700B blew one Right channel 5A supply fuse

[laatsch55]

There's a lot more to go on that one before I solder them.

 

[62vauxhall]

Slightly off topic but I was wondering if one of the 700 versions is considered superior to the others?

And, I was also wondering what the consensus is about keeping amplifiers powered up at all times.

Quite a few years ago, someone I knew with fewer bad habits, therefore more money, used to change amplifiers every so often. One he had for a while (possibly a Bryston 4B) had no power switch. The philosophy was that maintaining temperature did not stress components and that made sense. During the few years that I used this 700B, I did likewise.

My job at the time was evaluating and replacing lost or damaged home electronics for insurance purposes. One claim was a house fire caused by an Akai power amp left on and unattended. Being aware of Phase Linear's reputation and now knowing of such an event and its consequences, I ceased leaving it on when not in use.

What would opinions be from long time Phase Linear owners? Turn them off or leave them on?

 

[Gepetto]

Slightly off topic but I was wondering if one of the 700 versions is considered superior to the others?

And, I was also wondering what the consensus is about keeping amplifiers powered up at all times.

Quite a few years ago, someone I knew with fewer bad habits, therefore more money, used to change amplifiers every so often. One he had for a while (possibly a Bryston 4B) had no power switch. The philosophy was that maintaining temperature did not stress components and that made sense. During the few years that I used this 700B, I did likewise.

My job at the time was evaluating and replacing lost or damaged home electronics for insurance purposes. One claim was a house fire caused by an Akai power amp left on and unattended. Being aware of Phase Linear's reputation and now knowing of such an event and its consequences, I ceased leaving it on when not in use.

What would opinions be from long time Phase Linear owners? Turn them off or leave them on?

I don't like paying our towns exorbitant electrical rates so I turn everything off that I can, including PL amps. The on off cycles give me an opportunity to test the reliability that was designed into the White Oak board sets.

 

[62vauxhall]

To install those round heatsinks, I need to spread the gap a little to get them on?

It seem best to put them on first before before mounting the transistors but before I do that, I wish to make sure that they go on with fins up top.

And do they need any compound or are they good as is? If they do need compound, can I use that grey stuff I posted pictures of earlier? I know I am not to use it on the output transistors.

 

[Gepetto]

To install those round heatsinks, I need to spread the gap a little to get them on?

It seem best to put them on first before before mounting the transistors but before I do that, I wish to make sure that they go on with fins up top.

And do they need any compound or are they good as is? If they do need compound, can I use that grey stuff I posted pictures of earlier? I know I am not to use it on the output transistors.

No compound needed.

You can put them on before hand if you like.

 

[laatsch55]

I found it handier to install the heatsinks before installing the tranny's. No goop.

 

[laatsch55]

If Joe's got ya, I'll go back to battling the the tall prairie grass....

 

[62vauxhall]

There are two ceramic disc capacitors (same one in each channel) where something affected their surfaces. I think it's cosmetic and unless I'm mistaken, that type of capacitor had a wax coating of some kind. My first thought was mold or spatter but since it's very near Q5 and nothing else is affected, maybe heat from that transistor caused the spotty appearance?

 

[laatsch55]

Phase Linear Factory Gremlins, you CAN NOT go under 300 watts output AFTER MIDNIGHT......

 

[62vauxhall]

Was about to start on the electrolytics but comparing the new one's with what's on the board, I think not yet.

Thought it best to ask what goes where.

What's on the board now:
C6 - 100MF - 25V
C11, C15 & C16 - 50MF 35V
C13 - 47MF 25V

What I recieved:
(2) - 470MF 25V
(4) - 47MF 100V
(4) - 47MF 25V,

 

[laatsch55]

470/25 volt go in C6's place, 47/100 C3. 47/100C11, 47/25 C15,16.....

And then the back to back 1N4148's on the trace side leads of C6. Leave them just a hair long and it helps...

Have you checked all the diodes on the board. If you had a bad Q8,Q9 some diodes can be bad....

 

[62vauxhall]

OK, thanks.

Leave the trace side leads long on C6? Both leads or just one?
What capacitor leads get the diode POS or NEG?
Is it diode POS to capacitor NEG or diode NEG to capacitor POS? Or, POS to POS - NEG to NEG?

I am not looking forward to replacing all those diodes. They're so friggin' small, I've had better vision and use a 40 year old (like everything else I have) Weller iron..

 

[laatsch55]

Don't replace them all, only the bad ones.. I'll post a pic of the diodes and how you orient them...

 

[laatsch55]

Both leads, leave em about an 1/8" long...

 

[laatsch55]

Here ya go.....

 

[laatsch55]

OK, thanks.

Leave the trace side leads long on C6? Both leads or just one?
What capacitor leads get the diode POS or NEG?
Is it diode POS to capacitor NEG or diode NEG to capacitor POS? Or, POS to POS - NEG to NEG?

I am not looking forward to replacing all those diodes. They're so friggin' small, I've had better vision and use a 40 year old (like everything else I have) Weller iron..

I have a couple 40 year old Weller irons, that's why I still have them...

 

[62vauxhall]

The board is done except the bias transistors which I'll get to tomorrow. I did wind up replacing most of the diodes because I thought it would be shame not to use some of those brand new ones you sent.

The new capacitors for C6 are a substantial deviation from what was there. What is the end benefit of using that capacitor with the dual diodes over a direct replacement?

I did not replace D12 because it was under a capacitor but I did test them and if I was supposed to get about 1/2 volt one way and "OL" the other they're OK.

I also did not replace D1 & D2 because they are incorporated in one or those "flying connections" Gepetto spotted. They are paralleled and in series with what looks to be a resistor not on the schematic. Here's a close up of the rogue 6.8K Ohm (blue/grey.red) resistor in series with the paralleled D1 & D2. Any idea why and if it was a non documented factory modification or aftermarket?

 

[laatsch55]

To answer the cap question first. C6 is in the feedback path IIRC, Joe will correct me if I'm wron here, and a 100uf cap chokes the low frequency response of the whole amp. A stock Pl starts to roll off around 50Hz. Skynyrds stock 700B started rolling off at 100hz. With the 470 in place it's almost FLAT to 10HZ. And I can attest in some music there is a lot of program material between 20 and 10 hz. It really is amazing what just changing that cap will do. The back to back diodes do this.......http://forums.phxaudiotape.com/show...-latch-up-tendency-in-Phase-Linear-Amplifiers

Basically keeps the positive rail from going to the speaker outs, which can happen at any time the board components have drifted enough in value that the front end doesn't power up in the right order.

The diode/resistor mod I have seen on about a 1/4 of the 700's with the PL14 board in em. I have a manual that has pretty good documentation on the Pl 20 board but if any existed for the 14 boards in 700's it's lost to the mists of time....

So you are getting close, this is the point in time where I have gotten excited and screwed up......be cool and deliberate...

 

[62vauxhall]

Yes, you sent that Gepetto post before and I did read it. Didn't retain it but I read it.

I'm taking my time with this but I know what you mean about getting excited and rush to the end. Been there done that. But I have an antidote for my enthusiasm - finding a job. I've been searching for a long time and it's tedious so I dug out the Phase Linear as another project with a reasonable chance of success. Unlike getting employed.

I enjoy tinkering with stuff and will get totally preoccupied until the guilt sets in which tells me there are better uses of my time. Since my last job ended and throughout a re-training process, I completely restored, in and out, six pairs of vintage speakers, refurbished about the same number of Dual record changers, a dozen or so 8 track machines, and rebuilt around 800 8 track tapes. Would have probably started a job long ago if my attention weren't so easily swayed.

Seemingly the masochistic type, I have standing by, a Teac reel to reel to resurrect when this Phase Linear is done.

 

[laatsch55]

It would be neat if you would thread that..