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ToliTom's F-2624 Driver PCB Build Sansui 8080DB

BradWil said:
This just in. Beautiful QRX-9001 in dire need of, well, everything. 2 more Tolitoms on the way

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The QRX-9001 is very complicated, but only because of how much is stuffed into the space. It is pretty much the same circuitry as the 8080DB/9090DB. Just be sure to adjust the voltage to the quad boards to be at the "sweet spot" of 25v. That's where they perform best. A volt or so higher or lower won't "hurt", but won't sound the best. They are 18v minimum, and I believe 30v maximum. All transistors can be replaced with "the usual" replacements.
I love the green LEDs I used for the dial face. Originally 3 incandescent bulbs at the left end with color filters (which were burned dark). I replaced only the 2 upper bulbs with LED, and left the bottom out completely, plus added 2 layers of transparent "neutral density" film to the end of the "glass" to tone the brightness down. It gives it that "nostalgic" look akin to it's siblings the QRX-6001/7001.

Green Lamps.jpg
 
BradWil said:
That is beautiful. Very well balanced and original looking colours. The 9001 dial reminds me of a guitar fret board.Thanks for the tips.
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Thank you. This was in very rough condition when I got it. Even the aluminum dial frame was green with corrosion. Fortunately it is cast aluminum and easy to remedy in my "Hillbilly Machine Shop (tm)". :D Three of the aluminum button caps were missing, and those I found were the price of a Jaguar. :eek: So I got the black aluminum buttons from @EastPoint which are a little fatter, and shorter. I used two 1mm thick black plastic washers for spacers to bring them out, which also still allowed the buttons to firmly "snap" onto the stems. The stem notches are 2mm spacing. I removed the black bushings from the "glass" because of the larger diameter and it looks just fine without them. The green reflecting off the holes also adds a "touch of coolness". :beatnik:
I really wish Sansui would have kept the midrange controls as in the 9090DB. But as you can see, there was simply no place left to put them. :p
 
BradWil said:
That is beautiful. Very well balanced and original looking colours. The 9001 dial reminds me of a guitar fret board.Thanks for the tips.
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One more thing. I used an Amber SMD LED (pre-wired) for the dial pointer lamp. They are so small, they can be used in almost anything with the appropriate resistor(s), and come in various colors. I used white for the Marantz that come as white to begin with. Even the red pointer looks good in some units depending on the dial lighting and face design.
 
Skywatcher said:
The green reflecting off the holes also adds a "touch of coolness". :beatnik:
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I actually really like that and may consider removing my black bezels (retaining them of course). Often we have little choice but to improvise and if you can get away with it looking great, that's a win/win in my books. Seriously hate paying for spares. I'd rather spend the money on someone who's put the effort into recreating a part, like the Tolitoms or @LBPete antenna base
 
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Skywatcher said:
Even the aluminum dial frame was green with corrosion. Fortunately it is cast aluminum and easy to remedy in my "Hillbilly Machine Shop (tm)". :D
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Were you able to remove that frame to treat and repaint? Also looks like you've done the aluminium paint well on the front of the frame. That must have been difficult to get even ...
 
BradWil said:
Were you able to remove that frame to treat and repaint? Also looks like you've done the aluminium paint well on the front of the frame. That must have been difficult to get even ...
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Yes, the frame comes off the face plate. With it removed, "Hillbilly machined", then cleaned, it was easy to paint masking off the front edge with painter's tape. I have a very flat piece of thick plate glass (checked it with a straight edge) and use spray glue to stick sanding cloth sheets to it. One side coarser grit, the other finer "finishing" grit. Then use elbow grease power. I also flatten out heat sinks. A lot of people don't realize just how badly they can warp from the heat. Some so bad only the flanges of TO-3 will be touching. Many TO-3P the same way with the screw tight, but the die having a gap. And threads will raise up too needing flattened down. 2 piece sinks like the 9090DB (and others) will warp and won't mate correctly reducing their efficiency. Then wonder why their output transistors keep burning out.
 
Here is the inner heat sink from one of my 9090DB. I had just started to Hillbilly machine it just to show how bad it was warped. You can probably tell which of the 4 outputs had overheated and toasted. The outer was also badly warped and needed flattened out to fully mate. You can also see how many screw holes had pulled and raised preventing the outer/inner from mating properly.

9090db inner sink warped.JPG
 
Skywatcher said:
Here is the inner heat sink from one of my 9090DB. I had just started to Hillbilly machine it just to show how bad it was warped. You can probably tell which of the 4 outputs had overheated and toasted. The outer was also badly warped and needed flattened out to fully mate. You can also see how many screw holes had pulled and raised preventing the outer/inner from mating properly.

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Wow, now that I did not expect!!
 
BradWil said:
Wow, now that I did not expect!!
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Very few people even think about it. Aluminum warps very easily. All they tend to think about is the "electronic" part, and not the physical part. I don't worry about the anodizing. I coat them with thermal compound anyways and that seals the surface. Sometimes I'll use black ink if anything shows. It won't hinder the transfer of heat to the air like paint does.
 
Skywatcher said:
. Just be sure to adjust the voltage to the quad boards to be at the "sweet spot" of 25v. That's where they perform best. A volt or so higher or lower won't "hurt", but won't sound the best. They are 18v minimum, and I believe 30v maximum.

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Does this apply to the 9090db as well? I only see a voltage reference of -25 on the F-2624 schematic.
 
BradWil said:
initial bias was around 250mA with the trimmers set to centre
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Just carried out some further testing and can confirm, as per Toli's advice, that the bias trimmers should be set to their minimum values (close to zero). It seems counter-intuitive to me but I am not an EE (and Toli is a PhD EE!) and the results are correct.

In this case min values equates to around 14mA on full power and simply dial up from there. Much better than starting off with 250mA ;)

I've edited the trimmer section above.
 
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BradWil said:
Diodes: including LED-1/2 installed. Note: cathode of LEDs to centre of board (to the bias trimers VR-3/4).

Trimmers: I chose to use Bourns 25-turn trimmers angled slightly to allow for better access with the trimmer adjustment tool. EDIT: SET BIAS TRIMMERS TO MIN RESISTANCE

You may get away with 100ohm max value trimmers for the bias as 200ohm seems a little high from the testing I've done. This will of course depend on the components used but in my case 100ohm should be ample as 30mA is achieved at approximately 20ohms on the trimmers.

Electros: Input caps C-01/02, originally Muse ES bipolar, have been replaced with WIMA MKS2 stacked polyester, with a slight lead mod. C-09/10 the Nichicon KA series were subbed for Panasonic FM due to stock availability. I may sub C-07/08 Nichicon KL caps for PW series in future builds, for no particular reason other than I'm used to working with them for PS applications.

Ceramics installed. Thanks T's for the lead spacing foresight!

Although I'm sure it isn't necessary on these boards (with quality pass-throughs), I am being pedantic with the double-sided soldering where possible :)

Next up heatsinks, drivers, pre-drivers and diffential input pairs.

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EDIT: The BIAS trimmers need to be 500 ohms ...
 
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