Triode class A 6V6 PP?

[Satamax]

Hi everybody.

Well, i have an output trany which would be spot on for the triode 6V6 push pull in class A.

http://www.mif.pg.gda.pl/homepages/f...84/6/6V6GT.pdf here on page 2

But my power trany is on the high side 280 vac and no recto tap. I have 3 24V tap for the old solid state stuff of that amp which won't be used. Could i buck the 280V with thoses taps? How do i do it? Or may be i could use a zener trick with a bridge rectifier? http://music-electronics-forum.com/s...ead.php?t=2322

What i have would only drop 45V out of B+ for a 335V or thereabouts. Would be upping the Zout up to 13000Ω adviseable?

Well, soo many questions and so litle knowledge from my part!

Thanks a lot for your help huys.

Bye.

Max.

[Satamax]

Anybody could shed some light?

Hi guys.

Well guys. I seem to have no luck with replies nowadays. I should admit i'm no good at writing apealing titles. I could cope with some help.

Many thanks.

Bye.

Max.

[Old Tele man]

..that RCA spec shows 9.6K for triode Class A1 PP and 6.0K for Class AB1 PP, why'd you want to go UP to 13K? and both use Vp = 300Vdc.

[Satamax]

Hi Old Tele Man.

Thanks a lot for the reply. Well, i was thinking i'd need to go up in impedance for higher voltage B+, but i can't remember the theory and it might be the other way around. My output transformer is at 9200 for 5.33 Ω And i have a power transformer which is at 269vac. Which would give 369VDC. I was wondering if i could drop the voltage with the zenner trick BU806 inserted between the minus end of the bridge rectifier and ground. I would end up with 324VDC which would be rather close to the 300 advised on the specs.

Bye.

Max.

[Joe Bee]

I'll have a shot at this even though I am a rookie myself and I might not know what I am talking about.

First of all let me ask you a question: Is the "Triode Class A" a fixed design criterium, or could you live with something like Class AB?
The reason I ask is that as I see it, there should be no problem building an amp around your power and output transformers without any messy "Zener tricks" if you just work with what you have. I will try some calculations, let's see where it gets us:

Your OT presents 14kOhm anode-to-anode on an 8Ohm speaker, and your anode voltage is 380V. Thus the Class A part of your load-line will be 7k, the class B part 3k5 impedance. Drawing the loadlines from 380V to 55mA and 110mA we see that there is no way to push the Class A part up to go above the knee of the pentode characteristic curves, staying within the 15W dissipation limit.

Bummer, now I see why you feel drawn to triode connecting the things!

Here it looks a lot better, you can for example bias for 30mA quiescent current with -18V on the gate. Swinging from -30V to zero on the gate would get the current from 20 to 50mA, not quite symmetric so I hope this is not for a HiFi amp :-)


I hope this helps you a bit, if not try this: If you connect the 280V tap to the 24V tap (assuming they have no common ground reference!!! check this first), you can either get 304V or 256V, depending on the phase. If there are serveral isolated 24V tabs (which seems strange) you can series them to get down to 208V, but again make sure they dont have a common reference by testing for continuity with a DMM while the transformer is not connected to anything.

Data sheet I used:
http://boozhoundlabs.com/howto/pdf/6V6GT.pdf

[MWJB]

Don't forget that final plate volage will drop some with a current load, plus if you're going cathode bias you'll need to deduct cathode voltage...go ahead and build around what you have & then see if you want to drop B+ any further with zeners, you might find that a significant proportion of your spare 69v gets eaten up? You might end up less than 324v anyway.

[Satamax]

I'll have a shot at this even though I am a rookie myself and I might not know what I am talking about.

First of all let me ask you a question: Is the "Triode Class A" a fixed design criterium, or could you live with something like Class AB?
The reason I ask is that as I see it, there should be no problem building an amp around your power and output transformers without any messy "Zener tricks" if you just work with what you have. I will try some calculations, let's see where it gets us:

Your OT presents 14kOhm anode-to-anode on an 8Ohm speaker, and your anode voltage is 380V. Thus the Class A part of your load-line will be 7k, the class B part 3k5 impedance. Drawing the loadlines from 380V to 55mA and 110mA we see that there is no way to push the Class A part up to go above the knee of the pentode characteristic curves, staying within the 15W dissipation limit.

Bummer, now I see why you feel drawn to triode connecting the things!

Here it looks a lot better, you can for example bias for 30mA quiescent current with -18V on the gate. Swinging from -30V to zero on the gate would get the current from 20 to 50mA, not quite symmetric so I hope this is not for a HiFi amp :-)


I hope this helps you a bit, if not try this: If you connect the 280V tap to the 24V tap (assuming they have no common ground reference!!! check this first), you can either get 304V or 256V, depending on the phase. If there are serveral isolated 24V tabs (which seems strange) you can series them to get down to 208V, but again make sure they dont have a common reference by testing for continuity with a DMM while the transformer is not connected to anything.

Data sheet I used:
http://boozhoundlabs.com/howto/pdf/6V6GT.pdf

Thanks a lot for yout replies guys. Joe Bee. I know i should have plotted some curves I think the 24V are completely isolated from the 269 I'll give it a try


Thanks a lot again.

Bye.

Max.