PL 200 Help Please!

[bobdod]

I've tried running it with the 2000 pre, through some test speakers. Sounded good, but the DC issue will need to be addressed still, so Q1/Q2 will be replaced as the next step in trying to resolve that issue.

One other problem though is that the LEDs did not light up when I played music through the 200. I know the LEDs work, as they previously illuminated when the amp was out of sorts earlier. Any ideas on what would keep the LEDs from lighting?

 

[oldphaser]

bobdod,

I have resisted posting for as long as I could.

Unfortunately, the Phase Linear 200 series 1 amplifier is the worst/most unreliable amplifier Phase Linear ever made. I say this for many reasons. I will not list them all here.

I hope you don't intend on using this amplifier to drive any 4 ohm speakers. The amplifier will not clip symmetrically when driving a 4 ohm load! As a matter of fact one side of the sine wave will clip far earlier than the other side. (It has been a while but I can't remember if it was the positive side or the negative side.) You will also find that many 8 ohm speakers are not actually 8 ohms from 20Hz to 20kHz and actually have peaks and valleys in the impedance curve. (In others words, at some frequencies the impedance will be higher than 8 ohms and at other frequencies less than 8 ohms.) NOTE: I also recognize that the Phase Linear 200 series 1 amplifier was never rated into a 4 ohm load. However the reason many amplifiers were never rated into a 4 ohm load had more to do with the 1974 FTC "amplifier rule" than anything else. Yet all of the other Phase Linear amplifiers were capable of driving a 4 ohm load and clipping symmetrically.

I would also suggest that you replace the "STM" brand power supply filter capacitors as they had a higher than normal failure rate.

Phase Linear also used (3) vendors of power supply transformers. One of them at the very least had a higher failure rate than any other transformers Phase Linear used with perhaps the exception of the transformer used in the DRS-250 and DRS-400.

Working on the 200 series 1 amplifier LED style VU meter pc board can be a P.I.T.A. The stand-offs also break easily.

The Phase Linear 200 series two amplifier is a far better amplifier. It has a fully complementary output and used far better/more reliable output transistors. It will also drive a 4 ohm load and clip symmetrically.

By the way, I have (2) Phase Linear 200 series 1 amplifiers and plan on selling them in the future. I have installed (2) later 200 series 2 pc boards in (1) of them.

Perhaps Perry has some upgraded pc board design he can sell you?

Ed

 

[WOPL Sniffer]

Nothing here, I got a junk 200 I use for a paperweight.

 

[bobdod]

bobdod,

I have resisted posting for as long as I could.

Unfortunately, the Phase Linear 200 series 1 amplifier is the worst/most unreliable amplifier Phase Linear ever made. I say this for many reasons. I will not list them all here.

I hope you don't intend on using this amplifier to drive any 4 ohm speakers. The amplifier will not clip symmetrically when driving a 4 ohm load! You will also find that many 8 ohm speakers are not actually 8 ohms from 20Hz to 20kHz and actually have peaks and valleys in the impedance curve. (In others words, at some frequencies the impedance will be higher than 8 ohms and at other frequencies less than 8 ohms.) NOTE: I also recognize that the Phase Linear 200 series 1 amplifier was never rated into a 4 ohm load. However the reason many amplifiers were never rated into a 4 ohm load had more to do with the 1974 FTC "amplifier rule" than anything else. Yet all of the other Phase Linear amplifiers were capable of driving a 4 ohm load and clipping symmetrically.

I would also suggest that you replace the "STM" brand power supply filter capacitors as they had a higher than normal failure rate.

Phase Linear also used (3) vendors of power supply transformers. One of them at the very least had a higher failure rate than any other transformers Phase Linear used with perhaps the exception of the transformer used in the DRS-250 and DRS-400.

Working on the 200 series 1 amplifier LED style VU meter pc board can be a P.I.T.A. The stand-offs also break easily.

The Phase Linear 200 series two amplifier is a far better amplifier. It has a fully complementary output and used far better/more reliable output transistors. It will also drive a 4 ohm load and clip symmetrically.

By the way, I have (2) Phase Linear 200 series 1 amplifiers and plan on selling them in the future. I have installed (2) later 200 series 2 pc boards in (1) of them.

Perhaps Perry has some upgraded pc board design he can sell you?

Ed

Ed,

I've read about the limitations/flaws of the 200. I am not sure if I will wind up keeping it or not, but if I do, I am not too worried about clipping. This system would be paired with 16ohm speakers and I never listen at volumes that would be considered burdensome on most gear.

I'd like to get it running and fully functional before I decide on what to do with it, and getting the front panel lights to work is certainly a part of that. I took this on for the learning aspects of it, and it has certainly been coming through in that regard. It would certainly be very satisfying to get it fully sorted out and give me a bit more confidence in this new hobby.

 

[oldphaser]

Ed,

I've read about the limitations/flaws of the 200. I am not sure if I will wind up keeping it or not, but if I do, I am not too worried about clipping. This system would be paired with 16ohm speakers and I never listen at volumes that would be considered burdensome on most gear.

I'd like to get it running and fully functional before I decide on what to do with it, and getting the front panel lights to work is certainly a part of that. I took this on for the learning aspects of it, and it has certainly been coming through in that regard. It would certainly be very satisfying to get it fully sorted out and give me a bit more confidence in this new hobby.

I edited my previous post to include the following sentences in italics.
.......The amplifier will not clip symmetrically when driving a 4 ohm load! As a matter of fact one side of the sine wave will clip far earlier than the other side. (It has been a while but I can't remember if it was the positive side or the negative side.)

 

[WOPL Sniffer]

Go ahead and have some fun with it. It is good practice and if not beat on, will do fine for what you are doing. I have one here (under the bench I putz with when I have time).......

 

[bobdod]

I've had some time to look at this thing a bit and have made a little progress. I've replaced all capacitors as there were multiple failed ones. I've also replaced q1 and q2 on the bad channel, as well as the bad resistors on the meter board.

DC offset is now 95mv / 15mv, so a definite improvement. Voltages at cold/warm measures across the resistors described in the service manual start at 8mv cold and are steady at 39mv on both channels after warming up. Unit sounds good on both channels.

The meter lights are still a bit of an issue. They now work, but the sensitivity is not right somehow. I have to crank up the volume rather high before any of the lights start to go on. Moving the switch in the rear to adjust to -10db does make a difference, but still takes a lot of volume to get the first few lights going. Any ideas on what could be done to better calibrate the lights?

 

[oldphaser]

As you already know, the 200 series 1 service manual appears to be lacking some details in the meter sensitivity section. I will post it here for others to see.

Step #20 Apply enough input signal (2K Hz) to the left channel so that the -12 dB LED comes on, with the meter sensitivity switch on NORMAL. Switch the Meter Sensitivity to -10 dB; verify that now the -9 dB and -6 dB LED's are also on. Switch the Meter Sensitivity back to NORMAL.
Step #21 Repeat step #20 with the right channel.

Also here is step #11 for Offset
"Disconnect the signal generator and short the inputs of the 200. Measure the DC voltage across the output terminals and verify less than +/-150 millivolts."

NOTE: Section VI "TROUBLESHOOTING GUIDE" does not appear to provide any guidance on what to do if the DC offset spec is not met or anything concerning the VU meters.

I
ED COMMENT: I always wondered who designed the 200 series 1 amplifier. Usually on the Phase Linear schematic and parts/pcb board layout drawings you will see the initials of the designer either on the CHKD or APVD boxes in the revision history. All that you will see is "PICKENS" in the box next to DRAWN with the exception of M.D.C on Rev B revision history for the PL24 P.C.B. display board history. "PICKENS" is Sue Pickens and "M.D.C." was Mike Chandler (who has passed away in 2007).

NOTE: The designer was not always on drawings. Particularly the earlier series 1 products. I have been making a list of all the Phase Linear products pcb board history with the draftsman, checked and approved boxes and I am only about half-way done. So far, I only found RWC (Robert W Carver) on some early 4000 drawings found only on my first revision 4000 series 1 service manual.

Ed

 

[wattsabundant]

... The meter lights are still a bit of an issue...

If you don't have a signal generator you can get one for $25 on EBAY or download one on your phone. With a decent voltmeter and your phone you can generate a test signal to verify the calibration.

 

[bobdod]

I have a signal generator on my phone and have done the test to confirm operation of the sensitivity switch on the back of the unit. I might try swapping out R34 through R38 and R66 through R70 to slightly lower resistance to see if that improves the sensitivity of the meters.

 

[bobdod]

Tried messing around with different resistor arrangements, but didn't see too much of an improvement. Every resistor I tested was on spec. Strange. With it playing records through my PL2000 (which I am going to update next), I need to have the volume up to about 10 or 11 o'clock position just to get the first LED light to go on and its pretty dang loud at that point. Maybe its just normal that way? I don't know.

In any case, I'am pretty happy with the amp at this point from a sound quality standpoint. I've replaced all of the caps on both boards and replaced Q1/Q2/Q3. I ran it pretty hard for 2 hours yesterday, with no issues. voltages/bias remained stable. DC offset on the one channel still a bit high at 70mv, but certainly better than where I started at 750mv. This was a good learning experience for sure.

 

[WOPL Sniffer]

Just an observation but my speakers are so efficient (108dB @1 watt at 1 meter), they are bouncing around and rattling window long before my meters are doing much....

 

[bobdod]

Just an observation but my speakers are so efficient (108dB @1 watt at 1 meter), they are bouncing around and rattling window long before my meters are doing much....

Yeah, I think this is a case of speaker efficiency here. I think I got thrown off a bit because I just finished restoring an MCS 3125 receiver with LED meters, and that thing was lighting up at very reasonable volumes. I guess the sensitivity is a lot lower with this PL200 compared to that MCS. I am quite new to this whole vintage audio thing. Learn something new every time I get a new piece of gear.

 

[bobdod]

Ugh... face meet palm. I went to move the amp while running, heard a pop and it died. Opened it up and sure enough I am an idiot. I some how managed to lose a trimmed off lead in there and it wound up dropping down and shorting something. Testing revealed Q3/Q4/Q6/Q7 and outputs Q8/Q9/Q10/Q11 all shorted. Fuse blown. A few bad diodes.I am so disappointed in myself. I've been so diligent keeping track of leads as I cut them off. I don't know how it got in there. I have everything on hand to fix it, but no output transistors, so I guess this thing is now a brick after all of my efforts to finally get it working right.

Any ideas on replacing the pair of RCA 66546 and 66430 on the board? I am really kicking myself.

 

[bobdod]

From looking around I've found the following possible solutions to replacing the output transistors:

1. replace the 2 66546 and 2 66430 transistors with 4 MJ15024's (~$7 each)
2. replace the 2 66546 and 2 66430 transistors with 4 BUY69A's (~$2.50 each)
3. replace the 2 66546 and 2 66430 transistors with 4 RCA410's (~$7.50 each on ebay)
4. replace the 2 66546 and 2 66430 transistors with 2 66546 and 2 66430 transistors from ebay (~$60 total )

Any thoughts on this? Obviously, option 2 is most economical. Option 4 is not cost effective and if it is the only solution this amp is done.

 

[WOPL Sniffer]

yer worried about $28 for the outputs??? Guess you won't be building any WOPLS soon.... 24 outputs at going rate will run you $$$$$$

 

[bobdod]

No intention on building WOPLS. Have not gone anywhere close to far enough down the rabbit hole for that. Maybe if I find an 400 one day. Regarding the outputs, I've not found any definitive answers about which to use. I am not going to experiment and waste money. I've decided to move on from the 200. It was fun learning about it and getting it working, but now its gone to the great big orchestra in the sky.

 

[Gepetto]

Some things are just meant to be stepped on...

 

[laatsch55]

Aren't 66546's rebranded RCA 410's?

 

[bobdod]

Wanted to close this thread up. The 200 is running great now. Its feeding a pair of pioneer CS51s (16ohm). No issues to report after a few hours of continuous use. New output transistors did the trick (was able to obtain OEM RCA replacements at <$10 delivered). Total cost to completely rebuild this thing and get it working right is ~$45 at this point. Over and out.