RCA MI-1109A Recording Amplifier info needed.

[Audiofreek]

This unit powers up,but no signal passes,I believe it predates tape recorders,and was used for disk cutting.It has a mic input section using 6sj7 tubes,and a monitor/power amp section.A schematic for repair/restoration would be very helpfull.I will post pics as soon as I get it back from a tech who has no luck with repairing it.

 

[Mike Cleaver]

I recently downloaded an entire binder of RCA schematics and instructional sheets on gear from that era.
Let me see if I can find a schematic and instruction sheet for this.
It may take a day or two, the .pdf is several hundred pages.

 

[mjrippe]

Can you share a link to that PDF?

 

[Mike Cleaver]

Looking for the link again because for some reason, my download missed many of the pages.

 

[Mike Cleaver]

Here's the link:  http://rayrayburn.com/rca/RCA_manual.pdf

Hope it contains the information you need.

 

[Mike Cleaver]

Just scanned through all 300 some odd pages of this document and your specific unit isn't mentioned but I'm certain there are units that are very similar, just different MI numbers.
RCA documents are extremely hard to come by.
I think the company purposely destroyed everything when it went out of business.
The only surviving documents seem to be in the hands of people who actually own the gear.
I've had some luck recovering some information from filing cabinets of old engineering documents at the various radio stations for which I have worked.
Luckily, all the RCA gear I have came with the instruction booklets and schematics.

 

[emrr]

Sarnoff library.

http://davidsarnoff.blogspot.com/2007/12/kaimal-completes-broadcast-manual-index.html

It's closed, everything is now part of another broadcast archive.  It was all flooded several years ago, and I don't know current restoration status. 

 

[Audiofreek]

Thanks Mike,
The MI-11209-B monitor amplifier looks to be the same as the playback amp in the 1109A,there looks to an addition of 2 more input transformers,1 more 6j7,another attenuator and bridge/match control,Playback/Record switch, a VU Meter,and tabletop housing on the 1109A.

 

[Audiofreek]

here is a pic of the back of the unit:

 

[mjrippe]

From that back photo I have two questions:

1 - Did you try swapping the wires going to the cap of the 1620?  One comes from under the chassis and the other looks like it is wired to a jack that someone added to the side of the amp.

2 - Is that a broken resistor lead toward the front, or just a shadow?

New pic with notes:

 

[Audiofreek]

From that back photo I have two questions:

1 - Did you try swapping the wires going to the cap of the 1620?  One comes from under the chassis and the other looks like it is wired to a jack that someone added to the side of the amp.

2 - Is that a broken resistor lead toward the front, or just a shadow?

New pic with notes:\

1)No,I haven't tried anything since one of the capacitor cans blew when I powered it up.I asume that jack going direct to the cap should work as a transformer by-passed/Hi Z input.
2)No, the resistor lead in the front is not broken,it just looks that way in the photo because a black wire is crossing in front of it.

 

[mjrippe]

OK, well then I'd replace all the electrolytics and check coupling caps for leakage.  It CAN be made to work again.  I've restored 1940's RCA gear and it is worth the time and effort.

 

[Audiofreek]

Thanks Mike for the RCA bible,and all of your help.I borrowed a capictor tester, and found only five dead caps,most I tested were over value.I'll keep those in for now, replace the bad ones,and see how it sounds when I power it back up again.