View Full Version : Heathkit AR-29

Doug G.
12-21-2005, 11:32 PM
Hi everybody,

I recently received this receiver after having won it on ebay. I wanted it because I built the AA-29 (the amp part of the AR-29) amplifier in 1976 and still use it. I couldn't afford the whole receiver (about $315 compared to about $189 for the amp) and I didn't really care that I had a radio anyway.

FIrst of all, hats off to Mr. Owens from Seattle who originally built it in 1972 (I hope he is still with us). Absolutely a first rate job and I couldn't have done better myself. :thmbsp:

The receiver is in excellent condition overall. All five dial lights were burnt out (I actually got four of them to work again by snapping them with my finger).

Unfortunately, one of the 6000uf 40V caps for the power amps is bad and so I want to replace both of them. I have looked online and can find similar types(actually not THAT similar as far as value and size) but nothing identical. :sigh:

They are 2" in diameter and about 2 1/4" long. Radial leads. Although the length isn't really critical, I would like to be able to mount the replacements in the same clamps that the original caps were in.

Does anyone know of a source for these? I would be ever so grateful if I could get the amps working again.


12-22-2005, 01:15 PM
Hi Doug,

Great find ... I have a aa-29 in perfect working order ... along with 2 aa-15's 2 aj15 and a jewel of an AR15 :D .... as far as those big supply caps go .... What I have had to do .. is find the correct value with some parts house, Mouser, Digikey, Parts Express or MCM. As the cap will in all likely hood be much smaller than the one you are replacing ... I will leave the original one in place and attach the new one in some inconspicuous manner else where on the chassis... or along side the original one. It would be nice to find them the same size. You can do a search of the Heathkit forum or some such ... but I have had no luck in finding them ... I had some spares .. 1 aa15 and 1 ar15 both for parts. But alas no caps .... anymore ... :no:

I just had a thought ... if you cannot find any original ones ... pop the top off of the bad pair of caps ... clean them out ... and put your new ones in the shells and then reseal them ... wire them up ... :thmbsp: You should be good to go at that point ... !

Happy Holidays


Doug G.
12-22-2005, 02:22 PM
Hi Steve,

Always nice to hear from a fellow Heath lover. :thmbsp: If built well, they seem to last and last. I do know that the rest of the receiver works as I have it feeding my AA-29 and the reception seems to be excellent.

The AA-29 has wonderful, authoritative sound.

Thanks for the ideas. I never thought about hollowing out the old one and mounting the new one inside.

That being said, I think I may have found one that will work as is at Newark. It is a CDE and is 6500 uf @ 50V. 2" diameter but 3.125" length. I think I can get it to fit with that length. Only a little over 19 bucks too! :)

I wouldn't mind having an AR-15 either. Another great Heath design. I remember I didn't like the looks of its predecessor, the AR-1500, though. To me, it looks like a clock radio especially if you were to replace the four knobs on the left with an analog clock face :D

Anyway, thanks again and I'll probably order the CDE caps and see if I can get this baby totally functional again :yes:

I love "Kalamazoo" K--A--LAMAZOooo--oh what a gal, a real piparoo! :thmbsp:

Merry Christmas and a Happy New Year.


12-22-2005, 08:38 PM
I too bought and constructed an AA-29 back about 1970. I still use it today to drive my AR 3 loudspeakers. It is a fun amplifier and I am glad to see others own and appreciate it. :thmbsp:

Doug G.
12-22-2005, 10:59 PM
Hey great! And then there were three! :thmbsp:

Funny how it is accepted that the ARs and Advents (I run my stacked pairs with my AA-29) need a lot of power to reach listenable levels but I'll tell you what, there is no way I could turn the Heathkit up too much without bringing the whole apartment building's residents banging on the door! This is all of 35 watts per channel continuous (really 50 as High Fidelity mag. found back then). And, it seems to handle the 4 ohms or less load fine.

I ordered the caps from Newark so I'll report how they work to you guys so you can pick some up for yourselves. Does the AA-15 use the same value?

Also, above I called the AR-1500 the predecessor to the AR-15. I meant, of course, successor.


Doug G.
12-28-2005, 08:22 PM
Hey guys,

I got the two filter caps today and installed them. Checked the 35 volt supplies and made some quick resistance measurements on the output trannies and turned the AR-29 loose on one of the pair of Advents. I'm happy to report that both channels are operating wonderfully. So far so good. :)

These particular caps are Mallory (CDE) part number CGS652U050V3C if anybody else wants to get some. Like I said before, they are about 3" tall instead of 2.25 like the originals but fit fine in the AR-29 chassis in the original clamps. The value is 6500uf @ 50 VDC. The originals were 40 volt types so these should handle the load better. :yes:

I got mine from Newark but other parts houses may have them too.

Now back to listening to this great receiver back in action again! :thmbsp:


Doug G.
12-31-2005, 12:59 PM
I am now enjoying both the AA-29 and AR-29 with the AR driving the top pair of stacked Advents and the AA driving the bottom pair. I got new lamps for the dial so it is completely lit up again and beautiful. :thmbsp:

I also checked the FM and AM adjustments for optimal operation. Neither were very far off (actually only the deviation control for FM).

Another note that may be of interest to owners of these: the input ground plate that the RCAs are a part of is grounded to the input pre-amp board via one of the mounting screws and standoffs. I actually noticed on my AA-29 first that there was a hum problem with phono input and that pushing on the RCA jacks would affect the loudness of the hum. It turned out that oxidation had created poor continuity between these parts. Now, to keep everything original, I could have just disassembled stuff, cleaned everything up, and then reassembled. Instead, I decided to solder a wire to the plate and then to the ground foil on the board. This will obviate the problem in the future and isn't very noticable anyway.

I did this to both units.

They look pretty cool one above the other in the cabinet.


12-31-2005, 06:56 PM
Thought you might like to see a photo of my small Heathkit collection. Both dump finds; they both worked as-found. Pretty good condition 'cept for the broken treble slider on the AR-29.

Doug G.
01-01-2006, 11:14 PM
Thanks for the photos. Great finds!

I remember, at the time in 1976, I almost went for the AR-19 (or I think it was the AR-1302 by then) receiver but decided I wanted the extra watts. Since I couldn't afford the AR-29 (new family and all), I got the AA-29.


01-02-2006, 10:10 PM
Nice Pics .... been away for a few days ( 1 week actually) Not been on the ole computer much ..... Glad you were able to find those caps Doug . I will definately file that info away for a later date. Thought I would join in with the picture routine .... here is a ok picture of my AR15 Listening to Jazz with Bob Parlocha as we speak thru a pair of Minimus 7's and an old but cherry pair of Heath AS2's . If I have some more time in the near future I will take some pictures of some of my other Heath gear .. :music: Anyways ... here is the pic


01-03-2006, 07:56 AM
... "we" could start a "post your Heath gear photos" thread -- tho' most of mine isn't hi-fi. :-)

01-03-2006, 06:34 PM
... "we" could start a "post your Heath gear photos" thread -- tho' most of mine isn't hi-fi. :-)
LOL .... yea ... I have all of my dads old Heath test gear from the late 40's & early 50's. But I do have a lot of their Audio gear ... 5 pwr amps 3 pre amps 5 tunas .... 3 rcvrs 4 integrated amps and 4 other audio odds and ends including their RTA that I built in a wicked weekend of Solder smoke, beer and some vegetable matter smoke that makes me smile when I remember those days... way back when .... :D

05-15-2006, 06:09 PM
I just picked up an AR-29 in decent shape. I had to replace the fuse holder, the power cord, and a couple of light bulbs but other than that it works great. I powered it up using a variac since it looks like this thing has not seen any power for quite a while. I didn't even have to clean any of the switches or PC board connections. They are all quiet. It's quite dirty inside but I opted to leave it alone for now since it is otherwise working. The wood cabinet looks pretty good, considering it's age, with just a few scratches that are now pretty well hidden by Old English. The front panel has some marks but unless you are up close it looks pretty good too. It didn't have the original tuning knob but I had one that looks good but is just the opposite color scheme of the original. I am amazed at how well the AM and the FM tuner work on this receiver. The FM sensitivity and stereo separation are both excellent. I had AM stations up and down the dial, which is very good considering that there are only 3 locally. The amplifier section is also surprisingly good. This looks to be a very good receiver.
I found a schematic for it on the web but I can not find any manuals for it anywhere. If anyone has one (or are there two?) I would be happy to pay copy and other fees for them.

02-03-2009, 08:53 PM
I recieved a Heathkit AR-29 from my older brother, and I was just looking for any information on it. I am new to circuits and such, but I am interested in learning about these old amps. I want to refurbish it and use it as my amp. I think it would be a nice unit. Any help or information would be appreciated.

02-23-2012, 11:32 PM
Have been using my AR-29 for decades now, and it's always worked fine until now. No multiplex separation, ie, no stereo audio, just mono. Diagnosis is that the no longer available MC1305 IC went out, and now will be replaced by the available NTE722 IC, with minor changes to the circuitry to incorporate it, mainly cutting out the separation adjustment circuit to provide access to pin 9 as new +B input, rather than the old pin 8 of the MC1305. Evidently what happens, though, is that then the stereo light won't function, unless perhaps an interface transistor circuit is devised to get the stereo light to work. Also, of course, there will be no separation adjustment.

Has anyone devised such an interface circuit for this?

02-24-2012, 05:33 PM
Actually, now that I look closer, the existing circuit for the light is what I was looking for. Seems I can just measure the output from pin 6 of the NTE IC and if different from the MC IC, just replace the Q301 switching transistor for one with the correct switching voltages. Has anyone done this?

02-24-2012, 07:55 PM
Queries like this will get more and better responses if they post or link to the relevant docs.

02-25-2012, 12:45 PM
Well, it IS listed under Heathkit AR-29, in the "Vintage Solid State" category. What else should I do? I do reckon that anyone who knows anything about these receivers will be familiar with the correct AR-29 manual and circuit layouts. However, here is the circuit plan for the relevant sections:

Maybe no one knows anything about these receivers anymore.

02-25-2012, 04:19 PM
Several AKers are veteran audio technicians, but no one could possibly recall every detail of the thousands of chassis they've seen. I'm just sayin'... To allow these folks to handle as many queries as possible, make it easy for 'em.

I'll be happy to assist with a revised stereo indicator lamp (or LED) drive circuit, unless someone beats me to it. Just post the voltages that appear under mono and stereo conditions on the new MPX chip's stereo mode indicator pin.

02-25-2012, 05:22 PM
Agreed with BinaryMike, much of the knowledge I have from being bench tech back in the 70's is getting into its 4th decade. While I fixed a few Heathkit receivers mostly due to the builder not following directions, anything a poster does to make it easy to jog those memory cells will go a long way toward inviting me to take the time to reply.



02-25-2012, 05:50 PM
Ok, ok. I get the picture. I had presumed that anyone interested in answering would have the manual in hand. My mistake. I do realize that there are some real audio gurus out there who might be interested.

"jog those memory cells" Yup, there myself for sure.

Anyway, yes, I will measure the voltages and post those voltages that appear under mono and stereo conditions on the new MPX chip's stereo light mode indicator pin. That way, if someone knows offhand which switching transistor operates at those voltages, we are then off to the races, hopefully. Should be able to use the existing circuit, with just a new transistor, I think.

Then, the next problem would be to devise a small circuit to power the separation adjustment circuit, about 0.4 volts which the original MC1305 IC pin 9 supplied, which will be disconnected from the new NTE722 IC because of having to use pin 9 for the B+, bridged from the old IC pin 8 B+ circuit board location.

Maybe a simple zener diode regulator circuit?

Thanks for any input. I do appreciate it. I love my old AR-29, and cannot stand the idea of throwing it out, just because some darn IC is no longer available.


Doug G.
02-28-2012, 07:36 PM
This is interesting because, in addition to two AR-29s, I also bought a couple AA-29 amplifiers and an AJ-29 Tuner.

A couple of years ago the right channel out of the AJ-29 suddently became much weaker than normal and I concluded the MC1305 chip had gone on the fritz.

I communicated with a guy and traded an SN16852 quadraphonic decoder (he needed one for his Heathkit universal decoder) for an LM1305 (National Semiconductor) and installed it in the AJ-29. It works just fine and the tuner calibrated right up except the multiplex coil adjustments didn't seem to make any difference and I didn't investigate any further since the tuner seems to be at least the equal of my AR-29s in performance.

I guess I kind of surmised that the N.S. chip didn't need the optimization or is already internally optimized.

I have no idea where he got the LM1305 but maybe with some sleuthing, you could locate one.

And I think some of you guys were a little prickish to the new guy. Welcome to AK Del.


03-03-2012, 04:00 PM
No joy in AR-29 land. Installed the NTE 722 IC in lieu of the MC1305, removed the components for the separation adj circuit, as pin nine on the new IC is bridged from socket 8 for the new 12v input. Left the Q301 installed (someone suggested disconnecting it's base lead, tried that, but no change). Q301 is the stereo light switch.

So, no input for the sep adj. circuit. Found that it is difficult to come up with a small circuit using 12v to get the 0.4v required for that circuit, as zener circuits for instance don't supply below about 1.2v or so I guess. Must be another way.

Went through the recalibration/adjustment sequences, so that the signal and tune meters are adjusted correctly, can't do anything with the 19 and 38 khz adj checks.

What happens now is that when I turn the receiver on from stone cold in the morning, I get what appears to be slightly degraded stereo sound and the stereo light comes on. After several minutes, however, the stereo light goes out, and the signal becomes a stronger monaural. From then on, it is always mono until the next morning. Will have to remember to try measuring the voltage of pin six with the stereo signal before it switches to mono. Reads about 11.5v-12.0v at mono. Should read about 0.6 with stereo and the MC1305 IC, but who knows what it really is with the NTE722.

Anyone have ideas?



03-03-2012, 04:59 PM
this probably won't help at all - but the warm up effect suggests an elderly passive component (capacitor or resistor) is changing value as it... warms up. Got a can of "Freeze-Mist" component chiller? Start shpritzing stuff and see if you can force it back to its cold operating condition... and you might be on to something...

Doug G.
03-03-2012, 06:05 PM
Actually, the connection to pin 9 of the MC1305 is not a supply voltage to the separation circuit but is just what the DC level is at that point with a typical signal and the separation control adjusted to a typical value.

The separation control works on some transistors in the chip itself to improve the detection level and thus, separation of the two channels. It appears to me that the NTE722 does not require this control and should work fine without it or its associated circuitry.

Actually looking at the schematic and the pinouts of the two chips, it seems the NTE722 should work fine as the crucial pins are the same and the 722 doesn't seem to need some of the voltages of the MC1305.

It does seem that there may be another problem as Mark suggested. It's always a crap shoot substituting chips, though, unless you have very specific information. But, the fact that the operation is changing as the unit warms up suggests a thermal problem with a component.

The 722 isn't getting hot, is it?

Another thought, though. If you put the original chip in there, even though there is no stereo, does the operation stay consistent as it warms up? If so, it indicates a problem with how the 722 is working in that circuit.

BTW, proofreading my post alarmed me how many times I used the word "seem". :D


03-03-2012, 08:15 PM
... [technical stuff that I didn't understand :-P]...

It does seem that there may be another problem as Mark suggested. It's ...always a crap shoot substituting chips, though, unless you have very specific information. But, the fact that the operation is changing as the unit warms up suggests a thermal problem with a component.

The 722 isn't getting hot, is it?

Another thought, though. If you put the original chip in there, even though there is no stereo, does the operation stay consistent as it warms up? If so, it indicates a problem with how the 722 is working in that circuit.

Good question and good idea!

BTW, proofreading my post alarmed me how many times I used the word "seem". :D

How unseemly :-P

03-04-2012, 04:02 PM
Thanks for the replies. Doug's comments make sense. The 722 does remain close to ambient room temperature at all times, measured just above at ~80F.

There appears to be no difference in operation between the two IC's. The 722 IC outputs mono signals just as the 1305 had. The stereo light no longer comes on from stone cold. The readings at the pins of the 722 IC read as follows (with and without the base of Q301 stereo light switch disconnected), from 1 through 14 (Heathkit voltage values in parentheses):

1 12 (11.6)
2 2.8 (0.0)
3 3.1 (3.0)
4 2.6 (1.5)
5 12 (2.5)
6 0.3 (0.6)
7 0.0 (0.0)
8 12 (old B+)
9 12 (new B+)
10 4.5 (3.9)
11 4.5 (9.5)
12 4.5 (9.5)
13 4.5 (3.9)
14 0.0 (0.0)

Certainly, pins 4, 5, 6, 11, and 12 seem to be out of whack compared to the Heathkit manual voltage chart. Pins 8 and 9 will of course read 12v as input due to the bridge.

Maybe now the IC is blown. In handling it, everything was properly grounded, including myself, lol, but maybe having the base of Q301 connected eventually did something to the IC. This IC never did output stereo reproduction, however, except maybe for the apparent several times at the beginning after the installation of the 722 when the stereo light came on. I will pull the Q301 to check it out.

Also, have to admit, with the Heathkit diagnostic chart suggesting that amplifier coils L301, L302, and L303 might be a problem for having no stereo reproduction and no light. Don't how to check them, except that the solder connections are sound, or even if they are replaceable now. I do have access to another of the 722 IC, so may try again when I get it.

All of the other voltage readings on the Multiplexer board as shown in the manual are close to those required.

I'm beginning to think that restoration of the stereo reproduction may be a lost cause on this receiver. There may be something fundamentally wrong with the multiplexer board.



Doug G.
03-05-2012, 05:01 PM
Of course, the ideal thing to do is see if the composite FM waveform is actually reaching the multiplex board from the AM-FM IF circuit board at pin J3-6 of the multiplex board (pin 3 of IC302) with an oscilloscope because without that happening, you have no chance of getting stereo.

If that waveform is there, you at least know the problem is on the multiplex board itself. If any components in the 19kHz or 38kHz tuners (coil circuits) are bad, that will kill stereo since IC302 will not be able to decode the channels. In fact, that's what I suspect is happening and your original MC1305 may still be good which would be nice. \:^)

I doubt that anything other than a short or overvoltage would ruin the new chip. Of course, you may want to ensure twelve volts is getting to the chip too.


03-06-2012, 04:29 PM
Alas, I have no access to an oscilloscope, so I cannot check that composite FM signal from the AM-FM-IF board; however, it makes sense. Maybe I'll have to find someone locally who has a scope to check that signal.

I have checked all of the voltage readings for that particular AM-FM board, and all are correct, as are the relevant voltages on the multiplexer board. Also checked all soldering and the AM-FM circuit board itself for breaks, leaky capacitors, etc. Also checked the continuity of the L301 amplifier coil, and found nothing wrong there. I have never touched any of the amplifier coils, have assumed that they have remained tuned as from the factory. The voltage readouts at the pins of the 722 IC are as I reported in the last message, with the exception that pin 6 reads 11v, as the base of Q301 is connected right now, as I said.

Did discover that if pin 6 is shorted to pin 7 of the NTE 722, the stereo light does stay on continually. Pin 6, as it does read 11v with the base of Q301 connected, is then supplying power to pin 7, which is otherwise reading 0v. Pin 7 is connected to the light circuit through the collector of Q301.

03-07-2012, 02:15 PM
I reinstalled the removed components for the sep adj on the multiplexer board, removed the pin 8 to 9 bridge, and reinstalled the MC1305 IC. The pin voltages at the IC read exactly as given in the manual for no stereo output, ie, 11v at pin 6 for no stereo, the other pins as well matching the manual. Running a test for composite stereo output from the AM/FM/IC board, of having a no station hum with the treble turned up all the way, the mono switch makes no difference in the high frequency output, just the same constant volume usual no station buzz or hum. If there had been a change, it might have indicated that there was a composite signal.

Testing between D and E on the board (left and right signal out), with the unit off, and toggling the mono switch, the ohm meter reads13k ohms switch out to 2k ohms switch in. Normal resistance.

I think the NTE722 IC I had is kaput now, as originally, when I first installed it, the pin readings were close to the manual readings for the 1305, with pin 6 reading 11v for no stereo. Later the 722 IC readings became as listed in the earlier email, with pins 10, 11, 12, and 13 reading 4.5v, etc. Must have shorted it somehow. Another one should be arriving n the mail momentarily from a very slow outfit. Should have ordered this one from Mouser as I did the one I just fried. Mouser delivers almost immediately. Good outfit.

I'm beginning that the problems is with the AM-FM-IC board, although as I mentioned before, all the voltage readings for that board are correct, no bad solders, no breaks in the board, no leaky capacitors, and no coils, etc, have been touched, but show continuity as they should.

Well, at least I have good mono FM. AM is ok as usual.



Doug G.
03-08-2012, 04:33 PM
In all honesty, if I were getting signal to the multiplex board and I didn't have an oscilloscope, I think I would assume the complete composite signal was there and troubleshoot the multiplex board itself.

It sounds like either the 19 or 38kHz circuitry is malfunctioning and not allowing the decoder chip to separate the channels.

How about the two switches for those frequencies to switch between calibration and normal operation. I don't remember exactly what happens when they are switched but I would check them to be sure they are working and not intermittant.

Other than that, checking the components in the tuning circuits would be a good idea.


03-08-2012, 07:01 PM
Well, you are probably correct now that I think further on it.

The 19 and 38 kHz switches both work properly. When each of them is switched to adjust, the signal meter goes to zero. The adjustments called for in the manual have absolutely no effect.

All of the L coils have continuity. Those adjustment circuits are dead.
Also, 19 kHz sensitivity R310 has zero effect on the signal meter when the 19 kHz switch is thrown for adj.

The voltages for Q305L and R do read 6.5 volts as they should. The voltages for pins J11-1, -2, -3, -4 read 5.5v.

The only thing I notice which might be anomalous is that the slug for L303 is backed out about 6 full turns from the approx positions of those of L301, L302. Almost coming out, sticking out about 1/8 inch above the tube it is in, whereas the slugs for L301, L302 are sunken in about 1/8 inch below the top of the tube. Don't know if that means anything however, as I have never been able to get the signal meter to indicate anything but zero, completely dead, when adjusting coils L301, L302, or L303, as the manual says I should with the 19 and 38 kHz switches each in their adj positions.

One last thing, the signal meter almost always read a full 5 on the scale when tuned to a station, almost never anything lower at a station. Could never get it to adjust with the 19 and 38 kHz adjustments as mentioned in the manual.

I guess I'll just have to check more components on that board.

Just did find that capacitor C309, 2 microfarad, in the part of the circuit leading to the 19 and 38 kHz switches, is most likely open according to the test from the manual. Will change that. R306 is ok. C309 changed, no difference in signal.

03-18-2012, 08:03 PM
Still no stereo. Since the 722 IC before I fried it also didn't give stereo when installed, but all the voltage reading for both the 1305 and 722 IC's and the other board voltages were as per the manual, except for the monaural signal IC pin voltage being that for monaural rather than for stereo output at the IC, I guess since I still cannot find a bad component on the Multiplexer board, I'll just live with the monaural signal. Wish I had an oscilloscope but that's the way it goes.

I don't think anyone has any other answers.

Doug G.
03-20-2012, 12:35 PM
One thing I forgot to mention is that, circuitry connected to unused pins on the new IC will, of course, have no effect since there are no internal connections to those pins in the 722.

I'm not looking at the schematic right now but if that coil with the slug up above the windings is connected to active circuitry in the IC, that is definitely not normal. Normal adjustment should place the slug down into the coil. Of course, if that coil is connected to an unused pin on the IC, it doesn't matter.

If I remember correctly, none of those three coils had any effect when I did the adjustments on mine with the LM1305 chip in place but the chip does actually work and produces stereo just fine.

I think they just made the newer chips with the multiplex optimization internal to the IC instead of relying on external adjustments.


03-26-2012, 04:37 PM
Thanks for additional info. Still trying components on the multiplex board, but no faulty components found yet. Have checked the continuity of just about every circuit board connection on both the m board and the am/fm/if board,. Nothing wrong there. Sigh.