Well, if you tie the filament to the cathode, that rating does not apply.
Or, if you isolate the output tubes filaments windings.
Yes, some amplifier designs allow the filament windings to float.
Just do not use a common filament winding for all the tubes, otherwise
the very large cathode follower output tube's voltage swing will be impressed to all
the other tube filaments, and from there to the other tubes cathodes.
either capacitively, or resistively, or when the insulation breaks down.
Take it to the limit, but not beyond.
Does that explain my earlier statement?
Or, if you isolate the output tubes filaments windings.
Yes, some amplifier designs allow the filament windings to float.
Just do not use a common filament winding for all the tubes, otherwise
the very large cathode follower output tube's voltage swing will be impressed to all
the other tube filaments, and from there to the other tubes cathodes.
either capacitively, or resistively, or when the insulation breaks down.
Take it to the limit, but not beyond.
Does that explain my earlier statement?
Oh, you're referring to heater/cathode insulation ratings vs. not having heater cathode insulation ratings to worry about?
Yes, sure, this is a limiting factor, but driving an 838 doesn't take a whole ton of voltage. Even that 100V rating on an EL34 is DC, which would limit the AC swing to +/-200V on either side of wherever the filament winding is referenced. That is more than adequate.
Yes, sure, this is a limiting factor, but driving an 838 doesn't take a whole ton of voltage. Even that 100V rating on an EL34 is DC, which would limit the AC swing to +/-200V on either side of wherever the filament winding is referenced. That is more than adequate.
audiowise,
Yes, you are correct. Plenty of voltage range.
But I intended my comments for a more general application;
And . . . I should have stated that, my bad.
Sometimes, someone says: that will work for my application and output tube:
Well, an 845 is a good example of a tube that can have very large bias, so most Indirect Heater tubes used as cathode follower drivers either need to have the floating filament supply tied to the cathode, or at least have a really good float; and no other tubes in the amp can be connected to that filament winding.
I often find things on this forum, that I then apply to meet a need that I have for a new design I am trying to complete.
That happened today, I saw a TL783 in a tube application. I was not even aware of it (I generally do not 'follow' what solid state parts are available, even if they are common).
But now, thanks to this forum I "heard" about the TL783.
And now I checked its specifications, and it seems like the perfect part for one of my new vacuum tube designs (right specification, just a few parts, and simple to implement).
Yes, you are correct. Plenty of voltage range.
But I intended my comments for a more general application;
And . . . I should have stated that, my bad.
Sometimes, someone says: that will work for my application and output tube:
Well, an 845 is a good example of a tube that can have very large bias, so most Indirect Heater tubes used as cathode follower drivers either need to have the floating filament supply tied to the cathode, or at least have a really good float; and no other tubes in the amp can be connected to that filament winding.
I often find things on this forum, that I then apply to meet a need that I have for a new design I am trying to complete.
That happened today, I saw a TL783 in a tube application. I was not even aware of it (I generally do not 'follow' what solid state parts are available, even if they are common).
But now, thanks to this forum I "heard" about the TL783.
And now I checked its specifications, and it seems like the perfect part for one of my new vacuum tube designs (right specification, just a few parts, and simple to implement).
Careful with those ICs used as constant current sinks. Sometimes impedance vs. frequency reveals some issues.
Yes.
I checked all the frequency graphs in the TL783 data sheet.
It will be used to current source a doubly/singly low impedance.
The proof of the pudding will be the high frequency response of the amp, and the high frequency 2nd and 3rd harmonic distortion.
I have formerly used a choke, and used a bipolar NPN as well for the application.
I was warned about the distributed capacitance of the choke, HF roll off and 2nd and 3rd harmonic distortion were tested, but it did not end up being a factor (good choke).
The low frequency capability had already been accounted for (a 120Hz full wave reactor, would be used at down to 20Hz). By using a choke that had a current rating that was very much higher than the application required, and Lots of laminations, it worked all the way down to 20Hz. The low frequency roll off, and the low frequency 2nd and 3rd harmonic distortion were tested, and were good.
Know thy parts, know thy design.
I checked all the frequency graphs in the TL783 data sheet.
It will be used to current source a doubly/singly low impedance.
The proof of the pudding will be the high frequency response of the amp, and the high frequency 2nd and 3rd harmonic distortion.
I have formerly used a choke, and used a bipolar NPN as well for the application.
I was warned about the distributed capacitance of the choke, HF roll off and 2nd and 3rd harmonic distortion were tested, but it did not end up being a factor (good choke).
The low frequency capability had already been accounted for (a 120Hz full wave reactor, would be used at down to 20Hz). By using a choke that had a current rating that was very much higher than the application required, and Lots of laminations, it worked all the way down to 20Hz. The low frequency roll off, and the low frequency 2nd and 3rd harmonic distortion were tested, and were good.
Know thy parts, know thy design.
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