The ultimate dual 500 "rising from the ashes" build

[grapplesaw]

I guess the "bias resistor" might affect the bias circuit eh??

So why didn't you say something a week ago

ugh!!!'

30 minutes in and bias has dropped .012 v as heat goes up to 110'f. Output 1 watt (2.7v) 2k input with .121 N+THD.

Time to jack it a bit

 

[grapplesaw]

So pushed to 8 volts output and got jump again in bias by double to .8v . Sine wave very wide with multiple lines but in sinc high distortion


turned off and on with bias down to starting Bias.

Running at 8 volt out and stable. Then jump up to high bias again. Turned down voltage to 2.5v and bias dropped back for minute to normal then up high again with a wobble in the sine wave.

Turned off and back on ok again

note
bias in this drive channel read .5v right down to about 10v on rail

when repeat on off still shows 350mv on left and .53mv on right 2 volts on power caps

why one channel Doing this??!

 

[grapplesaw]

Going to get the canned air and find this thing

 

[grapplesaw]

15 minutes at 8 volts heat up to 134 and holding on transistors aux fan not working so problem there. Bias soots up again and amp overheat kicks in. Tried to get air can but all happened to fast. Cooling down with little blower and temp down to 120 and we are running again. I turned Bias down to .350v while passing 8 volt current to see what happens.

I think i will resolder all the backplate connections later today.

 

[laatsch55]

At that voltage out ya gotta have an oscillation to get that kind heat, I think....

 

[grapplesaw]

At that voltage out ya gotta have an oscillation to get that kind heat, I think....

Right. I got clean 2k sine wave and .05 % N+THD

stop for a little bit. I will run other channel under same conditions as see what happens



I will I'll upgrade to lf351 and change poet resistor to 7.5 k

i have bias turned down with veri resistor to about .2v not current and .35 passing current
when magor osilation happens the bias basically doubles what ever it is set at. That makes me think more bad soldering on back plate. The solder they used is shit.
I tried to spray cold air on verious parts at the higher bias. No instant change but with some time it recovers or overheats.

I will I'll run some more cooling and see what happens. I will try to find only oscillation at frequency. I will put on the computer and run the spectrum analizer as well.

Have gone from not running to now running and getting hot. So progressing.

 

[laatsch55]

It's been quite the battle....

 

[grapplesaw]

It's been quite the battle....

Yes Sir

here is cross hatch at 13 volts out 2k sine. First right the left

 

[laatsch55]

What's the middle line in the first 2 scope shots?

 

[grapplesaw]

What's the middle line in the first 2 scope shots?

Cross hatch ( bias )

 

[grapplesaw]

Can we say "Zobel"

It seams we may have a runner now. I tested the Zobel cap earlier in the week and it was fine but chose to only replace 10 ohm resistors then With continued problems. With new .1uf 100v poly cap and we have stable amp. Will work on proper bias setting vs heat tomorrow. I started low and have come up to .325 V with heat ok at 10,15 and 25 volt out at 2 k for 15 minutes each.

well Joe called it once again. Thanks everyone

 

[Northwinds]

Awesome to see you finally making progress Glenn!!!

 

[grapplesaw]

Ok just finishing up. 560 watts channel 8 ohms with AC line input about 110 volts so it can do better at 120v.

here are a couple of shots.

Edit: This has been a test of patience.

 

[grapplesaw]

Playing Santana

The tunes are pumping out. Nice clean sound , not hiss or hum.

 

[laatsch55]

Good job Glen!!!!

 

[grapplesaw]

Good job Glen!!!!

Thanks Lee
All of those who sent their ideas and
Ed helped me get there.

 

[WOPL Sniffer]

Ok just finishing up. 560 watts channel 8 ohms with AC line input about 110 volts so it can do better at 120v.

here are a couple of shots.

Edit: This has been a test of patience.

Very cool.
Great job

 

[grapplesaw]

So have had #1002 running today. It is preforming exceptionally well. I put the wood finish on it.

 

[laatsch55]

Coolness....

 

[Steve crane]

First step is take it apart. If any one knows how Phase linear Serial numbers work please pipe in

This unit is 1002. I am making up that it is #2 built. She is named Val

That's are many parts with date codes from 1977. The control boards are consecutive part numbers.

Here is some history on the 500

http://www.phaselinearhistory.stereomanuals.com/d500amp.htm

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