Audio Drive to Grids of 811A Modulator

[KB7HTV]

I am building a modulator section using a pair of 811A's to a ART-13 mod transformer. this will ultimately drive a single 813 final.
The tube tables suggest 6 to 8 watts of audio to drive the 811a's
The Original ART-13 used a 6v6gt to drive the modulator section

I am using a commercial audio microphone tube preamp to drive the audio
lineup in the rig.
The output of the Audio tube microphone  preamp is "line level audio" about 2V PP (or so I looked up) maybe inaccurate. audio will be supplied  to the
tube lineup by a UTC a-20 line to grid transformer.


The ART-13 used a 12SJ7 connected to the carbon mic transformer to drive the 6v6gt
Will the line to grid transformer drive the 6v6gt directly or do I need a 12ax7 or similar between the A-20 and the driver.

HTV

[W7TFO]

You might look into a cathode follower design, such as this Altec 1570 amp:

http://ampslab.com/vintage_altec1570b.htm

It is designed to flog 811's in class B, just like the ART-13, but with a lot better linearity and fidelity.  

73DG

Oops...fixed

[Carl WA1KPD]

You might look into a cathode follower design, such as this Altec 1570 amp:

http://coupmedia.org/realtime-us-radiation-map-1503

It is designed to flog 811's in class B, just like the ART-13, but with a lot better linearity and fidelity. 

73DG

I may be missing the punch line here but is this a joke? I suspect an error in link posting
Carl
/KPD

[Carl WA1KPD]

I am building a modulator section using a pair of 811A's to a ART-13 mod transformer. this will ultimately drive a single 813 final.
 

Do you have a schematic of your exciter and amp design that you can share?
I have wanted to build a single 813 w/ 2 811s for a while. I have the parts and some ideas but life keeps getting in the way

Carl
/KPD

[Steve - K4HX]

Consider a solid state amp and a tube output tranny with the normal output side (8 Ohms, etc) connected to the amp and the push-pull side connected to your 811A grids. Worked FB for me.

[WBear2GCR]

High ratio low level transformers are tricky... the A series UTC you have may or may not behave nicely, it's been a while since I looked at their specs (and I'm too tired to dredge them up now). But assuming they have the requisite bandwidth, and you do NOT drive the 6V6 into grid current, then you can drive it assuming you can produce the required swing on the grids. Once you drive it into grid current you will need some power from the preamp. Likely the "600 ohm" output will NOT have enough snot to drive the 6V6 into class A2 or AB2 (depending on if ur p-p or SE). But you can always check that by trying. A cathode follower will do the job, and also keep the primary of that xfmr solidly held in check - a big advantage in terms of how it performs, low impedance drive is good here.

I agree with the cathode drive scheme for the 811s too... a favorite of mine for various tubes and applications...

...my 2.5 cents worth.

                          _-_-bear

[WD5JKO]

Anytime we discuss an audio driver like this, the WA5BXO circuit should be a contender on the list of possible options:

http://www.qsl.net/wa5bxo/driver1.html

This circuit works very well.

Jim
WD5JKO