Morning All,
I have a set of HK A500 transformers. The amp used 7355 tubes which are rare and expensive. I'm looking for a design that will work with these transformers. B+ of 360. Output impedance of 4k and 25 - 30 watts of power. That low power and low impedance seems to require a rare output. The best candidate I've found is a 6550 strapped as a triode. Could I just use any PP 6550 schematic and then strap the outputs. Or do I need to start the design from scratch?
Kevin
I have a set of HK A500 transformers. The amp used 7355 tubes which are rare and expensive. I'm looking for a design that will work with these transformers. B+ of 360. Output impedance of 4k and 25 - 30 watts of power. That low power and low impedance seems to require a rare output. The best candidate I've found is a 6550 strapped as a triode. Could I just use any PP 6550 schematic and then strap the outputs. Or do I need to start the design from scratch?
Kevin
4k p-to-p would be good for push-pull-parallel EL84 or 6V6, triode or pentode.
You can get the Chinese 2A3's for not too much money. It's hard to beat a good pair of push-pull, class A 2A3's. 4k primary would be fine for that. +360V B+ would be good if you cathode bias them (2A3 max plate voltage = 300V, grid bias will be about -55V or thereabouts). Actually, I really like that idea. 2A3's will last as long as 300B's, but don't cost nearly as much. 2A3's are a lot easier to drive, too. You'll only get about 6 or 7 watts per channel, though.
I'm running triode-strapped 6L6GC into Dyna ST70 OPT's (4300 ohm primary). I use the 4 ohm secondary taps for 8 ohm speakers. The idea is to use the turns ratio to raise the apparent impedance of the primary plate-to-plate load. It means the OPT's won't be capable of as high power output, but I'm only asking them to deliver a max of 11 watts rms each.
You can do a lot of fun things with those trannies.
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You can get the Chinese 2A3's for not too much money. It's hard to beat a good pair of push-pull, class A 2A3's. 4k primary would be fine for that. +360V B+ would be good if you cathode bias them (2A3 max plate voltage = 300V, grid bias will be about -55V or thereabouts). Actually, I really like that idea. 2A3's will last as long as 300B's, but don't cost nearly as much. 2A3's are a lot easier to drive, too. You'll only get about 6 or 7 watts per channel, though.
I'm running triode-strapped 6L6GC into Dyna ST70 OPT's (4300 ohm primary). I use the 4 ohm secondary taps for 8 ohm speakers. The idea is to use the turns ratio to raise the apparent impedance of the primary plate-to-plate load. It means the OPT's won't be capable of as high power output, but I'm only asking them to deliver a max of 11 watts rms each.
You can do a lot of fun things with those trannies.
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Thanks Everyone,
This amp will be a "junkyard dog" I.E assembled out of parts I already have. I have five winged "C' 6550, two 6AN8's, two Dynaco Mark III boards and the HK transformers. Plus I have some big power transformers. And that 1.5% THD spec on the 6550 in triode ain't too shabby either.
Kevin
This amp will be a "junkyard dog" I.E assembled out of parts I already have. I have five winged "C' 6550, two 6AN8's, two Dynaco Mark III boards and the HK transformers. Plus I have some big power transformers. And that 1.5% THD spec on the 6550 in triode ain't too shabby either.
Kevin
Help with HKL A500 amp build
Greetings and Happy New Year to you all in the Asylum. I have been drulling over the info i have seen on the H-K A500 amp. Can anyone help me with schematics, and if possible if anyone has done a DIY on this amp could I ask for directions on how or where I can go to get what I may need-meaning schematics, parts list any directions. I would be grateful beyond what words can express. Please don;t make me beg, k.
Thanks in advance for anything that will steer me down right path. Humbly Yours Paul in Portland, Oregon.
Greetings and Happy New Year to you all in the Asylum. I have been drulling over the info i have seen on the H-K A500 amp. Can anyone help me with schematics, and if possible if anyone has done a DIY on this amp could I ask for directions on how or where I can go to get what I may need-meaning schematics, parts list any directions. I would be grateful beyond what words can express. Please don;t make me beg, k.
Thanks in advance for anything that will steer me down right path. Humbly Yours Paul in Portland, Oregon.
Avincenty, thanks for reply. You are correct. I found and did a download. I am going to buy a Photofact and think about building a replica.I want to build one cuz i love, to say I could and to enjoy what I can't afford to buy. It is remarkably designed like the Madison Fielding 360 I am restoring. I will keep status posted. Cheers, Paul
I did build a quasi clone. Quasi because it doesn't have the phono stage, also it only has bass and treble control. From what i can remember, the a300,a500 and a700 are all similar, the output valve changes for more power. I built mine with jj7591 and Hammond 1650 transformers. It sounds very good. The one fault I find is a very slight hiss coming from the first gain stage when I place my ear close to my 99db sensitive speakers.
12ax7 gain stage to bandaxal tone to 12ax7 gain stage to 12au7 concertina to 7591a.
Alfredo
12ax7 gain stage to bandaxal tone to 12ax7 gain stage to 12au7 concertina to 7591a.
Alfredo
Alfredo, I was looking over the photofact. You have my admiration for building this design. I am planning my first DIY amp. I am a novice so I am going to start with a kit. If nothing else it will insure I end up with a completed project. I am confident I could complete a project but do not have the equipment needed at the end. Speaking of 12AU7's, gain and hum, would a 5965 in place of a 12AU7 make sense due to it's lower gain. I have read allot of differant opinions on this tube. I have never read anyone comment in a before and after application. Have you substituted the 5965 for a 12AU7? I am curious to hear about them. Any thoughts?
Cheers, Paul
Cheers, Paul
This is the first amp that I've work on. Its been quite a evolution. I probably started seven years ago or so. Its still got the same 12AX7 driver tube and 12AU7 is still used
as the phase splitter but its a different kind its a cathode coupled splitter.I also now have a adjustable bias scheme with its own power supply so I can use different tubes.
as the phase splitter but its a different kind its a cathode coupled splitter.I also now have a adjustable bias scheme with its own power supply so I can use different tubes.
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