The ultimate dual 500 "rising from the ashes" build

[grapplesaw]

I like the green look in there. And your bench is looking more normal every day....

Thanks Lee
I am glad to see you made it home safe and sound.

The bench is always in flux, mostly downhill, I like the home feel this way.

 

[laatsch55]

Me too bud....

 

[grapplesaw]

I found this in my date bank for connecting Whiteoak board to comp PL backplane

 

[grapplesaw]

I have been putting off buying some parts. I made a list for Mouser and was a little overwhelmed with what I needed. So while watching the tube I did a little price check

the mj21196g are $3.10 for 100
At www.rocelec.com Rochester electronics in Ma states there are an authorized ON dealer
their price is only $2.30 each for a 100. They claim to have stock

so if I get 100 -mj21195g and 100 - mj21196g then that is $160 difference

anyone gone to this company for supplies? And advise is appreciated.

 

[laatsch55]

Good price on the MJ's.....

 

[grapplesaw]

Good price on the MJ's.....

Yes they are but is the Seller credible?

 

[Gepetto]

Yes they are but is the Seller credible?

they are not one of the Nationals Glen. Dubious they have the inventory they are reporting. ON doesn't even have that inventory level. Usually these small regionals pull from manufacturer stock when they get an order. They don't like to tie up their money in inventory either.

 

[grapplesaw]

they are not one of the Nationals Glen. Dubious they have the inventory they are reporting. ON doesn't even have that inventory level. Usually these small regionals pull from manufacturer stock when they get an order. They don't like to tie up their money in inventory either.

Thanks Joe. I have learned from the hard knock hotel that what looks to be to good to be true is to good to be true

 

[grapplesaw]

As I work down my list to purchase I question the use of the Zobel network resistors. The old Carson ones are way out of spec. I have some 5 watt Dale 10 ohm wire wound ones that I would use. Joe has gone to dale 2 watt metal film. Do these resistors effect the sound path if I use the wire wound ones. I know that the wire one have some inductance and that is my concern.

input please

 

[laatsch55]

Bad place for wire wound, yes they affect the signal path....

 

[grapplesaw]

Bad place for wire wound, yes they affect the signal path....

Right. Though as much

 

[Gepetto]

Right. Though as much

Double right Glen... The purpose of the zoebel is to counteract inductance in the speaker wires and speakers at high frequencies so you do not want inductive resistors for that. No inductive WW resistors for the emitter resistors either. For that matter, no inductive resistors anywhere inside a PL amp.

 

[grapplesaw]

Double right Glen... The purpose of the zoebel is to counteract inductance in the speaker wires and speakers at high frequencies so you do not want inductive resistors for that. No inductive WW resistors for the emitter resistors either. For that matter, no inductive resistors anywhere inside a PL amp.

Thanks Joe

What about the R1 and R2 7.5k 5 watt and the R101 and R201 7.5 K 2W , I had been using them there?

 

[Gepetto]

Thanks Joe

What about the R1 and R2 7.5k 5 watt and the R101 and R201 7.5 K 2W , I had been using them there?

R1 and R2 are just dropping resistors for the shunt regulators so no issue there. If the 7.5K 2W are the collector resistors for the class A amp section then no way. I will check those reference designators but I think those are the ones. Use metal film or carbon film for that application.

I checked the service manual and definitely no WW in location R101/201. These are directly in the audio path, the class A amplifier section and within the feedback path.
Use Metal film, carbon film or MO for these locations.

 

[grapplesaw]

R1 and R2 are just dropping resistors for the shunt regulators so no issue there. If the 7.5K 2W are the collector resistors for the class A amp section then no way. I will check those reference designators but I think those are the ones. Use metal film or carbon film for that application.

I checked the service manual and definitely no WW in location R101/201. These are directly in the audio path, the class A amplifier section and within the feedback path.
Use Metal film, carbon film or MO for these locations.

You the man Joe!!

thanks

 

[grapplesaw]

I made room for a dual 500 I got from Ed. He was busy moving so we made a deal. It was reported to have runaway over heat in the A channel. I checked main caps then put power through th DBT without fuses. Nothing was sucking big power but could only get it to 95 volts across the rails (240 rail volt amp) not to unusual. Powered direct from the Varic and brought up to 160 volts which is the lower of this amps two operating rail voltage choices. Was looking for something in the bias that was overdriving and causing heat. The bias was low at .270 each channel. The alarming thing is the DC offset was Hugh. 1 volt DC before adjusting bias to .360 mv and 1.4 after in the suspect channel. The other was high at .218 and .280 respectively. I tested each channel without fuses and the offset was larger by themselves

any ideas anyone?

 

[laatsch55]

PL36 board??

 

[grapplesaw]

PL36 board??

It is a pl32 board which is a pl36 with addition circuit for detecting high frequency isolation which turns down input voltage to the board till it stops. The bias circuit is different only by one resistor value. To sum it up aside of the high frequency circuit they are the same.

 

[laatsch55]

LF 351??

 

[grapplesaw]

http://forums.phxaudiotape.com/showthread.php/6202-Phase-Linear-Dual-500-schematics

Link to segmatics here