Any info on a Lear, inc. A-471 power amp?

[jigawatt]

Hello,
This is my first time posting to this forum, I have been enjoying it immensely!

I have two tube power amps, an A-471 and 472 made by Lear, inc. I want to refurb these and wondered if anybody here has ever heard of these. It is using 2 6v6GTs in a push-pull config with 2 6sj7s on the front end. I ultimately want to use these as a dual mono monitor amp. Are 6sj7 tubes suitable for this application? I know they are common in guitar amps. I have powered them up with no tubes on a current limiter, and all the voltages seem to be there and on the right pins?

I have a feeling this is an old RF amp for an airplane, just a guess because of the Lear name. Can't find anything about them, though, any help would be greatly appreciated!

[Enzo]

Lear Aviation makes jet planes, but Lear electronics makes amplifiers and stuff. As far as I know you can still get Lear car stereo gear. It still could be part of an aviation system though. Small PA system in the plane, headphone amp for the pilot, etc.

Those selenium rectifiers - lower left pic1 - are itching to be replaced. All those wax covered caps underneath will be leaky. And the electrtolytics as well.

This is clearly an audio amp. More than that I can't tell you.

[jigawatt]

Thanks Enzo,
Hey, I see you live in Lansing, I'm in Holt... small world!
I've got the replacement electrolytics and also diodes to build a new bridge. I just got standard 2A diodes instead of actually getting a rectifier - I hope it will be enough

I kind of suspect I won't be able to find a schematic on this, so I may gut the whole thing and start fresh. (I started reverse engineering it and about pulled my hair out!) I saw a similar design with 5965s instead of the 6sj7s, but I thought maybe I could use these as a dedicated power stage, and have an input stage for guitar and a different input stage for monitors- Or is there a way to do both with one "general" input stage?? Can I just put some impedance matching resistors on a switch and call it good? IDK did you ever have to finally decide?

[Enzo]

I googled a little, and found nothing. But this amp looks to be really simple, so if it were mine, I'd get out a sheet of paper and a pencil and just draw out the schematic for myself. So even if you want to convert it into something else, a lot of the wiring could remain.

6SJ7s are what they are, early Champ amps used them for example, so they show up in guitar amps now and then. All you can do is try a circuit using them, and you like it or you don't. This wasn't a guitar amp, but I have no idea what sort of fidelity it was designed for.

Guitar amps and PA amps are really different things. Preamp-wise I'd think you'd want separate circuits. Plug a guitar into a PA system sometime and hear how lifeless it is.

My shop is in the same building as His Productions recording studio, next to the MetroBowl on MLK. I am there evenings.

[sgelectric]

Lear A-471 and A-472 schematics and info

Last week I was given a Lear Dynaport portable wire recorder/phono(78 rpm)/AM radio system.
Built in 1947, it is apparently considered rather high-end for recorders of its type.The unit is housed in two travel cases: one containing the recorder, phono and control panel and the other the power supply/amplifier,the AM tuner and the monitor speaker.
Upon opening it, I discovered complete documentation: manual, operating instructions, schematics, etc..............I have attached the power supply/amplifier schematic and relevant information pertaining to it from the Engineering Description guide.The schematic references both the A-471 and A-472.
The specs are rather impressive from a fidelity standpoint and all the iron is vintage Triad.....Cool
Let me know if you need other information.......I hope this has not arrived too late to be of use.

[Enzo]

Oh, very cool.

[loudthud]

It's interesting that the diode symbols on the schematic are opposite the way we draw them today. I hope nobody makes the mistake of hooking substitute diodes up backwards.

[jigawatt]

YES!! This is it. I can't believe I am just getting to this now (doh) I pulled this ol amp out again this week and began drawing it out, got frustrated, and thought I giver the ol google try one more time an lo and behold! It was waiting here for me the whole time X) Thank you so much for posting that...wire recorder eh? I have a console faceplate with all the switch functions on it, not that I really need it, but the Lear logo looks cool. My intention is to tweak the amp so that it is suitable for using with a barcus berry piezo pickup on a violin. I am going to mount the amp into an old radio/phonograph console with a speaker and make a sweet lil' fiddle cabinet! Thanks again sg for breathing new life into this project!!!