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Post subject: TWIN REVERB 15" HELP PLEASE
Posted: Tue Jan 22, 2013 3:11 pm
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When my amp is on and playing
the middle two tubes are barely glowing
while the outer two are red hot and amp
sounds like it is going into a mild breakup
not as clean as I thought a twin would be

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Tue Jan 22, 2013 4:14 pm
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Sounds to me like you have a biasing problem or other failure which is causing two tubes to run very cold (if they are operating at all) and the other two to be redplating. Unless you are experienced with troubleshooting high voltage amp circuits, I suggest you take the amp to a qualified tech immediately before any permanent damage occurs.

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Wed Jan 23, 2013 6:25 am
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Presuming that you are talking about output tubes, are all four the same type/brand? "Red hot"? Are the Plates red, or are you seeing the orange filament glow, or....?

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Wed Jan 23, 2013 8:41 am
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the outer two are glowing normally
the inner two are very faint like
barely lit

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Wed Jan 23, 2013 10:54 am
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shimmilou wrote:
... are all four the same type/brand?...

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Wed Jan 23, 2013 12:16 pm
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all four white label groove
tubes

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Wed Jan 23, 2013 6:03 pm
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OK. Tubes are not red plating. Brightness of the tubes is no indication of whether they are functioning properly or not. What you are seeing is most likely the heater element. It is possible you could have a problem with the heater circuit, but more information would be required regarding what the amp is doing or not doing to make a meaningful diagnosis.

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Thu Jan 24, 2013 9:50 am
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clem160 wrote:
all four white label groove
tubes



Just because the are "four white label" tubes...they could be from different manufactures maybe two are Chinese and two are Russian but tested out the same at GT-Fender as a quad matched set but have different filament design or or OR do they have different hours of usage, two have been played 800 hours two were in a super reverb and played 12 hours....or the filaments could be shrouded on two tubes (the middle two) by things like plate design..

or they are crapping out, or ancillary circuitry is...LIKE loose socket pins or CORRODED socket pins)

get some of this or similar deoxit D 5% clean your tube sockets from time to time (amp off, unplugged for ...for 5 mins or so -follow everybody's directions...cuz..you can fry ...badly) and permanently if not careful

let the amp tech fry...he/she/it been fried before...

(BTW an IT is an old fried aerospace engineer who used to design tube powered space shuttle stuff....) they exist and they are scary dudes...first it's..."hey kid..i can make that amp rock"...and it just can get weirder from there...careful, good luck :mrgreen:

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Thu Jan 24, 2013 11:23 am
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rollo wrote:
(BTW an IT is an old fried aerospace engineer who used to design tube powered space shuttle stuff....) they exist and they are scary dudes...first it's..."hey kid..i can make that amp rock"...and it just can get weirder from there...careful, good luck :mrgreen:


I knew some of those guys at Goddard Space Flight Center back in the '70s. Visions of Young Einstein saving the world from an atom bomb come to mind. :shock:

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Thu Jan 24, 2013 12:54 pm
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It appears to function normally
however the tone seems almost
overdriven not very clean
not very characteristic of what i
would expect

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1960 Fender CS 3tsb Strat
1961 Gibson SG Wildwood Pelham blue
1966 Fender CS Firemist Metallic Silver Strat


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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Thu Jan 24, 2013 1:01 pm
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Location: Natural Bridge, Virginia
clem160 wrote:
It appears to function normally
however the tone seems almost
overdriven not very clean
not very characteristic of what i
would expect


Well, so what do you want us to do? You've provided very little information for us to make a diagnosis.

Check/adjust the power tube bias. If the tubes have been in use for some time, put new ones in and bias them. Or just take the amp to a tech and let them look at it.

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Thu Jan 24, 2013 10:04 pm
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I would start by getting one 12AX7, and one 12AT7, and use them as substitute tubes trying the new tube in each respective position in the amp one at a time checking the sound after each change, noting that the 12AT7 is used for reverb driver and PI, while the 12AX7 can be substituted in all other positions (the problem is probably not the reverb driver). No bias necessary with preamp and PI tubes, bias is only necessary with output tube changes. Only after trying the preamp tubes would I try the output tubes, but you might want to start with output tubes, either way. Just power off the amp before swapping tubes. :idea:

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Post subject: Re: TWIN REVERB 15" HELP PLEASE
Posted: Thu Jan 24, 2013 10:27 pm
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I have a feeling the OP is gonna need this:

http://support.fender.com/schematics/gu ... _Rev-E.pdf

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