Retro Amp 50W Single Supply

[Jrp27]

Where i live the temperatures go upto 45 Degrees Celcius in summers. So i guess a fan cooled arrangement would be apt.

[indianajo]

With fans My output transistors are just barely warm on a 3 mm thick AL flange. Up to 14 hours per day use. Idle current set to 8mv quiet, up to 85 mv loud.
The beautiful heat sink posted previously by Mr. Finch is not available here from major distributors like Newark(farnell) or mouser. That wouldn't fit in my chassis anyway. Little shops that will sell it might stiff me for $30-40 shipping charge (other do about 25% of the time), so I don't like to use new suppliers. UPS from newark is about $8, mouser $12 minimum.
First picture, the dynakit ST120 overview with fan accessory, one AX6 board top, one dyna PC15 with djoffe idle current control accessory board bottom.
Second picture, the fan accessory removed from under the amp. Two PCAT power supply fans run at 9 v instead of 12 v nominal, from a wall transformer.
Third picture, the point to point AX6 board, component side. Nema CE laminate.
Fourth picture, the point to point AX6 board, wire side.
Fifth picture,left the OT current test points, middle the idle bias diode stack & pot, right a ground test point, mounted on top of the OT flange.
Fifth picture, the 80v to 70 V regulator for both channels. Replaces dynakit PC14. That is old Pentium II CPU heat sink; I can't buy more of these.
Sixth picture, the AX6 schematic as modified by me to center the output quiet voltage 1/2 of regulated supply voltage, for best 2nd harmonic minimization. Also the 68 pf input cap kills radio stations from coming in on the 3 m RCA cables from the RA88-modified mixer.
New AX6 is very quiet idle, quite loud on the 8 ohm SP2-XT speakers when signal calls for it. Overall sound very good.
dynaco PC15 board with djoffe bias mod is slightly better sounding on high bell on LST-7415 Martin Denny Golden Hawaiian Hits band 5 the Hukilau song. I'll investigate replacing AX6 VAS D44-R2 and drivers TIP41C-42C with faster transistors with lower Cob when I get another amp running reliably. And cut up some TV's for color deflection drivers, I can't buy these 2SC-2SA numbers except from e-bay (real or not?). The 2SC3423 and 2SA1837 I bought from Newark & Mouser turned out to be *****ese clone house instead of sanyo or toshiba, and in F packages with no heat sink tabs.

[Bruce@bluff]

Will the AX6 work off 75v supply and if I use 4 output devices instead of 2 ?

[apexaudio]

Originally Posted by Bruce@bluff

Will the AX6 work off 75v supply and if I use 4 output devices instead of 2 ?

Yes

[indianajo]

Quote:
Originally Posted by mjona
....why is the bias transistor not fixed to the main heat sink.....

That's a solution for the general problem with thermal compensation for any quasi-complementary design. If you use the heatsink as the reference temperature it won't track the bias correctly - often resulting in a fire-prone amp unless very low bias is used. A common solution is to use the air in the case somewhere near the heatsink but not on it, just as Naim does. As discussed and referenced in the other thread, exact bias for a quasi' doesn't really make much practical difference anyway - it can only offer a compromise of bias current and thermal coefficients that don't encourage thermal runaway.
__________________
Ian
close Quote
Above from the 302454-TGM10 thread
So I guessed right again. As you notice in pictures 3,4,5 of post 212, my voltage spreader diodes are mounted in the air above the output transistors to collapse the bias current gently if the heat sink heats up. They are mounted on a Cinch solder terminal strip, 5 terminals, with the adjustment pot paralleled by a clamp diode .5 Vf in case the pot wiper loses contact. The left 2 terminal strip is the test points for the bias current across a .51 ohm emitter resistor, the right 2 terminal strip is a test point for analog ground.

[junior35]

Joe,would it be possible for you to post clearer photos? Maybe better lighting or a lens cleaning will help with whatever you use to take pics.
Cheers

[indianajo]

Was a new 1024 line camera right out of the box and using a LED flashlight.
http://www.mcmelectronics.com/produc...9749-/82-19749
I've recently scored a tiny tripod and will try that.

[xXBrunoXx]

Hello Mr. Apex , I want to build the amp ( with KD503 , can't decide which transformer to use I have a toroid 26-0-26 Vac 3.5A( 170W ) and a normal transformer 200W or soo 17-0-17 8A ( I can put it in series and have around 70V DC on the first one and 40DC on the second one, the wire on the first one is 1.2 mm, I know 1mm is around 3A, on the second one is 2mm. ) Also which PCB do you recommend ? The schematic in post 1 is the one ?
I've read the whole post but there are lots of PCB's and " mods " and Im a bit confused.
Thanks !

[apexaudio]

Originally Posted by xXBrunoXx

Hello Mr. Apex , I want to build the amp ( with KD503 , can't decide which transformer to use I have a toroid 26-0-26 Vac 3.5A( 170W ) and a normal transformer 200W or soo 17-0-17 8A ( I can put it in series and have around 70V DC on the first one and 40DC on the second one, the wire on the first one is 1.2 mm, I know 1mm is around 3A, on the second one is 2mm. ) Also which PCB do you recommend ? The schematic in post 1 is the one ?
I've read the whole post but there are lots of PCB's and " mods " and Im a bit confused.
Thanks !

Use 70V DC
Regards

[xXBrunoXx]

Which PCB do you recommand ? The schematic in post 1 is the one ?. Thank you.