Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: kagliostro on November 23, 2016, 04:14:11 pm
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Some time ago I discovered the spec of this tube
(http://i.imgur.com/8yyAhHS.jpg)
Today I was re reading the sheet and focalized my attention to the fact that the tube can also be used in various other mode and not only as a choke
https://frank.pocnet.net/sheets/127/6/6216.pdf (https://frank.pocnet.net/sheets/127/6/6216.pdf)
The question is, if this tube can be used also for other purposes like A or B class amplifier, can a 6V6 or an EL84 tube be used as a choke ???
Thanks
Franco
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Some time ago I discovered the spec of this tube
Today I was re reading the sheet and focalized my attention to the fact that the tube can also be used in various other mode and not only as a choke
https://frank.pocnet.net/sheets/127/6/6216.pdf (https://frank.pocnet.net/sheets/127/6/6216.pdf)
The question is, if this tube can be used also for other purposes like A or B class amplifier, can a 6V6 or an EL84 tube be used as a choke ???
Thanks
Franco
One of the few ways to find out is to test it. I would work with the 6v6, and an isolation transformer, a stepdown transformer or a variac working about 200v. If it works, then I would do the design work to convert to elevated heater voltages, and cathode voltages.
Some design questions not shown on the application drawing include
1. the 6216 heater operates at elevated voltages, Will need to assure the voltage differences between the cathode and the heaters are maintained within design specs. (150v vs 100v for the EL84 and 200v for the 6v6)
2. At 1.2 amps for the heater filament, that's a lot of power from the high tension
3. It would be a great application for a solar powered amplifier.
I would say that the 6v6 or el84 probably would not work. The big difference is that the 6216 has two taps on the cathode. I believe that if you find a pentode with two taps on the cathode, and a tap on the grid (#2?) closest to the anode you might have a chance. Then again the application drawing doesn't show both cathode taps being used.
Two 6216's in a PP application as a class AB amp sweet, and different wiring!
Great challenge and they say nothing new under the sun.
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Today I was re reading the sheet and focalized my attention to the fact that the tube can also be used in various other mode and not only as a choke ...
Of course, it's a beam power tube and (within its ratings) can be used like them.
The question is, if this tube can be used also for other purposes like A or B class amplifier, can a 6V6 or an EL84 tube be used as a choke ???
Yes, but you'd like the proposed filter reactor tube to have similarly high transconductance & high perveance (space-charge control of the electron stream).
You should be able to see that ultimately the sheet shows a pentode hooked up like any other pentode. The exception is G1 is connected to "ground" (where "ground" is also an a.c. voltage developed across a resistor) through a cap, and the plate load is the - end of a filter cap. The screen is powered like any other screen (from fairly steady d.c.), and the cathode is biased by a resistance with a variable tap to G1.
High Gm means a little G1 voltage controls a lot of plate current. So a little ripple current develops a voltage across the piece of R connected to the 0.05µF cap, and results in a lot of opposing plate current change to counteract the ripple current. So higher Gm helps the tube act like a more-H choke.
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Good explanation Many Thanks HotBluePlates
So, if I understand correctly a higher GM tube has more chances to be a good tube for this purpose
Something like EL84 beats 6v6 2 : 1
(EL84 = 11.3mA/V - 6V6 = 4.1mA/V)
Correct ?
Thanks Again
EDIT: On the datasheet on the link I posted (not the image) the GM of the tube is 12.5mA/V (if used as a reactor), this mean the EL84 will be satisfactory on that application ? (they say also that the tube has a Gm of 8.8mA/V if used as audio amplifier ....)
(http://i.imgur.com/AJHW4kl.jpg)
Franco
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It's not even a great choke.
The specific market is "high speed military aircraft". Here the weight of a choke is a Big Problem. A tube and an 8uFd cap weighs less.
Even so, I wonder. The tube drops more raw supply voltage so you need a bigger power supply. You also need the 7.6 Watts to heat it. That's also more heat to get rid of. You would think in a, say, Thunderchief (>1000MPH, 2000KPH) cooling would not be a problem? But the electronics were tightly packed, little space for air-ducts, and the aerodynamics did not encourage big cooling scoops. Somebody must have calculated it both ways. (The Thunderchief is older than the 6216, but my grandfather built them so I know how it goes.)
The cathode is not "tapped". We sometimes find two cathode leads for VHF service. Here I am sure it is about "resistant to vibrations ..high speed military aircraft". Big jet power in light airframe makes a violent ride. Snap-flips, bomb-release, carrier landings... everything would shake apart. The large cathode needed extra support. It is inside so gets limited support from the micas. The other option is tying it to base pins. 2 pins is much better than one. You want this, if you put tubes in your jet fighter. (Or jeep!)
The 6216 has several adaptations to make it "better" for pass-tube work, especially as Pentode. But ANY tube can be used as a pass tube. Millions of regulated supplies used 2A3 and 6L6-triode. Just some work better than others. Here the "regulation" has been reduced to "smoothing", saving the cost/weight of an added amplifier tube.
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Good explanation Many Thanks HotBluePlates
So, if I understand correctly a higher GM tube has more chances to be a good tube for this purpose
(EL84 = 11.3mA/V - 6V6 = 4.1mA/V) ...
You have the right idea: more mA per volt of error signal.
I agree with everything PRR said. Especially, "... ANY tube can be used as a pass tube. Millions of regulated supplies used 2A3 and 6L6-triode. Just some work better than others. Here the 'regulation' has been reduced to 'smoothing', saving the cost/weight of an added amplifier tube."
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Many Thanks PRR and newly Thanks HBP
PRR
What you are saying remembered me an old thread (of mine)
http://el34world.com/Forum/index.php?topic=16097.msg157174#msg157174 (http://el34world.com/Forum/index.php?topic=16097.msg157174#msg157174)
(http://i.imgur.com/GolwY8l.jpg)
and I can understand better the PS on that ciruit if I follow the explanation by HotBluePlates and yours
Franco
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Yep, plate of V5 is the filtered but unregulated power supply voltage, while the cathode of V5 is the regulated output voltage. A 6L6 is used for current-handling capability and Gm. C9 samples the regulated voltage and feeds it to the control tube V7, which compares a portion of the regulated output voltage to the reference voltage established by V6.
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> understand better the PS
That is very badly drawn.
Draw a small triode amplifier stage. But stand the cathode on a 105V battery (or gas tube). Tie a big cathode follower to the small triode plate. Feed raw power to big tube plate. Run an (adjustable) voltage divider from the big tube' cathode, to small tube grid, to ground. The cathode follower will tend to stand at a multiple of the 105V reference, and tend to ignore variation in raw power.
Here the divider is around 2.5:1, so we expect around 250V. This may be true as long as the big tube gets at least 300V, but not much over 650V (exceeds 400V rating of old 6L6). There will be some shift of output because the small tube 6SQ7 gets plate power from raw voltage, and its bias will shift. But a 2V or 4V shift added to the 105V fixed reference is not a large shift at output.
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Thanks HotBluePlates & PRR
Today I'm out of service because of the flu, however I think I've understand
Thanks
Franco