Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thread

mlucitt · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Installing the diodes solved the problem completely. I now have the main power fuses in and both channels driving a 400Hz test tone with the pre-driver transistors installed.

Thanks, Joe. This is a great mod to the board that will allow many users to get up and running quickly.

Mark

mlucitt · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

With just the pre-driver transistors in (Q11 and Q12) here are my outputs. They are a little fuzzy because the storage function on my 466 o'scope needs some help. The test signal is on the bottom and the output is on the top at about 50% "volume" in order to prevent clipping. Channel B (right) looks good but channel A (left) looks like the negative going signal is missing. Is this related to Q12 in the left channel? Maybe my Q6 is weak?

Remember, this amp never worked for me before today.

Thanks,
Mark
[attachment=1:hon3ncts]Driver Only Output Right Channel.jpg[/attachment:hon3ncts]
[attachment=0:hon3ncts]Driver Only Output Left Channel.jpg[/attachment:hon3ncts]

Gepetto · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Hi Mark
Good timing, glad it solved your problem. Just coincidence that I was completing the SPICE modeling showing this at the same time you were finding it in the wild.

I cannot help but think that this finding is one of the weaknesses that has given PL the reputation for eating speakers over the years. Probably others yet to be discovered but this latch up condition is real in the original design. It will only latch in the positive direction BTW.

mlucitt · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

I cannot imagine any speaker or array capable of handling +100VDC for any amount of time.

Yes, that was my experience. I had the - power rail supply fuse in both channels with no problems. When I put in the + power fuse, it would latch up with the positive voltage on the output depending on which channel was powered. For example, when I put a fuse in the left channel + power rail supply, the left channel output would go to rail voltage. When I put a fuse in the right channel + power rail supply, the right channel would go to rail voltage.

Mark

mlucitt · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Just another random observation. The board has been running for several hours with a .707 VRMS 400Hz input. The volume has been varied but left mostly at the 50% signal level. All of the transistors on the board are running cool with the exception of Q5L and Q5R which are very hot to the touch.

My supply voltage is 119.5 VAC (right now) and the rails are perfectly balanced at +99.6 and -99.6.

Mark

Gepetto · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Mark
Q5R and L are the only 2 transistors on the board doing any real work, that is normal and expected. The other transistors are well overrated for their tasks. Q5 is a transistor that operates in class A mode and sees the full 200V limited in current by R17 and R18 in series. You are likely to feel some heat in R17 as well. Phase had it as a 1W resistor and White Oak has upgraded it to a 2W resistor.

Gepetto · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Did you find the cause of your signal distortion on your left channel?

BTW, due to the grounding changes (improvements) I have made in my amps, I run 2.7 ohms in both R2L and R2R.

mlucitt · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

I have not yet resolved the distortion. I am going to change out Q12 first because that is easy. If there is no improvement I will change out Q7L and then Q6L because they will take a little more work.

I also used 2.7 Ohm resistors for both R2R and R2L.

I'll let you know what I find out.

Mark

Gepetto · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Check that you do not have D13L in backwards Mark. With only the predriver Q12 installed, you need D13 functional to provide base drive for Q12

mlucitt · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Both D13L and D13R have the cathode facing up on the board in the mounted position. When I replaced Q12, I powered the amp back up and the signals look good. I'm measuring 5 VAC on both channels with just Q11 and Q12 predrivers installed. I think it's time to put in the rest of the outputs.

mlucitt · Jul 31, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Ooops premature results above. I did not have the power rail fuses in, duh. So the replacement of Q12 did not change the symptoms and I am back to replacing Q7L. I'll report the findings.

Mark

mlucitt · Aug 1, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

I found the cause of the distortion on channel A. I had a open resistor that I had not seen before. This is R39 and it normally supplies B- bring-up to Q12 and sets the quiescent base voltage for the negative half of the output power transistors. Am I close because that was a stream of conscienceness?

Here is what I found. My PL700B is now happily running in pre-driver mode. I will install the output transistors tomorrow.

Mark

Gepetto · Aug 1, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Glad to see you found the culprit Mark. You have to look carefully at these old frames for cracked parts and aged solder connections. Hope you are enjoying great music soon out of that old 700B.

Gepetto · Aug 1, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Looks like that 10 ohm puppy was fried...

laatsch55 · Aug 1, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Gepetto said:

Ah Joe.........man, i have layed awake at nights wondering what happened to the 85+ Dc i saw on first power up!!!!! had it happen intermittenly to a cou[ple amps I was workin on AND DROVE ME NUTS!!!!1 that's the difference between an ELECTRONICS ENGINEER and a parts changer!! amn I'm glad your're on our side!!!!

laatsch55 · Aug 1, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

mlucitt said:

DUDE!!!!! you are,I haven't a clue what you're talking about most of the time.

mlucitt · Aug 1, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

I have already penciled in the 1N4148 diode pairs in the schematics Joe sent us...
I wonder if PL would still be in business if they had described adding those diodes in Service Bulletin #7722? Of course, they did not have the benefit of SPICE modeling but it makes you wonder...

Mark

laatsch55 · Aug 1, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

If Joe was at the helm, Bob would be much richer than he is.

Gepetto · Aug 2, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

Lee
I am very pleased with the change, that meter bounce on power up always bothered me but I lived with it, not knowing that it could be easily fixed. Now it is gone for good in my 2 amps. Would like your experience too once you put the change in.

Joe

laatsch55 · Aug 2, 2011

Re: Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thre

I'll do that tomorrow Joe on Jer's 700, sounds like ..........damn, it just keeps gettin better.
WHY did it lockup, did i miss it in your previous posts??

Jerry's " ONLY ONE IN THE COUNTRY" Phase Linear 700 Thread

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