ebay Phase Linear 700B rescue

[Billboard]

Just received the 700B that I purchased on ebay, The description said it sat in a shed for many years. I ordered a few cleaning items, such as no residue cleaner, contact cleaner, metal polish, and plastic polish.

The amp is missing all but one fuse caps and fuses, missing the big capacitor hold down strap, the hold down strap bolt is broken. Also the amp has a broken transistor Q5 is physically bent over and one of the leads is loose.

Waiting for the fuses and fuse caps I ordered to arrive, now I need to find a replacement for Q5. The amp looks un-molested and can't wait to dig in and get this beast running.

I would like to get it running before I look into modifications, the first will be a Whiteoak main board and LED update. In time I would like to convert to a full complimentary output using the Whiteoak back plane boards.

I will keep everyone up to date on the restoration, I am sure I will have lots of questions, if anyone here can get me a Q5 (40412V1) please PM me and I will send a paypal payment.

 

[laatsch55]

The cap hold down bolt is a 10-24 threaded rod. What did they have in place of the left channel 40412V???

 

[Billboard]

no idea what they used on the left channel Q5, the board is a pl20A, here is a better picture, the bottom of the board has flux on all of the
semiconductor pads, maybe someone replaced all of the semiconductors?

 

[laatsch55]

Maybe, part numbers are correct though.

 

[Billboard]

Received the fuses in the mail today, turns out I only ordered two fuse caps instead of four, I am sure I have some kicking around.

i need to build a DIm Bulb Tester, should have that by the end of the week.

i will keep everyone posted.

 

[Billboard]

PL700B is finally on the bench, I wanted to get my PL400 DCP board installed before I tackled this project.

It looks like the amp was dropped while it was rack mounted, the body has shifted a little, also every illumination lamp except for two has a broken lead.

I have the replacement transistor, fuse caps, so should be ready to go.


First look at the outputs and they do NOT look shorted. I plan on having the missing transistor replaced and attempt to fire it up with a DBT.

I will report back with what I find.

 

[Northwinds]

Crossing fingers for ya brah

 

[laatsch55]

Amen, pray for no smoke....

 

[Billboard]

No Smoke, but not 100%

I installed the replacement for the defective 40412V1 transistor, I used a 2N3439.

Fired the amp up on the DBT all looks good at this point, rail voltages were approximately 90 and -90 (I didn't right it down), the DC at the speaker terminals were R 60mv, and L 23mv.

So I put a set of speakers on it (Baby Advents, don't care if they caught on fire) and played music with my iPad, sounded good low volume level, but the left output transistor were getting hot, so hot it tripped the thermal cutout.

I waited for it to cool down a bit and grabbed my IR thermal thermometer and the right outputs were running at about 110 degrees F, and the left was running over 140 degrees and climbing. So I shut things down for the night.

I need help with this

The right side has 10 PL909 outputs using a SJ2741 and a RCA410 for drivers
The left side has 10 2SD555 outputs using two RCA410s for drivers.

reminder I have no idea who or why anyone has done what they did to this amp.

 

[laatsch55]

Highg heat is USUALLY a bias issue, USUALLY, but not exclusively. Have you checked bias ?

 

[Billboard]

No I have not, I will check in the morning.

Do the output and driver transistors look oK, I would think the drivers should match on the right channel, but that side seems to be performing normal.

 

[laatsch55]

The drivers do not have to match , the outputs have to be the same on the same channel.

 

[Billboard]

Bias adjustment, target 300-400mv:

as found Right R38/R39 493/460mv
as found Left R38/R39 600/592mv

max adjustment R20 max adjustment
Right r38/r39 388/305mv
Left r38/r39 348/381mv

I ran the amp for a few minuets and it stayed much cooler, transistor temperatures were around 100F

 

[Billboard]

One question before I tear it apart and start cleaning it, the gain seems low.

With the amp connected directly to my iPad and a set of baby advents the gain seems low.

I was able to turn the iPad all the way up and the amp input adjustments all the way up and the speakers did not turn into a ball of fire, in fact the meters were just coming off of the low end.


Is there not enough output form the iPad headphone jack to drive the amp or do I have a problem?

 

[WOPL Sniffer]

I used my Ipod and it worked enough to test, but a good clean Pre is needed. You will notice when you switch.

 

[laatsch55]

Max out on a 700 requires 1.75 volts input.

 

[orange]

To me, that's incredible.

 

[Billboard]

Now that I am resonably sure the amp runs, I am going to make it a little more presentable, the poor PL700 meust have spent 20 years in a backyard shed,

How do you guys clean up the meter surounds? steel wool and some flat black spray paint? I did see a couple of guys powder coated them, seems a little overkill, but I am willing to go that route if that is what is recomended.

I took apart the faceplate, and cleaned it up, I am not going for perfection, just want to make it look like it doesnt belong in my basement. I cleaned the face plate with Simicrome and a buffing wheel.

The meter clear plastics were cleaned with Novus PC-10 cleaner, I am too afraid to touch the meter faces, and they dont look too bad anyway.

The knobs were cleaned on a cotton buffing wheel with different compounds ending with Simichrome for a final shine.

 

[laatsch55]

Nice ressurection on the knob....

 

[Billboard]

Nice ressurection on the knob....

Thanks, one of them flew from my buffing wheel at about the speed of sound across my basement, luckily I was able to find it.

It was pretty funny, no one was injured, good times...