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Post subject: Brownface Capacitor Value Question/Replacement
Posted: Fri Jul 20, 2018 8:13 pm
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So I'm finally getting around to replacing all of the electrolytic caps on this old Fender Brownface amp. Anyone have any preference for caps? I was thinking about ordering from amplifiedparts unless someone knows of a better place to get them from.

Most of the values are available with Sprague Atom or F&T. Does anyone have a preference or another brand I should look into? Also, I need to replace a few 25uf/100v caps that are only available with Illinois brand caps. Should I go with that brand or try to find a better brand with a slightly different value? If so, what brand and value would you recommend?

Finally, I need to get a 100uf/50v cap but I can't find this exact value. Would it be ok to up it to a 100uf/100v or what would be a good substitution for this cap?

Thanks for the help guys!


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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Fri Jul 20, 2018 8:25 pm
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Specifically, which brownface Fender amp?

Arjay

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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Sat Jul 21, 2018 1:42 am
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Wiche amp ?

I use always Sprague Atom or F&T, these are the best.
Don't buy Illinois cap , these are cheap .

About the 100 mfd/50 volts caps . Higher voltage work fine, better than lower voltage. Use caps with more voltage than the amp feed them.
Cons ; Higher voltage are more expensive and bigger.

I always bought caps from Tubes and More , Amplifier Parts are same than Tubes and More reserved for professional IMO

https://www.tubesandmore.com/products/capacitors

Or from https://www.tubedepot.com/t/diy-central/capacitors


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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Sat Jul 21, 2018 4:52 pm
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I have purchased recently from

Newark Element 14
http://Canada.newark.com
I am sure they have a USA site and also UK. Some of the parts I ordered shipped from the UK...at extra cost be forewarned...

And
Partsconnexion
https://www.partsconnexion.com/
[https://www.partsconnexion.com/[/url]

I recently purchased some high voltage Illinois Capacitors...and while I certainly wouldn't know good from bad, they seemed well made, solid with thick wire leads... not the clearly cheap Asian knockoffs.

I also purchased F&T and Sprague Atom for slightly more cost.

Partsconnexion has a variety of more expensive caps for high end audio. I almost sprung for some Jensen Caps for my 1965 Bandmaster...but went with F&T because of recommendations as above.

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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Sat Jul 21, 2018 7:08 pm
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Thanks for all of the info guys. It's a Brownface Deluxe so I want to make sure that I replace the caps with high quality parts and keep it as close to original as possible. I think I'll up the voltage for the 25uf/100v and 100uf/50v as recommended and pass on the Illinois brand caps. They probably work fine in most applications, but I do not mind spending a bit more for better quality caps for this amp. I'll check out some of the sites that were recommended for the best price.

Thanks!


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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Sat Jul 21, 2018 8:22 pm
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A picture of the chassis/ board exposed would be nice.

Don't know which schematic you're using, but all I see at least from the 6G3 layout is:
25u x 25v for all the cathode bypass caps
25u x 50v for the negative bias supply cap
then the rest of the electrolytic caps for the power supply are
3ea-16u x 450v
8u x 450v

You may have to buy slightly larger capacitance, maybe 10u in place of 8u or 20u in place of 16u. If you don't want to increase the capacitance shop around, you may find someone with the right values.
Adding capacitance changes the tone slightly towards a better lower frequency handling capability.
Increasing the voltage ratings doesn't change much. No need to overdue it here, measure your voltages and work towards what the schematic says.


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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Sun Jul 22, 2018 12:26 am
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fenderguy81 wrote:
Thanks for all of the info guys. It's a Brownface Deluxe so I want to make sure that I replace the caps with high quality parts and keep it as close to original as possible. I think I'll up the voltage for the 25uf/100v and 100uf/50v as recommended and pass on the Illinois brand caps. They probably work fine in most applications, but I do not mind spending a bit more for better quality caps for this amp. I'll check out some of the sites that were recommended for the best price.

Thanks!


Tubes And More stocks Sprague Atom electrolytics in a 16uf/475VDC flavor -- use those for the filter array under the doghouse. Be sure to check the values of your power-rail resistors and replace any that are out-of-spec (metal-oxide types are superior for that purpose). A higher DC voltage is perfectly acceptable for the bias-supply cap, ditto for those used in cathode-bypass circuits but try to stick to the capacitance values shown in the 6G3/6G3-A schematic. Inspect your screen-grid resistors on the power-tube sockets and ditch any that look wonky. Metal-oxide types are recommended for their superior longevity. Be sure to re-heat/re-flow any solder joints that appear "frosted". If you're replacing the power tubes, check the plate and bias voltage (365VDC and -26VDC, respectively) before installing the new bottles.

Arjay

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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Tue Jul 24, 2018 5:17 pm
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Here is the chassis that someone requested. Thanks again everyone! I'll be ordering the caps this week.

Image

Image

Image

Image

Image


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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Tue Jul 24, 2018 11:56 pm
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Don't forget the main PSU filter caps, under the doghouse (other side of chassis). Those are the most important (along with the bias supply cap) to replace.

Image


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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Wed Jul 25, 2018 3:06 am
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fenderguy81 wrote:
Here is the chassis that someone requested. Thanks again everyone! I'll be ordering the caps this week.



Replace this bias cap by a 100 mfd, 100 volts . Be careful it is reverse polarity on the circuit ç.

Image



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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Wed Jul 25, 2018 9:28 am
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100uF cathode bypass caps are overkill IMO, but if that's what you want to replace them with, that's your prerogative. The schematic calls for 25uF.

The power cord has been replaced with a 3 conductor cable, so the "death cap" can be removed.

Grid stoppers have been added, nothing wrong with that idea, but the implementation could be improved by not leaving one end hanging "in the breeze".

What year is this amp? I'm just curious about when Fender changed to the brass ground plate versus soldering the tag board grounds directly to the chassis.

Thanks for the pictures.
Image

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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Wed Jul 25, 2018 10:33 am
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vinyl wrote:
100uF cathode bypass caps are overkill IMO, but if that's what you want to replace them with, that's your prerogative. The schematic calls for 25uF.
[/img]


If you are talking about my answer, I talk about the negative voltage bias circuit cap, not bypass caps :?

That is why I show photo


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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Wed Jul 25, 2018 10:41 am
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Louis,
Sorry to be unclear, I was only talking about the cathode bypass caps. Your advice about the bias supply cap is very good.

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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Wed Jul 25, 2018 11:42 am
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vinyl wrote:
Louis,
Sorry to be unclear, I was only talking about the cathode bypass caps. Your advice about the bias supply cap is very good.


Thank's for your answer. You are right about bypass caps value


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Post subject: Re: Brownface Capacitor Value Question/Replacement
Posted: Wed Jul 25, 2018 8:16 pm
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Thanks for posting the pictures!! They make a great reference when working on your own equipment..

The biggest issue I see has already been pointed out, the grid stop resistor's (attached to the output tube grids pin 5 is usually routed directly over the tube socket between pin 1 and 5) then the yellow wire is attached at pin 1. Easy enough to clean up.. This is an AB763 mod for your amp, usually 1.5k 1/2watt or 1 watt carbon comp or carbon film. Some say you should add a screen grid resistor also, 470 ohm 2 or 3 watt carbon film or metal oxide.

The only other modification I would consider, would be a bias potentiometer but as long as your careful you may be ok without one.

Looks like you have a great amp in the works.


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