RCA BA6a Pics

Here are some links to some BA6a compressor pictures:

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_3.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_4.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_5.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_6.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_7.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_8.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_9.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_10.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_12.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_13.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_14.jpg

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba_15.jpg

Schematics and articles:

http://vacuumbrain.com/The_Lab/TA/Ba6a/ba6a_article_lowres.PDF

http://vacuumbrain.com/The_Lab/TA/Ba6a/BA_6A.pdf

Nic eone CJ. Have you hacked the transformers open yet ? When can we expect Brian Sowter to start producing exact replicas to the specs you`ve given him ?

Interesting. Sure shames my 12AU7 limiter.

What is that, about 25 bucks worth of tubes at today's prices?

I love the low/high-level balance trim. That gives some hope of low-thump operation with two carelessly matched vari-gain tubes.

In its day, this beast would have been maintainable in Third World countries. Those tube types were old standards in 1950. (Today I'd have to order 6SK7 from Arizona or Canada, but there are warehouses full of them.)

The interstage tranny is 90% the size of the 10 Watt output tranny.... is it full of iron or air?

Note that the interstage tranny primary is loaded in 10K resistive.

Can you rough-guess the interstage turns ratio? Should be enough to inject a signal generator with power off, and measure 1KHz voltage on both windings.

Like the Fairchild 670, it uses a 10 Watt rectifier driver, only it uses this amp for output too.

They were very proud of their 2-position time constant control, but you could add other settings when imitating.

not to sound cocky, but I've got you beat by a few thousand. My BA6A is serial #56. Heehee!!

sorry to be off topic.

Jeff

[quote author="cjenrick"]Here are some links to some BA6a compressor pictures:[/quote] You'll note that CJ did not say that these were pics of his comp nor did he say that he took these pics himself.

Just an observation... :grin:
Charlie

hmm, true enough. :razz:

Jeff

Thanks to Charlie for the pics!
Brian Sowter has disected the innerstage UTC. It is high nickel with a gap, which is very weird. Most of the time you see M6 used with a gap.
I am thinking the gap is for when the compressor is working at max gain reduction where PRR mentioned that the tubes, even if carefully balanced at idle, will exibit a mis-matched condition, thus allowing dc into the core, which reduces inductance sharply and thus produces a thump.
cj
Oh yeah, I believe Brian has released the BA6a transformer set. Did you see the selinium rectfiers in that beast? Looks like a kludge wiring job, but you can't beat it's rep.

[quote author="cjenrick"]Thanks to Charlie for the pics![/quote]Nope...thanks to evilbay for the pix! I certainly wasn't fishing for credit, CJ. But thanks for hosting, I hate not being able to share.

I am thinking the gap is for when the compressor is working at max gain...which reduces inductance sharply and thus produces a thump.

Click to expand...

They talk about "signal-to-thump" ratio in the owner's manual. I'll read that again for clues. I did mention that I have a scan of the whole owner's manula didn't I? :twisted:

Brian Sowter has disected the innerstage UTC...Oh yeah, I believe Brian has released the BA6a transformer set.

Click to expand...

Crap, crap, crap! Don't tell me that, CJ! I want to DIY one SO BAD! But this one won't be that cheep, I'm afraid...but no matter, it would be worth it!

Thanks!
Charlie

I`m glad Brian`s on the case. That is definately one that I`ll be doing in the future !!

[quote author="cjenrick"]Oh yeah, I believe Brian has released the BA6a transformer set.[/quote] Yes, he is showing on the Sowter site now...Just in case you can't convert quickly, this works out to around USD$420 for a set. Yikes! But where else are you going to get it? I'm saving my DIY pennies now!

Peace!
Charlie

CJ

If you still have the original BA-6A at your disposal, would it be possible to take some test voltage readings? We don`t even know what the HT is for this circuit. Any readings would really help anyone who builds this.