Recording Studio Design 800B

[ksrigg]

Hven't done anything on the active crossover yet. I have been trying to get the RSD running, and working on the Phase Linear 700B. I think the PCB arrived today, os I am ready to proceed. I now have everything in hand. I also found Joe's email to me concerning the wiring of the meter board in my email that I ususlly only use for PayPal. Didn't know it was there, os it's printed and I'm ready to start working with it. I don't get much done on weekends as it is family time, and during the week it is chore time. I'm now painting upstairs...so I'll have to find time to work on the 700B.
For the Active Crossover, I have to make sure I have enough 1/4" to RCA adapters. I know I do, just got to round them all up. I really wanted to have the 700B finished to use as one of the amps for the bi-amp...but looks like I may have to pull one from the rack to double check my wiring of various things anyway against Lee's work..

 

[laatsch55]

This has got to be a PL 400 clone. It's running 2N5415 for the negative pre-driver and 40327's for positive pre-drivers. Still peruising pics. Built much better than a 400. Wish I could sick the AP on it.

 

[laatsch55]

Sutton are the 2-non-heatsinked TO-39's 1304's and 1305's???

 

[laatsch55]

Sutton, on pic 0455, the first 2 resistors from the bottom up that span 2 traces, are they 150 ohm 1 watt??

 

[Gepetto]

Sutton
I do not think this amp has sockets for the power output transistors. It looks to be built like the Crown DC-300 where the transistor Base and Emitter solder directly into the backplane board.

 

[ksrigg]

Yep, Lee .....one of the non-heat sinked transistors is a 2N1305, and the other carries NO MARKINGS...almost like they have ben wiped off...and Yes, the two resistors are 150 ohm...or really close...looks like 148.7 and 149.4 or something...but sure enough they re 150 ohmers. and there are sockets behind that PCB wall...I removed one of the transistors just to make sure. You can kinda peek and get a glimpse of black plastic...but the transistor will come out..so it does appear to be a Phase Linear clone, using RCA 410's and 3773 instead of the Phases drivers and outputs, although they may be the same thing in one of the 400's interrations...

 

[laatsch55]

No , 400's never had 3773's. Put your mini grabbers on each side of the 150 ohmers and see what ya get. This should bwe just like measuring accross r38 in the 400 and 700 for the bias. The pot on the bottom PCB is what they call a "thumbwheel" pot. That should be the bias adjust pot.

 

[ksrigg]

OK....The wife has me taking pictures of Karli, our 12 year old, for aBeauty Pageant which is tomorrow, and this is for the Most Photogenic so may be a half hour or so. I was just told to get the camera ready...."We are loosing light..."

THANK YOU GUYS.......................

 

[laatsch55]

Yep, gotta go to dinner at a ranchers place 60 miles north of town. Jani's cousin who's land borders hers up there. It's usually a good time and I need to get Jani out of the house. Be back around 9.

 

[ksrigg]

Bias is currently at 572 mv for right channel and 585 mv for the left channel. I wonder where it is suppose to be.500MV.....550 mv......575 mv.......or 350mv...? I don't have any more idea now than I did before I took the readings...Does bias have a tendancy to go up or down oer time? I must defer to those of you who could make an educated guess, knowing what we know about this amp, its' components, circuitry and vintage...

 

[laatsch55]

Move the thumbwheel back and forth, see if it affets it. Are the heatsinks warm at idlew??

 

[ksrigg]

I checked bias on the top resistor on that board, and it was close to 350mv. Moving the thumbwheel, I took each side to 350 mv. I think this must be the proper place to measure. I changed out the transistors on one channel of the amp to new 3773's and 15024 drivers. I now have to do the other side. As soon as I can get some larger clamps, I'll try to fit the 35,000 uf 80VDC caps in place of the 10,000uf 75 VDC caps, and I think I will have done about everything I will do to the amp. It is soundeding better and better the more I play it. There is no real noticeable difference in sound form the new and old transistors. Just having ones that are about 35 years younger in the amp makes me feel better. I think it sounds pretty darn good. The build quality of this amp is awesome. It really looks and feels far superior to the PL build...I just wonder if they quite producing this amp because it was an infringement on PL copyrights or whatever. The transistors barely get warm at full power with the massive fan pushing all that air. Man, it is one nice amp..

It even has the turn off thump about 5 seconds after shutdown...

 

[Gepetto]

They must not have figured out the Rev C secrets Sutton

 

[ksrigg]

No, it doesn't have your PCB. I wish you and Lee could have some time with this thing to see what the Brits were up to with this amp. I think they may have figured a few things out from Bob's initial design and it's inherent issues...and everything I can SEE are all contained on the four boards...so I don't know where all the emitter resistors are, or if it is a different design altogether...my only real issue with the amps is the fan is SOO loud....of course this was a touring amp so it didn't matter...
I can't imagine the turn off thump with racks and racks of these things after a Pink Floyd Concert..

I did put all the new transistors in her and she does sound very good now. I hope I can get the larger caps to fit...and hope that will give me a little more transient and bass attack...but it may be the fact that I'm only listening right now with 6 1/2" woofers...

 

[laatsch55]

Not a bad call from 2,000 miles away. Glad to see it's working right.

 

[ksrigg]

Yep..............you called it right on the money. I wonder why they removed the designation from the non-heat sinked transistor....and left the designation on the other one? Just a batch with no markings? Wonder where the emitter resistors are?

It has some pretty Mullard Tropical Fish capacitors on the boards...and looks like they must have gotten a hadle, of sorts, on the oscillation tendancy in the PL amps...BUT...it looks like it did go in for service in 1978 and had all the outputs replaced, but I don't know that for certain....heck they may have replaced the outputs with 3773's to help with oscillation. Are they a slower transistor than the ones PL was using at the time, or what would the logic have been in using them over others that were available during the 1977 time period? I may be trying to figure out something that didn't even happen...

After I try to get the larger caps to fit in her, she may have to come visit you just so she can show off. I'd love to see what you think and for your analyzer to put her through her paces...maybe there is a better choice for drivers and outputs...and you could find out the best ones to use..

 

[kevin]

OK....The wife has me taking pictures of Karli, our 12 year old, for aBeauty Pageant which is tomorrow, and this is for the Most Photogenic so may be a half hour or so. I was just told to get the camera ready...."We are loosing light..."

THANK YOU GUYS.......................

LMAO..... By all means !!!!! Call in the dogs and piss on the fire..... Trish has spoken !!!!!!!

 

[ksrigg]

She won Miss Photogenic, and WalMart made me sign a form saying I took the photos...they thought they were taken by a PRO. Yeah ME !!

 

[kevin]

did ya tell them you got all your practice from taking pics of amps and stuff......

 

[laatsch55]

Send her on any time Sutton. I'll put her through the paces.