Here are some curves for a Sylvania (USA) 25HX5
a) pentode 50V/div Horiz., 50mA/div Vert., -2V steps, 125V grid 2
b) triode mode (plate conn. to g2) 50V/div Horiz., 50 mA/div Vert., -6V steps
next up will be a National (Japan) 25HX5
a) pentode 50V/div Horiz., 50mA/div Vert., -2V steps, 125V grid 2
b) triode mode (plate conn. to g2) 50V/div Horiz., 50 mA/div Vert., -6V steps
next up will be a National (Japan) 25HX5
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Here are curves for the National (Japan) 25HX5.
a) pentode 50V/div Horiz., 50 mA/div Vert., -2V steps, 129V on grid 2
b) triode mode 50V/div Horiz., 50 mA/div Vert., -6V steps
Th National Pentode has a little more screen current wiggle in it at low current. And it took 129V on grid 2 to get the same peak current as the 125V on the Sylvania. The triode is pretty close, just slightly higher Mu. (like 129/125 ratio times 4.65 = 4.8)
a) pentode 50V/div Horiz., 50 mA/div Vert., -2V steps, 129V on grid 2
b) triode mode 50V/div Horiz., 50 mA/div Vert., -6V steps
Th National Pentode has a little more screen current wiggle in it at low current. And it took 129V on grid 2 to get the same peak current as the 125V on the Sylvania. The triode is pretty close, just slightly higher Mu. (like 129/125 ratio times 4.65 = 4.8)
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Here are curves for a Sylvania 6EX6, which is an up-rated 6CD6. I've mentioned 6EX6 occasionally as a low cost Sweep. ($3) 22 Watt
a) pentode 50V/div., 50mA/div., -2V steps, 140V grid 2
b) triode mode 50V/div., 50mA/div., -6V steps
a) pentode 50V/div., 50mA/div., -2V steps, 140V grid 2
b) triode mode 50V/div., 50mA/div., -6V steps
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I have mentioned it because I have well over 100 of them for an average cost of under 50 cents each. A few are old style 25 volt 6DN6's with a wimpy plate rated at 15 watts of dissipation. Compare that to the 15+ watt heater and on paper this tube looks like a real loser.
Open up some boxes and you will find that most have plates like those in the 24 to 28 watt sweep tubes. A single pair can make 100 watts of continuous sine wave forever without breaking a sweat.
These have become my go to test tube for experiments that may not end well. So far I have not blown one.
That RCA 25DN6 had the large plate. The only one I have, so I don't know if all the wiggles at low current are normal or if it was someone's reject ( came from Ebay cheap).
Here is that 25DN6 using Grid 2 drive. 50V/div Horiz., and 50 mA/div Vert. Grid 1 at 0V.
a) +10V steps on grid 2
b) approx. +10.7V steps on grid 2
Looking at the datasheets for 6DN6. 6DQ5, and 6LG6 I see screen current as 10%, 5% and 2% respectively of plate current, so that grid 1 drive wiggle may be normal. 6DQ5 starts to show noticeable kinks.
Here is that 25DN6 using Grid 2 drive. 50V/div Horiz., and 50 mA/div Vert. Grid 1 at 0V.
a) +10V steps on grid 2
b) approx. +10.7V steps on grid 2
Looking at the datasheets for 6DN6. 6DQ5, and 6LG6 I see screen current as 10%, 5% and 2% respectively of plate current, so that grid 1 drive wiggle may be normal. 6DQ5 starts to show noticeable kinks.
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These curves are using a Tektronix 576 Curve Tracer (normally for SS components) which has had some mods to allow higher "gate" (grid) voltages for stepping.
Up to +/- 168 V step range (or 14 steps of up to 12V) so it can do grid 2 stepping as well. (even higher with a fixed supply added in series) The step amplifier got some mods obviously with higher V transistors, normally does 10 steps up to 2V/step for FETS. I just had to pull one IC pin out to get 15 traces, instead of the usual 1 to 10 traces (well, a mod to the step D/A too).
A few more mods done too. Has a variable knob for step size now, beside the usual switchable step selector (so I can adjust display to full screen). The 1500V max collector (plate) V scale got dropped to 750V max for safety. (rectifier wiring mod), although I usually use the 350V Max (400V peak) scale for tubes as for the above curves.
The DUT module (bottom) got modded so that each DUT position (toggle switch front, Left or Right) gets its own Screen V selected from external Xantrex power supplies. Also another two Xantrex supplies for heater power, which keep the 2 DUT tubes warmed up full time. So even different tube types can be compared by flipping the DUT toggle lever.
The wiring to the tubes is done by banana plug to individual 0.04" pin sockets/terminals. I use some Pomona or Vector tube extenders on the tube so that the pin-out wire-up only has to be done once for a tube type. Can run a bunch of tubes thru test then. I also have adapters made up to convert Octal, Loctal, and Magnoval and sub-mini wire to 0.04" pins.
Some connectors added on the side for X and Y display options (I just brought them out to BNC connectors, TEK had them available in the plug-in DUT module for fancier tests). Can use a Tek AM503 / A6302 DC current probe (clip on) to display screen current for example.
Can test tubes up to 220 Watts or 2 Amps. Switchable load or max Watt ranges. But works just fine for those sub-mini Lilliputions too.
OH, and I bought a spare working TEK 576 (EBAY) for spare parts. You can not get parts for these from TEK anymore.
Up to +/- 168 V step range (or 14 steps of up to 12V) so it can do grid 2 stepping as well. (even higher with a fixed supply added in series) The step amplifier got some mods obviously with higher V transistors, normally does 10 steps up to 2V/step for FETS. I just had to pull one IC pin out to get 15 traces, instead of the usual 1 to 10 traces (well, a mod to the step D/A too).
A few more mods done too. Has a variable knob for step size now, beside the usual switchable step selector (so I can adjust display to full screen). The 1500V max collector (plate) V scale got dropped to 750V max for safety. (rectifier wiring mod), although I usually use the 350V Max (400V peak) scale for tubes as for the above curves.
The DUT module (bottom) got modded so that each DUT position (toggle switch front, Left or Right) gets its own Screen V selected from external Xantrex power supplies. Also another two Xantrex supplies for heater power, which keep the 2 DUT tubes warmed up full time. So even different tube types can be compared by flipping the DUT toggle lever.
The wiring to the tubes is done by banana plug to individual 0.04" pin sockets/terminals. I use some Pomona or Vector tube extenders on the tube so that the pin-out wire-up only has to be done once for a tube type. Can run a bunch of tubes thru test then. I also have adapters made up to convert Octal, Loctal, and Magnoval and sub-mini wire to 0.04" pins.
Some connectors added on the side for X and Y display options (I just brought them out to BNC connectors, TEK had them available in the plug-in DUT module for fancier tests). Can use a Tek AM503 / A6302 DC current probe (clip on) to display screen current for example.
Can test tubes up to 220 Watts or 2 Amps. Switchable load or max Watt ranges. But works just fine for those sub-mini Lilliputions too.
OH, and I bought a spare working TEK 576 (EBAY) for spare parts. You can not get parts for these from TEK anymore.
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Well, a lot of smaller tubes (pentodes) don't show signs of screen current.
This is the 6197 / 6CL6 ($0.33 7.5 Watt tube)
For $2, and a bunch of sockets, I could get a 45 Watt tube with no kinks, 66000 gm, and linear as H---.
This is the 6197 / 6CL6 ($0.33 7.5 Watt tube)
For $2, and a bunch of sockets, I could get a 45 Watt tube with no kinks, 66000 gm, and linear as H---.
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Those and most of the other Sweep tubes on it went out of stock in the first 6 months of the $1 list, like 10 years ago. Vacuumtubes.net started it, and ESRC copied it till recently.
Maybe we should call it the "Weep" list now. The 12/38HE7 with an approx. 15 Watt Sweep pent. was on the list till the end (when ESRC vanished last year). 25BQ6's too.
Maybe we should call it the "Weep" list now. The 12/38HE7 with an approx. 15 Watt Sweep pent. was on the list till the end (when ESRC vanished last year). 25BQ6's too.
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