Hi there
I bought an old, broken RCA beat frequency oscillator model 154. See page 6 here for schematic: http://www.segalandassociates.com/Documents/Radios-Televisions/Schematic/RCA/RCA_m-154-bfo.pdf
The tube complement+voltages are perfect for an old school tube mic preamp. Or actually two mic pres.
It has 2 x 6j7s, a 6C5 and a 6J5.
I’m thinking it’s perfect for a Gates SA-70-type build - the kind of pres I've read user emrr rave so much about.
First question: The 6C5 being a predecessor tube of the 6j5 according to what I’ve read.. Am I correct in assuming that I can use it in place of the 6j5 that the SA-70 schematic calls for for one of the channels with little or even without any modification?
Both triodes, the operating characteristics are pretty similar in the tube charts, same voltages and amplification factor.
Second question: The oscillator has an output transformer with multiple secondary taps, including a 500 ohm tab.
Wouldn’t this be fine to reuse for one channel of the pres?
Last question: The power supply is tube rectified with a 5W4 followed by a choke input filter. Can I just reuse the power supply for the mic pre? Or is a power supply for an oscillator not gonna cut it for a mic pre noise wise?
I should add that I’m gonna need to use a step-down because we have 230v here in Denmark. Am I better off rebuilding the power supply completely with a new PT?
Thanks!
