Restored an old Heathkit AA-1 Audio Analyzer

Ragwire

Member
I originally planned to restore this for resale, but it has turned out to be kind of handy for other projects I have going...business and hobby. I am quite fond of it by now. Handy loads and power reading at the turn of a switch. Measures IMD too. I just thought it was cool. :)

cheers
Rob

 
I have an old magazine article (somewhere!) on upgrading this model for much improved performance. The results were well worth the effort.
And don't overload the internal load resistors,as they will go open. A buddy was doing some ''high-power'' testing once and it cost him an output transformer when that happened.
I'll see if I can find the article and post it here.
 
arts, that would be great, if you can find that article!

I think the manual says 24W intermittent, but since all but one of the original loads resistors was open (the 600 ohm was the good one naturally), I put in 20W non-inductive resistors on a couple terminal strips. So now the 4 ohm and 16 ohm can go to 40W, the 8 ohm to 20W. Of course, intermittent use with cool-down will allow quite a bit more. I may upgrade the power handling when I get around to getting more resistors. Right now all I have used it for is a 15 watt 6V6 push-pull guitar amplifier I am building for a buddy. It calibrated up nicely to the calculated IMD levels against my scope's FFT function, and I really like the built it VTVM for manually power output on a speaker or for checking small signal levels in the preamps.

(This is a toy I do not really need, but I always wanted one and I like using it.)

cheers
Rob
 
I just started restoring mine,I would also be interested in the article.After this I am going to restore my IM-58(same as HD-1)harmonic distortion analyzer
 
@ s-petersen:
I'm glad I'm not the only one interested in these old things. Thanks you guys.

cheers
Rob
 
Ok,I finally found the article. It's for an IM-48,but as far as I can tell this is the same as the AA-1,just a different colour and a newer-style meter.Simple stuff,and while there is certainly a lot more that could be done to tweak this unit,this will give you somewhere to start.

Rob,you are definitely not alone! I think you'll find that,around here at least,most of our test benches are rather heavily populated with ''Benton Harbor Lunchboxes''.
I know mine is:)
 

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Way cool! Thanks, arts!!!!
Yeah, I love heathkit and 1950s HP millivoltmeters. (I have too many though, and one HP400C listed for sale on the bay right now).
I can fix those up and actually have some pretty good stuff that I can almost afford. : )

cheers
Rob
 
You're very welcome Rob,and I'm glad to help. I know what you mean about having too many! I have the HP 400D and the HP 3400A. Of my Heathkit VTVM's, the IM-23 & IM-28 are my faves; big meters for old eyes gets my vote anyday:)

Mike- I believe most Heath's used a 200ua meter movement,so you could find a salvageable VTVM with a nice meter and just transfer the scale.Oddly enough,that's the one model I DON'T have.

Art
 
Mike, I missed that part of your post. What are the measurements? I might be able to help with a meter. If you need just the scale, I make those if I have a readable master to scan. I do have several good Heathkit 200uA movements from benchtop VTVMs. Alas, the needle on my AA-1 is a bit sticky...it is actually a 100uA and I don't have that one.

cheers
Rob
 
Thanks Rob! It's an identical meter to what you'd find on a V-7 or an IM-11 (200ua), just with at different scale. I've got the front panel (label? scale?) to use for the scale, I just don't have a physically good example to perform the transplant on. The only working one I have has a cracked plastic front and a bent needle.

The scale on the WM reads -5 to +18dB, or from 0 to 50 watts on a slightly offset scale.

Shoot me a PM if you think you've got a candidate to bring this bad boy back to life!
Mike
 
Rob,if you could scan the meter scale for the watt-meter,preferably with a ruler in the picture for scale,I'd really appreciate it.

Thanks, Art
 
Mike, PM sent. (well, will be in a second).
Art, Do you need the AA-1 meter scan? I don't have the dedicated wattmeter, but can scan you the AA-1 scale.

cheers,
Rob
 
If I ever get one, Art, I will post it. Sorry. Maybe Mike can scan his. He has the scale but needs the mechanical meter assembly.

All this talk about meters, I put one of my 200uA meters into the AA-1 to see if it would calibrate/linearize--it did. No more sticky meter. And the "glass" is not yellowed like the old one. I got a box with these meters in it at auction. They were from a University lab and probably spent most of their lives stored in an air conditioned store room instead of a barn like most of the stuff I get.

Mike, I sent a PM. I do have a meter like that for you, and it looks good. The scale plate should swap right out.

cheers
Rob
 
Art - I'll give it a shot this week.

A big thanks to Rob for his generosity with his VTVM parts :D

Mike
 
I'm having some trouble calibrating the VTVM the linearity adjustment does not work correctly. and it looks like someone replaced the diode(to the control) (it's different than the others) I am missing the parts list and assembly pages from the manual(s) I found online.the schematic calls them crystal diodes.I tried disconnecting the control as was suguested in several places, but it is worse. If I switch the 2 meter diodes will it change anything?
 
I found a complete manual, The diodes are supposed to be 56-2 (Heathkit #) I am not able to find a cross reference, I'll try 1N34a and see what happens
 
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1N34A Should be close enough. If not, believe it or not, try a silicon power rectifier like a 1N4005 or similar. The reason I say that is that the Fluke 85RF radio frequency probe (for digital multimeters) used germanium diodes for signal rectification but a small silicon power type in series with a resistor for linearizing the output voltage. I suppose the curve was right. But try the 1N34A first.

Nice scan, Mike. Hope you get that back working. That's a handy meter to have.

cheers
Rob
 
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