systemtruck
Well-known member
Which I still can’t find haha.
RCA BC-6B Console Project
- Thread starter tablebeast
- Start date
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ruffrecords
Well-known member
It will certainly sound different on the new path unless you match up the magnetics with either new or old parts. I’d look for orig parts over time until they show up; they do.
systemtruck
Well-known member
Yeah you would be better off either waiting to find one more original transformer, or just getting a pair of something new and stop using the one old transformer. It’ll never sound original, but it surely could sound terrific I would assume.
The Cinemag 9600T has a tertiary winding that is about 26:1 or 27:1 ratio, as David told me just recently. I believe there’s a very good chance that this will mean the NFB signal from transformer won’t be strong enough to match the tertiary winding of the original RCA which is still an unknown. But, maybe it is strong enough if a low enough value NFB resistor is used. I haven’t done any guess-math on the original tertiary.
I very much considered building this program amp, and maybe I’ll come back to it, but for now I’m focused on single ended program / pre amps.
I’m also not sure about the impedance of the original transformer. The Cinemag is 9600T is meant to be 15K. The peerless 217D is also 15K, and that one is used in the Pultec EQP-1A which has basic Push Pull 12AU7’s, where as the RCA is parallel push pull. So from this I would assume that the transformer primary for the RCA should actually be somewhere around 7.5K. But I haven’t really confirmed this either.
Lots of unknowns but one thing that’s fore sure is it won’t sound the same as the RCA transformer.
The Cinemag 9600T has a tertiary winding that is about 26:1 or 27:1 ratio, as David told me just recently. I believe there’s a very good chance that this will mean the NFB signal from transformer won’t be strong enough to match the tertiary winding of the original RCA which is still an unknown. But, maybe it is strong enough if a low enough value NFB resistor is used. I haven’t done any guess-math on the original tertiary.
I very much considered building this program amp, and maybe I’ll come back to it, but for now I’m focused on single ended program / pre amps.
I’m also not sure about the impedance of the original transformer. The Cinemag is 9600T is meant to be 15K. The peerless 217D is also 15K, and that one is used in the Pultec EQP-1A which has basic Push Pull 12AU7’s, where as the RCA is parallel push pull. So from this I would assume that the transformer primary for the RCA should actually be somewhere around 7.5K. But I haven’t really confirmed this either.
Lots of unknowns but one thing that’s fore sure is it won’t sound the same as the RCA transformer.
MidnightArrakis
Well-known member
[I very much considered building this program amp, and maybe I’ll come back to it, but for now I’m focused on single ended program / pre amps] -- Which one(s)?.....
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I have a bit of an overvoltage issue and am wondering how much of a deal it is? I used the highest tap to get it down, but I still have like 350Vdc instead of 295 etc... My monitor amp is not running and I wonder if it needs all the modules to work to get it down? Is there any damage going on if I leave it that high?
For instance, the -190 is at -240. The 290v at about 350... etc...
For instance, the -190 is at -240. The 290v at about 350... etc...
systemtruck
Well-known member
The RCA BA-2 and UA 610 preamps, and the GATES SA-134 Program Amp.
My negative won't come down with the monitor amp now running which makes sense per the schematic. However if I run a Sim of the resistors that I can find in series and shunting to ground I get -240 instead of -190. So I'm not so sure why or if that matters?
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MidnightArrakis
Well-known member
[The RCA BA-2 and UA 610 preamps, and the GATES SA-134 Program Amp] -- THANKS!!!.....
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systemtruck
Well-known member
I’ve skimmed through the whole 20 pages of listed tech docs and also done a search in this site and google. Any ideas where the 230B manual ended up?
systemtruck
Well-known member
Never mind found it !
OK, sorry, wasn't seeing the negative voltage value. That's only used for bias in the preamp stages, practically no load. The later consoles do away with the negative rail entirely, I've posted about that in one of these threads, all differences are shown. Most people aren't aware that version exists.
Your options are raising the series resistance values and/or lowering the load resistor value, but the load is really more of a bleeder than a load, it's not the main place to address it....usually....I think there's so little draw that raising series R may not do anything for you. Finding a weaker 6X4 could help too.
Are the + voltages better?
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The + ones are much better now. Someone had exploded the 25uF cathode cap on the monitor amp and then removed the output tubes. After putting those back in place it seems fine and the voltages came down.
I could for sure add more (less) resistance, but what if I don't? Just less gain with the -240 vs 190?
I could for sure add more (less) resistance, but what if I don't? Just less gain with the -240 vs 190?
MidnightArrakis
Well-known member
[the GATES SA-134 Program Amp] -- FYI: I just came across this little ditty a short while ago here in the New Year that you may have an interest in knowing about.....
Any of the Gates remote amps with built in PSU have an unavoidable hum level due to high gain and power transformer proximity. The Fearn will win that battle. Sound again is a matter of taste. Many people swear by 134's, I know guys with large commercial facilities who have a half dozen of them. The middle pictured unit, and others of that pre-1947 era all have pretty high hum level so good for loud sources, but not quiet ones. The unit replacing SA-134 is the M5530, and it's quieter by a long shot, but pentode small bottle tubes versus triode front end octal on the SA-134. Different responses in the iron. etc etc etc. Lots of variables that will come down to taste. The large transformer SA stuff (like early cast aluminum case SA-39 input transformer type) is the best IMO, but it's pretty rare to find compared to the remote amps. There's SA stuff with smaller plain aluminum can transformers that do not sound as good IMO, and you see more of that when you see it at all.
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systemtruck
Well-known member
Yes I had seen that too, but thanks.
Im not restoring original units, I’m copying / building circuits and seeing how they compare. I am using all external power supplies, so at least that shouldn’t be an issue. Also using new iron, so we’ll just have to see how it sounds!
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