Even a PCL82 supports 600Vdc on anodes, continuously, but then it is a little 7W tube not very linear...
Yes, it needs to, 'cause it also was dedicated for frame deflection service, generating HV pulses of about 1.5 kV at the pentode's plate.
Best regards!
Best regards!
HV pulses during retrace... I have an old Telefunken TV that I have restored, and it uses XCL82 for V stage and also XCL82 for audio stage
I remember when I played with a PCL85 vertical amp and applied a sawtooth with "zero" retrace time: the PCB sparked badly. The PCL85 and vertical output trafo survived. After that, I applied a sawtooth with 85% "active" ramp (long retrace time) and achieved typical values. My plan was to apply on a "modern" tube TV with TDA9373 processor and so making it a hybrid TV 😛🙂 (the audio already is hybrid, with a 6EM7 after the TDA9855 stereo decoder)
NOTE: I assembled the entire TV, including PCB (not the cabinet; is from a existent model)
I remember when I played with a PCL85 vertical amp and applied a sawtooth with "zero" retrace time: the PCB sparked badly. The PCL85 and vertical output trafo survived. After that, I applied a sawtooth with 85% "active" ramp (long retrace time) and achieved typical values. My plan was to apply on a "modern" tube TV with TDA9373 processor and so making it a hybrid TV 😛🙂 (the audio already is hybrid, with a 6EM7 after the TDA9855 stereo decoder)
NOTE: I assembled the entire TV, including PCB (not the cabinet; is from a existent model)
My goal in driving the screens of the 6DQ5's (with the control grids tied to cathode) was to ultimately incorporate the 'crazy drive' scheme. As it turned out, just driving the screens with a transformer worked so well that I never got around to making it any better. I haven't given up on the 'crazy drive' idea (I think it's brilliant) but that project keeps getting pushed aside by other things in life. I had acquired many parts for the project and built a dual rail power supply for a mosfet driver but that's all... so far.
Only the heaters.
There will be 6 tubes per channel.
The plates require 2 floating supplies
(Circlotron) Grid drive requires around
300 to 350V and a voltage divider
feeds both the screen and control
grids via a cathode follower.
There will be 6 tubes per channel.
The plates require 2 floating supplies
(Circlotron) Grid drive requires around
300 to 350V and a voltage divider
feeds both the screen and control
grids via a cathode follower.
If I am not happy with the dual grid drive then
the alternative is to run the control grids at
around +10V reference to cathode. It's not as
linear but it can drive lots of current at very low plate
voltage.
the alternative is to run the control grids at
around +10V reference to cathode. It's not as
linear but it can drive lots of current at very low plate
voltage.
Continuously? Little, yes, but up to Pout = 8 Watt not so bad in pp.
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4X 72VAC power transformers are on order for the Dyno Dave OTL...
When paralleling grid drive; I use 5W 4.7 Ohm wire wound resistors in series.
(With Each Grid)
Drive is a frame grid pentode (another TV tube that I have a massive stash of)
--One section of a 6KV8 or 6JT8; I was getting these at 0.50 a few years ago.
I have already built several hybrid OTL's and a couple of Mac MC2100's
--The OTL used complementary symmetry output; the MC2100's were
Circlotron with all N-Channel FET's. With cathode follower output need 2 voltage
amp stages to get the output in phase with the input; the MC2100s only
required the one stage; plus the FG drivers; I grounded the center tap of
the autoformer to get the phase inversion.
When paralleling grid drive; I use 5W 4.7 Ohm wire wound resistors in series.
(With Each Grid)
Drive is a frame grid pentode (another TV tube that I have a massive stash of)
--One section of a 6KV8 or 6JT8; I was getting these at 0.50 a few years ago.
I have already built several hybrid OTL's and a couple of Mac MC2100's
--The OTL used complementary symmetry output; the MC2100's were
Circlotron with all N-Channel FET's. With cathode follower output need 2 voltage
amp stages to get the output in phase with the input; the MC2100s only
required the one stage; plus the FG drivers; I grounded the center tap of
the autoformer to get the phase inversion.
The complementary symmetry OTL's I dubbed 'Quarter Pounders' built back in the early '80s; yes I did get paid in buds...
Don't do that 😱! The heater to cathode isolation doesn't provide anything in terms of security. It's better not to risk anyone's life, and a 1:1 isolation transformer or even a custom wound tranny is much cheaper than a coffin plus funeral.
Best regards!
If the heaters short to the cathodes; there is not a safety problem. The Circlotron requires a high current center-tapped choke to chassis ground from the cathodes to complete the circuit. DC resistance will be milli-ohms. Chassis will be earthed and a GFI will trip before anything can explode. Some 1A slo blo fuses on the heater string will also prevent problems.
Now in EU you would need a step-down transformer to run the heater string; our voltage is 1/2 that of the EU
Inverted mode was a term created by Steve Bench many years ago to describe a mode of operating a triode where the plate (with a negative voltage) was used as the control element and the output was taken from the grid. Gain (loss) could approach 1 over Mu, so the 6AS7 / 6080 was the tube of choice. The advantage was supposed to be low output impedance without feedback.
My experiments tended to create glowing grid syndrome as opposed to glowing plates.....I had several hundred well used 6AS7's, some of the ugly ones died by experiment, and the shiny ones were sold or given away......15 years later I still have a box full.
My experiments tended to create glowing grid syndrome as opposed to glowing plates.....I had several hundred well used 6AS7's, some of the ugly ones died by experiment, and the shiny ones were sold or given away......15 years later I still have a box full.
Here is the 13GF7 large triode section ( equiv. to 6EM7) in native mode and using the new series Schade Fdbk ( = George's CED, UnSet).
The series Schade version is set up for 1/2 the Mu of the native triode in order to get some loop gain for correction. Input V steps are 6V for both, with 50 mA/div Vert. and 50V/div Horiz. scale. With the limited loop gain (5.4 /2) you get limited correction, but still looking fairly good. A lot less roll-over in the curves, but still some present. A super cheap way to turn the $1 13GF7 into a 2A3.
For really super correction, a beam Sweep tube ( $1 21HB5A here) has high gain available for correction, so almost vanishing roll-over in the corrected "triode" curves, and low Rp with high gm besides. A super cheap 211 that runs on reasonable B+ voltage. (one can get less correction by setting a higher net gain, so 2A3 like curves can still be done with a Sweep tube if desired )
a) native 13GF7 (big triode section)
b) series Schaded 13GF7 ( " " )
c) series Schaded 21HB5A sweep tube
d) native internal triode 21HB5A
The series Schade version is set up for 1/2 the Mu of the native triode in order to get some loop gain for correction. Input V steps are 6V for both, with 50 mA/div Vert. and 50V/div Horiz. scale. With the limited loop gain (5.4 /2) you get limited correction, but still looking fairly good. A lot less roll-over in the curves, but still some present. A super cheap way to turn the $1 13GF7 into a 2A3.
For really super correction, a beam Sweep tube ( $1 21HB5A here) has high gain available for correction, so almost vanishing roll-over in the corrected "triode" curves, and low Rp with high gm besides. A super cheap 211 that runs on reasonable B+ voltage. (one can get less correction by setting a higher net gain, so 2A3 like curves can still be done with a Sweep tube if desired )
a) native 13GF7 (big triode section)
b) series Schaded 13GF7 ( " " )
c) series Schaded 21HB5A sweep tube
d) native internal triode 21HB5A
Attachments
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