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  1. H

    Official AudioKarma G.A.S. Owner Club - The Great American Sound Company!

    Oh, doh! I see it clearly now. This is not a parallel push pull like I'd expect to see in a 200W amp capable of low impedance drive. It runs each NPN/PNP half in series. Different, but I suppose SOA is SOA at the end of the day!
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    Official AudioKarma G.A.S. Owner Club - The Great American Sound Company!

    Oh boy...so a customer of mine has dropped off what he claimed to be an Ampzilla to get sorted. It has all sorts of little issues, including a previous tech's poor workmanship on the fuse holders and sadly, the customer isn't even sure of the list of symptoms. It needs a new fan and with an ESR...
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    G8700 with an unusual and *severe* tuner problem

    I have a signal generator for alignments, I just need to find some time to come back to this unit again so I can run more tests and brainstorm some more. It still bugs me that TC04 doesn't have any effect and that's making me think I have front end issues. Following the dial accuracy adjustment...
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    G8700 with an unusual and *severe* tuner problem

    Sadly, cleaning seems to have had no effect on performance.
  5. H

    G8700 with an unusual and *severe* tuner problem

    It's possible it may indeed be that dirty. I've got some 99% Isopropanol in a can that should work well for this sort of thing. (It's not only handy with the straw on the can but its sealed so it won't turn to 85-91% on the shelf via hygroscopicity.)
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    G8700 with an unusual and *severe* tuner problem

    The fins have been cleaned with a canned gas duster. I may repeat the cleaning. The front end has power as well. What really perplexes me is the lack of effect with TC04. Turning that should cause a drastic frequency shift.
  7. H

    G8700 with an unusual and *severe* tuner problem

    So I'm fixing up a rather badly damaged 8700 and I thought I was going to get it down tonight but the Tuner is being a huge pain in the butt. AM: Dial and frequency readout reasonably accurate but the reception is so poor, the signal strength meter won't budge. I'm in DFW and not even the...
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    Let's see if we can't save this M91 someone else had a crack at...

    Well, the previous guy said he checked everything....we already know that to be false since he missed a fusible resistor. What else did he miss? Half of a 2SK129A blown open circuit. I'm betting once that's swapped out for a matched pair of 2SK117 that this thing will start to behave. I'll let...
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    Let's see if we can't save this M91 someone else had a crack at...

    He used The GIMP to stitch one together. It's a work of art and is helping me process this strange amp a little better. It seems that PA-0016 is a device that looks at the voltage across the emitter resistors and fiddles with the output of the input stage to compensate, either by varying the...
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    Let's see if we can't save this M91 someone else had a crack at...

    We may go that route if we can't fix the document ourselves using image manipulation. This is one of those amps where little things really count. (Big direct coupled power amps are notoriously unforgiving; only big SMPSes are worse.)
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    Let's see if we can't save this M91 someone else had a crack at...

    What I was actually hoping for was someone familiar with the PA-0016 and its quirks. (ie, someone looking at my voltages on the pins that could tell if it was still good.) Heck, I'm not even sure how the thing does bias tracking...there's no thermal feedback that's obvious. Speaking of PA-0016...
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    Let's see if we can't save this M91 someone else had a crack at...

    I've probably fixed a few hundred of the things by now. I use a variac. This one's just got me stumped and there's either something I'm not seeing that is blindingly obvious or a bad part sub. I know it's something in -Ve. The OPS failed well after plugging it in. A short test was made before...
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    Let's see if we can't save this M91 someone else had a crack at...

    So I've got in an M91 with a bit of a history. The person that handed it off to me claims that some "really good guy" in the D/FW area had a go at it and wasn't successful, so here it is at my home lab to try to get sorted. It won't come out of protection and I have humongous DC offset on one...
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    STK 4044V - any chance of getting a real one on eBay?

    They are prone to counterfeiting and some of the counterfeits are actually quality devices and similar to the NTE devices you used to be able to get easily. Others are anything but quality. It's a bit hit or miss and very easy to tell if you got a good one as soon as you power up. If you...
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    GE RC1650 amplifier signal path break, PEC suspected (SE 6AQ5 +12AX7)

    Yep. I got out the resistor kit, found 180K, soldered it in and called it good. Balance is spot on.
  16. H

    GE RC1650 amplifier signal path break, PEC suspected (SE 6AQ5 +12AX7)

    Well well well....what have we here? Let's get out the good old Fluke 45 and see what the resistance between he good anode and B+ is.... 189K Closest thing I have is 220K, so let's put a 220K in between the dead anode and B+.... Well look at that, I now have audio on both channels!
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    GE RC1650 amplifier signal path break, PEC suspected (SE 6AQ5 +12AX7)

    The root problem seems to be very low anode voltage on one of the anodes. Anode 1: 103VDC Anode 2: 0.3VDC
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    GE RC1650 amplifier signal path break, PEC suspected (SE 6AQ5 +12AX7)

    See corrections. I had the pinout backwards.
  19. H

    GE RC1650 amplifier signal path break, PEC suspected (SE 6AQ5 +12AX7)

    Unfortunately I don't have a diagram of what's in it. There are a few things it could be.
  20. H

    GE RC1650 amplifier signal path break, PEC suspected (SE 6AQ5 +12AX7)

    Swapped a PEC around and the fault traveled with it so it is a bad PEC. Pinout: 1: 12AX7 cathode 2: Output Xfmr secondary / positive speaker lead 3: Cap coupling to 12AX7 cathode (0.068uF between pins 1 and 3) 4: Screen(Pin 6) of 6AQ5 5: 12AX7 anode (pin 1) 6: Appears to be going to a cap and...
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    GE RC1650 amplifier signal path break, PEC suspected (SE 6AQ5 +12AX7)

    So I have a pesky GE RC-1650 hifi from 1963 in tonight and everything is just peachy after a recap and deoxit run save for the left channel which is dead silent. I do not appear to have anything going to the grid pin on one half of the 12AX7. Sending grid input from the working side to the...
  22. H

    2265 DC offset "fun"

    R709 on left channel: Expected: 4.7k Measured: 68M....just a wee bit out of spec. :D Replacement of R709 results in easily nulled offset. :thmbsp:
  23. H

    2265 DC offset "fun"

    I think you've nailed it. Voltage across R709: L: 48V R: 45V Resistor swapping will commence shortly.
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