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autoformer Iron? [message #30332 is a reply to message #30329] Sun, 30 January 2005 09:17 Go to previous messageGo to next message
PakProtector is currently offline  PakProtector
Messages: 957
Registered: May 2009
Illuminati (2nd Degree)
please elaborate on the autoformer Iron 'thing'. Sounds like parafeed would be required to keep the speaker isolated from B+.

I have gone through a few really nice EL34 amps, and then got an eye opener from the 6L6 family. While older G and GA types are a bit on the 'spensive side, NOS 807 and Svetlana 'Winged C' 6L6GC are nice valves in the cheap end of the pool. There are *MANY* good sounding valves in the cheap end BTW.

For low NFB designs, I got a really nice design from Heyboer. It's a copy of the Peerless S-265, a 20-20 Series, 10k:16,8,4,2/40 Watt design with a core bigger than the Dynaco 60W Mk.3 design. The winding design leaves it really easy to put U-L screen taps where the design calls for them( semi-custom designs do have their benefits, No? ). Or putting in more than a single pair of taps if you want to experiment a bit. No matter what sort of religious dogma might be heard about winding OPT's, it isn't all that dificult to get a good design.

Just pick a design which can be used in a few different circuits. For example the 265 can be done with 807's, 813's and GM-70/845 designs. If proper care is taken, silly B+ is not required, and 40W is a lot of power if you have efficient speakers.
regards,
Douglas

Re: autoformer Iron? [message #30333 is a reply to message #30332] Sun, 30 January 2005 09:50 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17478
Registered: January 2001
Illuminati (33rd Degree)
Heck, 40 watts is plenty even for speakers with not-so-high efficiency. A lot of these tube guys are happy with 2 or 3 watts. I like 10 or 20 myself, and 40 would be great.

Re: autoformer Iron? [message #30334 is a reply to message #30332] Sun, 30 January 2005 10:32 Go to previous messageGo to next message
Damir is currently offline  Damir
Messages: 1005
Registered: May 2009
Illuminati (2nd Degree)
Hi, do you made some measurements with S-265 copy (Frequency response, Lp,...)? What about max. DC primary current? Sound?
I agree with simple design, but personally don`t like "cheap" / compromise solutions, or expensive and complicated 2W designs. I like 6L6 "family" too, but 807 needs top cap...
Maybe 6B4G, NOS is not too expensive (but not cheap, either), and Russian version is good. But, DHT, not so easy to drive and we`ll end with ~7W...enough?
Or "bite the bullet" and do PP 300B, Raa=10k seems just right. Again, DHT, not easy to drive (more complicated splitter/driver needed), but ~15W DHT triode A-class is attractive:-)
Maybe for the begining use simple, but versatile and good solution - amp with individual bias per tube, UL or triode, that can "accept" various tubes, say EL34, 6L6GC, KT66, 6550...
And later in phase 2 amp with more "exotic" (300B) tubes?
Just some thoughts...


Re: autoformer Iron? [message #30336 is a reply to message #30332] Sun, 30 January 2005 11:52 Go to previous messageGo to next message
cheetah is currently offline  cheetah
Messages: 70
Registered: May 2009
Viscount
Yeah it does involve para-feed. Uses a center tapped autoformer for the phase splitting duties. Simple and elegent.

Joe

Re: autoformer Iron? [message #30337 is a reply to message #30332] Sun, 30 January 2005 12:45 Go to previous messageGo to next message
Manualblock is currently offline  Manualblock
Messages: 4973
Registered: May 2009
Illuminati (13th Degree)
I haven't used more than 20 watts in years. I like 6L6 also.

Oh... [message #30338 is a reply to message #30336] Sun, 30 January 2005 12:59 Go to previous messageGo to next message
PakProtector is currently offline  PakProtector
Messages: 957
Registered: May 2009
Illuminati (2nd Degree)
I tried some of that stuff. I built a few versions, and helped another winder as well with his version. Jack has probably done a better job than MQ did.

Tried them as phase splitters, in-circuit and on the bench. While the ones designed for phase spliting work well on the bench, they did not sound as good as a simple diff amp.

Such things do make good PP grid chokes. Leave teh CT split and you can do individual fixed bias.
regards,
Douglas

Re: Oh... [message #30339 is a reply to message #30338] Sun, 30 January 2005 13:01 Go to previous messageGo to next message
cheetah is currently offline  cheetah
Messages: 70
Registered: May 2009
Viscount
Just throwing out ideas. Thought one of those would be a good starting point.

Joe

Re: Oh... [message #30340 is a reply to message #30338] Sun, 30 January 2005 13:05 Go to previous messageGo to next message
cheetah is currently offline  cheetah
Messages: 70
Registered: May 2009
Viscount
For what its worth, I think Poinz's PP 6V6 would be a good choice as well.

Joe

from Homer's cloning Hammock [message #30341 is a reply to message #30334] Sun, 30 January 2005 13:08 Go to previous messageGo to next message
PakProtector is currently offline  PakProtector
Messages: 957
Registered: May 2009
Illuminati (2nd Degree)
I did not measure the copy(yet). I got them 2 days before the 2004 Oswalds Mill Tasting meet. I slapped them in, 30% taps to the E-Linear driver, 50% taps to the g2. Got 6 Watts from a pair of HY69's. Sounded pretty good.

I got an improvement when I put g2 to the 30%. 9.5 Watts and a bigger more natural sound. I keep grinning to myself every time I hear something soooo inexpensive sound so good.

I ran the amp with a signal generator, and go no misbehaviour at the frequency extremes. 9.5 watts down to where my signal generator got a bit loopy( ~16 cps ), and it ran out into the ultra-sonic with out any wiggles in the curve. I will do a more comprehensive measurement when I am done with the new linestage.

As far as other ratings, like DC I would stick with the originally published specs. I think it was 120 mA per leg, and 10% imbalance. With fixed bias, I can get to a small fraction of that easily.
regards,
Douglas

Re: Oh... [message #30343 is a reply to message #30339] Sun, 30 January 2005 14:24 Go to previous message
PakProtector is currently offline  PakProtector
Messages: 957
Registered: May 2009
Illuminati (2nd Degree)
Those are fine amps, and a modification of Poinz's amp, running 6V6's or one of the close subs like 6EV6 or 6EY5 is one I am considering for my own personal consumption. 20% U-L taps and a 10k a-a OPT. E-Linear rig something like a 12AY7 and we're off to the races.

Something like a properly done Dynaco Mk.4. Choke input filter. Oil cap for the PS energy storage and a 20 Hy/200 mA choke. I will probably step back to 15 Hy because I have a pair of them the size of Mk.3 outputs. Killer overdone PS. Hell, it will be taking no more than about 80 mA. 35 each for the power valves and 5 or so for the front end.

good ideas are just that: good. Keep 'em comming.
regards,
Douglas



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