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In Reply to: RE: and you're still wrong...and so is Doc Hoyer...:) posted by Michael Samra on May 07, 2016 at 11:15:36
"There are things going on inside the OPT trafo that are taking place that we probably can't explain."
Not in this case. There are equal turns count on plate and cathode...within manufacturing variability anyway. That yields a specific, predictable behavior.
So, let's try this: Apply a volt to the grid, what does the cathode do?
If you suggest anything other than, 'follows the grid' I may suggest that you go and measure just exactly that quantity.
I'll run ahead a bit, but with your signal generator set up to deliver a volt to the grid, take a diff probe and measure anode-cathode on either of the finals. You should get something like 2V. Actually, given the circuit values, and tube performance, it has been adequately predicted that you'll get something like 1.7-1.8V.
"Doug,don't you think it's possible there is something going on inside output trans that we can't see and the way it reacts to the circuit?"
No, not a chance...no way in hell.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Follow Ups:
I see what your saying now..Go directly to output grids and that will take the driver out of the equation and I should see a gain increase by 2 to 1,right? I will remove the 12BH7 because I want to see what the output stage does by itself without the 12BH7..
A friend you get for nothing,an enemy has to be bought
Edits: 05/07/16
the driver is irrelevant; a means to an end...it has nothing to do with how the output stage works. You can apply signal to the nominal input and adjust until you have what ever voltage you want on the grids...can be 2V, or 20 V or? measure grid input, and measure anode-to-cathode.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Doug
I can go up much higher on the generator but you still need to explain the rationale for bootstrapping the driver if the added voltage gain can be achieved in the opt stage..I know it can be done as such,but I don't believe this is.
One more thing..Why can get 15v at the output with no 6L6s installed,and then it goes up a mere 3v overall in the case of 1v at the input..BTW,you can see the 8 ohm power resistor loading the terminals but I want to tell you that I was getting 325v on G1 and the cathodes with and without the outputs installed.
A friend you get for nothing,an enemy has to be bought
All of that is largely irrelevant. It is obvious the output stage is low gain. I asked you to look at this one piece at a time so that the whole can be examined. Think about the questions, write up your answers, and then go and take measurements.
While you are answering questions, why don't you explain how the driver's positive FB has *ANYTHING* to do with the gain of the power stage?
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
You say it's irrelevant but I don't think it is.I just think it would have been much easier to ease off the driver and design the output stage to step up the gain if that was Mac's intent.
If what your saying us true,it is very low gain compared to a conventional amplifier..All this amp does is basically divide the total impedance between the plate and cathode windings.I just want to see some type of step-up as I did on the st70.Even since we halved the impedance at the plate,shouldn't there still be a proportional total gain being measured at the outputs?
A friend you get for nothing,an enemy has to be bought
If you insist in ignoring the task of examining it, I will turn over the task to somebody else with more patience than I have. I am sure it is not beyond you, should you decide to apply yourself.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
I shall do that.
A friend you get for nothing,an enemy has to be bought
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