Hello,
Iron ( input and output transformers) from RCA BA21-A.
Those module were used in broadcast/radio console from 50's ( BC-5A) as either mic/phono amps or passive mixbus amplifier. They offered a fixed +40db gain and a max output of +18dbm, with input impedance of 37,5/150/600ohms ( input transformer configuration defined) and 150/600ohms output impedance ( here again defined by transformer configuration).
The original modules are based on 6072/12ay7 tubes ( a pair by modules) and use feedback through output transformer tertiary winding. Those one are special and are (very) rare.
The 'sound' of the BA-21A modules come from these 2 heavy pieces of iron.
You can find every info needed to build it here (technical manual):
https://www.steampoweredradio.com/pdf/rca/manuals/RCA%20Type%20BA-21A%20Pre-Amplifier%20Manual.pdf
The RCA reference number for this transformers are: M-8366 for input and M-8367 for ouput.
M-8366 is an UTC A-10 derivative made to RCA specification.
M-8367 doesn't have sibling i'm aware of: it is speced to be driven by a pair of push-pull 12ay7/6072 and offer 20db feedback through tertiary feedback.
Overall the circuit is on the 'clean' side ( i heard original module+psu used as mic preamp in studio sessions years ago and loved it) because of feedback and regulated psu.
You can see and listen a pair here:
I was lucky to be offered some some years ago, as those are scarce items as the consoles they were used in had been put into junkyard when transistors was the 'new flavour of the day' and anything vaccum tube had to be discarded during 70's, and being located in EU they were even more rare.
I initially bought them with the will to make an MC phono preamp ( 2 in serie (80db gain) minus 20db loss for riaa between the two modules) but these won't happen so some are on sale here.
I'm ok to let one pair ( 2x input and 2x output) go atm.
Initial asked price is 1200euros ( for the 2 set of in/out transformers). Preferably in EU.
If you are interested you can make an offer and let's discuss but don't expect miracles (they are so rare around here) and i won't split a set (in/out).
If you are persuasive i could sell them all...
Thank you watching.
Iron ( input and output transformers) from RCA BA21-A.
Those module were used in broadcast/radio console from 50's ( BC-5A) as either mic/phono amps or passive mixbus amplifier. They offered a fixed +40db gain and a max output of +18dbm, with input impedance of 37,5/150/600ohms ( input transformer configuration defined) and 150/600ohms output impedance ( here again defined by transformer configuration).
The original modules are based on 6072/12ay7 tubes ( a pair by modules) and use feedback through output transformer tertiary winding. Those one are special and are (very) rare.
The 'sound' of the BA-21A modules come from these 2 heavy pieces of iron.
You can find every info needed to build it here (technical manual):
https://www.steampoweredradio.com/pdf/rca/manuals/RCA%20Type%20BA-21A%20Pre-Amplifier%20Manual.pdf
The RCA reference number for this transformers are: M-8366 for input and M-8367 for ouput.
M-8366 is an UTC A-10 derivative made to RCA specification.
M-8367 doesn't have sibling i'm aware of: it is speced to be driven by a pair of push-pull 12ay7/6072 and offer 20db feedback through tertiary feedback.
Overall the circuit is on the 'clean' side ( i heard original module+psu used as mic preamp in studio sessions years ago and loved it) because of feedback and regulated psu.
You can see and listen a pair here:
I was lucky to be offered some some years ago, as those are scarce items as the consoles they were used in had been put into junkyard when transistors was the 'new flavour of the day' and anything vaccum tube had to be discarded during 70's, and being located in EU they were even more rare.
I initially bought them with the will to make an MC phono preamp ( 2 in serie (80db gain) minus 20db loss for riaa between the two modules) but these won't happen so some are on sale here.
I'm ok to let one pair ( 2x input and 2x output) go atm.
Initial asked price is 1200euros ( for the 2 set of in/out transformers). Preferably in EU.
If you are interested you can make an offer and let's discuss but don't expect miracles (they are so rare around here) and i won't split a set (in/out).
If you are persuasive i could sell them all...
Thank you watching.
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Hi, i can't upload the doc, it's too heavy for the forum.
Try this one instead.
https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.steampoweredradio.com/pdf/rca/manuals/RCA%20Type%20BA-21A%20Pre-Amplifier%20Manual.pdf&ved=2ahUKEwiZteSenMiNAxUIK_sDHQWDK0cQFnoECCUQAQ&usg=AOvVaw1iA0cJAyliC6M1LQPEHtb6
Thank you pointing the issue👍
Try this one instead.
https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://www.steampoweredradio.com/pdf/rca/manuals/RCA%20Type%20BA-21A%20Pre-Amplifier%20Manual.pdf&ved=2ahUKEwiZteSenMiNAxUIK_sDHQWDK0cQFnoECCUQAQ&usg=AOvVaw1iA0cJAyliC6M1LQPEHtb6
Thank you pointing the issue👍