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Nutone 2401 Tube Project

C_Little

C_Little

New Member
A few months ago I was driving down my street and saw a bunch of stuff set out on the curb, as I passed by I saw the gleam of a few tubes catch the sun, my heart skipped a beat and I immediately slammed on the brakes!

Turns out the guy down the street had ripped a Nutone 2400 intercom system out of his wall as part of a remodel. As I looked at it I realized it was a pretty decent stereo tube amp and tuner, so I began to hatch a plan. I didn't want to tear open my walls to install it, but I have been wanting a decent vintage tube setup to go with my empire turntable.

A few months later I've got it all together20211231_112823.jpg

Turns out the Nutone system is from 1961, which goes awesome with my 1962 empire. I briefly tested it out with a pair of garage sale Quadraflex soundlab 1 speakers I had sitting around. The highs and mids sound really good, but the bass is non existent. My guess is that they are being way under driven.

Anyone happen to know how many watts per channel these amps put out? I've looked everywhere and can't find any info. I've got connections for up to 8 channel A and 8 channel B speakers that would have been for the intercom system. Would it make sense to connect 2 or 3 outputs together to try and drive the speakers better? For that matter I can't find any info on specs for the soundlab 1's either. Lol. If anyone has info or ideas it would be much appreciated.
 
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it makes what it makes, using multiple outputs just divides the total power down so doing that and re-combining it at the speaker would still be the same total power.

What output tubes does it use? Can usually guesstimate pretty accurately just knowing that.
 
Well, I have the Sams Photofact folder (530-10 from 5-61) for the 2401 and 2402 - photo looks slightly different in the dial area but otherwise very close. A few things that could limit bass response: coupling cap size, output transformer size, and tone controls. The first two don't look so bad, but don't know about the tone control circuit. Unfortunately, it follows the volume control in the circuit, so would be harder to bypass. This has push-pull 6AQ5s for about 10 watts per channel. A weak one would really kill the bass in that channel. Matched ones are required due to the shared cathode bias resistor. I can copy the Sams folder or send you an original - the latter would be from the duplicate files at the Antique Wireless Association - they'd appreciate a donation in return.
 
So, just tried using a seperate pre amp and running through the aux/tape input, and it is amazing! Before I was having to crank the volume to the max to get any decent listening volume, now I'm half way to 1 and it is plenty. Maybe bad pre-amp tubes? Any ideas?
 
if this is in all original as-found state, fair guess its not working exactly like it should be anyway. Might be tubes, quite likely has some bad caps and possibly bad resistors as well.
 
C_Little said:
So, just tried using a seperate pre amp and running through the aux/tape input, and it is amazing! Before I was having to crank the volume to the max to get any decent listening volume, now I'm half way to 1 and it is plenty. Maybe bad pre-amp tubes? Any ideas?
Click to expand...

Are you plugging your turntable straight into the phono input? I think it's probably intended for a high output ceramic cartridge, so would sound weak and bad with a magnetic cartridge... the separate phono preamp takes care of that. How does the radio work?
 
That's interesting. I hadn't thought of that. I always assumed it would have been a magnetic cart setup since it is from 1962 and was pretty expensive at the time, but the turntable was pretty clunky, and a fold down/portable type model, so maybe a ceramic cart would have been used.
 
Sure enough, just checked some of the original literature that came with the setup and it came with a ceramic cartridge.

The only bummer is that I thought I was going to be able to use the built in tube preamp, and now I have to go solid state.
 
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Back then, ceramic cartridges were the norm, except for in higher end systems. If you want an inexpensive tube phono stage, the various EAR 834p clones on Ebay are tremendous value.
 
I scanned the Sams folder, 14 pages. Since they add up to 15 MB, I put it on a free download site rather than sending multiple emails... https://we.tl/t-4X1MDNWj7b

But I need to rescan the schematics since they don't quite overlap - there's a little missing in the middle. The rest should be useful in the meantime.
 
Schematics are too big to post - in fact I was going to upload them to radiomuseum.org and they're to big... will need to resize them. Anyway, email for the scans: tbavis(at)rochester(dot)rr(dot)com
 
You can get these refubished at Northside Service - Chris does excellent work!
Christopher Peters
Northside Service Company
5251C HWY 153 #128
Hixson TN 37343

moderator note - personal data edited out.
 
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