211 Push pull operation points

[Svetlana]

Given the RCA 211 Graphs, Would +150VDC plate, and +100VDC screen seem good for Push Pull operation?

[Tweeker]

The 211 is a transmitting triode. +1,000VDC plate and -60VDC to -80VDC grid bias more in range.

+150VDC plate with +100VDC grid bias would give about 85ma of grid current and soon melt it.

[CijTele52]

Those parameters don't sound like 211 transmitting tiode for me. Can you provide more detail?

[Svetlana]

http://www.mif.pg.gda.pl/homepages/f.../049/2/211.pdf

With say 120 VDC on the plate and + 100 VDC on the grid, the plate looks very linear.

At these conditions, The grid looks less linear, but could this be off-set by the driver? What would the implications of non linearities to the grid?

Keeping to a plate at 120-125VDC, maybe the grid is more linear at +125VDC, and you could swing this with maybe ~200V of audio?

[Tweeker]

You need at least 500 volts B+ to really do anything with a 211. There are a couple of parameters that will be exceeded by wide margins for any power output otherwise.

Maximum average plate current is 175ma.
Maximum peak grid current is 50ma.


Regulator pass tubes are a better choice if your looking to make a low voltage high power pp amp. 6C33C comes to mind as the heavyweight here.

[i_should_coco]

Originally posted by Svetlana
http://www.mif.pg.gda.pl/homepages/f.../049/2/211.pdf

With say 120 VDC on the plate and + 100 VDC on the grid, the plate looks very linear.

At these conditions, The grid looks less linear, but could this be off-set by the driver? What would the implications of non linearities to the grid?

Keeping to a plate at 120-125VDC, maybe the grid is more linear at +125VDC, and you could swing this with maybe ~200V of audio?

Those operating conditions would be no good for class-A audio operation. They are deep into class A2. You would need to supply many watts of power to drive the grid. Not an easy proposition.

You're better off using conventional A1 operation. Don't be fooled by the curves - they make look nice & linear, but any improvement in linearity you would gain would likely be outweighed by caning the driver. The input impedance would be in the order of 1K or less at that operating point. You would need a driver with an output impedance of a maxiumum of 100 Ohms!

Edit: Actually, you'll melt the grid anyway, as pointed out above.

Cheers,
Pete

[Svetlana]

How did you work out the input impedance?
How do I work out how many watts drive to use?
If "it would melt the grid" why does the data sheet map it to that point? (And much much more current at lower plate voltages?)
How do I work out how many watts output I would get?

[Tweeker]

They are provided for conditions during power up/down and if theres a failure such as losing the bias supply. Some are also of interest for class C operation, where it might only be seeing the grid and plate currents during a quarter of the cycle.

The graph on the very bottom of the datasheet gives grid current. Any time you drive the grid of a tube positive, the input impedance drops dramatically (<1k typically) and the grid dissipates power.

Lower voltage doesnt necessarily allow higher current in a tube, particullary as it applies to grid or screen current limits. I squared*R.

[Tubenstein]

The Plitron PAT-4149 suggested running the tube in 1200V, so this is possible operating the 211 in A1.

http://shop.plitron.com/specs/414900.pdf

How much power you think the amplifier can get from a pair of 211 running in class A1 with this Plitron transformer?

Originally Posted by i_should_coco

Those operating conditions would be no good for class-A audio operation. They are deep into class A2. You would need to supply many watts of power to drive the grid. Not an easy proposition.

You're better off using conventional A1 operation. Don't be fooled by the curves - they make look nice & linear, but any improvement in linearity you would gain would likely be outweighed by caning the driver. The input impedance would be in the order of 1K or less at that operating point. You would need a driver with an output impedance of a maxiumum of 100 Ohms!

Edit: Actually, you'll melt the grid anyway, as pointed out above.

Cheers,
Pete

[DavesNotHere]

800 volts is where I ran the 211 amps I've built. grid bias from a variable -100V supply.

what are you using to drive them. I used 5881 in a push pull line stage to drive mine.

Plitron transformers rock my design at 100W as I perfer to use them for these and 2A3's.