Re: RCA Ba2A Pre amp qestions & answers
« Reply #360 on: September 18, 2017, 02:44:13 PM »
That Edcor looks like it's intended for SE 6BQ5 or 6V6 and just right for flea watt guitar amp duties but the sec is given as a 600r only (no speaker taps). Interesting.

You can possibly get better bottom response from running the output tube at much higher current to lower the source impedance.  Running it at 10 -12 ma may knock it down to 8-9K which is better than the 12-14K it normally runs at. 

You'd probably be looking at a rebuild or separate project but that Edcor OT would be just right for running 6BQ5 or 6V6 triode strapped.  Dave P designed a SE 6BQ5 mic pre and I think the thread and schematic are still up in the archives.



burdoto

Re: RCA Ba2A Pre amp qestions & answers
« Reply #361 on: September 18, 2017, 04:04:11 PM »
Output is strapped with 620 resistor. So it sounds like 6j7 and that OT are sucking my bottom end down?

So I should try a different OT? You know off the top of your head of an affordable option to swap one out?

One thing I'm confused about is preservation sound dude built the OP6 with an BA2A first stage and used an edcor wsm 15k:600 matching transformer and didn't seem to have problems like I'm having. As far I know I duplicated that same circuit and used the same OT. So I built bthe BA2A circuit with the SE OT I mentioned earlier and the hybrid OP6 circuit which the wsm OT, but both circuits exhibit the same low end loss. Makes me think I'm missing something else in the circuit. Is there something else I should be looking for?


« Last Edit: September 18, 2017, 04:09:04 PM by burdoto »

Re: RCA Ba2A Pre amp qestions & answers
« Reply #362 on: September 18, 2017, 05:15:55 PM »
I'm pretty sure Cinemag has made at least one SE OT that aspires to work well for a direct coupled output like the BA2.  I would email Cinemag and tell David what you're looking for and see what he has available.   About 4 years ago he was looking into doing a replica with a nickel core but I don't know if they completed that project or not. 

kosi

Re: RCA Ba2A Pre amp qestions & answers
« Reply #363 on: January 02, 2019, 10:08:23 AM »
Small question, as I'm in the process of building one:

What's the purpose of the cathode resistors in series ? On the joints between the resistors are connections to the  MI-11599 plug, pin 7&8.

Thanks for any info !


EmRR

Re: RCA Ba2A Pre amp qestions & answers
« Reply #364 on: January 02, 2019, 10:11:11 AM »
Small question, as I'm in the process of building one:

What's the purpose of the cathode resistors in series ? On the joints between the resistors are connections to the  MI-11599 plug, pin 7&8.

Thanks for any info !

External tube check meter.  You can combine into one R if you like. 
Best,

Doug Williams
Electromagnetic Radiation Recorders

"I think this can be better. Some kind of control that's intuitive, not complicated like a single knob" - Crusty

"Back when everything sounde

kosi

Re: RCA Ba2A Pre amp qestions & answers
« Reply #365 on: January 05, 2019, 05:39:25 PM »
Thanks  EmRR


 

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