WOPL 400 Linda Linda

girbob75

girbob75

New Around These Parts
Joined
Feb 8, 2023
Messages
17
This thread has been a long time coming. I started this journey back in 2023 purchasing a Phase Linear 400 in very nice shape with two issues. One of the gauge bezels was missing and there were two blown transistors. Thanks again Lee for all the parts and information, couldn't have gotten started without you. I rocked this thing for a few months and purchased a control board from Joe and built it my spare time. As time went on I started purchasing parts for a rebuild. It was then I blew a transistor by driving the amp a little too hard. POP! I realized that I wanted to do a full rebuild. I purchased the backplane boards from Joe sometime last year and just recently grabbed a new housing and the transistors. Thanks to this group and Joe's kits with instructions Linda Linda lives again. Reading everyone's rebuild questions really helped out a lot. I can't forget about Don. His dc protection board and triac switch are the parachute and safety net everyone appreciates in their builds. Everyone is working correctly at the correct voltages and bias but the transformer is buzzing more than before. I think I need to crank down the bolts or reposition the cover slightly I don't know. It looks like I'll be pulling the caps out in the next few weeks. I'll just listen to everything a little louder until then.

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Eric is right, just cut R1, C8, and R2, C9 off the DCP Board. And thanks to Dr. Otto J. Zobel of Bell Telephone/Bell Labs for inventing and patenting an "image impedance" filter network that reduced voltage from reflecting off the woofers and back into the amplifier in about 1920.
 
In the photos, the triac (solidstate) AC switch board is mounted between the two driver boards. It was originally intended for the 700" as they have a power switch. The main power switch controls the triac. The triac can withstand greater than 150 amps of excitation current into the transformer. The mechanical switch contacts should last forever.

Since stock 400's don't have a power switch I assume some kind of switch is mounted on the front panel. A mini toggle switch rated for 3 amps or so could be used. In the photo the board is mounted very close to the screw for the thermal overload switch. Make sure there is adequate clearance. The triac must be mounted directly on the chassis for cooling.

I don't recall having seen the thermal switch fail. Of course you wouldn't likely know if it did fail as the likely failure mode would be welded contacts. An option could be to wire the thermal switch in series with the power switch. In that case, if a thermal overload did occur, the thermal switch would turn off the triac.
 
Nice to see another Phase Linear 400 rebuild in progress. I've been slowly working on mine, replaced the output transistors and power capacitors, then moved into a house, that was four years ago and the PL 400 hasn't had the bias adjusted yet. Also found after I moved the PLL 400 started making a screech sound when turned on, I believe it maybe due to a foil trace and wire coming off from the Drive Board Assembly, Model PL400C. I have a replacement used Drive Board but haven't installed it yet. And also have the Speaker Protection Relay Board. but haven't installed that either. The past few years was attending university for a master in business administration while working 80 hours or more per week, only got one to three hours sleep per night, almost killed me several times, a walking zombie. So, now I'm slowly regaining my health and clearing out and cleaning up the house and workshop-office for a continuation of work on Phase Linear equipment, as I'm also a collector of Phase Linear, have more than a few pieces, several amplifiers, pre-amplifiers, equalizer and, delay. Anyways, will try to participate and follow along. Thank you all for the input and fellowship.
 
Hexis22 said:
You need to remove the RC zobel network on the DCP board when using White Oak backplane boards.
mlucitt said:
Eric is right, just cut R1, C8, and R2, C9 off the DCP Board. And thanks to Dr. Otto J. Zobel of Bell Telephone/Bell Labs for inventing and patenting an "image impedance" filter network that reduced voltage from reflecting off the woofers and back into the amplifier in about 1920.
Click to expand...
Thanks guys I was not aware of that alteration to that board. Just another reason to post build photos.
Click to expand...
 
wattsabundant said:
In the photos, the triac (solidstate) AC switch board is mounted between the two driver boards. It was originally intended for the 700" as they have a power switch. The main power switch controls the triac. The triac can withstand greater than 150 amps of excitation current into the transformer. The mechanical switch contacts should last forever.

Since stock 400's don't have a power switch I assume some kind of switch is mounted on the front panel. A mini toggle switch rated for 3 amps or so could be used. In the photo the board is mounted very close to the screw for the thermal overload switch. Make sure there is adequate clearance. The triac must be mounted directly on the chassis for cooling.

I don't recall having seen the thermal switch fail. Of course you wouldn't likely know if it did fail as the likely failure mode would be welded contacts. An option could be to wire the thermal switch in series with the power switch. In that case, if a thermal overload did occur, the thermal switch would turn off the triac.
Click to expand...
Hi Don, I couldn't bring myself to drill into the original face. The switch is placed just above the triac and is a black push button. It's a tight squeeze but everything has sufficient clearance including the thermal switch. You bring up an interesting point putting the thermal switch in series with the push button. Would this reduce the likelihood of a thermal switch failure because of the reduced current load?

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Screenshot 2026-01-10 093758.jpg

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A few observations:
1) Given the position of your power switch on the rear of the amp, I would place the output driver covers back on to prevent accidental contact and DC shock hazard.
2) Recommend swapping the Red and White wires attached to the Triac. The load should be connected to the first two terminals on the right in your picture. The two left terminals should be connected to the power switch.

Although the Triac wiring will work as you have it connected, it’s not ideal based on the PCB layout with a very small trace feeding the terminal you currently have the white wire connected.
 
For reference, you currently have AC power feeding your entire amp running through this trace (one on each side of the PCB).

Triac2-L.jpg
 
Hexis22 said:
A few observations:
1) Given the position of your power switch on the rear of the amp, I would place the output driver covers back on to prevent accidental contact and DC shock hazard.
2) Recommend swapping the Red and White wires attached to the Triac. The load should be connected to the first two terminals on the right in your picture. The two left terminals should be connected to the power switch.

Although the Triac wiring will work as you have it connected, it’s not ideal based on the PCB layout with a very small trace feeding the terminal you currently have the white wire connected.
Click to expand...
Hi Eric,
Completely agree with the covers just didn't have a photo up.
As for the triac wiring Don may have revised the board for the thin trace. Attached photo of the work instruction and back of the board. I love the constructive criticism. You're first WOPL really inspired me to take on this project. Thank you for the support. 1000008151.jpg1000008156.jpg
1000008154.jpg
 
It does appear the layout has changed. Sorry for the added work and disassembly.

Previously, I sent Don a note about the discrepancy between the instructions and the PCB layout I have.

Your picture above with a different layout explains many questions I had.
 
Hexis22 said:
It does appear the layout has changed. Sorry for the added work and disassembly.

Previously, I sent Don a note about the discrepancy between the instructions and the PCB layout I have.

Your picture above with a different layout explains many questions I had.
Click to expand...
Not a problem Eric. I'd rather be safe than sorry. I was in it anyway removing the RC zobel network.
1000008157.jpg
 
Hexis22 said:
It does appear the layout has changed. Sorry for the added work and disassembly.

Previously, I sent Don a note about the discrepancy between the instructions and the PCB layout I have.

Your picture above with a different layout explains many questions I had.
Click to expand...
I built a couple of these (PL400 protect boards) over the summer, and the docs from Don were 100% accurate. Perhaps you are confusing this with with the board for the 700, which is quite different?
 
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