Anyone ever try making a parallel-output single-ended class-A parafeed guitar amp, where you use a big expensive coupling capacitor to block the DC to a conventional output transformer instead of a really big really heavy really expensive typical SE output transformer with a gap?
I'm considering making something like a Champ without tone controls but with a switchable extra gain stage, super-quiet preamp with DC heaters and an adjustable input network, and a parallel single-ended output section with grid chokes and plate chokes. That's getting popular with the SET HI-FI guys, and it seems to me it would make a great guitar amp too. It might require some careful 'tuning" of the output with dampers so the output caps and output transformers don't have any ringing but it might make a cool amp with enough power for a usable clean tone and also more of the tube breakup instead of trans saturation when it get dirty.
I'm considering making something like a Champ without tone controls but with a switchable extra gain stage, super-quiet preamp with DC heaters and an adjustable input network, and a parallel single-ended output section with grid chokes and plate chokes. That's getting popular with the SET HI-FI guys, and it seems to me it would make a great guitar amp too. It might require some careful 'tuning" of the output with dampers so the output caps and output transformers don't have any ringing but it might make a cool amp with enough power for a usable clean tone and also more of the tube breakup instead of trans saturation when it get dirty.
Do you mean a choke loaded Parafeed (also a current source instead of choke) SE?
Intresting , for low power amp , to reduce costs of output transformer ...
What made me think is about power distortion - break up , we're used to the classic power section distortion , wonder if a parafeed sound better or worse ! Try it
Intresting , for low power amp , to reduce costs of output transformer ...
What made me think is about power distortion - break up , we're used to the classic power section distortion , wonder if a parafeed sound better or worse ! Try it
Has the Big Dumb Blonde One ever plugged a guitar preamp into his 300B SE amp???? You better believe it!
I have tested every amp I design by plugging in my old ADA MP-1 into it cranking it up to 11 and cutting loose. I do not have a parafeed amp, but I have abused several DHT and iDHT SE amps. I find that an SSE with a smallish OPT sounds quite like a champ, especially with a wimpy rectifier (5Y3) and small caps in the power supply. A TSE with a 300B in it doesn't sound much different from an SSE with an EL34 when cranked to 11. The big difference in these two amps is when turned down or run right at the edge. The 300B doesn't transition into distortion as easilly as an EL34 in pentode. The "edge" is more blurry with the 300B, it is a good sound for blues.
The OPT makes the biggest difference, with the Hammond 125CSE being my favorite for a small SE guitar amp that is going to be cranked, or driven with pedals. The 10 pound Edcor CXSE.....far too clean, and really heavy on bass, too much bass for a small speaker. It is a good combination for an acoustic or rythym player using a full range speaker. Even a bass guitar sounded real clean and sharp.
Changing subject a little, the 6V6 Champ I have is from a kit by STF electronics. I expected the power transformer to sag like an authentically small reproduction of a cheap amp at the low end of the Fender line, but with them being a Hammond distributorship franchisee I was hoping for a large single-ended output transformer perhaps bigger than the power transformer. But the output transformer is truly teensie. This is certainly not one of your monster tube amps, but would you recommend an output transformer upgrade for the little Champ? The good part is that little transformers at this end of the scale are pretty cheap, so an upgrade is not painful in the wallet.
I'd better stop dreaming and prioritize my projects.
I'd better stop dreaming and prioritize my projects.
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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.
And very much doubt the sound will "improve", considering it's a guitar amp.
I bought a pair of these about 10 years ago:
FENDER CHAMP STYLE 5W OUTPUT TRANSFORMER TF103-48 Single Ended Ultra-Linear 4 / 8 Ohm MADE IN USA
I can't read the sticker on your transformer, but it may be the same one. I tried them but they are still on the shelf, so I must not have found anything that I liked them in.
The little OPT will saturate when tested into a dummy load, but saturation was not seen on the scope when driving a small speaker. This is because the impedance of a smallish (5 to 8 inch) 8 ohm guitar speaker goes way up as resonance is approached, and resonance is up into the guitars normal fundamental frequency range, 82 Hz and up. The little OPT may indeed saturate if you try to drive a 12 or 15 inch speaker with a Champ.
I used the Hammond 125CSE OPT's in many of my "champs". The 125CSE is about twice the size, maybe bigger. It has a fatter sound with more bass. The 125CSE does not saturate at any power level seen from a 6V6 that is not glowing like a light bulb. I also like the 125CSE because you can intentionally mismatch it for a variety of sounds.
Your power transformer is a Hammond, but I can't read the sticker. I used an Allied 6K56VG in some of my early Champ clones that used the 6V6. It is made by Hammond but cheaper, and similar to the 270EX. B+ is about 300 to 320 volts depending on rectifier choice.
I started making Turbo Champs using an Allied 6K7VG power transformer that resulted in 430 volts of B+. The output tubes were EL34, 6L6GC or KT88. I made several of these about 15 years ago. Most used the 125CSE OPT. Each one was different, and each sounded different. I made one with a KT88 and a pair of 6X9 inch car speakers. I thought it sounded terrible, but one of my daughters friends that played rythym guitar with an ES335 just loved it, so I gave it to him.
The OPT makes a big difference in a small amp with a small speaker where speaker resonance is "in band". The combination of speaker / OPT / cabinet will affect the tone more than anything else. Parafeed????? No one has tried it, so no one can say. It may sound bad to one player, and be loved by another. There is only one way to tell......
I got started in the whole tube amp business when I was about 12 years old by making Champ clones from discarded TV's and radios. I had discovered a formula for an amp that cranked using a 6SJ7 driving a 6BQ6 with a vertical output transformer from a TV for an OPT. That was nearly 50 years ago. Much later in life my daughter started playing guitar, and was in the high school band. I made her an amp, then her friends wanted one, that led to........
Old turbo champ schematic. I drew this from memory about a year after I built them all. It may not be totally accurate, and each amp I made was different. The schematic is most like the last one I made.
I had acquired about 25 old HP tube type audio oscillators that were scrapped for the metal value. I got an idea to use the parts for small guitar amps. Most did use the 125CSE OPT, but a few were P-P and more powerful. Many of the Turbo Champs were made using parts from disassembled HP audio oscillators. The power transformers, power supply choke, and many of the resistors and caps were sourced from the HP's. In fact I started by making a guitar amp "head" out of the HP oscillator itself. The oscillator circuit already had a P-P amp using a pair of 6K6's. The OPT had a 600 ohm secondary, so it was replaced with a P-P OPT stolen from a console stereo.
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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.
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.
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.
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
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.
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