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Geschwader · May 21st, 2007, 11:03 AM

While doing a full Cap Job this weekend in my AB868 silverface Deluxe, I noticed that the circuit seems to be "missing" some of the caps that the AB763 circuit has. From right to left the AB763 circuit has three pairs of 25uf 25v caps, and then one in the vibrato section. However, only the far right set was there. The other two had only one 25uf 25v cap. Since this stage of the circuit seems virtually identical to the AB763 one, why the "missing" caps? Should I add them?

Any help would be most appreciated.

Bluesbob · May 21st, 2007, 04:54 PM

Are you sure they're not just different makes? I know my '73 DR had all the same kinds of bypass caps, but it's possible Fender started to use a new batch right in the middle of assembling your amp.

jjmantele · May 21st, 2007, 07:31 PM

Sounds like a possible "mod" to reduce gain and reverb?

A1270 is probably the era for your amp. PI component values are different from AB868.

Geschwader · May 22nd, 2007, 10:46 AM

I bought this amp 25 years ago from the original owner. No mods were done, and from the look of the circuit board, the full allotment of caps was never there to begin with. Very odd....

Bluesbob · May 22nd, 2007, 02:37 PM

Need a picture.

Wally · May 22nd, 2007, 04:17 PM

Check the backside of the chassis. In the SF era, Fender moved a couple of bypass caps to ground points on the back panel.

Chris Callahan · May 22nd, 2007, 04:29 PM

Quote:

Originally Posted by Wally

Check the backside of the chassis. In the SF era, Fender moved a couple of bypass caps to ground points on the back panel.

I noticed this in my 72 SF Twin. Any idea why? When I recapped it, I wired it like the "layout". It didn't make any apparent sonic difference.

Wally · May 22nd, 2007, 04:38 PM

Chris, I don't have any idea...other than that when you have EE's on the payroll, they have to do something, right?

May 21st, 2007, 11:03 AM	#1 (permalink)
Geschwader TDPRI Member Join Date: Nov 2006 Location: Boston Posts: 7	Coupling/bypass caps in '72 Deluxe Reverb While doing a full Cap Job this weekend in my AB868 silverface Deluxe, I noticed that the circuit seems to be "missing" some of the caps that the AB763 circuit has. From right to left the AB763 circuit has three pairs of 25uf 25v caps, and then one in the vibrato section. However, only the far right set was there. The other two had only one 25uf 25v cap. Since this stage of the circuit seems virtually identical to the AB763 one, why the "missing" caps? Should I add them? Any help would be most appreciated.

May 21st, 2007, 04:54 PM	#2 (permalink)
Bluesbob Tele-Afflicted Join Date: Mar 2003 Location: East Suffolk L.I. Posts: 1,364 19 Photos	Are you sure they're not just different makes? I know my '73 DR had all the same kinds of bypass caps, but it's possible Fender started to use a new batch right in the middle of assembling your amp. __________________ What, me worry?

May 21st, 2007, 07:31 PM	#3 (permalink)
jjmantele Tele-Holic Join Date: Aug 2003 Location: New Jersey Posts: 975	Sounds like a possible "mod" to reduce gain and reverb? A1270 is probably the era for your amp. PI component values are different from AB868. __________________ JJman If it says "Vintage" on it -it isn't.

May 22nd, 2007, 02:37 PM	#5 (permalink)
Bluesbob Tele-Afflicted Join Date: Mar 2003 Location: East Suffolk L.I. Posts: 1,364 19 Photos	Need a picture. __________________ What, me worry?

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May 22nd, 2007, 10:46 AM	#4 (permalink)
Geschwader TDPRI Member Join Date: Nov 2006 Location: Boston Posts: 7	I bought this amp 25 years ago from the original owner. No mods were done, and from the look of the circuit board, the full allotment of caps was never there to begin with. Very odd....

May 22nd, 2007, 04:17 PM	#6 (permalink)
Wally Doctor of Teleocity Join Date: Mar 2003 Location: Lubbock, TX Posts: 13,730	Check the backside of the chassis. In the SF era, Fender moved a couple of bypass caps to ground points on the back panel.

May 22nd, 2007, 04:38 PM	#8 (permalink)
Wally Doctor of Teleocity Join Date: Mar 2003 Location: Lubbock, TX Posts: 13,730	Chris, I don't have any idea...other than that when you have EE's on the payroll, they have to do something, right?

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