aphex_nsw
New Member
Hello all, I've recently been digging back into a bunch of old vintage solid state stuff that's been on the backburner for a decade. Quite a few treasures here and there in my gear collection but unfortunately ive gotten a bit rusty on my electronics knowledge.
This week's amp is a Philips 22RH520 (I understand 22RH550 is basically same model for reference), weird little low rms amp with stereo matrixing that as I understand it works as class A at low power and AB at higher volume with excellent distortion for the time period. This particular one was an ewaste find and is in pretty good condition overall except for rotten wood cover, pity. Anyway, a few things about approaching this amp's problems are confusing me and it would be great to hear from the experts on here! Fair warning: I have just enough knowledge about how to repair and diagnose these things to get me in trouble and have a lot to learn, apologies in advance for the long post!
1. The inputs of this amp have me a little confused, especially in regards to connecting RCA line level sources. They're all 5-DIN inputs, but from reading the service manual (can't find a user manual unfortunately) these all use a bit higher input impedance from what im used to seeing on these amps (100kOhm) and also mention a voltage (100mV for tuner input, and 250mV for tape) and a bit of googling I found a few people saying that the 5-DIN used by these uses a "current" based system instead of a voltage (1-2V) based system... with out much elaboration on how that works. I assume a modern-ish line level source will need attenuation to more closely match the higher input impedance, but do I also have to be concerned about voltages supplied by the source?
If I wanted to use some portable digital source like a phone or DAP, which usually expect low impedance loads, what sort of attenuation circuit will I need to construct to avoid overloading?
I've attached part of the schematic that shows the inputs and their ratings/pinouts.
When dim bulb testing this unit I (perhaps foolishly) fed RCA line level straight into the board piggybacking off the tape DIN terminals after getting DC bias readings that looked safe to test the unit. Sound was very low volume/hollow with massive crosstalk between inputs. With line level going into Tape input, selecting Tuner you could still hear the source at the same volume level if not louder. Phono circuit did not seem to have crosstalk from this. Is this most likely a problem with how im feeding the source in, or should I expect power amp section?
2. This amp is apparently "Tropicalized". I found a few people online talking about this mainly in the context of Philips earlier portable transistor radios and people mentioned a number of things this process could include such as application of insecticides/fungicides, sealing the case from external hazards like humidity or dust kind of like modern IPxx ratings or simply using overspec components to account for heat and bad power sources. I think my unit frighteningly fits in that first category as there's nothing to indicate ingress protection. On my board and other units ive seen disassembled on the net, wire junctions and solder connections have this weird, gross brown sap/gum like material applied over them. A lot of it has flaked/dried or scratched off over the years so in many spots you can see stains where this sealant material once was. The underside of the board also seems to have an old, greasy but still quite dry substance smeared over it. I assume this is some kind of moisture protection or worse some bizarre fungicide or something. I retouched a bad solder joint and got a brief whiff of what I can only describe as a truly evil chemical smell, and the coating made a little sizzling sound as well.
Is this a dangerous material? Am I handling a board essentially coated in agent orange and inhaling little tokes of concentrated dioxin every time I touch my iron?
3. I suspect multiple caps are failing + other aged components. My board has had one sides output transistors replaced by the look of things. These are the only components that look changed. Bias pots are sealed with that sappy stuff or at least appear to be so I dont think the prev owner adjusted bias after the repair. On tape input no load, volume at near minimum ive measured 0.28 and 0.15 on left and right outputs respectively... again Im very ignorant but these don't look too extreme for DC bias but this design is pretty different from the Japanese stuff im normally working on and that 0.28 could be danger territory for this unit for all I know. It does sound distorted. This amp also uses caps on the output, and the channel reading 0.28 has a hum that sounds like mains to me, should those output caps be my first suspect?
4. Final question, I promise! What on earth does the "Contour" switch on this unit do? Is it related to the 4ch matrixing circuit?
edit: after further searching this seems to be what Philips called their loudness circuit.
Thank you so much for anyone who takes the time to reply!
This week's amp is a Philips 22RH520 (I understand 22RH550 is basically same model for reference), weird little low rms amp with stereo matrixing that as I understand it works as class A at low power and AB at higher volume with excellent distortion for the time period. This particular one was an ewaste find and is in pretty good condition overall except for rotten wood cover, pity. Anyway, a few things about approaching this amp's problems are confusing me and it would be great to hear from the experts on here! Fair warning: I have just enough knowledge about how to repair and diagnose these things to get me in trouble and have a lot to learn, apologies in advance for the long post!
1. The inputs of this amp have me a little confused, especially in regards to connecting RCA line level sources. They're all 5-DIN inputs, but from reading the service manual (can't find a user manual unfortunately) these all use a bit higher input impedance from what im used to seeing on these amps (100kOhm) and also mention a voltage (100mV for tuner input, and 250mV for tape) and a bit of googling I found a few people saying that the 5-DIN used by these uses a "current" based system instead of a voltage (1-2V) based system... with out much elaboration on how that works. I assume a modern-ish line level source will need attenuation to more closely match the higher input impedance, but do I also have to be concerned about voltages supplied by the source?
If I wanted to use some portable digital source like a phone or DAP, which usually expect low impedance loads, what sort of attenuation circuit will I need to construct to avoid overloading?
I've attached part of the schematic that shows the inputs and their ratings/pinouts.
When dim bulb testing this unit I (perhaps foolishly) fed RCA line level straight into the board piggybacking off the tape DIN terminals after getting DC bias readings that looked safe to test the unit. Sound was very low volume/hollow with massive crosstalk between inputs. With line level going into Tape input, selecting Tuner you could still hear the source at the same volume level if not louder. Phono circuit did not seem to have crosstalk from this. Is this most likely a problem with how im feeding the source in, or should I expect power amp section?
2. This amp is apparently "Tropicalized". I found a few people online talking about this mainly in the context of Philips earlier portable transistor radios and people mentioned a number of things this process could include such as application of insecticides/fungicides, sealing the case from external hazards like humidity or dust kind of like modern IPxx ratings or simply using overspec components to account for heat and bad power sources. I think my unit frighteningly fits in that first category as there's nothing to indicate ingress protection. On my board and other units ive seen disassembled on the net, wire junctions and solder connections have this weird, gross brown sap/gum like material applied over them. A lot of it has flaked/dried or scratched off over the years so in many spots you can see stains where this sealant material once was. The underside of the board also seems to have an old, greasy but still quite dry substance smeared over it. I assume this is some kind of moisture protection or worse some bizarre fungicide or something. I retouched a bad solder joint and got a brief whiff of what I can only describe as a truly evil chemical smell, and the coating made a little sizzling sound as well.
Is this a dangerous material? Am I handling a board essentially coated in agent orange and inhaling little tokes of concentrated dioxin every time I touch my iron?
3. I suspect multiple caps are failing + other aged components. My board has had one sides output transistors replaced by the look of things. These are the only components that look changed. Bias pots are sealed with that sappy stuff or at least appear to be so I dont think the prev owner adjusted bias after the repair. On tape input no load, volume at near minimum ive measured 0.28 and 0.15 on left and right outputs respectively... again Im very ignorant but these don't look too extreme for DC bias but this design is pretty different from the Japanese stuff im normally working on and that 0.28 could be danger territory for this unit for all I know. It does sound distorted. This amp also uses caps on the output, and the channel reading 0.28 has a hum that sounds like mains to me, should those output caps be my first suspect?
4. Final question, I promise! What on earth does the "Contour" switch on this unit do? Is it related to the 4ch matrixing circuit?
edit: after further searching this seems to be what Philips called their loudness circuit.
Thank you so much for anyone who takes the time to reply!
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