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Classe A 6550 40W
Classe A 6550 40W
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Old 16th February 2005, 02:05 PM   #1
s2kov is offline s2kov  Canada
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Default Classe A 6550 40W

Did someone tried to build this? Can somebody help me translate specs of the OPT intended for this amp?

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Old 16th February 2005, 02:39 PM   #2
Frank Berry is offline Frank Berry  United States
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Looks like 4.5k center tapped primary with ultralinear taps 16% each side of the center tap.

Strange. Most UL transformers are tapped at 40%.
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Old 16th February 2005, 10:44 PM   #3
richwalters is offline richwalters
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Nice little circuit....simple to build.......the 460v B+ is at the upper running limit for 6550's with UL taps. Dropping the B+ to 400V will give 35W with 400 ohm cathode resistors and allows versatility with all sorts of o/p tubes.
I see alot of these types of circuits in guitar amps typ B+400V......and work well with mixed tubes in o/p stage from 5881's.....EL34's KT88's 66's & all work in lieu...

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Old 17th February 2005, 02:06 AM   #4
s2kov is offline s2kov  Canada
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Is there any Hammond transformer or other brand that i can use for this? If I task the local winder to make custom wound transformer, what rated power of the OPT should be needed to handle the power of the amp?
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Old 17th February 2005, 06:29 AM   #5
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A 50W OPT would be fine.And if the OPT is a good quality one maybe you will not need the RC network at the secondary.This network is used for bad quality OPTs.
Where is a French guy to explain what "prices ecran a" means.Maybe taps are at 34% and the guy wrote it at the"wrong" way.The common UL taps are from 30% to 45%.
At 40% is for more linearity but with less power and around 33% is for more power but with less linearity.

Notice that there is only one tap at the secondary!
OPTs with only one tap secondary,with all secondary windings in parallel behaves better than those with multitaps.See Lundahl specs.
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Old 17th February 2005, 01:31 PM   #6
Bandersnatch is online now Bandersnatch  United States
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You might want to consider the 16% as a load percentage. root(.16) leaves a more notmal screen tap point, exactly 40%.

It is certainly class AB1 and I must say I would not consider building the front end that way. Looks simple enough, and as to sound, I have never heard it....

Do this one with a 6BQ7, 6550's and B+ of ~350v and a 5k OPT for about 35 Watts. It will be Class A if you put the bias at +100 mA.

The balanced NFB scheme is called E-Linear.
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