RainDog's 700B resuscitation

Oh yeah.. good supply of AGX fuses... 5 and 8 amp.. plus (optional) 1 or 2 amps for initial power up (Joe mentioned that trick of using the lowest rating fuses for the FIRST time you power it up after working on it, as an added safety factor).
 
Yes, new transistors coming my way. Can you please spec the caps that are needed on the bridge rectifier and 4uF caps you mention? I still get a little lost on when to use which type of cap.

Seems like silpad and mica + grease isn't a 100% consensus. Joe recommended the silpads. I'll have both on hand.
 
RainDog911 said:
Yes, new transistors coming my way. Can you please spec the caps that are needed on the bridge rectifier and 4uF caps you mention? I still get a little lost on when to use which type of cap.

Seems like silpad and mica + grease isn't a 100% consensus. Joe recommended the silpads. I'll have both on hand.
Click to expand...

Gotta get some BR caps myself and a few other things. Haven't spec'd 'em in awhile, so I'll need to review past orders.. Lee might know quicker...
 
.01uf 400 volt polypropylene for the bridge, self healing. For the backwall we are now spec'ing .33uf/100 volt poly's also.
 
RainDog911 said:
Some pictures attached. Disclaimer - my workmanship is better than what is shown. As soon as it is working properly, all wires are shortened to a proper length, re-terminated and ty-wrapped.

Resistors on DCP - Large blue bodied, 6 ohm, look to be 5W or so?

I measured from chassis to the body of each output transistor and driver. I read from 1.1 to .8 ohms. Does this indicate a partial short?

Battery crapped out before I could photograph the last tower and right side of the PL14_20.

View attachment 11789View attachment 11790View attachment 11791View attachment 11792View attachment 11793View attachment 11794View attachment 11795View attachment 11796
Click to expand...


Yep, you should read infinity or 300-400K depending on the polarity of the leads...
 
I've never seen Joe recommend sil pads, have not seen him use them either, after they are torrqued up and seated , you don't want to use them again. Better heat transfer with Mica and grease, We KNow, a PITA but much better.
 
The one rhing that can drive you crazy is an intermittent short caused by something between the socket and rhe chassis. It's not a myth, it happens...
 
laatsch55 said:
Yep, you should read infinity or 300-400K depending on the polarity of the leads...
Click to expand...

OK, so I probably have poorly insulated transistors and that is turning the amp into an alarm clock. Joe sold me Bergquist Sil-Pad Transistor Thermal Pads with the transistors. I'd assume that counts as a recommendation...

Does anyone know the part number or specs on the bridge rectifier?
 
Showing a low resistance between the collector of the TO-3 and the chassis does not mean a shorted output. There are a lot of things that can short to the collector of the outputs. This is where it gets fun...
 
Relief!

While I let this thread stagnate a bit, I was spending all my free time either waiting for parts or working through issues on this amp with guidance from Joe.

A quick slip of the meter probe across Q1 C and E leads promptly caused Q1, R37R, R37L, R81, D80 and VR1 to earn a very short meantime between failure rating. Not having a warehouse of parts available, I waited for Mr. Mouser to deliver reinforcements.

Once repaired, the WO PL14_20 board was reinstalled. Since my last post, I found a sneaky RCA input to normal/direct switch ground reference. I added all the capacitors listed in the WO single point grounding scheme. I also bought new MJ21196 output transistors and new RCA 410s for drivers.

She fired up with out the alarm clock buzzing noise coming through the speakers. I have a DC offset of -0.08 VDC and bias holds nice and steady at .380 VDC.

I hooked her up and let it rip. What an amp! It is smooth and responsive. Quick but not harsh. Detailed but natural sounding. Clean and quiet. As a matter of fact, it revealed a low amount of hum coming from my turntable. I'll have to get after that...

Now I'm watching the backplane thread. More gears are turning...
 
If you worked through those issues you're ahand Bud. I cannot tell you how many probe slips I've had, but some were utterly spectacular...Good Job, it's hard to tame the beast, but well worth it when you're done.
 
When you guys run your 700B, do you keep the L/R volume pots at 100% and use your pre-amp for volume control?

I'm not sure I trust my meters. With my meter switch on 0db, I drive my speakers to pretty anti-social levels and the meters stay in the lower 1/3 of the range. I'm driving JM Labs that run about 91db efficient. Does this seem right? Is there a calibration procedure for the meters?

Lastly, do transistors 'break in' like speakers, caps and tubes? Will new transistors change their sound characteristics to any appreciable degree over time?
 
RainDog911 said:
When you guys run your 700B, do you keep the L/R volume pots at 100% and use your pre-amp for volume control?

I'm not sure I trust my meters. With my meter switch on 0db, I drive my speakers to pretty anti-social levels and the meters stay in the lower 1/3 of the range. I'm driving JM Labs that run about 91db efficient. Does this seem right? Is there a calibration procedure for the meters?

Lastly, do transistors 'break in' like speakers, caps and tubes? Will new transistors change their sound characteristics to any appreciable degree over time?
Click to expand...
View attachment Phase Linear Meter Calibration.pdf
 
RainDog911 said:
When you guys run your 700B, do you keep the L/R volume pots at 100% and use your pre-amp for volume control?

I'm not sure I trust my meters. With my meter switch on 0db, I drive my speakers to pretty anti-social levels and the meters stay in the lower 1/3 of the range. I'm driving JM Labs that run about 91db efficient. Does this seem right? Is there a calibration procedure for the meters?

Lastly, do transistors 'break in' like speakers, caps and tubes? Will new transistors change their sound characteristics to any appreciable degree over time?
Click to expand...

Try the procedure, it is easy. My experience is that the meters are quite close from a calibration perspective. You have to get used to all that power.
 
RD, you have very close to 500wpc on tap man.....it does take some getting used to.
 
Indeed, it is about 5x the power I'm used to so I'm certain to go through some conditioning.

Thanks for the document, Joe.
 
I am happy for you man! Someday I hope to have the same problem :mrgreen:
 
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