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Old 16th October 2012, 12:26 AM   #1
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Default SE 6550

Single ended 6550 schematic? Hammond has an SE transformer, 1640SEA, that is listed as using parallel 6550 or 6CA7 tubes. I rebuilt a little Zenith into an RH84 and it sounded wonderful. But not nearly enough power. I'm thinking about using a pair of these transformers to build such an amp. At thirty watts and 200ma this would be either two or three tubes? And in the Duncan amps data page when it lists 'Class A' is that synonymous with single ended? And does anyone know of such a schematic?

Thanks for any help you might provide, Kevin

Last edited by mr2racer; 16th October 2012 at 12:34 AM.
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Old 16th October 2012, 05:47 AM   #2
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The Duncan amps data page Class A is for one (single Ended) tube.
So you need to parallel two to get the desired power.
Search for schematics with KT88's, they are very close in specs.
6CA7 is equivalent to EL34, so if you want to go with 6CA7, look for EL34 schematics.
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Old 16th October 2012, 10:14 AM   #3
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Thanks Costis,

Am I correct in assuming that if I find a schematic that uses one 6550 or KT88 and I parallel two tubes that the Z out will be cut in half? And that the amperage will double? I have some nice 6GK5 triodes. Would a 6GK5 be able to drive two 6550's? I'm still trying to find a good explanation of 'drive.'
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Old 16th October 2012, 11:20 AM   #4
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Quote:
Originally Posted by mr2racer View Post
Thanks Costis,

Am I correct in assuming that if I find a schematic that uses one 6550 or KT88 and I parallel two tubes that the Z out will be cut in half? And that the amperage will double? I have some nice 6GK5 triodes. Would a 6GK5 be able to drive two 6550's? I'm still trying to find a good explanation of 'drive.'
Yes, half the Z, because you have doubled the transconductance. Double the amperes though.

"Drive" is a term that has been abused a lot! Think of it as the ability to swing signal in the face of the input capacitance of the output tubes. "Good" dive is to charge and discharge that capacitance (and the coupling capacitor if there is one) quickly and with little distortion of the signal. People have used hi-current driver tubes (in common cathode), cathode followers, and PowerDrive (TM), in ascending complexity order . In my EL34SE, I use a CCDA cathode follower.

In that light, a 6GK5 looks like in can be made to work, but ask somebody else, I' m in europe, never seen never used....

Last edited by costis_n; 16th October 2012 at 11:27 AM.
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