New idea: RE084 drives RS282

[Zoran]

I can suggest to use this 1:1 interstage transformer 110Hy
as input transformer.
And to order some L of 250Hy for 10-15mA DC current.
Low capacitance and as much low Rdc.
It can ber useful for many other tubes...

 

[banpuku]

Zoran & 50AE - Thanks again for the help. What is the appropriate current needed from the driver tube? The RE084 will deliver 5-7mA, which 50AE indicated was too low. What is the desired amount of current? Thanks, Pat

 

[banpuku]

Here is what I found for minimum driver current:

I >> A Cag 2 pi f Vpk

A = 12.5
Cag = 6pF
Vpk =
I = 12.5 * 6x10^-12 * 2 * 3.14159 * 90 * 20000 = 0.0015613 = 0.85 mA
Then, someone mentioned that we want 2 or 3x the calculated current of 0..85mA, so let's take 3 * 0.85mA = 2.5mA

Assuming my calculations are correct, then 5mA from the re084 driver is more than sufficient.

 

[euro21]

Pat,

I'm afraid, not the power tube Miller capacitance will be the biggest problem.

Are you read carefully RS282 datasheet in your #1 post?
Search "Gitterstrom".

Rob used this tube as preamplifier, so output power was almost subsidiary.
If you want significant power, each large transmitter tube eats the grid current... and requiring power to driving.
I think, without beefy driver, or CF/SF this tube cannot be used as good power amplifier.

p.s.
Here is the 40mA anode current driver tube control the RS282:
https://www.jogis-roehrenbude.de/Leserbriefe/Volker_Kluft-RS282-Amp/strategos.htm

 

[euro21]

With this "driver" tube (no gain, low current, high impedance, high distortion ... ) this is the "ultimate" solution:

2.9W output with 100W power tube.
Worth it?

1:4 SUT, 10Y/801a, FET SF, fixed bias RS282 8k4 OPT (1200V B++) the simulation shows 14W output .... but with 8.6% distortion.

 

[banpuku]

Thanks Bela, helpful. I have been emailing with Rob who uses the RS282 as an output tube SE at appr. 600V, 50A. As an alternative to the RE084, I could use an EML 12B or EML 20B. My interstage transformer has a max current of 30mA. Load lines of the EML 20B attached as an example of how I could use the tube. Thoughts?

 

[euro21]

Sample: 1:2 SUT, EML20a, IT, fix biased RS282, 8k4 OPT.

 

[banpuku]

Thanks Bela for running that simulation. 8.7% distortion is too high. What is causing this much distortion.

My OPT (new from Alexander) is 9.6K primary. In talking with Rob, I would use 600V on the RS282, just like he uses.

 

[euro21]

"What is causing this much distortion."
With this spice model, the simulated distortion is high ... higher, than Zoran suspected.
The real measurement would be different ... but these large transmitter tubes aren't distortion champions.