fitz43's Phase Linear 700 B White Oak Conversion

[laatsch55]

Ladies and Gentleman!!! IT'S ALIVE!!!!!!!!!!!!!!!!!!!!!!!!! A non-exciting initial power up is always GOOD!!!
Bias and offset voltages........ hard to see the offsets , but they were .001, and .007

 

[fitz43]

Lee, for the uninitiated like myself, what is the significance of using 2SD555's as drivers?I'm assuming they are different than the stock part used. Do they supply lower noise? higher gain? thanks. Doug

 

[laatsch55]

The 2SD555's were and NEC product and ity and it's compliment the 2SB600 were used in a lot of amps. It was a hot rod 40 years ago and still is. The significance for them being in the driver role is to be determined./ They were the standard output for quite awhile for the PL stuff from the factory. Thefore they did not use them as drivers, couildn't have the drivers and outputs being the same device. Higher gain is the objective, and foolish as I am sometimes haven't even checked the data sheets for the figures on that. Already a glaring difference was the amount of adjustment to obtain the desired bias. Whether it's in the hoped for direction is still unknown. I'm really interested to see if the little crossover notch is still present. This amp had it also starting about 15K and could be dialed out with enough bias. It will be interesting to see if the changes made had and effect on all this. One thing about bthe NEC devices, they SOUND good. They are excellent in my Spec 2's.

Gonna be a few hours before we can test. Just gota call. Gotta go.

 

[Pure_Brew]

I have those exact devices in my PS Audio amp. One of the best sounding amps I ever owned. Too bad it's on the fritz.

 

[laatsch55]

Well we've been known to fix an amp or two..........................

 

[laatsch55]

Preliminary tests conclude the 2SD555 may not be a good candidate for a driver. Getting some oscillations. Got a couple more things to check.

 

[laatsch55]

Just ran FR and THD & N withg MJ 15024's as drivers, everything cleaned up and normal. I can say withpout reservation the 2SD555's were a BAD idea for drivers.

 

[Gepetto]

What's with the dual trace on your plot Lee?

 

[laatsch55]

Now, all of this is taking place with no faceplate, no meters, no meter board, with the wires cut and hanging. Pots not grounded to the chassis. Joe---will this configuration have an adverse effect on THD & N??

 

[laatsch55]

That was the Frequency response graph. It will graph both channels in "Level" mode but only one in "THD & N mode.

 

[laatsch55]

This has me a wee bit concerned......

 

[Pure_Brew]

Well we've been known to fix an amp or two..........................

Your inbox is too full

 

[laatsch55]

Sorry Joe. I'll get it tidied up.

Right channel, 5KHZ

 

[Gepetto]

Yeah you have some wierd stuff going on with this frame Lee...

 

[Gepetto]

Somewhere around 140-150 Khz the best I can gauge from your scope shot

 

[laatsch55]

Well, god I hate admitting this ----BUT--- I did not have the 1304's 1305's soldered on all three legs, just the base leg to hold em in place. Things gt hot, lost a rail fuse and then they got real hot. Took out Q1Q2Q3 on right and Q1 Q3 Q4 on left. I'll post a pic. I'll get these swapped out and see how it looks then.

 

[laatsch55]

Back up to snuff now. Lookin good. Final test results in the morning.

 

[Pure_Brew]

Sorry Joe. I'll get it tidied up.

Right channel, 5KHZ

Dooood, you found a DNA strand!

 

[laatsch55]

That's exactly what it looks like isn't it??

 

[Gepetto]

Have you switched over to your new Tek scope yet Lee so you can USB connect it to your computer and capture traces using that method?