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Old 26th January 2013, 02:27 AM   #11
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Join Date: May 2010
Location: Chicago IL, Long Beach CA, Vienna VA
Originally Posted by JMFahey View Post
I'd believe that needing a big f*ck*ng inductor (rated for proper Class A current, which will be considerable) which will be heavy and large anyway, need gap, etc., plus a "good" although somewhat smaller than usual output transformer, will end up costing *more* than getting the normal OT which goes there.
And very much doubt the sound will "improve", considering it's a guitar amp.

The chokes are optional. Could just use grid resistors and plate resistors with an output coupling cap for each output tube with a gapless transformer shaller than single-ended usually requires.

I'm starting to like chokes though. Grid chokes aren't big. Plate chokes are bigger, one for each of the parallel output tubes.
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Old 26th January 2013, 02:49 AM   #12
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Tubelab: interesting.

I built my first guitar amp when I was about 13, perhaps 46 years ago, with my dad's oversight. For the power transformer I unwound the secondary on what I had laying around, and wound a new secondary with insulated stranded hookup wire without disassembling the iron core laminations, just lacing the wire thru the core. Big big filter caps. I wanted a tube amp but my dad pushed for transistors; it was transistor and had two channels. Schematic was stolen directly from a transistor data sheet "120 watt amp with quasi-complimentary coupling". Two power output channels. The transistor preamp hissed and was totally without soul. Used it as a bass amp. At first it would work for a while then misteriously blow up. Eventually I got it on a scope and saw ultrasonic oscillation just before slf-destruct. My dad told me to beef up the ground wire and the power wire on the perfoboard and I threw in a few picofarad mica caps on both the signal line and the power line and it was OK as long as you didn't short the speaker line. Got me thru my first bass gig. Man I was terrible.
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Old 28th January 2013, 03:02 PM   #13
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Location: West Virginia panhandle
I built my first guitar amp when I was about 13
I "built" my first guitar amp when I was about 8. I cut and stripped a guitar cable and twisted the wires to the wires in the tone arm of my parents old Magnavox HiFi (they had upgraded to stereo). Real "breadboards" made with old TV and radio parts screwed to a piece of pine using Fahenstock clips came a few years later. A local ham radio guy showed me how to do this. They were all tube powered since discarded radios TV's and HiFi sets were plentiful and free.

My father bought me a GE Transistor Lab kit when I was 11 or 12. It was the grandaddy to the kit shown here:

Transistor Museum Historic Profile Len Buckwalter Page 4

There were 50 or 100 "projects" using crude Germanium transistors. The final project was a 5 transistor radio that drove a speaker. I "invented" several more projects including a fuzztone that drove the old Maggie (2 X 6V6 P-P) into serious scream territory, making my father rather displeased. This was one of the few bright spots in an otherwise unhappy childhood, thus I remember it well. Note the similarity between the kit and the Tubelab breadboarding system....and its name.

The Tubelab

For the power transformer I unwound the secondary on what I had laying around, and wound a new secondary with insulated stranded hookup wire
I used old TV power transformers, pounded the lams out, removed the old secondaries, and wound new ones using magnet wire. I used household masking tape for insulation. Some of these transformers were used daily for 10 years or more. About 1970 I and some of my friends were making solid state guitar amps this way. We used the preamp circuit from the Heathkit guitar amp and mostly one of the "Tiger" series power amps from Popular Electronics magazine. I made several rather big power amps based on the transformer coupled totem pole output circuit popular in 60's vintage solid state stereos. I copied the Heathkit AR13A circuit, since I built one of those kits for my neighbor in the 60's.

The biggest one used a military surplus heat sink that contained 34 X 2N3773 transistors running directly from rectified wall outlet. The driver transformer provided user isolation. Driven from a Kustom PA head it put out over 1000 watts into a 2 ohm load. I saw it at least 10 years after I made it, still alive!

I started making tube guitar amps again maybe 20 years ago. I made quite a few when my daughter was in high school, then quit. There are more coming soon.
Tubelab, it's 5 year mission. To explore strange new tubes, to seek out new circuits and topologies, to boldly go where no tube has gone before......
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Old 2nd March 2013, 11:34 AM   #14
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Actually I have started similar project lately. I want to use psu choke and simple PA 100V speaker transformer e.g. from Monacor's. I use them with satisfactory results in my E180F 6C4C SE parafeed hifi amp.
12ax7 and 6П9/6Ag7 or 6П15П/EL83 will be used
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Old 2nd March 2013, 11:43 AM   #15
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Anyone ever try making a parallel-output single-ended class-A parafeed guitar amp,
Gordon Rankin of Wavelength even sells them.
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