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Topics - Hawk

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1
Tubes and Hybrids / Fender Deluxe AB763... vibrato not working
« on: May 10, 2018, 11:06:53 AM »
Vibrato not working..can hear a very feint ticking sound. Suggestions?

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2
Tubes and Hybrids / Gibson Maestro Reverb Issue
« on: May 08, 2018, 10:34:37 AM »
Reverb is very weak or non-existent, hard to tell. Cable checks out. Amp works otherwise....Reverb pot has none or very little effect...reverb pot checks out okayhttp://cloud.tapatalk.com/s/5af1b3de20ea5/ga1rt%20%281%29.pdf

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3
Tubes and Hybrids / Capacitor identification Gibson Maestro GA-1TVT
« on: May 04, 2018, 02:11:04 PM »
Looking to change caps but not 100% sure how to identify. See pic....the large black Sprague caps have a red ring on them but I don't think they are polarized. The smaller black caps--how to identify? One of the caps tells us it is .03 ohms. Under the resistors there are 4 caps that have been flattened... can't read them--coupling caps? Guess I'll have to remove resistors to get at these caps. Thanks!http://cloud.tapatalk.com/s/5aeca230849eb/gibson-ga-1rvt-amplifier-schematic.pdf

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4
Amplifier Discussion / Astron Duplex Multi-Cap
« on: April 29, 2018, 05:34:01 PM »
I might need to replace a multi cap--Astron Duplex multi-cap on a Gibson Maestro Reverb Echo amp. Haven't tested it yet but I want to understand how it works before I check it out.  On the side of the cap is says that the black wire is common. The other wires are for 20,10, and 10 ufd. Is the black wire the common ground wire for all three caps and does it tie the negative ends of all the caps to ground? Are the other wires the positive ends of the 20,10 and 10 caps and got to circuit? Thanks

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Tubes and Hybrids / Gibson Maestro Reverb Echo speaker impedance
« on: April 24, 2018, 09:50:25 AM »
I'm troubleshooting a Gibson Maestro Reverb Echo amp and wondering if anyone knows the impedance of the 8 inch speaker? It shows a very low resistance reading .7 ohms so I know it's done.
Thanks.

6
Hi!

Well, no matter what channel I use in this amp, if I crank the bass on any channel the amp modulates on and off rapidly. I can crank the amp without bass and all sounds good but once I dial the bass in in there is a big modulating problem--like a loud bap,bap, bap sound that continues for quite some time until the sound dies out.  Power supply unable to keep up with low frequencies? Any thoughts? I replaced the output IC but same problem....anyone experienced this before? Suggestions? Thanks.

I also ran the amp through another speaker and the same problem exists.

Also hear clicking sound from power amp when this happens--relay?

7
Amplifier Discussion / SWR Studio 220 Squealing Sound/Intermittant
« on: May 19, 2016, 12:42:02 PM »
Hello Folks,

This amp sounds great, except in the last 30 minutes it's made two high-pitched squealing sounds which sound like sirens. This siren-like sound last for 1-2 seconds then stops. Thoughts? Cap issue (s)?

Thanks.

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Amplifier Discussion / Peavey Renown
« on: June 26, 2015, 09:12:28 AM »
Trying to repair an amp for a friend. Keeps blowing fuses. Drawing over 5 A current rating at 40v, not good. Check PT and found .3 ohms from Red/Centertap, both sides. Other fuses on lower voltage are fine. Need to pull board to check diodes--one half of their legs are under the board. Caps show good on ESR meter.

Did the lightbulb test on the PT, RG Keen's method, and no light at all...hmmm, internal short? Any other tests just to make sure?

I've included the schem and a pic of the output transistors. Always felt intimidated by these output transistors. Do I need to take out the pcb to check them?  :-[

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Tubes and Hybrids / Peavey Classic 30 Output Tube blows
« on: June 12, 2015, 11:01:39 AM »
Hi,

So I thought I had a microphonic power tube next to the phase inverter--it squealed if moved slightly in its socket but not always and then it would sometimes squeal on its own but not always. I swapped tubes to see if that made a difference and when I turned the amp back on that tube blew in the suspect socket and now none of them work (fuse is still good and amp turns on). The tube may not have been sitting in properly as  the tube holder was a little loose. I had cleaned the tube socket earlier with De-Oxit and let it dry for a good half hour to remove any gunk from the tube socket.

These amps are a pain to take apart but I'm wondering 1. Loose solder joints?  Or 2. Can a tube that doesn't sit tightly in its socket cause arcing and possibly create a microphonic situation?

The tube  furthest away from the phase inverter seemed a little microphonic when I moved it a little as well. But I can't test that now as these tubes are in series so no dice. I'll have to pick up some more tubes. I should probably check to make sure all voltages are correct as well.

Thoughts on how to proceed without  blowing more tubes and spending more money? :-\

Thanks,

Hawk

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Tubes and Hybrids / Capacitance Meter
« on: June 03, 2015, 09:24:44 AM »
I'm using a blue ESR meter for caps 1uf and above and I love this meter! But what about those little tiny caps? What are techs using to measure these little guys? Can anyone recommend a cap meter? I'm currently using a cheap Mastercraft Meter but I question the cap readings. I also know these little caps need to come out of the PCB in order to test properly. So, I'm putting it out there, what do people recommend? What works for you?

Thanks.

11
Tubes and Hybrids / Amp Cradle
« on: June 01, 2015, 02:19:51 PM »
I've been putting off buying an amp cradle due to cost. Everyone using one? Or have you found a cheaper alternative to working on a tube amp chassis....thanks!

12
Tubes and Hybrids / Universal Transformer Hook Up Peavey Classic 30
« on: May 25, 2015, 04:07:16 PM »
Hello Folks!

I'm trying to replace a Power Transformer for a Peavey Classic 30, 120V operation , with a Peavey Universal Transformer. The original transf. had two yellow secondary wires that attached to a connector which slid over a set of two pins on the board. There were also two red secondary wires which went to another connector and that connector slid over the other two pins on the board. Easy stuff.

But the universal transformer in the attached pic has two yellow wires with separate connectors and two reds with separate connectors. I'm guessing I need to remove the connectors and solder each of the four wires to the pins. Makes sense?

Also, the tech notes that came with Peavey transformer tell me to connect both the blue and brown to the hot side of the supply and the blue  and white to the neutral side which, again, appears easy enough.

I've never used a universal transformer replacement so I'm a little confused on this one.
 :-\
Thanks!

13
Tubes and Hybrids / Peavey Classic 30 Output Tube Filament Wiring
« on: April 21, 2015, 09:09:50 AM »
From what I understand the EL84 output tube filaments in a classic 30 are wired in series so if one tube malfunctions then that stops the voltage going to the other tube filaments so the other tubes will also stop working. If that is true is there a way to wire the filaments in parallel? Or is that something we wouldn't want? Was the output section designed that way for a good reason?  Thanks.

14
Amplifier Discussion / Thermostat/Fan
« on: April 15, 2015, 10:35:00 AM »
Hope this is okay to post as this is an audio amplifier rather than a guitar amplifier, but same concepts. I've attached a schematic (see bottom of schematic)

Trying to understand how the thermostat works. It is supposed to turn on the fan when the fan gets too hot. The fan is rated at 12V but the voltage on one side of the fan at R108 is 18v (won't that fry the 12v fan?).
What does this thermostat look like? Is it a thermistor?  I find no voltages on Q101,102. Is it safe to assume that there is no voltage as the thermistor is an open circuit until  the temp gets too high and therefore no voltage on transistors? Hmmmm...
Thanks! :-\



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Amplifier Discussion / Marshall Valvestate 8100
« on: March 13, 2015, 01:53:11 PM »
 Probably a simple fix but when I turn the effects knob (eff)  to the right the volume cuts out, starting at about 12 o'clock and then goes completey dead when turned all the way to the right. I used Deoxit and got rid of all the scratchiness but same problem. I removed the pot and measured 22K as it should be. As I turn the pot to the right it's as if the signal is being shorted to ground and then at the far right: dead, volume completely cuts out. ???
 

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