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Post subject: 68 Silverface Twin, trying to determine AB763 or AC568
Posted: Wed Jan 23, 2019 12:51 am
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Hi all,

I have an 1968 Twin Reverb which is an export model with the red voltage selector on the back left hand side of the chassis. I am trying to determine without opening the chassis whether it is an AB763 or AC568 circuit since if I understand correctly the AB763 is more like the earlier Blackface twins internally.

The chassis number is A12059 which if I understand correctly would put it somewhere in the first half of 1968.
There are no black vertical lines on the original faceplate.

The other EIA and serial numbers from the transformers are:


REVERB TRANSFORMER: 22921 and 606-8-04

OUTPUT TRANSFORMER: 022889 and 606735

CHOKE: 022699 and 606-8-03

POWER TRANSFORMER: 022704 and 606647

Any input would be appreciated!

If it likely to be the AC568 then if I understand correctly my local amp tech should be able to convert it to AB763 specs according to this thread over at thegearpage.net:

https://www.thegearpage.net/board/index ... y.1813869/

Thanks in advance,

Dan


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Post subject: Re: 68 Silverface Twin, trying to determine AB763 or AC568
Posted: Mon Feb 04, 2019 12:00 am
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Joined: Wed Mar 31, 2010 12:48 am
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Location: Tombstone Territory
The AC568 revision was introduced on the production line during the first week of May in 1968. Thus, any '68 chassis with a date stamp (found adjacent to the bias-supply pot on the inside of the chassis) of 1868 or lower is likely the AB763 circuit. But a visual inspection of the bias-supply configuration and the power-tube sockets is the most reliable method to determining the amp's pedigree.

The EIA codes on your trannies do seem to correlate to an early '68 model.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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