Suppresor Grid used for Feedback?

[smoking-amp]

Re-did the GU50 triode curves, 2nd set is an enlargement of the bottom quarter of the 1st. And tried g2 drive, and it worked OK for the limited step voltage available.

Plot1: triode mode: 20 mA/div vert., 50 V/div horiz., 5.5 V steps on g1

Plot2: triode mode: 10 mA/div vert., 50 V/div horiz., 5.5 V steps on g1

Plot3: g2 drive mode: 10 mA/div vert., 50 V/div horiz., 5.5 V steps on g2, g1
at +4 V, g3 at +2 V

[smoking-amp]

Tried to start on the 6F12P, but running into hum problems in the pentode curves now. (notice squeezed grouping by twos on left side) Triode mode came out not too bad surprisingly. I'll try again tomorrow when the tracer has cooled off. If I can't get rid of the hum problems, then I'll have to check the power supplies.

Plot1: pentode: 2 mA/div vert., 50 V/div horiz., 0.27 V steps on g1, 100 V on g2

Plot2: triode config. 1 mA/div vert., 50 V/div horiz., .55 V steps on g1

[Sch3mat1c]

Do you have any 7KY6 or similar frame grid pentodes? I did one once,

http://webpages.charter.net/dawill/t.../Data_7KY6.gif

This graph was made by compositing photographs, so it's not too accurate. Fairly linear, and you can't beat the gain or the price.

Tim

[Wavebourn]

Originally Posted by Sch3mat1c

Do you have any 7KY6 or similar frame grid pentodes?

Right above: 6F12P

[smoking-amp]

Still having problems with power supply ripple, seems to be more obvious on smaller scale factor plots. I think I will just put some binding posts on the back of the tracer for an external reg. supply. But in the mean time I will try to finish up the tube plots as best possible for now.

"Do you have any 7KY6 or similar frame grid pentodes? "

Sure do. Here are plots for a Magnovox (Japan) 7KY6, and an RCA 11HM7, which seem to be identical tubes except basing, & fil. I've got 12HL7 and 12HG7 too, which I'll add to the pile to do.

Then a couple more tries on the 6F12P

Plot1: 7KY6 pent. 10 mA/div vert., 50 V/div horiz., 100 V on g2, .25 V per step on g1

Plot2: 7KY6 triode mode 10 mA/div vert., 50 V/div horiz., 1.4 V steps on g1

Plot3: 11HM7 pent. ditto per 7KY6

Plot4: 11HM7 triode ditto per 7KY6

Hmmm, looks like the pentode curves are close but the triode curves are different. I'll have to recheck that one. May be just a DC bias adjust shift between plots. The tracer has an A:B compare switch so I will put them back in under same settings later to check.

Plot5: 6F12P pent. 2 mA/div vert., 50 V/div horiz., .27 V steps on g1, 100V on g2

Plot6: 6F12P triode mode 2 mA/div vert., 50 V /div horiz. .55 V steps on g1

[smoking-amp]

Re-did the 11HM7 triode curve to match up the DC bias with the 7KY6, looks better matched now, but the 11HM7 curves are leaning over more at the HV end.
Only got one or 2 of each type, could just be that tube. Would have to test a few to see if that is consistent or not.

[smoking-amp]

Next up, 6U9/ECF201 and 6X9/ECF200

Plot1: 6U9 pent. 2 mA/div vert., 50V/div horiz., 100 V on g2, .55V steps g1,
0 V on g3

Plot2: 6U9 pent. 2 mA/div vert., 50 V/div horiz., 100 V on g2, .55V steps g1,
+11V on g3

Plot3: 6U9 triode mode 2 mA/div vert., 50 V/div horiz., 2.75 V steps on g1

Plot4: 6X9 pent. 2 mA/div vert., 50 V/div horiz., 95 V on g2, .27 V steps g1,
0 V on g3

Plot5: 6X9 pent. 2 mA/div vert., 50 V/div horiz., 95 V on g2, .27 V steps g1,
+11V on g3

Plot6: 6X9 triode mode 2 mA/div vert., 50 V/div horiz., .55 V steps on g1

6U9 looks like remote cutoff. 6X9 looks nice.

[Wavebourn]

Originally Posted by smoking-amp

6U9 looks like remote cutoff. 6X9 looks nice.

Thank you Don!

[smoking-amp]

Here are the actual triodes in the 6U9 and 6X9.

Plot1: 6U9 real triode 2 mA/div vert., 50V/div horiz., 2.8 V steps on g1

Plot2: 6X9 real triode 2 mA/div vert., 50 V/div horiz., 1.4 V steps on g1

[Wavebourn]

Thank you!

Can you try 6P15P with negative G3?