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Post subject: Silverface Twin Reberb 135w late 70'
Posted: Wed Mar 11, 2015 9:18 am
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Location: Nanterre, France
Hello,

Just bought a Silverface Twin Reverb 135w late 70'. This amp is in a bad shape, so I started to check it to see what to change (it doesn't work...) and try to fix at first the capa which are a bit old.
Unfortunately, I can't match thus inside the dog house and the schematic.
I found the 80µf/75V, 70µf/100v and the 2 x 220µf/285V but I have in addition 3 x 20µf/500V while on the schematic only one appears.
As you can see on the picture, some were already replaced especially the 220µf by radial rather than axial but I'm going to change it.

Image

Any advice would be welcome.
Is there anything I have to take care ? (expect the high voltage but this is not the first amplifier I repair or build)

Have a nice day
Pascal

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Post subject: Re: Silverface Twin Reberb 135w late 70'
Posted: Wed Mar 11, 2015 9:19 am
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It seems that I have an issue to display the picture.
Which server are you using to attach the picture ? (I tried Dropbox and Picas but noway...)

Pascal

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Post subject: Re: Silverface Twin Reberb 135w late 70'
Posted: Wed Mar 11, 2015 2:06 pm
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Here are the caps under the doghouse (red dots next to caps). The way Fender drew the schematic during this era is confusing. Not as well planned as the ones done prior to this era. You really need to hunt for them.

BTW... the 80mfd/75VDC and 70mfd/100VDC are filters caps in the bias supply. Please be careful about polarity of these caps and the first 220mfd/285VDC cap. Best to draw the orientation of the caps on paper or take a photo --- prior to replacing them.


Image


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Post subject: Re: Silverface Twin Reberb 135w late 70'
Posted: Wed Mar 11, 2015 9:35 pm
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If the fuse isn't blown, the caps probably are"servicable" and not the source of "no sound"
Check and clean the external speaker jack switching.
Don't plug speaker to Ext.
Tighten input and speaker jack nuts
Inspect speaker plug for loose connection. If you can twist tip or barrel, replace.

Is there hiss or hum present?


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Post subject: Re: Silverface Twin Reberb 135w late 70'
Posted: Thu Mar 12, 2015 9:13 am
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Awazleon wrote:
I tried Dropbox and Picas but noway...

If you want to use Dropbox, just post the link :arrow: Link

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Post subject: Re: Silverface Twin Reberb 135w late 70'
Posted: Thu Mar 12, 2015 9:17 am
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Correction, just add '?raw=1' to the Dropbox URL and the picture will display:

https://www.dropbox.com/sc/au99qc5rxjic ... rrza?raw=1

Image

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Post subject: Re: Silverface Twin Reberb 135w late 70'
Posted: Fri Mar 13, 2015 10:14 am
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Location: Nanterre, France
Guys,

thx for your advices.
Until now, I'm cleaning the amp. When I say cleaning, I mean that I wholly unmounted everything to only get the naked enclosure.
I don't like to work on a dirty amp. It is from 78'. I found that by looking on the OT.

I already took pictures of everything to avoid to miss something when rebuilding it.
Of course (and because this is not the first one I rework) I noted the capas polarity.

To be honest I don't know where the problem come from. As I said, I prefer open, clean and check everything before to power on. I like safety, especially with such amp :mrgreen:
The first goal is to replace the old capas in the dog house, then some decoupling capa (25uf/25v) because some are leaking.

BTW, how to set the bias of this amp ? I only found 1 pot but looking on the schematic, it sounds that it is more a balance pot rather than a real bias.
Where to check when "playing" with this pot ?

Have all a nice day
Pascal

PS : thx for the trick to attach picture.

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