I think you're wrong about the bias bit. 54mV across .66 ohms yields about 80+ mA idle current. 26 mV across the pair of resistors equates to about 40 mA idle current. This is much more in the range to be expected for this class amp. Further, the higher bias on both channels would explain your higher current draw at the mains. I think the inability to adjust is caused by a problem elsewhere. I would ask if the amp seems to idle rather on the overly warm side at the heat sinks.
Really nice to see this amp in such great shape; a little tune up goes a long way. Pristine examples from the receiver/watt wars are getting hard to find out in the wild. They are performing in homes and listening rooms keeping the music alive. Thank you for your time!
My KA 701 is going to the shop on Monday.keeps going into safe mode seconds after turning on. I've owned this since 1980 or so. Bought it when I was in the Army. I hope it isn't in bad of shape. I love this amp. It did DJ duties at our wedding, lol. 🙏 To the amp gods .. Great video and beautiful amp.
Hey joe, Great layout at your bench/ workstation...nicely done service as well, and yes often times schematic's leave a little to be desired. They can be easily be misinterpretted, misprinted, etc.. Good call. ✌️❤️😁.
I had the same problem. The precision bias-adjustment trim-pots and also the DC-offset adjustment trim pots tend to fail on this amp. They don't even work properly when cleaned. You have to replace all of them with new equivalent trim pots with the lowest possible tolerance (I used "Burns" brand) and both adjustments (bias at 26mV on each channel and DC-offset at "zero" mV on both channels) are done smoothly and easily as suggested in the service manual.
I just noticed something at the beginning of your video that when you first powered up this Amplifier you had the volume control at around 11 o'clock. This is an very bad thing to do on these vintage receivers ,and even when they are new, as this will cause the contacts in the relays to ark and effectively shorten their life. These Receivers/Amplifiers should always be powered up with the volume in its minimum position during its soft start cycle. I worked in the QC Lab in Fort Worth from 1976-1983 for Tandy and have done various tests on various PCBs in the Realistic line and we have found with these hard power-ups it cuts the life of the relays by 2/3 of their manufacturer expectancies. It is always a good practice to follow by remembering that keeping the output at its minimum at power up is a good preventative maintenance lesson to follow.
Another fine session at your bench. Your right to use common sense when reading schematics and service manuals, as they often can be wrong. From what I have read, many companies make errors on their manuals. Apparently Marantz is famous for marking polarity wrong on the boards etc.... Anyway, I look forward to having my receiver next up on you bench. It should prove an interesting session for your viewers to see.
Thanks Joe, very interesting and great idea with the plastic straw over the screwdriver! Could you tell me what you were reading on the meter when testing the filter capacitors. I could see the probes but not the meter. Thanks again!
I just came across your channel after watching audio repair videos for years, and subscribed. A fellow Maritimer? I pick up a PEI accent, I think. I could be way off.
When you hit the power switch, after a short delay you hear a click from the transformer...and then you get power. What is that sound? On my 701 the clicking sound became longer and longer a wait. Finally it stopped working. Then I discovered if I removed the top casing and stuck a blow drier in there to warm things up I could trigger the power to go on. It's a PITA to always do this. Would love to get this resolved for once and for all.
Nice work Joe!👍 I wouldn't mind finding one of these clean & serviced to own! I already have the Kenwood matching companion tuner to complement this amp!⚡
The bias adjustment problem that you and others are experiencing is because the service manual is calling for the DC offset & bio adjustment within the same illustration, but theoretically the bios setting adjustment should be done under an 8 Ohm load this will make the difference, and they also want you to check the offset is at 0 with the "same VR" and that is without the 8 Ohm load from the spk terminals. The service manual omits this because it was actually common practice when they set the bios to these units in the factory with the 8 Ohm dummy load.
ouffff! I'm not sure the customers would absorbed the high cost of these fuses...maybe you can elaborate on these fuses, I'm interested to hear your views on them.
@@VintageAudioFever OMG! I cannot express how impressive these fuses are. I have a modest system, comprising of a Cambridge Azur 851 N Preamp DAC, a pair of Focal Solo 6; I started by upgrading to ceramic fuses, then went to the synergistic orange fuses and then to the synergistic purple fuses. The increase in sound quality was unbelievable ! Pricey, I know, but the improvement in sound quality was well worth it. Of all the dollars that I’ve spent on this stuff, including IsoAcoustics, audience cabling-used of course), this was the most significant.
sir gud am, i have def. kenwood integ. amp, can i perform dc biasing for my ka990d without connecting output transistor, thnk you so much for your reply...
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I think you're wrong about the bias bit. 54mV across .66 ohms yields about 80+ mA idle current. 26 mV across the pair of resistors equates to about 40 mA idle current. This is much more in the range to be expected for this class amp. Further, the higher bias on both channels would explain your higher current draw at the mains. I think the inability to adjust is caused by a problem elsewhere. I would ask if the amp seems to idle rather on the overly warm side at the heat sinks.
Really nice to see this amp in such great shape; a little tune up goes a long way. Pristine examples from the receiver/watt wars are getting hard to find out in the wild. They are performing in homes and listening rooms keeping the music alive. Thank you for your time!
My KA 701 is going to the shop on Monday.keeps going into safe mode seconds after turning on. I've owned this since 1980 or so. Bought it when I was in the Army. I hope it isn't in bad of shape. I love this amp. It did DJ duties at our wedding, lol. 🙏 To the amp gods .. Great video and beautiful amp.
Good luck with your amp and keep us updated on the repair
Hey joe,
Great layout at your bench/ workstation...nicely done service as well, and yes often times schematic's leave a little to be desired. They can be easily be misinterpretted, misprinted, etc..
Good call.
✌️❤️😁.
Thanks Rob!
I had the same problem. The precision bias-adjustment trim-pots and also the DC-offset adjustment trim pots tend to fail on this amp. They don't even work properly when cleaned. You have to replace all of them with new equivalent trim pots with the lowest possible tolerance (I used "Burns" brand) and both adjustments (bias at 26mV on each channel and DC-offset at "zero" mV on both channels) are done smoothly and easily as suggested in the service manual.
I'm really enjoying the ceramic screwdrivers for adjusting pots in a powered amplifier.
something to thing about....good point!
I just noticed something at the beginning of your video that when you first powered up this Amplifier you had the volume control at around 11 o'clock. This is an very bad thing to do on these vintage receivers ,and even when they are new, as this will cause the contacts in the relays to ark and effectively shorten their life. These Receivers/Amplifiers should always be powered up with the volume in its minimum position during its soft start cycle. I worked in the QC Lab in Fort Worth from 1976-1983 for Tandy and have done various tests on various PCBs in the Realistic line and we have found with these hard power-ups it cuts the life of the relays by 2/3 of their manufacturer expectancies. It is always a good practice to follow by remembering that keeping the output at its minimum at power up is a good preventative maintenance lesson to follow.
Another fine session at your bench. Your right to use common sense when reading schematics and service manuals, as they often can be wrong. From what I have read, many companies make errors on their manuals. Apparently Marantz is famous for marking polarity wrong on the boards etc.... Anyway, I look forward to having my receiver next up on you bench. It should prove an interesting session for your viewers to see.
Thanks Joe, very interesting and great idea with the plastic straw over the screwdriver! Could you tell me what you were reading on the meter when testing the filter capacitors. I could see the probes but not the meter. Thanks again!
I see it now...the Capacitor Wizard.
I just came across your channel after watching audio repair videos for years, and subscribed.
A fellow Maritimer? I pick up a PEI accent, I think. I could be way off.
welcome onboard, I am from the east coast yes...but not the island haha!
When you hit the power switch, after a short delay you hear a click from the transformer...and then you get power. What is that sound? On my 701 the clicking sound became longer and longer a wait. Finally it stopped working. Then I discovered if I removed the top casing and stuck a blow drier in there to warm things up I could trigger the power to go on. It's a PITA to always do this. Would love to get this resolved for once and for all.
Nice work Joe!👍 I wouldn't mind finding one of these clean & serviced to own! I already have the Kenwood matching companion tuner to complement this amp!⚡
Yea.they are nice amp!!! If you keep your eyes open...one will pop up for you....
Rare but there are some floating around.
The bias adjustment problem that you and others are experiencing is because the service manual is calling for the DC offset & bio adjustment within the same illustration, but theoretically the bios setting adjustment should be done under an 8 Ohm load this will make the difference, and they also want you to check the offset is at 0 with the "same VR" and that is without the 8 Ohm load from the spk terminals. The service manual omits this because it was actually common practice when they set the bios to these units in the factory with the 8 Ohm dummy load.
Good video and cool explanation
Bon Travail 👍
Man they knew how to make a good looking amp back then, just needs a couple of big meters :)
Highly recommend, a fuse upgrade to the synergistic purple!
ouffff! I'm not sure the customers would absorbed the high cost of these fuses...maybe you can elaborate on these fuses, I'm interested to hear your views on them.
@@VintageAudioFever OMG! I cannot express how impressive these fuses are. I have a modest system, comprising of a Cambridge Azur 851 N Preamp DAC, a pair of Focal Solo 6; I started by upgrading to ceramic fuses, then went to the synergistic orange fuses and then to the synergistic purple fuses. The increase in sound quality was unbelievable ! Pricey, I know, but the improvement in sound quality was well worth it. Of all the dollars that I’ve spent on this stuff, including IsoAcoustics, audience cabling-used of course), this was the most significant.
Ok....well it's good to know....and thanks for sharing
@@mikeeygauthier2959
Thank you for the info..
Haw close are the specifications at rated output
sir gud am, i have def. kenwood integ. amp, can i perform dc biasing for my ka990d without connecting output transistor, thnk you so much for your reply...