RCA BA-73A Rack
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dmp
Well-known member
Sure- I could later. Are you thinking of making a clone in the same form factor? Not sure if the metal work is special about these, I considered stripping them to mount them in a 2U but decided it wasn't worth the trouble.
MidnightArrakis
Well-known member
Hi, again!!! -- As I have been futzing around with various details on this "RCA - BA73 Program Amplifier", something has come up that makes me question the accuracy of your 170mm PCB width dimension. And, that is.....the BA-73 Program Amplifier manual states that the channel metal-work depth is 9.00" and as is also evidenced by your photographs, the "PCB Mounting Plate" is as deep as the channel base metal work. As is also shown within your photographs, the PCB itself is -- almost -- the same dimension as the metal-work (save for some natural clearances). However, as I have created CAD-models of everything and then started to put everything together, it then becomes obviously apparent that the PCB length dimension falls rather short. See the image below:
The "grey" metal-work is 9.00" wide and the "green" PCB is 6.69" (170mm) wide. The "space" shown on either side of the PCB is just a tad over 1.00" (actually.....it's 1.09" to be exact). So, is it possible for you to remeasure the PCB again or possibly point out what it is that I am doing incorrectly here??? THANKS!!!
[I considered stripping them to mount them in a 2U but decided it wasn't worth the trouble] -- While "stripping" them out would probably be far more trouble than it's worth to package them into a 2U enclosure, taking the basic circuitry and designing a whole new PCB with more modern and upgraded components and possibly even packaging it all into maybe a 1U rack-chassis wouldn't seem all that far-fetched to me!!! Of course, the UTC transformers would need to be replaced by some PCB-mounted EDCOR transformers in order for that to happen, but.....it's all possible and workable!!! I'm guessing that you could probably easily get 8-channels of circuitry, complete with EDCOR transformers and NEUTRIK PCB-mounted XLR connectors, to comfortably fit into a 1U rack-chassis. And, that would even include a 30-Volt @ 3-Amp power-supply!!! What do you think of that???
Just a thought.....
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dmp
Well-known member
I haven't opened the box up again to get some measurements, but I think the 9" is an OVERALL length, including the metal handle on the front (that I removed) and the connector on the back. When I get a chance I'll pop the top off again.
Yes, the WSM series of Edcor has ratios that are close. The input is a 1:1.58 ratio and the output is a 7.45:1
I think CJ dissected the input somewhere if you search. As I recall it had lams similar to a Neve input. Since the VTB9045 can be wired 1:2, it might be the best bet for a clone? But there is a WSM in 1:2 also. I expect 1:2 will only be slightly off optimum for noise matching into the input (2.4k vs 1.5kohm)
Not sure what to recommend for the output... ungapped ~33k:600... maybe the VTB2291 wired 9600:150 (8:1)? Or there is a WSM 8:1 (10k:150).
iampoor1
Well-known member
No need to strip them to fit in 2u, just mount them 90degrees on the side 
@emrrInteresting observation about not seeing many e's in the wild. I have like 12 of these ba-73s and only 1 e. I haven't seen another e for sale in the last few years either. So I agree they seem pretty rare comparatively!
@emrrInteresting observation about not seeing many e's in the wild. I have like 12 of these ba-73s and only 1 e. I haven't seen another e for sale in the last few years either. So I agree they seem pretty rare comparatively!
mylesgm
Well-known member
Off topic but how about a pcb with footprint for a lundahl 1517 that replicates the Calrec ua8000 output circuit?
MidnightArrakis
Well-known member
[how about a pcb with footprint for a lundahl 1517 that replicates the Calrec ua8000 output circuit?] -- Anything is possible!!! I just made mention of the EDCOR's because I know that they are low enough in height to fit within a 1U rack-chassis. I am not that mechanically familiar with the other two transformer types you mentioned for me to immediately know if they would easily fit within a 1U rack-chassis. I would need to look that up.
Meanwhile.....while continuing to futz around with the BA-73, I have come up with this so far:
Futzing around doing stuff like this is what happens when you become an official "Old Fart" and you don't have anything else to do all day!!! NOW!!!.....if I just had the Part Number for that P101 24-pin connector and the C102 2900uF/50V electrolytic cap!!!
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mylesgm
Well-known member
https://www.lundahltransformers.com/wp-content/uploads/datasheets/1517.pdf
Here’s the circuit, I can send more detail later
Attachments
MidnightArrakis
Well-known member
[Here’s the circuit, I can send more detail later] -- My response back to you here is also "off-topic", so maybe you and I should PM each other and discuss things in a more private mode? Ya think???
I also visited your website and listened to a few of your productions!!! There's some pretty nice stuff there. And, just as a slight side-note.....your track of "Samba Tanz / Hello Tut Tut" is listed twice. It's shown as "Track 2" and as "Track 15". Just sayin.....
But.....as I was browsing your studio website, I was thinking....."Why does all of this look kind of familiar to me"??? I then did a search within my e-mail address and discovered that you and I had been communicating with one another in August of 2022. Towards the end-of-the-month, I had asked you some questions about one of your mic-preamp rack-chassis designs and.....I had never heard back from you again!!! Then, I saw that I had contacted you on October 10th, 2022 asking you if you had received my last August message, to which I again received no reply. So, I merely turned my attention to other matters. As it turned out, I had gone ahead and had designed two complete rack-chassis for you..........only to have them fade away due to no response from you. Oh, well.....
Here is one of the transformer datasheets that I had downloaded in order to know what dimensions I was working with for the design of your chassis. Look familiar?
So.....what are you needing to accomplish this time?
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mylesgm
Well-known member
Aha! I thought I recognised your forum name. Emails it is.
dmp
Well-known member
That big cap I don't think there is anything close in size factor today. The can caps available are for tube amps. I took it out of circuit, left it in place, and put a modern axial in underneath (MUCH smaller)
The 24 pin connectors are 26-4209-24s in the female. I'm not sure what the male is (if different)
Nice looking drawings.
The 24 pin connectors are 26-4209-24s in the female. I'm not sure what the male is (if different)
Nice looking drawings.
