vintage 1967 deluxe reverb filter caps?

[echo44]

Hi I have a 1967 blackface reverb that I got last year on ebay.
Everything is original including all the filter caps,
It sounds great except for a buzzing in the original speaker i think its starting to go and doesn't occur when i try a different speaker.

So I inspected the caps under the pan and there is the most tiny of bubbles
starting to form on the ends. they are so small you have to really look close to see them. There is no leakage. So I have heard two schools of thought.
some say change them regardless the amp will sound better and either way they will fail soon anyway. Another friend who owns a guitar store said "hey the amp sounds great don't mess with it until you have to."

Than there is the whole "all original" value of the amp that will be lost if I change out parts. I am not sure how I feel on this as I bought the amp to play.
just wanted to get others opinions to see what they would do in my situation.

[NickC]

Those blisters on the ends of the caps are a sure sign they MUST be replaced ASAP. Do not run the amp. If those caps fail (i.e. explode), they'll spew molten electrolyte all over (hence the "doghouse").

Electrolytic caps must be replaced periodically (every 10 or so years). However, you will still see amps with original eCaps that have been run for 40+ years. They're living on borrowed time.

Recapping a Blackface is a necessity and should not hurt the value. What's the point of having a vintage amp if you can never run it? Amps were made to be played. You'll enjoy it for a long time after doing that essential recap.

[Phil_S]

What Nick says....some people preserve the vintage look by saving the outer tube of the original caps and stuffing the new ones inside. Personally, I don't see the point. Use good quality caps. This isn't the time or place to go cheap.

BTW, that guy who says to leave it alone obviously knows nothing about electronics even though he's probably got good intentions.

[HeeBGB]

Replace the caps and keep the original ones in a ziplock bag in the bottom of the cab.

[echo44]

Ok so I decided to go forward and change the caps have noticed some issues:

This cap I think it is a bias cap is 50uF/ 50 V looking at the schematic shouldn't it be
25uF 50 V?

Also found a strange blue thing will post pictures

first here is the cap that I think is wrong value

[echo44]

Ok so here is a picture of a blue component I have never seen these before?
I think it doesn't belong? Someone told me it may be related to stopp popping noise with vibrato effect?
also what is the component next to it with a rubber cover on it?

[echo44]

here is another picture from the other side

[echo44]

here schematic

[NickC]

..............
also what is the component next to it with a rubber cover on it?

That is the optocoupler ..... aka the "bug". It's part of the vibrato circuit.

[Firestorm]

50/50 is fine for the bias cap. Later versions use. 50/70. The blue cap is the original Fender fix for ticking vibrato. The later service bulletin took that cap to ground instead of the top of the 10M.

[echo44]

can i use a 25uF 50V instead of the 50uF 50 volt as that is all I have
and out of curiosity if the schematic calls for a 25/50 why is there a 50/50?
It looks original?

[Firestorm]

can i use a 25uF 50V instead of the 50uF 50 volt as that is all I have
and out of curiosity if the schematic calls for a 25/50 why is there a 50/50?
It looks original?

The bias supply has 60Hz ripple, which is hard to filter. Fender eventually bumped the cap up to 50uF to smooth it a little more. Your amp was built later in the AB763 series (it has the dual 25uF bypass caps with the red and yellow ends rather than the earlier caps with brown cardboard covers) so it shows where Fender was headed at this point. You can use the 25uF; most bias supply hum is phase cancelled in the output.

[echo44]

Do the earlier versions before AB763 sound different ? would this still be considered the typical blackface circuit I know around the time this amp was made was when CBS took over and they were heading towards silverface era?

Thanks!! I am always amazed how much information you guys know!!

[Firestorm]

Still typical blackface. Long before CBS bought them, Fender had the habit of using whatever they had in stock, regardless of what the schematic said.

[jelle]

That blue thing is a cap to stabilize the vibrato circuitry. I would prob put it in a bit nicer. The filter caps...yes, imagine driving 120 mph with tires that old. I prefer new ones. Doghouse, bias cap and the cathode bypass caps. Good luck!