Concept 12.0D refurbishment in honor of fcarpcarp

[w1jim]

Our New England FrankenFest sponsor and mentor Frank Carpenter passed away last year and his family had an estate sale amongst the local audio community to raise money for his grandchildren and clear out his collection.

Frank was an avid collector of Concept (Pacific Stereo’s house brand) gear.

I picked up this 12.0D receiver (S/N 200398) that - while operational - is in need of some love.

Since Concept was a house brand there is very little in the way of servicing information, though hifiengine.com has the operating manual and schematic.

As far as I can tell there is only one person who has the manuals but since he also specializes in servicing these he has never released much if any usable information.

Plan is to:
Clean it up.
Fix some problems with the tone control section (might just be cracked solder joints on the PCB and dirty controls).
Recap - replace the electrolytics, replace the tantalums with poly or electrolytics and better caps in the rest of the audio path.
Install 5-way binding posts on the A channel to allow for larger wires.

Here are some before pictures:

 

[w1jim]

One of the amplifier modules - modular and easy to remove.

Before:



Opened up with the grounded shield displaced:




Reassembled, 4 caps replaced.
2 - 100uf / 100v
1 - 47uf / 50v
1 - 4.7uf / 35v tantalum replaced with a Wima film cap (50v used)
Note that on the right power amp PCB the polarity of capacitor C606B is marked incorrectly. The + side should be facing the signal input connector.
The original cap is installed correctly.
The left board is marked correctly.

 

[w1jim]

Time to dive on in.
Removed the faceplate which gives access to the tone and switching boards and the underside of the power supply and tuner PCBs.
At least 14 tantalum caps in there in the signal path that I’ll replace with film caps.

 

[w1jim]

Lots of capacitors on the tone board and they’re easy to replace.

4 of the tantalums are 1uf with 8 - 0.47 and 2 - 2.2uf. The 2.2uf’s look like they’re at the input to the phono stage - I replaced them with Nichicon FG electrolytics.

 

[w1jim]

Tuner board.
This is of course a tricky area to fool with since you don’t want to screw with the alignment.
Fortunately, the electrolytics are used for power regulation and audio coupling. I replaced those 6 caps but decided to leave the few tantalum alone.

 

[w1jim]

Digital display and memory board.
If it ain’t broke don’t fix it (or break it).
This section works perfectly.
Since early large integrated circuits are static sensitive and I’m sure these are unavailable there’s no sense making trouble and messing around in here.

 

[w1jim]

Making great progress - the power supply / protection board required 27 new caps.

Beware - the cap with the yellow asterisk is in backwards!

 

[w1jim]

Added 5-way binding posts parallel with speaker output “A” that will allow for the use of larger “modern” speaker wires.
Properly spaced to utilize the 2-wire banana plugs.

 

[w1jim]

I realize that the Concepts are a rare beast, especially on the east coast but hopefully my efforts will prove of reference value to someone in the future.

All finished (I think) - a few minor things during the pre-power check; a broken wire at a wire wrap post and s reversed cap on the power supply board.

The scribe in the first picture points out the mismarked polarity on the right amp board.
The second picture shows the correctly marked left amp board.

Time to let it run on the junque speakers in the basement before the big “reveal”.

 

[w1jim]

All finished (I think)!
Time to let it run on the junque speakers in the basement before the big “reveal”.

 

[w1jim]

It never occurred to me - the signal strength scale on the right is supposed to be illuminated.
Popped it open and replaced the 12v/150ma tube style bulb with an LED fuse bulb.
Also replaced the burnt out “Quartz Lock” and “Stereo” bulbs (8v/50ma).
Looks great now!

 

[NAD80]

Nice work. The receiver looks good. How does it sound?

 

[w1jim]

Sounding good, but I’ve yet to connect it to my big speakers for the ultimate test. FM is quite sensitive; I’m using a random piece of wire in the basement for an antenna

 

[NAD80]

Good tuner if picking up those stations from the basement with a short wire for an antenna. Lik the 5 way binding post addition.

 

[johnfalc]

Nice job ... I have a couple of these to go through. I too had forgotten that the reticule-like-grid is to be illuminated.

 

[johnfalc]

Nice job ... I have a couple of these to go through. I too had forgotten that the reticule-like-grid is to be illuminated.

Do you recall what you used in place of the, for example, "Quartz Lock" bulb? It would be nice to have them on hand before pulling faceplates.

 

[w1jim]

Do you recall what you used in place of the, for example, "Quartz Lock" bulb? It would be nice to have them on hand before pulling faceplates.

It's been a while but you should be able to use any 8v wire lead bulb. If you can't find those I bet a 12V/50ma bulb would work fine.
I have a lot of stuff on hand and don't recall where I sourced them. They were rated at 50ma, so I wouldn't use anything that draws more than that.
I also wouldn't use LEDs since they dispersion angle would be inadequate.
You can see the 3 tube bulbs to the left of the flourescent display in the picture aboe.

I did use a "fuse style" LED lamp for the grid. I soldered wires to the ends.

 

[johnfalc]

Thanks. I'd like to have it looking sharp and working well before deciding how to move it/ them along to someone who'll enjoy it.

 

[johnfalc]

It's been a while but you should be able to use any 8v wire lead bulb. If you can't find those I bet a 12V/50ma bulb would work fine.
I have a lot of stuff on hand and don't recall where I sourced them. They were rated at 50ma, so I wouldn't use anything that draws more than that.
I also wouldn't use LEDs since they dispersion angle would be inadequate.
You can see the 3 tube bulbs to the left of the flourescent display in the picture aboe.

I did use a "fuse style" LED lamp for the grid. I soldered wires to the ends.

Finished up the recently received Concept 12.0D and ELC II. The 12.0D had a bad series transistor that feeds the front end, a bad speaker protection relay, noisy controls, intermittent switches, and burned out lamps. All fixed, lamps replaced with LEDs the brightness of which I adjusted to match original bulbs.

https://photos.app.goo.gl/NPNNx8WNeguBWF3Q9 for a short album of both items.