Power transistor help

[George S.]

If everything was good with 3 rows in, then a issue with the 4th, you probably have a grounded case. When you snug those transistors, STOP as soon as the silpad edge starts to curl or wrinkle. Get down close and personal and really watch the sil pad edges, especially by the bolt end ears. None of them are installed tight, just barely snug.
And I cut the high spots off the heatsink holes with fine cut wet and dry sandpaper under a finger tip before assembly. Very important there are no burrs or ridges to puncture the silpad.
If you haven't done so, do as Sniff said, pull the 4th row, retest for bias. If good, check for burrs, reinstall 4th row carefully, retest bias.

 

[WOPL Sniffer]

Id assume to test the C and E voltage, the amp is powered up. Red lead on C from meter? Black lead on meter to copper bus? And than the same for E terminal?

Be careful, one slip and it's all over. You need to check the earlier stuff first, if the 3 rows of transistors worked (with good Bias voltage) you got other issues.

 

[George S.]

If you have the 4th row out, and no bias, then you have more issues. Joe does have a way of bypassing the bias transistor, but can't remember as I've never needed to try it. If you have bias with 3 rows, don't mess with the bias transistor at this time. Concentrate on the 4th row only.

 

[WOPL Sniffer]

If you have the 4th row out, and no bias, then you have more issues. Joe does have a way of bypassing the bias transistor, but can't remember as I've never needed to try it. If you have bias with 3 rows, don't mess with the bias transistor at this time. Concentrate on the 4th row only.

Pretty sure he said all was good till the last row and then No Bias

 

[Gepetto]

First Good morning, everyone...
Last night I installed my new repaired backplanes boards. (Thanks again Joe). Installed first roll of transistors, did all the electrical checks and everything passed with flying colors. Installed second roll of transistors. did all the electrical checks but this time also adjusted the Bias voltage. Left channel set to 0.350, right channel set to 0.351. All is good so far. Third row installed. Everything measures good. Installed fourth row. Measured amp again but this time have no Bias voltage.
Voltage off the capacitors: 161.0 volts
No fuses blown including fuses mounted of circuit boards.
I have 15 volts +&- on the control board.
Protection relay closes after about 3 sec. and stays closed unit power down.
0.00 volts on the outputs binding post.
Normal or is something wrong?

You have no bias on both channels? Or just one channel? Remember, each channel is independent.

 

[George S.]

Gary, also check the polarity the polarity of your storage caps. It was correct on the oldest photos but can't tell on the latest.

 

[MusicSteve]

You have no bias on both channels? Or just one channel? Remember, each channel is independent.

I would just work w just one channel either the left or right.
if one does not work , than pull them out and try the other channel. (w different Transistors)
you should be able to get one channel to work. and maybe find a bad transistor or identify a the bad socket.

Double check - like Sniffer said check each transistor.
and make sure you have the correct part number. *
Double check the slip pads for any tears, ripped or just look to rough or to many indents (or just use new ones)
Also check the Transistor for sharp edges and that the pins are straight and when installing them make sure they go in smoothly.
Good luck

 

[Gepetto]

Hi Gary
Any progress to report?

You should check, is one channel working properly and the other not so? Each channel is completely independent.

On the failing channel, you should carefully use the two independent bias check points to see if you may have zero positive bias but perhaps proper negative bias. There is a bias test point for each half on each backplane board.

Joe.

 

[gary33030]

EVERYONE:

I have Bias voltage! .350 Left side. .351 Right side. Was all my fault. I'm anal on how things look. My son calls me the king of wire ties. On one bundle I decided had to many ties. So, I sniped a couple of ties and cut the two green 22-gauge wires from the fuse holder shell. Can you believe, no voltage in, - no voltage out. All transistors installed. Dim bulb dimming. No shorts to ground or chassis, etc. I'm going to start work on the front panel tonight... Thank you everyone for your help so far. Stay in touch. I'm sure I'll need something.

 

[gary33030]

Ive noitced some dont use the front gain controls. Just wire from the RCA jact to control board. Whats everyones tought on this?

 

[gene french]

EVERYONE:

I have Bias voltage! .350 Left side. .351 Right side. Was all my fault. I'm anal on how things look. My son calls me the king of wire ties. On one bundle I decided had to many ties. So, I sniped a couple of ties and cut the two green 22-gauge wires from the fuse holder shell. Can you believe, no voltage in, - no voltage out. All transistors installed. Dim bulb dimming. No shorts to ground or chassis, etc. I'm going to start work on the front panel tonight... Thank you everyone for your help so far. Stay in touch. I'm sure I'll need something.

congrats!!!

 

[WOPL Sniffer]

Ive noitced some dont use the front gain controls. Just wire from the RCA jact to control board. Whats everyones tought on this?

Read the thread.

https://forums.phxaudiotape.com/threads/pl-700-ii-replacement-main-volume-pots.10726/

 

[George S.]

Ive noitced some dont use the front gain controls. Just wire from the RCA jact to control board. Whats everyones tought on this?

Build it the way you want. You can wire the attenuator pots, bypass the pots leaving them in place, or bypass the pots and add some sort of LED pilot light or whatever in place of them.
Personally, I've never had a need for them on the amp, so I removed them and added a LED.

 

[e30m3mon]

I bypassed them and left the knobs….you make the call!

 

[gary33030]

Good evening, everyone.
It works!!!! When I got it, all the fuses were blown. Now I hear music. Never have I rebuilt anything electronic before. Thank you all. As you can tell, I did as Mark Comer did and put the amp into operation without being finished. Just had to hear this puppy. Will finish it up with a new black face plate from Joe and show all. What a great sounding amp.

 

[e30m3mon]

Congratulations!
Now start thinking about your next build!
you’ve been warned

 

[Vintage 700b]

Congratulations !
Enjoy the music, these are incredible amps.
..........but remember...............you can't build just one

 

[gene french]

Congratulations !
Enjoy the music, these are incredible amps.
..........but remember...............you can't build just one

sure you can....it just takes more discipline that we at phoenix have!!!
lololol
all my m&ms and lays bags are empty too...
lolololol

 

[Vynuladikt]

Wire ties are your friend, errant side cutters, not so much.
Glad you got it sorted out.

 

[gary33030]

Completed. Here is a shot inside of her new case not mounted in the rack yet. Thank you everyone for the help. I now have a Phase Linear 400, 4 fin to rebuild. This amp will get the full treatment. Also have a Carver C-500 I'd like to rebuild next.

The wife likes the bar graft better than the dot mode. I have no decided yet. First bit of music played was "More than a Feeling." From Boston. All I have now are bookshelf speakers, but it plays loud. What I'm really impressed with is the lack of background hiss or noise of any kind. Just brings back a lot of memories. I'm driving the amp with a Carver C-1 preamp. Perfect combination. Well, everyone I'm getting back to my album, have a good evening!!!