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6AS7GA as push pull output?
6AS7GA as push pull output?
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Old 10th December 2017, 04:23 AM   #171
Shef is offline Shef  Canada
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Originally Posted by mr2racer View Post
.. .all the answer I needed.
From how your design is progressing I feel that without those my other words your last reply would not be such a short sentence. You got what you asked for. .. be grateful ))
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Old 10th December 2017, 10:06 AM   #172
artosalo is offline artosalo  Finland
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The problem with CCS at the anode is that the voltage swing is highly limited.
With normal PP circuit, the transformer at the anode, the voltage swing is almost from 2 x +Ub to Uk but with CCS only from +Ub to Uk.

In practice this means that with normal transformer coupled PP, with 375 V +Ub the max. voltage swing at the anode is some 550 V to 190 V = 360 Vpp.

With CCS at the anode the max. voltage can not be more than +Ub, less the voltage required by the CCS to operate.
In case of the below simulation the voltage swing is some 300 V - 90 V = 210 Vpp.

And as we know the power is: UČ : R. Therefore the latter voltage swing produces only 1/3 of the power of the first.

Second problem is the OPT. It seems to be 4k. This is not optimum for parallel PP.
Some 2k to 2k5 would be ideal.

With your last circuit, only some 5 W of output power is expected.
One advantage is however achieved, the THD is very low.
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Old 10th December 2017, 12:52 PM   #173
mr2racer is offline mr2racer  United States
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6AS7GA as push pull output?
Thanks very much Arto. I have a Japanese LCR meter on the way that can measure up to 2 kilo-henries. My current meter's limit is 40 henries so I couldn't even measure the interstage. When I recieve it I'll be able to really model the amp in Spice and that will make things much easier for me. And I won't have to lean on you guys as much.

The output transformer isn't ideal but they were free. My winder can build me custom outputs for about $90 each. So I may go that way instead.

Thanks again, Kevin
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Old 11th December 2017, 11:17 AM   #174
goldenbeer is offline goldenbeer  Germany
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Quote:
Originally Posted by mr2racer View Post
Hey anyone, I'm back to TL783 as a constant current sink at the cathode of the outputs. [...]I?
I'm afraid your post makes aboslutely no sense to me. If used as ccs, the drop across the regulator will be whatever it takes to achieve the desired current. The 1.3V is just the minimum to get the regulator chip working. If using a ccs, you don't need to add resistors here or there to adjust. In fact, the additional resistors will do more harm than good. The ccs will automatically adjust its voltage drop as stated above.
If you want to burn less heat in the ccs, just lower your Ub+.
You will need to bypass the ccs'es if you're going to use 1 per cathode.
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Old 11th December 2017, 11:24 AM   #175
goldenbeer is offline goldenbeer  Germany
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Originally Posted by Shoog View Post
Running the 6080's with CCS in the cathodes has specific benefits which have to be understood as they come at the cost of limiting the circuit to low power class A operation (good for low distortion and DC intolerant transformers but little else).
Almost all 6080 pp circuits operate in class A anyways due to plate voltage limitations (250V) and the yuge voltage swing required for the drivers (~280Vpp for 5K Ra-a opt @13W class A power).
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