HELP! Rescuing Dad's old PL400 S2 (pics)
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While I wait for my new op-amp I set up my listening area. I managed to finish refurbishing one of the Infinity RS3A's as well. I am using a Luxman EQ in place of the preamp tone control until the op-amp arrives. Also a Luxman turntable. WOW it sounds good, in terms of a preview. Anyway, thought you might enjoy seeing my listening area where this will live when it is all done.
That is a custom wormwood cabinet I made to house my Mark of the Unicorn (MOTU) 828, which I primarily use for recording, but the DACs are super nice so when I play FLAC files I do it through that to the amp. It also has a nice headphone preamp for listening. There is also a compressor/expander/limiter and a hardware reverb unit, but I really only use those live/recording.
- Joined
- Jan 14, 2011
- Messages
- 74,873
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,873
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
- Joined
- Jan 14, 2011
- Messages
- 74,873
- Location
- Gillette, Wyo.
- Tagline
- Halfbiass...Electron Herder and Backass Woof
It came from around the suckface time, but it was matched with an LX-430. How do you like the turntable?
The LX-430 is, or I should say was, really nice in a well rounded way. The phono was really good on it and it matched the 101 nicely. In any case I tried to turn it on and saw an arc between the slightly oxidized case and something near the power supply. That will possibly be my next fixer-upper.
The LX-430 is, or I should say was, really nice in a well rounded way. The phono was really good on it and it matched the 101 nicely. In any case I tried to turn it on and saw an arc between the slightly oxidized case and something near the power supply. That will possibly be my next fixer-upper.
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- Jan 14, 2011
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- 74,873
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- Gillette, Wyo.
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- Halfbiass...Electron Herder and Backass Woof
Just over 10 years later, and I am encountering similar behavior in a PL-400 Series II I recently acquired. The unit had a blown 10 amp main fuse, but intact 8 amp rail fuses.
I replaced the mains fuse, connected a variac and DBT, and proceded to troubleshoot according to the Service Manual, though the symptom does not exactly match anything in it.
The symptom is no DC offset, no abnormal DBT behavior in-spec bias on both channels, and undistorted output waveform on both channels that represents the applied input as viewed via an oscilloscope with NO LOAD.
When an 8-Ohm load is attached, the DBT appears almost fully on and never dims, and about +7 VDC is present on both channels as measured with a DMM. I do not leave the unit in this state long enough to see what an input signal does to it. During power off, I see as much as 31 VDC on the outputs after several seconds have elapsed, before the mains filters drain off.
Also, if I power the unit up without a load and subsequently connect an 8 ohm load to it, the DBT remains as if the load was unattached during power up.
I removed and tested every transistor and died on the rear of the unit as will as every one on the driver board. I have measured the 0.33 ohm emitter and collector resistors (the amp is a quasi), as well as the bias resistors for both channels
The rail filter capacitors were a mix of an original and a mallory replacement. Both had 1978 date codes. The original one was measuring low and the Mallory replacement was at the limit of its working voltage. I replaced them with 12000 uF units as well the Bridge rectifier with items from White Oak, so I could add bridge snubber caps and connections for a to-be-installed-afterwards Watts Abundant Speaker Protect Relay Kit.
I replaced the original op-amps with TL072's purchased from Mouser, as well as the 15 volt zener diodes and correct value (7.5K vs 1.8K) ballast resistors. and 8-Pin DIP sockets while I was at it. I replaced the large carbon composite resistors on the driver board with flameproof metal film equivalents. and the 4 electolytic capacitors with higher voltage and thermally rated nichicons. (Two of them tested leaky and under capacitance). I readjusted the bias to 375 mV, on both channels, after over 5 mins because I had no confidence that the original settings had not been altered somewhere along the line. I verified that the variac voltage was not sagging below its required value.
The behavior persists after making all these changes.
I have the "Watts Abundant" kit as well as a White Oak Driver board kit, but the instructions for the WA lead me to refrain from installing it until after I have eliminated this incorrect power up/down behavior.
Any help would be most appreciated.
I replaced the mains fuse, connected a variac and DBT, and proceded to troubleshoot according to the Service Manual, though the symptom does not exactly match anything in it.
The symptom is no DC offset, no abnormal DBT behavior in-spec bias on both channels, and undistorted output waveform on both channels that represents the applied input as viewed via an oscilloscope with NO LOAD.
When an 8-Ohm load is attached, the DBT appears almost fully on and never dims, and about +7 VDC is present on both channels as measured with a DMM. I do not leave the unit in this state long enough to see what an input signal does to it. During power off, I see as much as 31 VDC on the outputs after several seconds have elapsed, before the mains filters drain off.
Also, if I power the unit up without a load and subsequently connect an 8 ohm load to it, the DBT remains as if the load was unattached during power up.
I removed and tested every transistor and died on the rear of the unit as will as every one on the driver board. I have measured the 0.33 ohm emitter and collector resistors (the amp is a quasi), as well as the bias resistors for both channels
The rail filter capacitors were a mix of an original and a mallory replacement. Both had 1978 date codes. The original one was measuring low and the Mallory replacement was at the limit of its working voltage. I replaced them with 12000 uF units as well the Bridge rectifier with items from White Oak, so I could add bridge snubber caps and connections for a to-be-installed-afterwards Watts Abundant Speaker Protect Relay Kit.
I replaced the original op-amps with TL072's purchased from Mouser, as well as the 15 volt zener diodes and correct value (7.5K vs 1.8K) ballast resistors. and 8-Pin DIP sockets while I was at it. I replaced the large carbon composite resistors on the driver board with flameproof metal film equivalents. and the 4 electolytic capacitors with higher voltage and thermally rated nichicons. (Two of them tested leaky and under capacitance). I readjusted the bias to 375 mV, on both channels, after over 5 mins because I had no confidence that the original settings had not been altered somewhere along the line. I verified that the variac voltage was not sagging below its required value.
The behavior persists after making all these changes.
I have the "Watts Abundant" kit as well as a White Oak Driver board kit, but the instructions for the WA lead me to refrain from installing it until after I have eliminated this incorrect power up/down behavior.
Any help would be most appreciated.
Originals with a history to them according to to Ed. They were part of a group loans to a former employee to start his own amp company and subsequently returned after they got their own stock.
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There is an interesting back story on those output transistors (marked "S 126-0073-0") that either Robin Gudgel or Terry Pennington told me about years ago. That is Spectro Acoustcs (the company Robin was co-owner of after his leaving Phase Linear) borrowed some TP9054 (Motorola MJ15024's) 126-0073's from Phase Linear to use in some Spectro Acoustics amps. When more stock became available, Spectro Acoustics returned whatever quantity the originally borrowed to Phase Linear. Hence the ink stamped transistors you have. By the way, TP in TP9054 is Terry Penningtons initials. The complimentary to the NPN MJ15024 is the PNP MJ15025 which had Dennis Bohn's initials on them and identified as DB15025. These complimentary pairs were used on fully complimentary output 400's and 700 series 2 amps starting in January 1981.
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Every one of them tested okay with my Sencore TF-166. I just confirmed that the behave does not occur if the load is attached after the bulb has dimmed.
>>
There is an interesting back story on those output transistors (marked "S 126-0073-0") that either Robin Gudgel or Terry Pennington told me about years ago. That is Spectro Acoustcs (the company Robin was co-owner of after his leaving Phase Linear) borrowed some TP9054 (Motorola MJ15024's) 126-0073's from Phase Linear to use in some Spectro Acoustics amps. When more stock became available, Spectro Acoustics returned whatever quantity the originally borrowed to Phase Linear. Hence the ink stamped transistors you have. By the way, TP in TP9054 is Terry Penningtons initials. The complimentary to the NPN MJ15024 is the PNP MJ15025 which had Dennis Bohn's initials on them and identified as DB15025. These complimentary pairs were used on fully complimentary output 400's and 700 series 2 amps starting in January 1981.
<<
Every one of them tested okay with my Sencore TF-166. I just confirmed that the behave does not occur if the load is attached after the bulb has dimmed.
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I have tried neither of those things, but can do so. My choice is loads is very limited, as I do not yet have loads capable of dissipating full power. I will place my pair of 8 ohm loads in series and connect it with each channel and see if the behavior persists. If not I will repeat with the other channel. It will take a bit longer to remove the transistors again…