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Post subject: '62 Fender Super Amp poping sound on start up and shut down
Posted: Thu May 13, 2010 9:11 am
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I have a '62 Super which pops on starting and shutting down.
Almost all caps have been replaced along with many resistors.
I suspect it is coming from the vibrato circuit since it pretty well
disappears when I remove the vibrato tube next to the phase
inverter tube.


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Posted: Thu May 13, 2010 12:12 pm
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Location: Province de Québec, Canada
It's when you use the power switch ? For ON and OFF ? Or Standby switch ?

For me it's the stanby switch, if you ear sound.

You need a new switch. Your switch is arcing between is contacts.

This switch is made for 250 volts AC and your amp put more than 400 volts DC.

Best it's a 600 volts switch but this kind of switch is too big to keep original look


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Posted: Thu May 13, 2010 3:09 pm
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Strattele52
Merci pour ton reponse mais j'ai deja changer le interrupter et
j'ai l'essayer avec le standby "bridged", il pop encore.
Pardon mon francais mais je suis anglophone qui vit en Quebec
aussi, Saint-Lambert.


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Posted: Thu May 13, 2010 4:27 pm
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cbbarry

I read on The Ultimate Tone by Kevin O'Connor, page 2-56, he suggest to put a 10 nf to 100 nf cap on the switch.
I never tried myself, but soon I will. I think I have a amp doing this pop

I'm living at Pointe-des-Cascades


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Posted: Thu May 13, 2010 7:07 pm
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Hey guys, if it's okay, I'll throw in my opinion. When the standby switch is closed the power tubes via the OT center tap and choke are being hit with a substantial voltage spike. If your wall voltage is anything like northern Illinois(127VAC), then the B+ voltage is more like 475VDC in the operational mode. So the 600VDC tolerance for the switch and filter caps is a safe margin. I would make sure that the 470ohm screen resistors on the power tubes are in good shape. I've found that the 2watt metal oxide are quite a bit more quiet, than the 1watt carbon comp power resistors. These resistors seem to damp out alot of that pop.The suppression cap across the switch seems like a good idea, but like Stratele, I haven't tried it. (BTW I have one of Mr O'Connors' books for my education). And ,welcome to the forum ! Art

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Posted: Fri May 14, 2010 3:04 am
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Kvin O'Connor suggest to replace all 470 ohms 1-2 watts (?) for 1k 5 watts


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Posted: Fri May 14, 2010 4:05 pm
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Yeah Stratele, those big resistors would certainly do the job. I've used them in Marshall amps for EL34's and KT88's. Art

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Post subject: '62 Super popping
Posted: Sat May 15, 2010 11:34 am
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Thanks guys, the majority thinks I should use bigger higher watt
screen resistors. I'll give that a try and get back to y'all (I'm
from southern Quebec).


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Posted: Sat May 15, 2010 1:53 pm
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The 1K 5 resistor won't stop your "pop" at the switch. This resistor is use to save, protect your tube

The problem is your switches. You have to change it


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Posted: Sat May 15, 2010 10:09 pm
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Right, a new switch rated for 600VDC is needed(or preferred). The larger screen grid resistors are optional. Healthy 470ohm 1or2watt are just fine. I use 470/1watt in my '67 Band Master with NOS GE power tubes(475VDC plate volts), with the original switch and get a mild thump. But once those switches start to arc, it's best to replace them. BTW, your amp is the 6G4-A Super, right? Art

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Post subject: 62 Super popper
Posted: Wed May 19, 2010 12:43 pm
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Yes the amp is a 6G4-a.
Changing the grid resistors didn't stop da pop.
The switch was swapped with the one from my '65
reverb unit and should be healthy. Does anybody make
a 500w switch that fits?
When I remove the last vibrato tube (next to output driver)
the popping pretty well disappears but I've changed almost all of
the caps, only the ceramic disc caps remain. Resistor??
Barry


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Posted: Wed May 19, 2010 1:02 pm
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Bigger switch 500-600 volts need a bigger hole ( I'm pretty sure)

I don't know if a capacitor between the two switch contacts will remove the arcing ?


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Posted: Wed May 19, 2010 8:06 pm
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Barry, I would try a .047uf/600 cap across the switch. You could just attach it mechanically with clips and test it(without all the heating and reheating of the switch). The cap uf value could be .01-.1, it's not that critical, but use one rated for 600VDC. By removing V5 the gain stages of the vib channel are removed, so yeah, you wouldn't hear them getting smacked with the inrush. Just wondering if your amp has a three prong AC power cable ? Art

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Posted: Tue Jun 01, 2010 5:03 pm
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Thanks for the tips.
I installed a .063mf 600v capacitor across the standby switch.
It didn't get rid of the popping but it did cure the thump when
the switch is closed. Is it okay to leave the capacitor there, I mean
it won't adversely affect tone or anything?
Barry


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Posted: Wed Jun 02, 2010 5:22 pm
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Yeah, Barry, you're good with that cap as far as tone goes. Once the switch is closed, it is out of the picture. I'm still with Stratele, about the need of a new switch(600 VDC). The absence of the"thump"seems to indicate, that the cap smoothed the inrush to the output trans center tap. Now the concern is an arc in the switch or the choke. So I would go for the higher rated switch,first. BTW IMHO The benefits of using a stanby switch at start-up are questionable, especially with the power supply used in the 6G4-A. If you take a look at the schematic, you'll see that the power tube's bias supply is a matter of a quick switching diode and the RC circuit with two small value caps(small caps = shorter charge & discharge time). Meanwhile, the GZ34 needs to be heated before producing it's full DC voltage, then the first cap reservoir is charged, then on up the line. This all takes time and is adequate for cathode heating in audio tubes and is less stressful on the choke and filter caps. Just my view and opinion! Art

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