Love the vids Trevor. For others in comments - On a cap coupled amp, not really called DC Offset, but DC centre voltage alignment. Yes you can hook up scope and adjust for 'even clipping" or another way if you don't have scope is to hook up to each DC coupling cap. Set vol to zero, tone controls centred, no inputs connected, select AUX, speakers disconnected . Connect DMM neg lead to GND (speaker neg or the amp chassis, should be the same, but check), and the DMM positive lead to the +ve terminal of respective Output Cap. Adjust relevant channel pots for ( 1/2) voltage rail ...This will get you pretty close...For bias on a lot of the vintage 20 -30W amps is around 12mV or thereabouts, which will give, assuming emitter resistor of 0.5R = 24 mA. If running Ok , staying cool could come up a bit but doesn't really change the sound, so bit lower is better. So your 10mV is around the mark
Your customer supplied faceplate really gave this piece its attitude back. Nice reconditioning on this little gem! Thanks for your time posting this video.
@@TrevorsBench I have read that microfarads on capacitors should stay the same value when replacing but you increased the value, does that only apply to those big filter capacitors? or did you make some sort of changes to the circuit? Thank you. Sorry to ask so many questions.
I don't know if this info is still relevant but the capacitance can be boosted, if the cap has filtering function. So the main filter cap can be bigger, however as we saw it doesn't make too much of a difference. I have the same model, i replaced that cap with 5600uF. In the power supply panel i changed the 220uF caps to 470uF because that's what i had at the moment. It won't harm, maybe it will help with better filtering. But when you have the cap in the signal path, it's better to stay with the original value, otherwise it can alter the frequency getting through.@@SDsailor7
Regarding the power sag, I use a Sencore PR-57 but for power output test I have to go direct to the line; there is a sag due to the PR-57 AC voltage delivered under load. It might have been useful to see if the full 120V was still delivered under load.
The problem with single ended power supply designs is that the DC offset is thrown off when the supply sags. I noticed at the end that the clipping was at the positive end only, because of the sagging. Why they chose to go with that design instead of dual rail is beyond me, but there it is.
Variation on the speaker ( small ) are due to small voltage fluctuation on power supply , leaky output caps need to be replaced ..............mostly they are still good . The second pot is for adjust symetrical clipping ( scope ) ..........without scope adjust for half the voltage on the main filter capacitor. In contrast to opinions of many modern technicians , Quasi complentary output can sound very good !!! ( Same output devices on PP = same tonality and similar electric behavior under DYNAMIC load /working consditions ...........that are things one can hear , no complementary transistors are realy identical even when adjusted under same idle current... So there's allways benefits or disadvantages to any design ......; Those amplifiers will allways pop on start up ( loading of the cap ) and at shut down .........the good practice is to switch on/off with Speaker switch in OFF position ............ In these amplifiers there's NO such thing like DC OFFSET ! .............only half of the power voltage present on the main filter cap is measured on the output cap ! ( matching output transistors is allways a benefit in this case )
Nice video,i just got a sx 626 from a friend as a gift. On all outputs it has like a hum or static sound,when i turn the volume up a can hear the static in the background. Will cleaning the potentiometers make any difference?
@@tomicajovevski Ground loops will introduce noise, typically hum or other noise on the power rails will come through. A steady rushing noise that's noticeably loud is most likely a noisy transistor, capacitor or resistor. All stereos will have some level of background noise when you turn them up full volume. If it's noticeable at normal listening levels then there is too much noise and it needs repair.
HI TYrevor , D5 is excelent for metal contacts, switches etc........but........For pots there's FADER deoxit ! ( the green can ) Indeed do not use D5 on pots ! Many do but it will reveal becoming a bad treatment after time !
I just dug my Pioneer 626 out. I'd like to try it. I bought this thing new. I haven't played it for years it's been stored dry but, outside. I was just wondering. Is there a way to get a hold of you if this 626 has any problems? Or, should it be gone through before I plug it in? Due to the recent of surge in vinyl. And the fact that my nephew just opened a record store in my hometown I want to use it with my Pioneer Pl 71 turntable, which I always loved and also bought new. From your video, you look very knowledgeable and I'm just checking you out. And thanks for the videos. PS I always babied my equipment and now that I'm retired and I'm locked down on covid sometimes.. I think this would be very good time in my life to listen to some good old music.
Hi Eric, If it were mine, I would open it up and inspect for any damage or evidence of critters. If it all looks ok try plugging it in and trying it out. If it's still working, it will take several days of use to wake it up before it starts to sound good again. Hope it goes well and I agree, too many of us put our old equipment away when we should be using them daily and enjoying it while we still can!
@@TrevorsBench no critters so far . This guy is wakeing up. The volume Control is a bit scratchy. Head phones coming alive. 😁 Taking care of Business was the first song in 20 years. This is kind of like Rip Van Winkle. Hay, can I try some makeshift speaker wire. I have two of the lugs ordered for the 626 mine disappeared somewhere. They won't be here till April from Germany at 25 bucks you said that they'd be about three times value I think. Anyway, I got a couple big realistic speakers I'd like to try.
i have a 626 which has been fine for the first few days since purchased..."last week".. and now when i power it on i am getting a popping/crackling noise through the right channel for a few seconds then seems to fade away !..only just noticeable when standing next to speaker ! however the bass pot is kind of "thumpy" when adjusted...i dont think its a dirty pot as it doesn't "crackle"...any advice would be appreciated..thank you.
The deoxit d5 shouldn’t be used on anything with a resistive type of track you would want to use fader lube f5. The d5 is best used on metal type contacts Sorry I commented before the end of the video
Deoxit D5 and D100 does actually work well on pots. I'm not sure about the long term effects it may have. Other TH-camrs have commented to not use D5 or D100 on pots because it destroys the carbon track. I've yet to experience this but I've also only started using deoxit products a short time.
@@TrevorsBench yes the D5 does work but it won’t last long. I don’t know exactly what happens but as you said there’s word that it will destroy some of the resistive tracks
Salut ! Am căutat tranzistor echivalent pentru 2sb557/2sd427 la magazinele locale si nu am găsit. Mă gândesc să le înlocuiesc cu tranzistorii de tipul BD 317/318 care sunt mai accesibili la noi. Crezi ca e ok ?
Looking at the circuit I can see there are DC blocking capacitors on both outputs. Also, there is two resistors total of about 23k that will allow current to leak through the capacitor. This is the voltage you're seeing. I would ignore it. If you place a speaker load on the outputs, this leaking voltage will disappear.
we lived in Japan for 14 years from 1960 to 1974, my dad only had Pioneer gear, once I was old enough I too only had Pioneer, the best by far!
Love the vids Trevor. For others in comments - On a cap coupled amp, not really called DC Offset, but DC centre voltage alignment. Yes you can hook up scope and adjust for 'even clipping" or another way if you don't have scope is to hook up to each DC coupling cap. Set vol to zero, tone controls centred, no inputs connected, select AUX, speakers disconnected . Connect DMM neg lead to GND (speaker neg or the amp chassis, should be the same, but check), and the DMM positive lead to the +ve terminal of respective Output Cap. Adjust relevant channel pots for ( 1/2) voltage rail ...This will get you pretty close...For bias on a lot of the vintage 20 -30W amps is around 12mV or thereabouts, which will give, assuming emitter resistor of 0.5R = 24 mA. If running Ok , staying cool could come up a bit but doesn't really change the sound, so bit lower is better. So your 10mV is around the mark
Thanks for your advice, good info
Your customer supplied faceplate really gave this piece its attitude back. Nice reconditioning on this little gem! Thanks for your time posting this video.
Thanks for watching Craig, more to come
@@TrevorsBench I have read that microfarads on capacitors should stay the same value when replacing but you increased the value, does that only apply to those big filter capacitors? or did you make some sort of changes to the circuit?
Thank you. Sorry to ask so many questions.
I don't know if this info is still relevant but the capacitance can be boosted, if the cap has filtering function. So the main filter cap can be bigger, however as we saw it doesn't make too much of a difference. I have the same model, i replaced that cap with 5600uF. In the power supply panel i changed the 220uF caps to 470uF because that's what i had at the moment. It won't harm, maybe it will help with better filtering. But when you have the cap in the signal path, it's better to stay with the original value, otherwise it can alter the frequency getting through.@@SDsailor7
@@a.f.1587 Thank you, good info.👍
The outside pot is for bias usually 10mv
The inside pot is Center voltage 1/2 off B+
Regarding the power sag, I use a Sencore PR-57 but for power output test I have to go direct to the line; there is a sag due to the PR-57 AC voltage delivered under load. It might have been useful to see if the full 120V was still delivered under load.
I was connected directly to the line during that test but you're right, I should check for sag in the line as well
Thanks for the very informative video Hope you keep doing this.
I've got one that has got some noisy controls. Just starting to get it working again. Thanks for this video
The problem with single ended power supply designs is that the DC offset is thrown off when the supply sags. I noticed at the end that the clipping was at the positive end only, because of the sagging. Why they chose to go with that design instead of dual rail is beyond me, but there it is.
Variation on the speaker ( small ) are due to small voltage fluctuation on power supply , leaky output caps need to be replaced ..............mostly they are still good .
The second pot is for adjust symetrical clipping ( scope ) ..........without scope adjust for half the voltage on the main filter capacitor.
In contrast to opinions of many modern technicians , Quasi complentary output can sound very good !!! ( Same output devices on PP = same tonality and similar electric behavior under DYNAMIC load /working consditions ...........that are things one can hear , no complementary transistors are realy identical even when adjusted under same idle current...
So there's allways benefits or disadvantages to any design ......;
Those amplifiers will allways pop on start up ( loading of the cap ) and at shut down .........the good practice is to switch on/off with Speaker switch in OFF position ............
In these amplifiers there's NO such thing like DC OFFSET ! .............only half of the power voltage present on the main filter cap is measured on the output cap ! ( matching output transistors is allways a benefit in this case )
Nice video,i just got a sx 626 from a friend as a gift. On all outputs it has like a hum or static sound,when i turn the volume up a can hear the static in the background. Will cleaning the potentiometers make any difference?
Probably not, cleaning pots will only help when they are scratchy when used. A steady static might be a failing transistor or a cracked solder joint
@@TrevorsBench Thanks, could it be possible that ground loop could also create that static sound?
@@tomicajovevski Ground loops will introduce noise, typically hum or other noise on the power rails will come through. A steady rushing noise that's noticeably loud is most likely a noisy transistor, capacitor or resistor. All stereos will have some level of background noise when you turn them up full volume. If it's noticeable at normal listening levels then there is too much noise and it needs repair.
I have with a matching cassette deck.
Mine gets loud and punchy.
HI TYrevor , D5 is excelent for metal contacts, switches etc........but........For pots there's FADER deoxit ! ( the green can )
Indeed do not use D5 on pots ! Many do but it will reveal becoming a bad treatment after time !
I just dug my Pioneer 626 out. I'd like to try it. I bought this thing new. I haven't played it for years it's been stored dry but, outside. I was just wondering. Is there a way to get a hold of you if this 626 has any problems? Or, should it be gone through before I plug it in? Due to the recent of surge in vinyl. And the fact that my nephew just opened a record store in my hometown I want to use it with my Pioneer Pl 71 turntable, which I always loved and also bought new. From your video, you look very knowledgeable and I'm just checking you out. And thanks for the videos. PS I always babied my equipment and now that I'm retired and I'm locked down on covid sometimes.. I think this would be very good time in my life to listen to some good old music.
Hi Eric, If it were mine, I would open it up and inspect for any damage or evidence of critters. If it all looks ok try plugging it in and trying it out.
If it's still working, it will take several days of use to wake it up before it starts to sound good again.
Hope it goes well and I agree, too many of us put our old equipment away when we should be using them daily and enjoying it while we still can!
@@TrevorsBench no critters so far .
This guy is wakeing up. The volume
Control is a bit scratchy. Head phones coming alive. 😁
Taking care of Business was the first song in 20 years. This is kind of like Rip Van Winkle. Hay, can I try some makeshift speaker wire. I have two of the lugs ordered for the 626 mine disappeared somewhere. They won't be here till April from Germany at 25 bucks you said that they'd be about three times value I think. Anyway, I got a couple big realistic speakers I'd like to try.
i have a 626 which has been fine for the first few days since purchased..."last week".. and now when i power it on i am getting a popping/crackling noise through the right channel for a few seconds then seems to fade away !..only just noticeable when standing next to speaker ! however the bass pot is kind of "thumpy" when adjusted...i dont think its a dirty pot as it doesn't "crackle"...any advice would be appreciated..thank you.
The deoxit d5 shouldn’t be used on anything with a resistive type of track you would want to use fader lube f5. The d5 is best used on metal type contacts
Sorry I commented before the end of the video
Deoxit D5 and D100 does actually work well on pots. I'm not sure about the long term effects it may have. Other TH-camrs have commented to not use D5 or D100 on pots because it destroys the carbon track. I've yet to experience this but I've also only started using deoxit products a short time.
@@TrevorsBench yes the D5 does work but it won’t last long. I don’t know exactly what happens but as you said there’s word that it will destroy some of the resistive tracks
Hi Trevor. My 626 just dropped the right channel. Are you interested in servicing mine? I'm from Saskatoon.
Hello to my friends in Saskatchewan, email me
Salut ! Am căutat tranzistor echivalent pentru 2sb557/2sd427 la magazinele locale si nu am găsit. Mă gândesc să le înlocuiesc cu tranzistorii de tipul BD 317/318 care sunt mai accesibili la noi. Crezi ca e ok ?
Da, ar trebui să fie bine
What part number did you use to replace the death cap.
There is no 'death cap' I was half joking. I replaced it with a 0.1uf Y2 rated safety cap. Later I learned that cap shouldn't exceed 4700pF
@@TrevorsBench What do you think of replacing this with a 3 prong and getting rid of that cap. Ground the chassis.
@@jimbeaux4988 Yes you can do that. The cap needs to stay for line interference suppression but grounding would make the unit safer
I am showing 0.5 volts at the speaker terminals on both channels an all speaker outputs. What should I look for?
Looking at the circuit I can see there are DC blocking capacitors on both outputs. Also, there is two resistors total of about 23k that will allow current to leak through the capacitor.
This is the voltage you're seeing. I would ignore it. If you place a speaker load on the outputs, this leaking voltage will disappear.
@@TrevorsBench thanks i really appreciate it.
I hate those Pioneer special speaker plugs.
Wife was OCD.