RCA Mi-9328 preamps

[mrtnasty]

Hi does anyone have the schematic for these preamps, or any information about them? Thanks!

 

[Rob Flinn]

I can't help you with a diagram, but they look like they would be fairly easy to draw your own diagram.

 

[jazzcrisis]

I believe these are similar to RCA BA1A (schematic attached) but don't know that from experience, just an unverified fact stuck in my brain.

 

[mrtnasty]

I believe these are similar to RCA BA1A (schematic attached) but don't know that from experience, just an unverified fact stuck in my brain.

Yea I knew it was similar, but not sure how close.

 

[dmp]

What are the numbers on the bottom of the transformers? If you post good pictures we can figure out a schematic. I've seen these for sale before and been curious. I'd suspect they don't have the same quality of transformers as a ba-1 or ba-2 or they would be highly sought after

 

[mrtnasty]

What are the numbers on the bottom of the transformers? If you post good pictures we can figure out a schematic. I've seen these for sale before and been curious. I'd suspect they don't have the same quality of transformers as a ba-1 or ba-2 or they would be highly sought after

I just bought them and they haven't arrived yet, as soon as they do I will post detailed pics. It looks to me though from the pics above to have the same size transformers as the ba1.

 

[emrr]

I have seen the schem online at some point. Ba-1ish enough. Same iron

 

[mrtnasty]

Here are some pics, I received 2, a black one and a silver one. The silver one has output transformer 900542-501, the black one has xt-2875. Both have xt-2874 input transformers. Both are MI-9328-A.

 

[dmp]

I thought the transformers were all different from the BA1/BA2, but then I saw in the picture the output is XT-2875, which is the same as the BA1 output.
Be easy to trace the schematic starting with the BA1 to see if there are any differences. Those will be really nice preamps

 

[mrtnasty]

I thought the transformers were all different from the BA1/BA2, but then I saw in the picture the output is XT-2875, which is the same as the BA1 output.
Be easy to trace the schematic starting with the BA1 to see if there are any differences. Those will be really nice preamps

It’s interesting that the silver one (which seems older judging by the wax capacitors) has a 900542-501 output transformer, Ive never heard of that number before, I’m assuming it’s equivalent to the xt-2875.

 

[mjrippe]

It’s interesting that the silver one (which seems older judging by the wax capacitors) has a 900542-501 output transformer, Ive never heard of that number before, I’m assuming it’s equivalent to the xt-2875.

The 900542 is used as output for the MI-12241 & MI-9375A Preamps. XT-2875 is also seen numbered 901740 and used in the BA-1 and BA-2. Since the 1620 tube is equivalent to the 6J7, any of them should work with the other.