Heathkit AR-1500A Power Supply Transistor Cross References

Winslow S.

Winslow S.

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I was recently given a non-working Heathkit AR-1500A. It powers up but that's about it. In circuit, I'm getting low outputs from the power supply: 10V where I should get 50V, and 3V where I should get 12V. Both + and - 43V lines are at 41V or so I assume the big caps are OK. Out of circuit, the easily removed PS board tests low at the transistor test points which lead to those underpowered rails so I'm suspecting one or more transistors are kaput. I haven't removed any yet for testing. I'm putting together a Mouser cart and can easily find modern cross references for the 2N3393, 2N5294, and 2N5496 components, but the S2090 (Q2 and Q5; the old "glob top" package) appears proprietary to Heathkit and I'm having a tough time finding a replacement. Any Heathkit experts know of a modern equivalent? 2N3904 looks close but I'm unsure. Thanks.
 

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I have used 2N5308s for that transistor in Heathkits and works.

This is one of the many instances where you can't google it and rely on the AI information which is totally screwed up for this. Depending on what you enter for a search, it will tell you the S2090 is a PNP or it's a NPN in a TO220 package or any number of other variations. AI is BS.

Doug
 
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Doug G. said:
I have used 2N5308s for that transistor in Heathkits and works.

This is one of the many instances where you can't google it and rely on the AI information which is totally screwed up for this. Depending on what you enter for a search, it will tell you the S20909 is a PNP or it's a NPN in a TO220 package or any number of other variations. AI is BS.

Doug
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Yup. It doesn't take much RS (Real Stupidity) to figure out when AI is just plain wrong.
 
To add to my post, I know the 2N5308 is a Darlington and it has been several years ago (July of 2009) that I remember using one in one of the AR-29s and I don't remember if I found the specs. for the S2090, somewhere or if I just measured voltages in the circuit and decided it would work but it has, since then.

Did you find the S2090 specs.?

The symptoms, for me, were kind of the opposite. The 12 and 50 volt sources were too high. There was also a 120 Hz low-level hum out of the speakers.

Sometimes, Heath engineers did the craziest things with using proprietary devices. The TZ582 in preamps is another example.

Doug
 
Doug G. said:
I have used 2N5308s for that transistor in Heathkits and works.

This is one of the many instances where you can't google it and rely on the AI information which is totally screwed up for this. Depending on what you enter for a search, it will tell you the S2090 is a PNP or it's a NPN in a TO220 package or any number of other variations. AI is BS.

Doug
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"Artificial Imbecile" for the loss, yet again . . .
 
New transistors arrive today. I am no expert on power supplies and wondering where I should start. On the schematic, power runs from right to left ending up in the low voltage rails I'm getting. Should I begin replacing in that order and test between each component installation?
 

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Doug G. said:
I always remove the relevant transistors and test them, then replace the bad one(s). Of course, you want to check the electrolytic capacitors, too.

Doug
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Thanks for your input here, Doug. Q5 tested OK. Q6 was the baddie. I replaced it and the unit lives! The panel lights are as dim/non-working as they were prior to the fix: barely any light light, and no phono/aux/etc input indicators light up. That suggests the dim display isn't a power supply problem from the power board. The display has five lamps that I can see: all work except the middle lamp (DR on the instructions). If I swap them around, that lamp works fine in other locations and known good lamps don't light up in that position so it's not the lamp. Also, it's wired differently from the others which are, I believe, wired in series. I think that's the input indicator lamp, but the schematics aren't helpful. Any suggestions for troubleshooting this part of the unit? There are two green wires that come off the transformer that are labeled "dial lamps" but I haven't traced those yet. Thanks again.
 

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Winslow S. said:
Thanks for your input here, Doug. Q5 tested OK. Q6 was the baddie. I replaced it and the unit lives! The panel lights are as dim/non-working as they were prior to the fix: barely any light light, and no phono/aux/etc input indicators light up. That suggests the dim display isn't a power supply problem from the power board. The display has five lamps that I can see: all work except the middle lamp (DR on the instructions). If I swap them around, that lamp works fine in other locations and known good lamps don't light up in that position so it's not the lamp. Also, it's wired differently from the others which are, I believe, wired in series. I think that's the input indicator lamp, but the schematics aren't helpful. Any suggestions for troubleshooting this part of the unit? There are two green wires that come off the transformer that are labeled "dial lamps" but I haven't traced those yet. Thanks again.
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After a bit of research, it looks like the middle lamp is the stereo lamp and shouldn't light unless (duh) there's FM stereo. I'm surprised the selected input isn't indicated by a lamp like similar units from the era. Still, the panel's too dark....
 
OK, good deal on the PS.

I don't have a -1500A but do have a couple -29s and Heath usually had these circuits the same from series to series in that era,

The two green wires from the transformer should measure about 6 volts AC and go to the four (five, including the one for the two meters) dial lamps which are wired in parallel. These are probably type #44 lamps and that number is indicated on the side of the lamp base.

The other lamp is actually the stereo indicator and should be a different type, usually a #1813. The two types are different voltages. The stereo indicator is separate from the others and is wired into the stereo multiplex board/circuit.

Check the voltage across the two green wires, not voltage to ground, to make sure it's there. If it is, check all the bulbs.

The stereo indicator should light whenever a strong enough stereo station is tuned in. If it doesn't measure the voltage at the socket. If it's there, the bulb may be burnt out.

Incidentally, I have replaced all the lamps in my Heathkits with LED equivalents, available on Amazon. Modern day incandescent bulbs are crap and don't last.

Doug
 
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I didn't see your last post before I posted but yes, the other lamp is the stereo indicator. Typically, If Heath printed the functions on the front plate, they didn't have the functions light up.

Doug
 
There was lamps that require too much current to operate. So like if the lamp that in the unit now has lamps rated at 6 volt @ .250 amps and the manufacture originals were rated @ 6 volt .150 amps then the wrong replacements would much more dimmer.
 
Yes. What did they do, put #47s in there?

A #44 actually draws more current than a #47 but is about 11 - 12 lumens compared to a # 47 which is about 6 - 7 lumens. I've never had any damage caused by the extra heat from the #44 lamps. Heath used heavy enough plastic for the dial.
 
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Doug G. said:
Yes. What did they do, put #47s in there?

A #44 actually draws more current than a #47 but is about 11 - 12 lumens compared to a # 47 which is about 6 - 7 lumens. I've never had any damage caused by the extra heat from the #44 lamps. Heath used heavy enough plastic for the dia
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PO had 1815s in there with an 1813 for the stereo indicator bulb. I'd like to see a substantial upgrade in the lighting. What are my options? Looks like the #44 has a lower voltage requirement but higher amperage, so it ought to be brighter and (as Doug G. says) still safe.
 
The originals, supplied by Heath, were #44s and were plenty bright enough but, as I said, modern day, foreign-made lamps are crap and don't last so, unless you can find some old ones... That's why I replaced them, in my Heathkits, with LED lamps.

These are variable as to brightness, too. You just have to find the highest lamp power ones for use with 6 volts. You can get ones that fit right into the same sockets.

Doug
 
A #1815 is a 14 volt bulb. No wonder they were so dim.

I also want to mention that I really wanted to keep my Heathkits original with incandescent lamps and originally installed #44s in them but they burnt out so quickly, sometimes a matter of just days compared to the originals which typically lasted years, that I gave up and used LED replacements, in stead. There is no real difference in light color temperature.

Doug
 
Another one lights the dust....:)

Cheapo 6v LEDs from Amazon seem to work fine where the #44s are supposed to go (and where the PO had extremely dim 1815s). I believe the FM stereo bulb should be 12-14v so I should be OK leaving the PO's 1813 in place. I haven't been able to test the radio yet, so I can't test that bulb/socket.
 

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I typically just leave the 1813 in there for the stereo light because they don't seem to burn out as much as the 44s. I did use an LED in my son's AR-29. I just found some of the correct voltage and it worked.

Doug
 
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