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Post subject: pro reverb squeal
Posted: Thu Feb 26, 2015 8:43 pm
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i recently recapped my blackface pro reverb and have played thru it 3 or 4 times with no problems. today, i played it extensively for about 1 hour. all of a sudden it started to squeal terribly. i turned the volume down but it didn't stop it. i turned other knobs down but nothing until i turned the reverb knob down a little. i continued to play it but in a short time it started to squeal again so i turned it off.

what should i look for to eliminate the squealing?

thanks,
mikeB


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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 2:16 am
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Did you only replace filter caps on the dog house ? Any mod inside you may do ?

Check for microphonic tube . Hurt gently each tube with schopstick , some may do normal noise ( like "tub tub " in speaker ) some not .

Dirty tubes socket ?


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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 8:52 am
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stratele52 wrote:
Did you only replace filter caps on the dog house ? Any mod inside you may do ?

Check for microphonic tube . Hurt gently each tube with schopstick , some may do normal noise ( like "tub tub " in speaker ) some not .

Dirty tubes socket ?


i did replace all of the electrolytics.
i'll check out the tubes as they are all new but that doesn't mean they are perfect.
thanks,

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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 12:50 pm
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MikeB wrote:

i'll check out the tubes as they are all new but that doesn't mean they are perfect.
thanks,



How do you check the tubes ?


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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 3:21 pm
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stratele52 wrote:
MikeB wrote:

i'll check out the tubes as they are all new but that doesn't mean they are perfect.
thanks,



How do you check the tubes ?


i haven't yet but i will check them with my tube checker. then i'll tap them like you suggested.
thanks,
mikeB.


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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 4:55 pm
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Tubes tester is not reliable to test tubes use in amps .

Tubes tester can't test squeal


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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 5:02 pm
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stratele52 wrote:
Tubes tester is not reliable to test tubes use in amps .

Tubes tester can't test squeal


so, the tap test is the only thing reliable? or, i guess swapping tubes.
thanks,
mikeB


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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 5:05 pm
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Finxing a amp by the web without seeing and hearing a amp is not easy .

Tapping is the fist thing I'll do


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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 5:09 pm
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stratele52 wrote:
Finxing a amp by the web without seeing and hearing a amp is not easy .

Tapping is the fist thing I'll do


i understand and i do appreciate your suggestions.
thanks,
mikeB


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Post subject: Re: pro reverb squeal
Posted: Fri Feb 27, 2015 7:16 pm
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I agree with Stratele, you have a microphonic tube(s). Since the Reverb control knob seems to stop the squealing, concentrate on V3 (12AT7), third tube from right on layout diagram. And V4 (12AX7), the fourth tube.

Check the other tubes, while you are at it. Lightly tap the tubes --- with eraser end of pencil. While the amp is on... volume low-mid. No guitar plugged in. Listen for ringing noise from bad tube(s).


Good luck! Keep us posted.


http://bmamps.com/Schematics/fender/pro ... _schem.pdf


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Post subject: Re: pro reverb squeal
Posted: Sat Feb 28, 2015 12:20 pm
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If the electrolytics are good and the preamp tubes are new, I would check the reverb wires and connections for good grounding. An open wire could cause squealing.
First, unplug the footswitch to see if that affects it.
Pinch the tabs on the RCA connectors to tighten them up. Clean the center pins as well. Check the connectors on the tank if that doesn't fix it.
If it continues, inspect the green and black wires inside the tank. Give each wire a slight tug with a pair of needle nose pliers to confirm they are solid connections. Sometimes, only the plastic insulation is holding it togather.


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Post subject: Re: pro reverb squeal
Posted: Sat Feb 28, 2015 6:03 pm
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TimsAudio wrote:
If the electrolytics are good and the preamp tubes are new, I would check the reverb wires and connections for good grounding. An open wire could cause squealing.
First, unplug the footswitch to see if that affects it.
Pinch the tabs on the RCA connectors to tighten them up. Clean the center pins as well. Check the connectors on the tank if that doesn't fix it.
If it continues, inspect the green and black wires inside the tank. Give each wire a slight tug with a pair of needle nose pliers to confirm they are solid connections. Sometimes, only the plastic insulation is holding it togather.


ah! one of the connectors on the tank was partially out. thanks!


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Post subject: Re: pro reverb squeal
Posted: Sun Mar 01, 2015 2:10 am
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MikeB wrote:

ah! one of the connectors on the tank was partially out. thanks!



No squeal before you work on , check , check and check your work :lol:


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