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Post subject: Twin Reverb amp date
Posted: Fri Jan 09, 2015 9:37 am
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I have a Twin Reverb amp that I am trying to put an exact date on. According to the Superior Music website that was mentioned here on another thread, it looks like it points to a 1970 amp. The serial number stamped in the chassis is A23373-107. It has 117 volts, 2.3 amps on it I believe, silverface with black cloth, AB763 on the tag. The tag appears to be torn a bit so I can't really come up with any markings on that other than the printed material. Thanks.


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Post subject: Re: Twin Reverb amp date
Posted: Fri Jan 09, 2015 10:18 am
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Location: Province de Québec, Canada
Easiest dating is with number on transformers , second is number on pots .

AB763 tag is not reliable , we see often wrong tag on CBS area amps.

Picture will help too .

http://www.hendrixguitars.com/FendAmpDate.htm

If you are not original owner , check if fuse ( on the back ) is the right one


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Post subject: Re: Twin Reverb amp date
Posted: Fri Jan 09, 2015 10:22 am
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The Tube Charts are notorious for being incorrect, especially in that era.

The Amp is a 1970 Silverface. The 1970 serial #s for the Twin Reverb run A21400 to A25600. Suspect yours was produced in the 1st half of the year.

It's unlikely that it's an AB763 Circuit as Fender (CBS) switched to the AC568 circuit after May '68, the AA769 after Sept. '69. They further modified the circuitry in Feb. '70 to the AA270 circuit, but this wasn't put into production until late 1970. Odds are that yours uses the AA769 circuitry.

cheers!

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Last edited by Lightnin MN on Fri Jan 09, 2015 10:42 am, edited 1 time in total.

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Post subject: Re: Twin Reverb amp date
Posted: Fri Jan 09, 2015 10:41 am
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Please see this topic and Stratele52's excellent reply as to why it is better to post pics, or provide transformer numbers at least. Your particular serial number was used on many amps, due to a problem with the machine that stamped the serial numbers on the chassis.

http://forums.fender.com/viewtopic.php?f=12&t=97383&hilit=A23373

Pics of the inside of the chassis would also reveal which circuit was actually used, either AA270 or AA769. Like Lightnin MN said, pretty much no chance of it being an AB763.

vinyl


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Post subject: Re: Twin Reverb amp date
Posted: Fri Jan 09, 2015 3:41 pm
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I was hoping not to post photos but here goes. I'm sure it is obvious the one caveat to this amp, the huge speaker. I'm trying to figure a value to this amp but the speaker modification will really throw it off.
Image
Image
Image


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Post subject: Re: Twin Reverb amp date
Posted: Fri Jan 09, 2015 3:42 pm
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More pics:
Image
Image
Image


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Post subject: Re: Twin Reverb amp date
Posted: Fri Jan 09, 2015 5:25 pm
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Codyyy wrote:
I was hoping not to post photos but here goes. I'm sure it is obvious the one caveat to this amp, the huge speaker. I'm trying to figure a value to this amp but the speaker modification will really throw it off.


Sorry, have to say that your post seems a little disingenuous to me.

You start asking about dating your amp and now you're seeking to have the board appraise it for you. It's not usual to seek information in such a roundabout way here.

There is no way to appraise this amp because of the mods done to it except to say that it will sell for much less than an unmolested SFTR would.

The Market will dictate the price because the Buyers Pool for a modified Silverface is much smaller than for an original.

Set your price and adjust accordingly to whatever it takes to get a buyer.

cheers!

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Post subject: Re: Twin Reverb amp date
Posted: Fri Jan 09, 2015 5:38 pm
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I'll give you the benefit of the doubt and assume you want to know the value for insurance purposes. Lightnin MN is correct, in his assessment, though.

Thanks for the pictures, but none of them help answer your question in your original post. I can say at this point the grille cloth is not original, and the cabinet is probably not either. I don't believe it was possible to fit a 15" speaker in a twin reverb cabinet, even after changing the baffle. It is the date code on the transformers and the INSIDE of the chassis that will narrow down the date of manufacture to something more than "sometime during 1970". Some silverface and blackface chassis had a date code stamped inside them that would narrow it down to the week and year, and certainly the transformers have week and year date codes embossed in them that would at least help narrow it down to "after" this week and year. Clear pictures of the inside of the chassis and the components on the circuit board and around the power tubes and bias balance pot will make it much easier to determine if your amp is the AA769 or AA270 circuit.

It would also tell us if the amp has seen servicing, if it has at least been modified to remove the "death cap" etc.

You can't asses a value strictly on exact date of manufacture alone, and after all, anything is only worth what someone is willing to pay for it. If you were to put this amp on ebay or Craig's list, I don't think you'd find a lot of interest, unless the price was right.


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Post subject: Re: Twin Reverb amp date
Posted: Fri Jan 09, 2015 8:11 pm
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I'm not asking the forums specifically for the value of this amp, I am just stating what my intentions are. Obviously the value cannot accurately be obtained because of the modifications done on this amp. However, if I knew better about the hardware in this amp and could put an exact date to it, I could search better and figure that out. Thank you for the information, I'll look into the transformers and get it there.


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Post subject: Re: Twin Reverb amp date
Posted: Sat Jan 10, 2015 8:20 am
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Photos of the numbers stamped on the transformers & pots will help narrow-down the manufacturing date. Photos of the circuitry (esp the area around the balance pot and the board area of the phase inverter) --- will help determine the specific circuit model.
-----

Examples:


Around phase inverter resistors area:


Image


Photo around the balance pot:


Image


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Post subject: Re: Twin Reverb amp date
Posted: Sat Jan 10, 2015 9:46 pm
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Hope these pictures help. According to the transformer code it may be 1970 or 1980. Guitar Center says it is 1980.
Image
Image
Image


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Post subject: Re: Twin Reverb amp date
Posted: Sat Jan 10, 2015 11:18 pm
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By the photo of the output tranny, looks like 1970, 16th week manufactured Schumacher iron. Does the amp have pull-volume control?


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Post subject: Re: Twin Reverb amp date
Posted: Sun Jan 11, 2015 9:13 am
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BMW2002Tii wrote:
By the photo of the output tranny, looks like 1970, 16th week manufactured Schumacher iron. Does the amp have pull-volume control?

I do not think so. If you look at post #5 I believe, the first picture I have up shows the front of the amp. Comparing that to a video I saw on Youtube, it looks like it is missing that master volume control knob. Are there any other distinguishable features that would differentiate a 1970 amp from a 1980 amp (other than the grill cloth)? I believe this has the early Fender front logo with the "tail" on it, but that isn't to say that hasn't been changed at some point.


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Post subject: Re: Twin Reverb amp date
Posted: Sun Jan 11, 2015 10:15 am
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Numbers from the output tranny, choke and reverb tranny might help narrow it down more, but the date code on the power tranny is definitely 13 week of '70, like Beemer said, so we know it was made sometime after that.

Based on the extra filter cap in the bias supply, it's probably the AA270 circuit.

JBL K140 speaker is designed primarily for Bass guitar or organ according to the K series data sheet:

http://www.jblpro.com/pub/obsolete/k_series.pdf

vinyl


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Post subject: Re: Twin Reverb amp date
Posted: Sun Jan 11, 2015 11:09 am
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vinyl wrote:
Numbers from the output tranny, choke and reverb tranny might help narrow it down more, but the date code on the power tranny is definitely 13 week of '70, like Beemer said, so we know it was made sometime after that.
Based on the extra filter cap in the bias supply, it's probably the AA270 circuit.

vinyl


I don't violently disagree with you at all.

But we must also be aware of the inaccuracies inherent in Tranny Date Code dating too.

As with all things electrical, mechanical or electronic, Failure Rates plotted on a graph will show two spikes over the expected life cycle of a component - the beginning and the end.

These components usually (but certainly not always) fail in one of two periods: their infancy (due to a manufacturing defect) or in their old age (due to simply wearing out).

That said, if the Tranny were to fail in it's infancy and be repaired, say under warranty, it's likely that a substitute tranny w/ similar date codes would be used to replace it. So you could have an amp which pre-dates the tranny code date, maybe by as much as 2 years.

Validity of Tranny date codes is better insured if all the trannys (and other components - pots, switchgear and such) all agree.

cheers!

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