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  1. In this instance, the preamp board isn't even...

    In this instance, the preamp board isn't even connected to the power amp board, other than the supply voltages on that multipin cable. The noise issue is entirely on the power amp PCB. That was the...
  2. I don't advise shorting out Q4 & Q5, since you...

    I don't advise shorting out Q4 & Q5, since you need their Vce drops to power Q2/Q2A. The 555 timer IC generates the delay-turn-on, which then turns Q4/Q5 on enough for their large voltage drop, with...
  3. That.....shorting out the bias circuit to make...

    That.....shorting out the bias circuit to make Q14/Q11's collectors common, and connecting R10 to it is essentially how you make the front end a high voltage op amp. That, unfortunately closes the...
  4. GK 1001RB got dropped, now random noise comes & goes

    Our Guitar Dept brought over a GK1001RB that got dropped, with the complaint that it now produces loud hum when turned on, connected to speakers. I was able to restore the output phone jacks, which...
  5. It's a horrible Sony Mavica that is low...

    It's a horrible Sony Mavica that is low resolution, stores on 3.5" floppy. I briefly had a better camera until it's display failed. Burdened with huge debt, just haven't tasked funds to buy a...
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    Roland Boss GT-5 PedalóNo Output

    Last month, while taking in some of the more obscure non-working effects pedals from our rental inventory, this Boss GT-5 Effects Pedal came along, it having no output. I had no documentation on it,...
  7. Further Adventures in Repairing Ampeg SVT4-Pro

    This came in from our rental inventory, marked No Output. Amp was set for Bridge Mono. There is always a momentary pause of dread seeing these, knowing how much ‘fun’ they are to disembowel as well...
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    I'd just replace them with the spring-based...

    I'd just replace them with the spring-based hold-down clamps. I have a growing collection of bear-trap clamps that I've removed, and with sockets that DO grip the power tube pins as well as the...
  9. If' you're not getting any output from Aux 1 Send...

    If' you're not getting any output from Aux 1 Send jack (above Mic 4 input connector, rear panel), try Aux 2 Send. Note you can push the Solo buttons below the Aux 1 & 2 Send Masters in the master...
  10. Cone Surround & Spider Testing with DC Power Supply

    Here, I've put an Aguilar JDK-12 8 ohm speaker on the bench, face up, with my Kikisui PAC 16-10 0-16VDC @ 0-10A Power Supply to check this speaker's clicking sounds heard when driven hard. Set the...
  11. Back from a couple weeks' straight effort at our...

    Back from a couple weeks' straight effort at our Inventory warehouse where my Loudspeaker Test Station is set up. While the instrumentation use to reveal excess cone excursion beyond what the...
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    Earlier in your post # 6, you were seeing the...

    Earlier in your post # 6, you were seeing the negative bias voltage on pin 5, yet here, it being the 'other 6 pins" with respect to pins 3 & 4, if you're now seeing 0V on pin 5, you WILL see your...
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    One of the problems I have had continually with...

    One of the problems I have had continually with the 1001RB, 2001RB is the solder joints on the bridge rectifiers, as well as the AC Secondary header plug that runs the two-tier bipolar supplies. ...
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    As to what else the Ė15V supply is feeding, itsí...

    As to what else the Ė15V supply is feeding, itsí the same as what the +15V supply is feeding: the collectors of Q8 & Q9 in the voltage gain stages. Iím wondering if D16 is bad? Each of these LEDís...
  15. I hadn't thought (or remembered) the shop vac...

    I hadn't thought (or remembered) the shop vac approach. Though, as I was in 'foreign territory' and not in my shop where my shop vac lives, that approach still awaits me. I'm not a fan of poking...
  16. Will do.....thanks!

    Will do.....thanks!
  17. The Right Ch which wasn't working, now IS...

    The Right Ch which wasn't working, now IS working. It was a gift from a colleague years back, and have been meaning to get to it.

    After looking at the back side of the lightweight 10" cones, I...
  18. The B & K bulbs are mostly 6.3V/250mA, same size...

    The B & K bulbs are mostly 6.3V/250mA, same size as a 3AG 1/4" dia x 1-1/4" long fuse.
  19. Loudspeaker Test Station & most common bass cabinet failures

    Friday I set up a small Loudspeaker Test Station at our Equipment Rental Depot (CenterStaging, LLC Burbank, CA) to start going thru all of the failed guitar and bass cabinets first, to see what I...
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    Welcome to the Forum! You have quite a challenge...

    Welcome to the Forum! You have quite a challenge on your hands with only a multimeter available for troubleshooting one of these. I've repaired a good many SWA 1501's, SWA 1801's as well as the...
  21. Restoring a classis Oscillator for Loud Speaker / bench work

    Having a spare moment in the shop, waiting for parts to arrive, I extracted a classic Oscillator from my pile of stuff in one corner of the shop. A Bruel & Kjaer 1022 Beat Frequency Oscillator. I'm...
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    YES. Remove the power tubes again, then measure...

    YES. Remove the power tubes again, then measure the range of negative bias voltage from min to max on the bias pot. Note the bias voltage where you have it set that gave you 62mV at TP30. Using...
  23. A Tektronix P5122 X100 probe is a bit over $300....

    A Tektronix P5122 X100 probe is a bit over $300.

    56002

    I found a Hantek 100MHz X100 probe that I know nothing about on Amazon
    ...
  24. You need to review the specs on the scope probes....

    You need to review the specs on the scope probes. Most low-cost X100 scope probes are NOT intended for high voltage, nor can handle high voltage. X100 probes that are good for, say, 1500VDC are NOT...
  25. I didn't get anywhere with Yamaha....not being an...

    I didn't get anywhere with Yamaha....not being an authorized service center, but, after calling up their list on their website, I found Valley Sound Musical Products still listed....Stretch's company...
  26. Disregarding the size issue due to the larger...

    Disregarding the size issue due to the larger diameter, seriously risking tube breakage in the Super Bassman, the KT-88's did bias up just fine, and incremented up from their starting point much like...
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    Dealing with Fan noise is a multi-faceted issue. ...

    Dealing with Fan noise is a multi-faceted issue. Before getting into the loading issue on how the fan interacts with the chassis, and whether in such designs, it's pulling air in from the outside,...
  28. Source for Cliff Stack-Jack Ampeg PreampOut/Pwr Amp IN?

    After installing the new J/J KT-88 Power Tubes into an Ampeg SVT-CL, having robbed it of it's Sovtek 6550 to use in the Fender Super Bassman, I discovered the upper Preamp OUtput jack on the rear...
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