Came across this reciever at a yard sale for 5 bucks. Physically not bad, all knobs there should clean up pretty nice. Bad news is when powered up lots of hum and noise in both channels. I plugged in cd player it will play music but all distorted. I'm thinking this unit will be a good thing for me to learn something about trouble shooting. Would I be correct in thinking maybe the caps are bad in the ps and perhaps should begin checking there first? I don't know what year it is from, but there is a service sticker on it. It was serviced by heathkit in 1977. Any advice will be much appreciated
heathkit AR-1302
- Thread starter zekez
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mhardy6647
Lunatic Member
P/S caps is a good place to start. It is awfully similar to the AR-29/AR-19 (FWIW).
mhardy6647
Lunatic Member
That's an AR-19 
The bottom one is the AR-29; they're both a little older than the 1302.
http://www.audiokarma.org/forums/showthread.php?t=82872
The bottom one is the AR-29; they're both a little older than the 1302.http://www.audiokarma.org/forums/showthread.php?t=82872
Doug G.
Lunatic Member
The AR-1302 replaced the AR-19 in about 1974 or 1975. Basically the same with some minor improvements (although I don't know exactly what they were :^)
It is almost guaranteed that your hum and distortion problem is caused by the two large filter caps (mounted on the chassis) for the supply rails to the power amps.
Doug
It is almost guaranteed that your hum and distortion problem is caused by the two large filter caps (mounted on the chassis) for the supply rails to the power amps.
Doug
dshoaf
That high voltage buzz
Heathkit gear is a good place to start learning about audio electronics with one exception: they were kits to start with.
This means that someone likely built it. On the assumption they were also wanting to learn about electronics, there may well be all sorts of little things that can now cause problems in addition to the aging capacitors.
I'd suggest you first go through the entire unit looking for cold solder joints and pinched wires. Look for any wire that turn corners, are tightly bound, may have been over heated. Wiggle all solder joints especially those where wires are attached to boards. Many of the boards were pre-stuffed in bigger Heathkit projects and the user only had to solder them together after assembling the chassis parts.
It is best if you have the original assembly manual, too, as this will have the step-by-step process for you to follow - something alone that will help your understanding. It will also have all the alignment and setup steps.
While you are in there, also look for bulging capacitors. That is, there may be electolytic caps where the small can or tube may have expanded. The tell-tale sign is the plastic shrink-wrapped used for insulating the exterior will appear to have shrunk and parts of the ends of the metal tube will appear to be extended beyond the ends of the insulating wrap. These have to go, of course. I am working on a HK Citation 16 of the same vintage as yours right now that has this problem.
Hope that helps a bit.
Cheers,
David
This means that someone likely built it. On the assumption they were also wanting to learn about electronics, there may well be all sorts of little things that can now cause problems in addition to the aging capacitors.
I'd suggest you first go through the entire unit looking for cold solder joints and pinched wires. Look for any wire that turn corners, are tightly bound, may have been over heated. Wiggle all solder joints especially those where wires are attached to boards. Many of the boards were pre-stuffed in bigger Heathkit projects and the user only had to solder them together after assembling the chassis parts.
It is best if you have the original assembly manual, too, as this will have the step-by-step process for you to follow - something alone that will help your understanding. It will also have all the alignment and setup steps.
While you are in there, also look for bulging capacitors. That is, there may be electolytic caps where the small can or tube may have expanded. The tell-tale sign is the plastic shrink-wrapped used for insulating the exterior will appear to have shrunk and parts of the ends of the metal tube will appear to be extended beyond the ends of the insulating wrap. These have to go, of course. I am working on a HK Citation 16 of the same vintage as yours right now that has this problem.
Hope that helps a bit.
Cheers,
David
The FM Tuner is the same. The AM/FM IF sections are different.
The other boards are the same; MPX, Input Preamp, Control Preamp, and Power Supply.
I think that the Power Amps use the same circuit board with different transistors and component values. The reference designations are the same. Both have 2N3055 outputs.
The AR-29 Power Amp rails are +/- 35V while the AR-1302 are +/- 28V.
A quick and dirty way to check the large PS Caps is to connect another large cap across each in parallel. If the hum goes away, then they are bad.
btmacdou
HH Scottsman
David, if the schematic for the power amps is the same but the AR-29 uses 35 volt rails while the AR-1302 uses 28 volt rails, wouldn't that make. The AR-29 a more powerfull amp?
Seems odd since the the 1302 is the newer receiver. Most companies were boosting power not reducing it.....
Seems odd since the the 1302 is the newer receiver. Most companies were boosting power not reducing it.....
If you change the output transistors, then you may need to change the bias resistor value (R621, R622). The bias diodes are not on the heatsink and I've seen these amps launch into thermal runaway. A lower value is safer, so you can just solder another resistor in parallel if the amps are overheating.