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Futterman Class C oscillator?
Futterman Class C oscillator?
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Old 18th February 2017, 07:55 AM   #21
Koonw is offline Koonw
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Here are of output impedance plots for //811a VTTC, the higher the current the low output Z.

Glad you like the Class C sim. Because the gain of 6c33c is only 3, is hard to get oscillation, maybe like you say have to use additional tube to boost the gain to 100-200v phase splitting, cap or transformer coupling is fine. I see if I can find suitable tubes, any suggestion?
Attached Images
File Type: png VTTC 811a output Z plot-1.png (62.5 KB, 33 views)
File Type: png VTTC 811a output Z plot-2.png (71.7 KB, 33 views)
File Type: png VTTC 811a output Z plot-3.png (61.9 KB, 32 views)

Last edited by Koonw; 18th February 2017 at 08:00 AM.
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Old 18th February 2017, 08:51 AM   #22
Koonw is offline Koonw
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Quote:
Originally Posted by Koonw View Post
Here are of output impedance plots for //811a VTTC, the higher the current the low output Z.

Glad you like the Class C sim. Because the gain of 6c33c is only 3, is hard to get oscillation, maybe like you say have to use additional tube to boost the gain to 100-200v phase splitting, cap or transformer coupling is fine. I see if I can find suitable tubes, any suggestion?
Wait.. the sch is wrong..
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Old 18th February 2017, 09:19 AM   #23
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by woodrough View Post
One of the reasons why I want to be able to input my own frequency vs be phase locked with the secondaries secondary coil (via tickler) is to be able to have more control over the different resonance modes. For instance, a grounded resonator can resonate at 1/4λ, 3/4λ, 5/4λ, 7/4λ... while a free resonator will resonate at 1/2λ, 1λ, 3/2λ, 2λ, etc.
Lately I have been finding it pretty insightful to have control over what mode of resonance a coil is in.

Manually adjusting the input frequency also comes in handy for experiments involving concatenated coils. (Two coils serial connected coils that are not magnetically coupled to one another) This is a subject matter that gets irritating with Tickler feedback circuits.

The 6c33c totem pole design sparks my curiosity because it can handle darn low impedances. Primary coils are most effective with the least number of turns possible, demanding for a low impedance transmission circuit to drive it.
Anyway, driving two tubes in parallel, thus abandoning the self oscillating idea, is much easier than in an OTL arrangement. And, btw, source impedance is quite the same, as in OTL both tubes actually are paralleled, AC wise.

Best regards!
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Old 18th February 2017, 09:38 AM   #24
Koonw is offline Koonw
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Here are plots for corrected schematic.
Attached Images
File Type: png VTTC 811a output Z plot-4.png (63.8 KB, 35 views)
File Type: png VTTC 811a output Z plot-5.png (64.0 KB, 33 views)
File Type: png VTTC 811a output Z plot-6.png (72.0 KB, 7 views)
File Type: png VTTC 811a output Z plot-7.png (71.5 KB, 9 views)
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Old 18th February 2017, 01:11 PM   #25
Koonw is offline Koonw
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Here is the completed VTTC amp. ECC88/6DJ8 is a high freq tube, should be good as driver. The square off waveform helps to limit the current in amp, as well the max. output. Transformer is chosen so balance drive the totem pole is easier to achieve, the coupling between 3 coils can be very tight and seal if necessary.
Attached Images
File Type: png 6c33c OTL Class C VTTC amp-1.png (93.2 KB, 12 views)
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Old 18th February 2017, 06:22 PM   #26
woodrough is offline woodrough  United States
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Quote:
Originally Posted by Koonw View Post
Here are plots for corrected schematic.
Im curious what your interpretations of your 811a simulations of it are

You mention in your graphs things like 'no oscilations' with phase angle etc. I was wondering if you could elaborate on these graphs a bit because I have had a problem where oscillations would eventually cut-out the more voltage I give it from the Variac. (resulting in drawing of too much current) I believe it happens around 200 or 300 volts at the plate. The variac feeds a microwave oven transformer that is voltage doubled. I have a current probe monitoring the current going into ground so I can see the wave form when it decides to collapse after a certain point when turning up the VAC.

Not quite sure if its an impedance missmatch phenomenon or a damaged something.

But for the most part, I've been able to oscillate the coils reasonably when staying bellow that point on the variac.

Click the image to open in full size.

Also in your last simulation with the 6c33c, I had a couple questions

(1) what is the amount of grid bias you set here?
(2) you mention that the square wave from the first stage limits the current, is that because the ECC88 is clipping? Im cool with that style of current limiting, but what if I want to push the tubes harder (1amp example), does that mean the driver tube choice needs to be able produce more voltage swing?

Click the image to open in full size.
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Old 19th February 2017, 02:19 AM   #27
Koonw is offline Koonw
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"Also in your last simulation with the 6c33c, I had a couple questions

(1) what is the amount of grid bias you set here?
-150v each tube

(2) you mention that the square wave from the first stage limits the current, is that because the ECC88 is clipping? Im cool with that style of current limiting, but what if I want to push the tubes harder (1amp example), does that mean the driver tube choice needs to be able produce more voltage swing?"

Yes, yes.

Back the plots.

"Im curious what your interpretations of your 811a simulations of it are

You mention in your graphs things like 'no oscilations' with phase angle etc. I was wondering if you could elaborate on these graphs a bit because I have had a problem where oscillations would eventually cut-out the more voltage I give it from the Variac. (resulting in drawing of too much current) I believe it happens around 200 or 300 volts at the plate. The variac feeds a microwave oven transformer that is voltage doubled. I have a current probe monitoring the current going into ground so I can see the wave form when it decides to collapse after a certain point when turning up the VAC.

Not quite sure if its an impedance missmatch phenomenon or a damaged something.

But for the most part, I've been able to oscillate the coils reasonably when staying bellow that point on the variac."

811a is a triode, so I think the output Z is much less than that of the pentode, so the output Z looks reasonable. When it say "no oscillation" simply means the coupling in simulation is disable, sec coil is isolated, so measuring combined Z of the pri tank coil (exclude sec), cap and tube. The peak value of Z also is where the gain is high, I see that the peak for single tube is about 1MHz, but the peak Z for // is about 0.7Mhz, so I think there is a mismatch there. You should see that the peak is very near to freq you operating. Second, regard the relation of power supply voltage in relation to gain and output Z, the more current draws, the less is gain, so if you increase the voltage there is a point where the gain drops until oscillation stop. I attach a plot of el509 plot from 250 to 1.4kv. Can you also lebel on your schematic exactly the component value to see if I can plot again more accurately, and hopefully like you said it's mismatched.
Attached Images
File Type: png EL509 VTTC resonate voltages -1.png (74.8 KB, 13 views)
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Old 19th February 2017, 04:32 AM   #28
Koonw is offline Koonw
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Here are the plot as I now tuned the primary using a single tube, then plot again with 2 tubes, by connecting C2=2.1n // with pri coil, the peak freq does not vary much except with HT is above 1kv but the response width is wider and Z (max peak gain drop form 96db to 82db=14db HT=500V) drops with 2 tubes. It appears to me Z=5k, HT=1kv is the lowest you can get, you can compare see how.
Attached Images
File Type: png VTTC single 811a output Z plot-8.png (76.8 KB, 7 views)
File Type: png VTTC double 811a output Z plot-9.png (85.5 KB, 6 views)

Last edited by Koonw; 19th February 2017 at 04:43 AM.
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Old 19th February 2017, 08:13 AM   #29
Koonw is offline Koonw
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Here are plots of fully sim tuned plots. The pri and sec are fully tuned (to 1.26Mhz), then pri is coupled to grid winding, sec winding is excluded, found that the freq peak shifted to the left below 1Mhz. However when all winding are engaged, the freq peaks at correct freq. There are very sharp spike on left on impedance plot, they have to do with amount of couplings between the winding, too high coupling has a severe impact of output impedance, and has to try many value before optimal result is obtained.
Attached Images
File Type: png VTTC double 811a output Z plot-10.png (76.4 KB, 8 views)
File Type: png VTTC double 811a output Z plot-11.png (77.4 KB, 10 views)
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Old 19th February 2017, 11:00 PM   #30
woodrough is offline woodrough  United States
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Quote:
811a is a triode, so I think the output Z is much less than that of the pentode, so the output Z looks reasonable. When it say "no oscillation" simply means the coupling in simulation is disable, sec coil is isolated, so measuring combined Z of the pri tank coil (exclude sec), cap and tube. The peak value of Z also is where the gain is high, I see that the peak for single tube is about 1MHz, but the peak Z for // is about 0.7Mhz, so I think there is a mismatch there. You should see that the peak is very near to freq you operating.
Interesting to note that the peak Z value of the Pri Tank Circuit is greatly constrained by the Tube choice. This sounds like it leaves a narrow window of effective Frequencies I should design the coils to based on the tube of choice. I remember reading on Steve Ward's site of this concept on getting the sweet spot for reactive power in these designs.

The 6c33c designs you have been modeling, do you think that by having the low gain & low impedance properties, this design would perform better over a broader/more agnostic range of frequencies? (less prone to impedance sweet-spots for efficient usage?)

Quote:
Second, regard the relation of power supply voltage in relation to gain and output Z, the more current draws, the less is gain, so if you increase the voltage there is a point where the gain drops until oscillation stop. I attach a plot of el509 plot from 250 to 1.4kv. Can you also lebel on your schematic exactly the component value to see if I can plot again more accurately, and hopefully like you said it's mismatched.
This sounds really important, but im not sure I have a full grasp around why more current produces less gain to the point of oscillation stop.

Here are more detailed numbers of the components I used in my setup:

Click the image to open in full size.

And here is the setup in which im tuning the coils with.

Click the image to open in full size.

Interesting note on the issue of high coupling too.
Im finding that a tickler here seems to perform best with a fewer turns & further away. Raising the grid resistance beyond 500R -1000R apears to hurt the oscillations..

Last edited by woodrough; 19th February 2017 at 11:05 PM.
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