Elusive alternative needed: Aa driving EML50 or EML45B

[sidn28790]

Here is how I see the schematic. That said, I am trying to eliminate the signal going thru a coupling cap and resistor. The way I see it, I need to change the Aa driver to a lower Rp driver so an IT can be used. Or, direct connect. Does this sound correct?

 

[andyjevans]

There are some things in your schematic you could take a look at:
- a grid stopper on both tubes
- A dropper resistor and cap between B+ and plate choke/IT. I suggest a DC Link final capacitor, something over 10uF.
- a larger cathode bypass cap on the 50, e.g. 50uF.
- the Aa is directly heated - you have drawn an indirectly heated tube. Are you going to use Rod Coleman filament regs or what?

The bias on the input tube is unclear - what gives you the 2v?

Did you mean to post a revised schematic?

Back a few posts euro21 suggested one of Ale's gyrators. That might work with the Aa. He sells the PCBs so you'd have to build it and test it.


.

 

[sidn28790]

Andy - per your suggestions, the updated schematic not including the grid stoppers. Regarding the gyrator, I am trying to keep the design as simple as possible using iron where possible, much like Thomas Mayer's approach.

 

[euro21]

With 100H inductance the "last" frequency where
Z=2*Ri
is met: 95Hz.

Below it the load impedance is lower, so distortion growing.

p.s.
I hope that 50R is typo.

 

[sidn28790]

euro21: updated schematic should have indicated 50K, good catch. I am likely not pursuing much further the Aa --> EML50. Will be looking for a new driver tube or going back to the C3g.

 

[euro21]

C3g is satisfactory driver.... another question of #50 loading.

As you can see, for the Ri:1800 tube the 5K transformer is OK ... but if it has low inductance, the LF bandwith creeps up.