve_audio_amplifier

Biasing

Keith Snook's —The Valve ( and Hi-Fi ) Audio Interest pages—

Fun With Tubes

Thermionic Valves - Theory

just a small bit of it

a tip
when you google, try go to images
there may be a world of info hiding behind any of them
and when 'google', be careful with the words and terms you use
it can make a huge difference
and when you find a site, it may not show anything, at first
but look it through, and try see if there are links to other stuff
lots of good info is found that way

and please, when you find something, save it
a lot of it could be really hard to find again
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Old 20th April 2011, 08:54 PM   #7
Sheldon is offline Sheldon  United States
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Quote:
Originally Posted by mfaughn View Post
I'm still curious about my original proposition. I really would like to use what I've got on hand....though I do have some heptal sockets...so, maybe...
Try your EF86 then. You'll have a little less than half the gain, but that should be adequate with your sources. With an appropriate operating point, the EF 86 will have at least double the output impedance, so you should calculate the effect on the HF roll off for driving the EL34. If necessary, you could add a simple FET source follower between the driver and output.

Sheldon
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Old 20th April 2011, 10:05 PM   #8
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EF86 is a great tube. Copy the circuit of the Eico HF60. It's a fantastic amp. But build a proper power supply. Essentially the Mullard circuit.
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Old 21st April 2011, 03:28 AM   #9
SHiFTY is offline SHiFTY  New Zealand
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I can vouch for this schematic- I built it using triode wired fixed bias KT88s and it sounds great!
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Old 21st April 2011, 06:39 AM   #10
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I have used the EF-86 in the Mullard 3.3 SE EL-84 circuit and it has a lot of gain. They really need the good miltary tube cooler/damper to keep the microphonics down. Strapping them isn't something I have tried but seems like a good idea if you don't need the gain from the little pentode.
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