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Post subject: Help with 1971 Twin Reverb
Posted: Fri Apr 01, 2011 4:06 pm
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Ok , brief history, 10 years ago or so my twin stopped working
I recently decided it was silly to have it collecting dust and wanted to know how old it was
serial number puts it at a 71

what it does is hums very loudly and does not work

also, at some point the 2.5 slow blow was replaced with a 20 amp auto fuse

so , I bought a fuse, powered it up, the fuse didn't blow and it hums badly with nothing plugged in

the #3 tube was visibly blown, ordered one waited patiently for arrival, changed it, fingers x'ed, same problem

removed power tubes, no hum, tried each one by themselves in each spot and hum was present in all 4

a very noticable pop can be heard then switching standby switch, more so with tube in 3 and 4 position

I'm assuming the power tubes are bad, and the rest should go as well, but don't want to spend the cash if it could be something else

any suggestions?


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Post subject: Re: Help with 1971 Twin Reverb
Posted: Fri Apr 01, 2011 5:47 pm
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Your filter and biasing caps are shot. Proceed no further until that issue is addressed.

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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Post subject: Re: Help with 1971 Twin Reverb
Posted: Fri Apr 01, 2011 7:21 pm
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thanks,figured I couldn't be lucky

now i have to see if the repair costs are worth it


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Post subject: Re: Help with 1971 Twin Reverb
Posted: Sat Apr 02, 2011 12:44 am
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Unless the amp is truly trashed, it's usually "worth it".

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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Post subject: Re: Help with 1971 Twin Reverb
Posted: Sat Apr 02, 2011 3:57 am
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If you are looking to sell this it would probably go for about $700-1000 as of right now in working shape.If that gives you any help


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Post subject: Re: Help with 1971 Twin Reverb
Posted: Sat Apr 02, 2011 2:27 pm
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thanks
the question at this point is putting (I assume) $200-300 into it and selling it for $700 worth it, or just buy a small practice amp for a hundred or so

it's not like I am going to need to play out anytime soon with it ,and it's been sitting for so long now, maybe just wait another ten years for it's 50th birthday and redo it then

maybe I'll have grandkids who want to play


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Post subject: Re: Help with 1971 Twin Reverb
Posted: Sat Apr 02, 2011 3:27 pm
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In that case I'd sell it "as-is" and use the proceeds for another amp.

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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Post subject: Re: Help with 1971 Twin Reverb
Posted: Sun Apr 03, 2011 6:30 am
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i had a similar issue with my fender twin reverb, it is a 1972 or 73 not sure no push pull button..when i bought it it was converted to a pre-cbs blackface and shoved into an original dual showman head ..there is a hum coming from the reverb when it is cranked past 3..i took it to an amp tech..he told me that the hum is caused by the location of the reverb tank being close to the chassis...and the twin was not meant to be in such tight enclosure..it was designed to be in a 2x12 cabn or 4x10 superreverb..although he is a very good amp tech...i just want to get a second opinion..i know there are some rare original twin heads. why those don't hum ?


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Post subject: Re: Help with 1971 Twin Reverb
Posted: Sun Apr 03, 2011 3:56 pm
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I would like to see one of those "rare original twin heads".

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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Post subject: Re: Help with 1971 Twin Reverb
Posted: Tue Apr 19, 2011 7:42 am
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Hi I am a guitarist/valve amp repair specialist and collector in the UK I have been collecting Fender amps for 30+ years and I have several Twin Reverb's from Blackface to 70's (Don't like the ones produced after that). I agree with ARJAY on this you will not find a Twin Reverb Head there is no such thing. You will find a Dual Showman Head but they did not have a reverb tank, at least I have never seen one. Fender new that because of the massive power and output transformers in such confined area the magnet fields would be far to close to include a reverb tank. Your amp guy is correct. It will definitely hum.


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Post subject: Re: Help with 1971 Twin Reverb
Posted: Tue Apr 19, 2011 9:11 am
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kenda47 wrote:
Fender new that because of the massive power and output transformers in such confined area the magnet fields would be far to close to include a reverb tank.


Which is why when reverb finally made it to the Showman in May of '68, Fender presented us with a monstrously-tall head cabinet that, when mated to the complimentary speaker enclosure, resembled the huge robot in "Kronos".

:lol:

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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Post subject: Re: Help with 1971 Twin Reverb
Posted: Tue Apr 19, 2011 9:24 am
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Retroverbial wrote:
Your filter and biasing caps are shot. Proceed no further until that issue is addressed.

Arjay

+1.....
just bought a BMR for a VC project with that same issue. New filter caps and no more hum.

gotta start there...good luck!!!


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Post subject: Re: Help with 1971 Twin Reverb
Posted: Wed Apr 27, 2011 6:36 pm
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actually decided to peak inside again and found a resistor that was burnt and the wire next to it was melted to it, I cannot determine its value , there is a red stripe first but the rest cannot be seen, this is under the filter cap housing, based on what I can tell it was probably red voilet red silver
does any one know what it should be
looks like there is a 10k next to it and two 220k's run under two of the caps
should it be a 1 watt 2.7k?

thanks everyone


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Post subject: Re: Help with 1971 Twin Reverb
Posted: Wed Apr 27, 2011 8:06 pm
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Looks to be a 2.2kΩ, 1-watt -- part of the voltage-dividing network to spread the load among the filter caps.

Here's the schematic that I think matches your amp......

http://www.ampwares.com/schematics/twin ... _aa270.pdf

HTH

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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Post subject: Re: Help with 1971 Twin Reverb
Posted: Sat Apr 30, 2011 3:25 pm
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thanks, much to my surprize I came home from work today to find my resistor had arrived
I got a carbon film 1 watt , but it looks much smaller than the carbon comp that is in there

is it ok to use this? and should I switch the other 3 as well or can films and comps live happily together ?

or should I search out a carbon comp?

thanks


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