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Heathkit question

Ziradog

Ziradog

AK Subscriber
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I have 2 projects in front of it, but I went ahead & purchased a nice, un-restored Heathkit SA-2 amp. It came with a model AJ-10 mono tuner, with an MPX output. I would like to eventually run a stereo Heathkit tuner through the SA-2. Does anyone know what stereo models were concurrent with the SA-2 amplifier? Maybe FM-4? That one lacks AM (which is not a big deal) and tuning eyes but it is stereo. Other options would be a Heathkit MPX adapter (AJ-11?) or solid state adapter, both of which seem a little pricey for a $20 - $30 tuner, or use a different brand tuner (tube or solid state). There's not a lot of high-quality FM content around here these days but there are a couple music programs that I listen to regularly so I do want passably decent FM sound.

Thanks for any help or suggestions.
 
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Some MPX adapters quite frankly are not that great. I think it was one of Heath's earlier designs that drifted enough that it either worked when cold, or when hot, but not both. Honestly for a lot of FM programming, I'm fine with it in mono. Better SNR values and half the time you really don't notice it unless you're doing serious listening to it.
 
AFAIK there are only about 3 tuners that will match cosmetically. The AJ-10, FM-4, and PT-1. The FM-4 as you know already is FM only and mono. The PT-1 is an AM-FM simulcast type tuner, so not really practical for stereo these days without an MPX unit. They also command a bit higher price. The AJ-10 is probably the most cost effective solution for a matching stereo tuner, but also needs an MPX adapter if not a stereo model.
 
simulcast tuners are a good way to give yourself a headache. Nothing like 2 programs going on at once in the same room. They do tend to have excellent AM sections though, and some had a switchable bandwidth control to make them both selective or high fidelity as needed.
 
Two different programs going at the same time is the norm here, I have teenagers.

Probably just stick with the AJ-10 until I get inspired. I guess I can do one of the solid state MPX adapter kits with it if nothing else.
 
I built a SS FM MPX adapter for my HK Citation III when I couldn't find an original HK MPX. It's been awhile, but I believe it was something like this one:

mpx.gif
 
At the risk of yet again exposing the vast depth of my ignorance, what is the advantage/disadvantage of this circuit compared to the LM4500 one sold here http://fmmpx.com/? I am in the process of building one of these for my Sherwood S-3000iii.
 
Mhardy sent me some nice catalog scans (thanks!), and all the tuners they show for that time frame were mono only, AM/FM stereo (one channel on AM, the other on FM) or "Crosby" MPX adapter. I am guessing "Crosby" was a different MPX format than we use now. Can I still use that output as-is for a "regular" MPX adapter?

Babblefish, interesting site. I have no idea what the different chips are, but I can probably waste many hours looking them up & trying to decide what to try..
 
Ziradog said:
Mhardy sent me some nice catalog scans (thanks!), and all the tuners they show for that time frame were mono only, AM/FM stereo (one channel on AM, the other on FM) or "Crosby" MPX adapter. I am guessing "Crosby" was a different MPX format than we use now. Can I still use that output as-is for a "regular" MPX adapter?
Click to expand...

Sorry, but I have no idea. Maybe someone else older than me :) can answer that one.
 
You can use about any FM MPX circuit you want. They all should reference from the detector in the tuner. Personally, I would use a small modern solid state unit and build it inside the tuner. If you want to stay tube, you could probably fit an old Fisher 500 style inside the case. If you want to go outboard on the cheap you could re-purpose an old Magnavox adapter. The world is your oyster and there are many options.
 
There is a Fisher MPX unit out of a receiver for sale on barter town currently. I have run those as an external, or you could plant it inside the case if there is room for it.
 
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