Last post I see about Heathkits is dated in 2014 - time for a new one?
I've recently acquired a Heathkit AR-1500A from my brother. I actually built this thing back in February of 1971, and he has had it since. I've recently started 'collecting', so he dug it out of storage and returned it to me.
Does anyone know the whereabouts of a manual for a Heathkit AR-1500A? Of course I didn't save the one I had from 1971. Can't seem to find anything online.
This thing is *HEAVY*. I fired it up to get the dial lights so I could take a picture. Looks pretty good for a 48 year old receiver. Dusty on the top surfaces but clean on the underside. If I don't say myself, workmanship looks excellent! I'm going to be stripping this down and cleaning it the best I can, and then reassembling, testing, repairing any noted issues, and putting it in my collection.
Is there any interest in me posting more of the 'refresh'? If not I won't waste forum bandwidth.
I've recently acquired a Heathkit AR-1500A from my brother. I actually built this thing back in February of 1971, and he has had it since. I've recently started 'collecting', so he dug it out of storage and returned it to me.
Does anyone know the whereabouts of a manual for a Heathkit AR-1500A? Of course I didn't save the one I had from 1971. Can't seem to find anything online.
This thing is *HEAVY*. I fired it up to get the dial lights so I could take a picture. Looks pretty good for a 48 year old receiver. Dusty on the top surfaces but clean on the underside. If I don't say myself, workmanship looks excellent! I'm going to be stripping this down and cleaning it the best I can, and then reassembling, testing, repairing any noted issues, and putting it in my collection.
Is there any interest in me posting more of the 'refresh'? If not I won't waste forum bandwidth.
Attachments
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If you don't mind paying for the manual "d8apro.com" has it. This is where I got my AA-1640 manual, nice clean copy.
Craig
Craig
Thanks for the link llwhtt, but they want $35 for that manual. I can do a lot of seat of the pants troubleshooting (if I find I need to do any troubleshooting) for $35. But as a last resort.....
Preliminary data
Output DC levels
-110 mV left
-60 mV right.
Looks like that could use a little work, but shouldn't damage my speakers.
Output DC levels
-110 mV left
-60 mV right.
Looks like that could use a little work, but shouldn't damage my speakers.
Very nice shape, but if the volume control is noisy, you may want to clean all the controls,
and also replace the bias controls.
Would a schematic do for the documentation? I have a manual here I could scan. You will have to tape the pages together. Take me a couple of days though.
A schematic would help a lot. But I have another lead on a schematic, so hold off for now.
I still have the one I built while in high school, 1977, SN 8824. Nice to see another one.
This is where it all began!
It's one of those projects I want rebuild. I have the manual that came with the kit.
I will follow along as you do the rebuild. The controls were noisy early on.
Can you get the light bulbs?
BDP
This is where it all began!
It's one of those projects I want rebuild. I have the manual that came with the kit.
I will follow along as you do the rebuild. The controls were noisy early on.
Can you get the light bulbs?
BDP
I believe I've complete my work on the output amps on this AR-1500A. Another user was kind enough to send me a schematic of the AR-1500; I compared my boards with the AR-1500 schematic and found the AR1500A has a few added parts in the output amps. See the items circled in Red in the attached.
In addition, as I posted earlier, the output offset voltages were rather high on both channels, and there were no provision for adjustments. I added an offset adjust - it can be seen circled in YELLOW on the attached. Currently, with the unit fully warmed up, I have the offsets adjusted to +2 mV on the right channel, and +1 mV on the left. Idle currents run about 10 mA, depending on temperature, time of day, phase of moon, etc.
I sim'd the circuit using LTSpice, the .asc file is attached. As I could not find models for all of the old Heathkit transistors, so I had to make some educated guesses for substitutes. I'm not extremely proficient with LTSpice, but I think I have everything set up right. The sim looks like it is running very close to true class B, although the actual item has an idle current of 10 mA as mentioned above. Sim'd performance is quite impressive.
With an input of 1 volt peak at 1 KHz, I get an output of 91 watts. At this power level, LTSpice tells me the THD is 0.03%. That's hard to believe... Frequency response is 3 dB down at 2.4 Hz and 58 KHz.
In addition, as I posted earlier, the output offset voltages were rather high on both channels, and there were no provision for adjustments. I added an offset adjust - it can be seen circled in YELLOW on the attached. Currently, with the unit fully warmed up, I have the offsets adjusted to +2 mV on the right channel, and +1 mV on the left. Idle currents run about 10 mA, depending on temperature, time of day, phase of moon, etc.
I sim'd the circuit using LTSpice, the .asc file is attached. As I could not find models for all of the old Heathkit transistors, so I had to make some educated guesses for substitutes. I'm not extremely proficient with LTSpice, but I think I have everything set up right. The sim looks like it is running very close to true class B, although the actual item has an idle current of 10 mA as mentioned above. Sim'd performance is quite impressive.
With an input of 1 volt peak at 1 KHz, I get an output of 91 watts. At this power level, LTSpice tells me the THD is 0.03%. That's hard to believe... Frequency response is 3 dB down at 2.4 Hz and 58 KHz.
Attachments
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Most old designs will perform much better with modern sourcing.
70/80's Japanese designs will go from .05% to PPM levels when redesigned
with modern components.
OS
70/80's Japanese designs will go from .05% to PPM levels when redesigned
with modern components.
OS
There are many things, most simple, that could be done with that power amp for a large improvement. Bob Cordell, in his Power Amplifier handbook starts with a circuit that is somewhat similar to this and incrementally adds minor improvements. The end result is a distortion reduction of 3 orders of magnitude. This unit has the power supply to back it up as well.
His circuit does start with full complimentary output and current sources instead of the bootstrap capacitors. Other improvements include emitter degeneration resistors and current mirror load on the input stage. Darlington voltage amplifier stage.
His circuit does start with full complimentary output and current sources instead of the bootstrap capacitors. Other improvements include emitter degeneration resistors and current mirror load on the input stage. Darlington voltage amplifier stage.
Heathkit AR1500A
Still have mine (built in 1976) in operation. Rebuilt with premium capacitors/resistors/ transistors and "hot rodded" several years ago. 3mv/5mv DC offset. Output is 75wpc (8 ohms) and 110 (4 ohms) before clipping. Harmonic Distortion reduced by approximately 50% to .12%. Not near as quiet as my Marantz PM8006 but more enjoyable tone and timbre.
Still have mine (built in 1976) in operation. Rebuilt with premium capacitors/resistors/ transistors and "hot rodded" several years ago. 3mv/5mv DC offset. Output is 75wpc (8 ohms) and 110 (4 ohms) before clipping. Harmonic Distortion reduced by approximately 50% to .12%. Not near as quiet as my Marantz PM8006 but more enjoyable tone and timbre.
Hi,
I need manual for AR1500, so if somebody wants to share with me will be great.
Thanks,
Ivica
I need manual for AR1500, so if somebody wants to share with me will be great.
Thanks,
Ivica
