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Post subject: Ceramic disc caps in a '64 Twin Reverb
Posted: Tue Feb 18, 2014 9:57 am
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Need some advice. The amp in question had never been serviced before. I just changed out all of the electrolytic caps in a friends '64 Twin Reverb. It was great for about a month, all the voltages were close, and then the Vibrato channel started to get microphonic and the volume control was erratic. Normal channel is fine. I did replace the pot, disconnected the bright switch and tried different V2's. The tap trick lead to the suspect cap, the .02 ceramic, V2 - pin 6, but do get microphonic tap noise all the way to the volume pot, just more at the .02.

I'd like to replace all the ceramics while I have it apart. Sourcing these cap values is the problem. The 250 and 500pf's can be Silver Mica's. The .1 on V4 - pin 6 can be an Orange Drop, but the rest are being elusive. Should I just go with close Orange Drops? I don't think I'll replace the .003 reverb cap.

Thanks for any input


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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Tue Feb 18, 2014 10:45 am
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Yeah, just go with SBE Orange Drop 716P's. If you can't find the exact equivalent cap, try placing a little silicone sealer or glue gun goop on the noisy disc cap. This sometimes helps the microphony issue.

In the tremolo section that has the classis 0.01, 0.01, 0.02 mica caps --- I had great success with (of all things) Sprague black buffer caps (aka: Black Beauties). These caps make a nice quiet, sensitive vibrato/tremolo section.


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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Tue Feb 18, 2014 2:02 pm
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BMW2002Ti wrote:
If you can't find the exact equivalent cap, try placing a little silicone sealer or glue gun goop on the noisy disc cap. This sometimes helps the microphony issue.


+1

The clear GE silicone in the small tube seems to work best. Try to work a dab on both sides of the cap if possible.

Arjay

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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Wed Feb 19, 2014 2:32 am
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Some stuff like that may change capacitance or / and make a short on capacitor , be carefull .

It's happened to me .


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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Wed Feb 19, 2014 2:37 am
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upnorth wrote:
The tap trick lead to the suspect cap, the .02 ceramic, V2 - pin 6, but do get microphonic tap noise all the way to the volume pot, just more at the .02.

Some time it is normal , no need to replace them

I'd like to replace all the ceramics while I have it apart. Sourcing these cap values is the problem. The 250 and 500pf's can be Silver Mica's. The .1 on V4 - pin 6 can be an Orange Drop, but the rest are being elusive. Should I just go with close Orange Drops? I don't think I'll replace the .003 reverb cap.

Don't replace them if you don't need , Ceramic cap and other are mostly good for life . Microphonic is not a problem in many circuit of the amp , you can't ( and don't need ) to fix it . Most of the time you can't .

Thanks for any input


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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Wed Feb 19, 2014 6:21 pm
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I didn't have any trouble sourcing the caps that you mention just last week. In fact I found several sources.

I got them from MoJoTone... @$0.19 IIRC.

cheers!

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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Wed Feb 19, 2014 6:45 pm
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Thanks. In fact I just went to Mojotone's site earlier today and see they're set up well for these. I'm just wondering if I should use the OD 716's for the .02 I need (which would be .022 in them) or the .02 ceramic disc. I'm sure either would be fine.

Thanks again for everyone's input, very helpful forum.


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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Wed Feb 19, 2014 7:59 pm
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Upnorth,

Either the OD or a ceramic disc cap will work fine. One note, ceramic disc caps can be noisy from the get-go. If you are going to use an OD cap, use a 600VDC rated one. Disc caps are often used in places where high voltage rating is needed (DC blocking is important). Tone sections and other time-constant sensitive places.


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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Sat Feb 22, 2014 7:32 pm
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You didn't take out the molded blue caps, did you?

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Post subject: Re: Ceramic disc caps in a '64 Twin Reverb
Posted: Sat Feb 22, 2014 8:04 pm
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Jim,

I think that he is talking about the ceramic disc caps. Like the "triplets" in the Vibrato/Tremolo section. Or those seen on Bright switches and treble portion of tone stack.


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