Recapping and restoring and upgrading a Heathkit AR-1515 receiver

[dlucy]

One of our outstanding local AK'ers, @nj pheonix , asked me to recap and restore his monster-of-a-receiver Heathkit AR-1515.



It is quite a beast, lots of power, an unusual design (on the inside), has the rare Dolby FM card, and was a lot of fun (read as "learning experience") to work on. This will cover the unit, the recap (with BOM), the upgrades and the result.

FYI: He has the resulting kickass unit up over in a Bartertown thread.

There are a few threads here covering the amp-only version of this, the Heathkit AA-1515:

• https://www.audiokarma.org/forums/i...kit-aa-1515-how-to-set-bias-dc-offset.788553/
• https://www.audiokarma.org/forums/index.php?threads/heathkit-aa-1515.378729/

 

[dlucy]

The styling is very Heathkit stereo-gear unique and obviously kit-worthy.

 

[dlucy]

Opening up the top, these nudies show some of how this is an unusual design: modular cards for each function.

 

[dlucy]

And the early stage of the power supply are accessed via the underside:


(the above photo is from @nj pheonix second unit)

 

[dlucy]

The modular card design isn't really a card cage, but instead it lets each card rotate on a single corner... it flips up so you can adjust or work on the card. Odd, but interesting....

 

[dlucy]

The topside, secondary power supply was not part of the swing-up modular card design. It used an old connector scheme.

 

[dlucy]

The chassis-attached part of the power supply was a bit more rugged and serious than I was expecting.

The two power reservoir caps used a bar to the main rectifier and to ground:





The main rectifier bridge was a serious, chassis-mount can type (but that didn't stop me from blowing it eventually):



The lower voltage, 10V, was regulated... at 5A... so another serious can-style device:





And one last rectifier made of just two diodes:

 

[dlucy]

The preamp and source selector board was the first modular card to be taken out.



The selector shaft ran all the way forward and had to be disconnected before it would come out:



The inputs came right off the rear input panel and into the selector:



Oxidization?



There were a few naughty tantalums in the signal path. They'll have to be replaced:



This AR-1515 is the first "truly" vintage receiver I've seen that uses an opamp. Very cutting edge, Heathkit! Being an old opamp, it'll likely have a modern, higher performance replacement. We'll have to test to see if that makes a difference:



The Heathkit assembly manual did a great job of listing the parts and indicating how to test your work before final assembly:





Sadly there were some parts which had Heathkit-only part numbers. Most of these were cross-reference-able at the Heathkit parts list sites like:

• https://www.qsl.net/w6ovp/heathkitparts.htm
• http://www.d8apro.com/heath3.htm
• http://www.d8apro.com/HCross.htm

 

[NAD80]

https://www.electroschematics.com/wp-content/uploads/2008/07/ua739-datasheet-specifications.pdf Looked up the specs just in case. Like that Heathkit.

 

[NAD80]

Thanks doug. Have had to repair old controllers at work using the metal can op amps.That IC was used in one of the units.

 

[fred soop]

There were earlier Heathkits that used op amps. Both the AR-15 and AR-1500 had op amps in the FM IF section. The AR-1500 also had a single chip multiplex decoder, but that's not exactly an op amp. Looks like the mechanical engineers learned a few things about accessibility after the AR-15. The AR-15 mechanical layout was obviously done by a former automotive engineer that would start with a heater core, then build the entire car around it.

 

[dlucy]

The Heathkit AR-1515 had an optional Dolby FM decoder board and the unit @nj pheonix asked me to restore included this rarity.

 

[dlucy]

The control circuit board hosts all the front panel potentiometers and function switches.

 

[dlucy]

Each channel has its own power amp board, each board is on opposite ends of the chassis, has a plug for power, a RCA jack for input signal, and huge heatsinks for the output transistors.

 

[dlucy]

Another unusual bit on this receiver is the digital display. The AR-1515 is an analog tuner with a digital readout. The digital readout is really a frequency counter with digital display. So, the tuner tunes by analog, produces a signal, and the frequency counter counts it.



The digital readout sticks through the meter and indicator light assembly:



The digits are simple, vintage LED display modules:







Each plugged into a socket:



With a display driver board:

 

[dlucy]

The RF board was relatively simple... and had interesting adjustment screws sticking out the back...

 

[dlucy]

The muting board was kinda hidden and fairly simple.

 

[dlucy]

The frequency counter, IF, and FM multiplex boards we very straightforward, easy to work on:

 

[dlucy]

Ok, down to the recap/restore/upgrade.

The preamp / selector card got:

all carbon comp resistors replaced with high precision metal film resistors
all electrolytic caps were replaced with low leakage Nichicon KL series electrolyitc caps
the small signal transistors were replaced with modern low noise devices
the one diode, a Zener, got replaced with a modern version
and the coupling caps were replaced/upgraded to Panasonic film caps

and finally...

the one opamp got replaced with a modern device... which required using a German-built SMD to DIP adapter.



Replaces the original opamp with LME49720 mounted on a SMD-to-DIP adapter from eBay seller revox-online

 

[dlucy]

The power supply board was nearly 100% rebuilt.



It didn't make any sense to put in axial electrolytics at premium cost when Nichicon PW series, mounted on their sides, would work best and be inexpensive:



Their leads just had to be extended with some station wire and heat shrink tubing:





The original design omitted unnecessary holes for unused leads:



And the one strange cap + resistor combo was repeated, just with modern, better components:



and the modern ones: