Noob. Help PP EL34 / EF86 both as triode schem.

[mfaughn]

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.

 

[boywonder]

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...

http://www.diyaudio.com/forums/tubes-valves/156699-mullard-5-20-kt88-pp-blocks.html

 

[boywonder]

* 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

 

[Soonerorlater]

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

 

[mfaughn]

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

 

[tinitus]

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_audio_amplifier_–_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

 

[Sheldon]

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

 

[sepolansky]

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.

 

[SHiFTY]

I can vouch for this schematic- I built it using triode wired fixed bias KT88s and it sounds great!

 

[Thatch_Ear]

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.
Thatch

 

[tinitus]

also used in Quad II, it seems

http://www.keith-snook.info/Schematics/QUAD II Schematic.pdf

 

[mfaughn]

OK, at this point I am considering either Poinz's Music Machine (EL34/tube rectified) or a Mullard 5-20 variant.

I have a feeling that the Music Machine would be my path to good sound with less fuss but that going with a 5-20 variant would be a path to more tinkering and experimentation (i.e. learning more). Both have their appeal.

I can't just copy a 5-20 variant willy-nilly. I've got no screen taps with this iron. How much would I need to change other parts of the circuit if I simply took a 5-20 and triode strapped the EF86 and the EL34? or even put switches in to go back and forth from triode to pentode?

 

[boywonder]

OK, at this point I am considering either Poinz's Music Machine (EL34/tube rectified) or a Mullard 5-20 variant.

If you go the Poinz Music Machine Route, keep in mind that there are two versions around, you want the newer version with the 6GK5 LTP.

 

[mfaughn]

If you go the Poinz Music Machine Route, keep in mind that there are two versions around, you want the newer version with the 6GK5 LTP.

Yep, that's the one I'm looking at.

The PS schematic is a for a monoblock I think. I've reference to using a different PT for the 10m45 source, the Amveco 62035. What I don't understand is how you get 66V out of those?

 

[boywonder]

Yep, that's the one I'm looking at.

The PS schematic is a for a monoblock I think. I've reference to using a different PT for the 10m45 source, the Amveco 62035. What I don't understand is how you get 66V out of those?

There are versions around with stereo and mono supplies, both SS and tube rectification. I built mine as monos with SS rectification. My B+ power supply has different components (Fairchild Stealth 1200V 8A FREDs, etc) than the schematic as I used what I had and modeled with PSUDII.

I did the bias supply pretty much like the schemo, except that I used a pot for each tube, pretty much any of the small Amveco toroids will work for the negative rail. Since there is very little current draw out of the Amveco, the voltage will run higher than 44V, and when rectified, will easily get -66V or more. I had to play around with the R values around the pots to get the adjustment range needed, but that is very straightforward.

 

[mfaughn]

OK, for the sake of making sure I haven't made any dumb assumptions or overlooked any options...

I have iron from an HK A500 (well, a TA260 but same iron and people are more likely to find info on the A500 / A50K). Photofact schematic says 4.3K CT primaries while specs of replacement part is 4K CT. No screen taps.

What is a good BEGINNER project for this iron? I am not really interested in sticking with the 7355 that this iron originally paired with as they are rare/expensive. That is why I was trying to head towards EL34. Might I be better off with 6L6?

 

[boywonder]

Check out Duncan's amp pages TDSL page:

The table for each type has typical operating conditions listed. 4K may be a bit low for a 6L6GC. The load is appropriate for KT88's in triode.

TDSL Tube search

 

[Thatch_Ear]

Found an EF-86 ampifier, PP EL-34 power tube amp. Radford STA 25

http://www.drtube.com/schematics/radford/sta25ren.gif

nice layout, but I think the PS was mostly SS and that takes away the chance to roll rectifiers, which can really open the soundstage up. Huge difference in my opinion. You trade something that probably won't fail for loss in soundstage. SS is a bit easier and puts out less heat, so there is the plus side.

Thatch

Someone a bit better at this please get the schematic up, it is pretty, the amp part anyway.

 

[sepolansky]

Found an EF-86 ampifier, PP EL-34 power tube amp. Radford STA 25

http://www.drtube.com/schematics/radford/sta25ren.gif

nice layout, but I think the PS was mostly SS and that takes away the chance to roll rectifiers, which can really open the soundstage up. Huge difference in my opinion. You trade something that probably won't fail for loss in soundstage. SS is a bit easier and puts out less heat, so there is the plus side.

Thatch

Someone a bit better at this please get the schematic up, it is pretty, the amp part anyway.

I agree about the rectification, easy enough to change to VT rectification, add a choke or two, etc., but where's the EF86?

I'm not crazy about the phase inverter setup; the 6U8 is a nice sounding tube; the outputs could be changed to EL34s; not sure how they get away with 330k grid leaks on 6550s unless it's because of the auto-bias circuit (which is nice, but not sure how it fits into a simple, first time project). Just looking at it quickly, can't see why one would need a cascode in front of a pentode, seems like a lot of gain, but maybe not since the 6U8's pentode plate resistor is pretty small.

I still vote for the Eico/Mullard 5-20. Just build a proper VT rectified power supply.

Stuart

 

[mfaughn]

Thanks very much for all the help everyone. Indeed I am slowing osmosifying a bit into my head.

Zout for EL34 PP Triode is 5000 ohms. It seems then that 4K primaries would load the tube a bit less than what would be ideal. Can I still make this work alright with my iron? I can't easily afford to spring for a decent quad of KT88 right now. I'm gonna be scrounging as much as I can from existing parts for all of this. If I can make it work I think I am going to go with something derived from the 5-20.

Next question -- If'n I wanted and easy tool with which to draw my schematic what might I use? I've used Eagle before and that's an option. I am a Linux user and prefer not to drag out the the ol' Windoze machine but I have a few around and can if I need to. I'll note here for other Linux users that PSUD II does run in Wine.