SE 6AQ5 with AES PT-31 OPT

[happybear]

SE 6AQ5 with AES PT-31 OPT. The OPT's are older units, not the current production. 5751 driving stage.

There were some issues regarding load dependent stability while figuring out the feedback circuit.

Grid stop resistors and Zobel network across OPT resolved the stability problems.

RT Channel : THD @ 1W = .73% , THD @ 2W = 1.45% , THD @ 3W = 2.55%

Schematic with operating points posted.

 

[happybear]

Square waves for the SE 6AQ5 amp at 1KHz & 10KHz.

There was a bit of ringing at 10KHz but nothing terrible. The 680pF cap bypassing the 3K ohm FBK resistor helped damp the ringing a lot.

Bandwidth and Phase vs. Frequency Graphs added.

 

[Tinkerbelle]

Looking good and hopefully sounds it. Thank you for sharing.

 

[drteming]

Well, this is weird. I am currently working on a very similar amp, but using a 6AV6 driver. This is not the first time that someone posts an amp using a relatively unpopular tube at the same time I'm doing the same.

 

[gadget73]

I wonder if making R6 smaller might help out the distortion figure. From idle to full output you'll get almost double the current flow, so the screen voltage would dip quite a bit. Or maybe a zener diode to keep it at a fixed voltage drop from B+ would do the trick.

 

[nerdorama]

The 6aq5 data sheet for an SE amp specs 250v for both the plate and screen. In Dave Gillespies update of the Magnovox EL84 console amp, he uses a 1.5k resistor in the supply to the screen (and I think the driver tube) so not much voltage drop.
John

 

[happybear]

I wonder if making R6 smaller might help out the distortion figure. From idle to full output you'll get almost double the current flow, so the screen voltage would dip quite a bit. Or maybe a zener diode to keep it at a fixed voltage drop from B+ would do the trick.

At nominal listening levels, the SE 6AQ5 amp will be using less than 1W of power with either Altec or Magnavox 2-way horn speakers.

At the 1W or less power output level, THD% will be satisfactory. Of course, your suggestion will be kept in mind for further examination.

Thanks,

happybear