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Well no, i speek Dutch.Here i try to write something resembling English
.In an effort not to make too many errors i keep my interventions short.
Probably your Dutch is worse 😀
In the mean time, a little contribution.I don't like bias circuits that loose the negative voltage if a wiper malfuntion.
At the input a self adjusting current source, keeps the anode voltages on a constant level (if one goes up more than the other down the current is adjusted to keep the two around te same level).
Mona
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Thanks, Mona, and I agree. There are a lot of housekeeping items not on the schematic yet. In my professional work where very high reliability is required, necessary pots are always deployed in what I call a "guarded" manner, where the loss of wiper contact can only result in a certain maximum deviation. In the case of the bias adjustments, the loss of wiper contact can be guarded such that the voltage will go to either the maximum or minimum range (or close to that) but not disappear altogether.
Meantime, I am very curious as to the thoughts out there on the overall idea and structure.
Keep it coming.
Rene
Meantime, I am very curious as to the thoughts out there on the overall idea and structure.
Keep it coming.
Rene
Well, no of course not. If everything works out right, the cathodes of the pentodes will see a voltage somewhere around a couple of volts above zero, as there is both plate and G2 current flowing. There is a total of about 38mA flowing through R23, and about half that through each 600 Ohm.
As for the triodes, the constant current sink will by necessity adjust the cathode voltage to about 2 volts above ground at the cathodes, in order for the total of 8mA to flow.
There may be a need for transient protection in the manner of clamping diodes, easy enough to implement.
Rene
There are quite a few 9DX base tubes (6JV8 like), so it might be interesting to make some bias/ CCS adjustable for later tube rolling adventures.
The OT will be the bottleneck to wind. Make sure you have it designed right. Maybe an extra set of CFB taps at some optional %CFB. Get the # of turns balanced everywhere.
6HJ5 provides two pins for each tube element, for additional cooling, if some wire is attached to all the socket pins.
The OT will be the bottleneck to wind. Make sure you have it designed right. Maybe an extra set of CFB taps at some optional %CFB. Get the # of turns balanced everywhere.
6HJ5 provides two pins for each tube element, for additional cooling, if some wire is attached to all the socket pins.
Why I asked, even datasheet suggests only 22 mA current.
Well no, i speek Dutch.Here i try to write something resembling English
In an effort not to make too many errors i keep my interventions short.
Probably your Dutch is worse 😀
My dutch is zero, but it is not why I did not draw my phase splitter schematic using Dutch language. 😛
Yes, i found the same thing, 16mA anode and 6mA screen.
Aha, that's why 😀
The problem i see with your circuit is that V2 and V3 have same cathode and grid voltage, it's up to the tubes what the anode voltages will be, hope not too different.
Mona
So we are all in agreement that the pentode sections are being operated within limits. Each tube is at below 22mA plate current.
Y'all please remember what I said, many of the details are missing, the idea is to broadcast the overall idea and philosophy, details and good engineering practice come a little later.
That said, it's the little ideas and caveats that can sometimes make a big difference so, do keep them coming.
Mona, I am anticipating that the fairly significant cathode degenaration on both stages will force balance but, if not the case, I am prepared to force the balance.
Thanks again,
Rene
Y'all please remember what I said, many of the details are missing, the idea is to broadcast the overall idea and philosophy, details and good engineering practice come a little later.
That said, it's the little ideas and caveats that can sometimes make a big difference so, do keep them coming.
Mona, I am anticipating that the fairly significant cathode degenaration on both stages will force balance but, if not the case, I am prepared to force the balance.
Thanks again,
Rene
So what? Grid voltages are actually different, since there are different values of grid bias resistors drawn. Now they are equal, and additional degeneration resistors 1.5k in cathodes added. But as is, we measured the amp with SY, and saw only -80 dB of 2'Nd harmonic when below 40W power. The rest was under the noise floor on his screen.
The amp already looks pretty well. Probably no dominant pole compensation will be needed, since the amp has probably not enough gain by the loop for instability. I would start breadbording it. However, since you already have feedback by voltage on first grids of power tubes, I would try also a version with cathode feedbacks to driver tubes.
My concern was automatic; I usually care of a power supply MOSFET dissipation in my amps. ;-)
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Those 1k5 resistors are a solution but at the cost of loosing gain.
Sort of voltage balance between the screens to get equal current better solution ?
Mona
In the driver stage you put 600Ω where i have proposed 100Ω.With a current of 22mA there is a drop of 2.2V.Compared to the -Vg of 1.7V that's allready alot.
On the first stage there is room to spare at the anodes, some difference is no problem.I think no need for cathode resistors.
Mona
Yes, to optimize the whole thingy instead of making it suboptimal optimizing parts in it. 😛
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