[fenderhead]

Hi, I have a '77 Fender Deluxe Reverb with super weak output. You
can't hear it pass any signal until you dial to ten, then you can hear
it but just barely. About as loud as a quiet conversation. It's the
same for any input. I tried swapping tubes around but no difference.
Anybody ever seen this symptom before? The amp was supposedly gone
through by a pro not long ago and has new looking Fender tubes. Newer
Eminence speaker. It looks really clean and not cruddy like a bar room
amp. Thanks for your time.

[Paul Stamler]

"fenderhead" wrote in message
...
Hi, I have a '77 Fender Deluxe Reverb with super weak output. You
can't hear it pass any signal until you dial to ten, then you can hear
it but just barely. About as loud as a quiet conversation. It's the
same for any input. I tried swapping tubes around but no difference.
Anybody ever seen this symptom before? The amp was supposedly gone
through by a pro not long ago and has new looking Fender tubes. Newer
Eminence speaker. It looks really clean and not cruddy like a bar room
amp. Thanks for your time.

Did you only try swapping the tubes that are already in the amplifier with
each other? If there's a bum one, this won't find the problem.

Since you say the problem's the same for any input (I presume you mean both
the normal and the reverb channel), the problem is almost certainly in the
sections common to both channels. Those would be the power amp and the power
supply, and the most likely culprits are the rectifier tube (5U4) and the
phase splitter/driver tube (12AT7). Replace them (they're not expensive
unless you buy boutique tubes) and I bet the problem goes away. If it
doesn't, then put the old tubes back in and keep the new ones for spares,
since you'll need them sooner or later, more likely sooner. (Fenders eat
12AT7s and rectifier tubes more quickly than preamp or power tubes.) At that
point, take the amp to a tech, maybe not the same one, and have him (it'll
always be a him) check the amp out again.

Looking clean vs. cruddy doesn't really tell you anything about the
condition of the tubes. Mine looks like hell, but when the tubes are new it
sounds great. (Which reminds me, *my* 12AT7 is about gone...)

Peace,
Paul

[Gareth Magennis]

"fenderhead" wrote in message
...
Hi, I have a '77 Fender Deluxe Reverb with super weak output. You
can't hear it pass any signal until you dial to ten, then you can hear
it but just barely. About as loud as a quiet conversation. It's the
same for any input. I tried swapping tubes around but no difference.
Anybody ever seen this symptom before? The amp was supposedly gone
through by a pro not long ago and has new looking Fender tubes. Newer
Eminence speaker. It looks really clean and not cruddy like a bar room
amp. Thanks for your time.



Amp techs have the luxury of being able to put in a complete new set of
valves. This tells you in one minute whether it is a valve problem or not.
Paul is right that simply swapping around valves is not always going to make
much of a difference if the faulty one is just moved to another critical
position.


What you could try is pulling all the preamp valves except the phase
splitter V6. (Leave the output valves in) Putting your ear to the speaker
means you should hear a quiet hiss and hum. Plugging the other preamp
valves here should give an identical noise. If one results in a much
quieter noise or nothing at all then that will be faulty. Don't assume
there is only one faulty valve though.

But thre are many other things other than faulty vales that can cause this,
but I wouldn't attempt to go any further than this without a decent
knowledge of valve amps. Remember there are VERY dangerous voltages inside
that can stay there long after the amp is switched off. Trust me, you do
not want to experience them first hand, you could die.



Gareth.

[Gareth Magennis]

"fenderhead" wrote in message
...
Hi, I have a '77 Fender Deluxe Reverb with super weak output. You
can't hear it pass any signal until you dial to ten, then you can hear
it but just barely. About as loud as a quiet conversation. It's the
same for any input. I tried swapping tubes around but no difference.
Anybody ever seen this symptom before? The amp was supposedly gone
through by a pro not long ago and has new looking Fender tubes. Newer
Eminence speaker. It looks really clean and not cruddy like a bar room
amp. Thanks for your time.



Ah, just thought. You havent plugged your speaker into the Ext speaker jack
instead of the internal one? If so the output transformer will be shorted
and you will get exactly the symptoms you describe.



Gareth.

[Scott Dorsey]

In article ,
fenderhead nill wrote:
Hi, I have a '77 Fender Deluxe Reverb with super weak output. You
can't hear it pass any signal until you dial to ten, then you can hear
it but just barely. About as loud as a quiet conversation. It's the
same for any input. I tried swapping tubes around but no difference.
Anybody ever seen this symptom before? The amp was supposedly gone
through by a pro not long ago and has new looking Fender tubes. Newer
Eminence speaker. It looks really clean and not cruddy like a bar room
amp. Thanks for your time.

It's broke. It could be a power supply problem, could be a gain stage
problem, could be a speaker problem.

You put signal in, you get out the scope, and trace the signal from the
input to the output. Where the signal disappears, that's the stage where
the problem lies.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Gareth Magennis]

"Gareth Magennis" wrote in message
...

"fenderhead" wrote in message
...
Hi, I have a '77 Fender Deluxe Reverb with super weak output. You
can't hear it pass any signal until you dial to ten, then you can hear
it but just barely. About as loud as a quiet conversation. It's the
same for any input. I tried swapping tubes around but no difference.
Anybody ever seen this symptom before? The amp was supposedly gone
through by a pro not long ago and has new looking Fender tubes. Newer
Eminence speaker. It looks really clean and not cruddy like a bar room
amp. Thanks for your time.



Ah, just thought. You havent plugged your speaker into the Ext speaker
jack instead of the internal one? If so the output transformer will be
shorted and you will get exactly the symptoms you describe.



Gareth.


To clarify, this doesn't mean the output transformer is dead. Try the other
speaker socket instead, it may well work as it should.



Gareth.

[neel & bob]

On Thu, 1 May 2008 11:17:21 +0100, "Gareth Magennis"
wrote:


"fenderhead" wrote in message
.. .
Hi, I have a '77 Fender Deluxe Reverb with super weak output. You
can't hear it pass any signal until you dial to ten, then you can hear
it but just barely. About as loud as a quiet conversation. It's the
same for any input. I tried swapping tubes around but no difference.
Anybody ever seen this symptom before? The amp was supposedly gone
through by a pro not long ago and has new looking Fender tubes. Newer
Eminence speaker. It looks really clean and not cruddy like a bar room
amp. Thanks for your time.



Amp techs have the luxury of being able to put in a complete new set of
valves. This tells you in one minute whether it is a valve problem or not.
Paul is right that simply swapping around valves is not always going to make
much of a difference if the faulty one is just moved to another critical
position.


What you could try is pulling all the preamp valves except the phase
splitter V6. (Leave the output valves in) Putting your ear to the speaker
means you should hear a quiet hiss and hum. Plugging the other preamp
valves here should give an identical noise. If one results in a much
quieter noise or nothing at all then that will be faulty. Don't assume
there is only one faulty valve though.

But thre are many other things other than faulty vales that can cause this,
but I wouldn't attempt to go any further than this without a decent
knowledge of valve amps. Remember there are VERY dangerous voltages inside
that can stay there long after the amp is switched off. Trust me, you do
not want to experience them first hand, you could die.



Gareth.

Thanks everyone. It was the .001 cap that feeds pin 2 on the phase
splitter. The Optivisor revealed it to be visibly disconnected.
Also, someone removing one of the power tubes had twisted it as if it
were a bayonet type preamp shield and snapped off the locator pin,
which was left stuck in the socket hole so the replacement 6V6 they
stuck in wasn't inserted etc. but did ram the broken stub into the 5
watt resistor that goes across the socket. (grid?) This is the second
one of these I've seen this winter- must be a rock and roll thing.
The amp was completely unmolested, just like a time machine when I
opened it. It does have an Eminence Legend 12" speaker. This is a
replacement, right? It sounds fabulous, with incredible punch- the
reverb makes me weep. I'm fixing it for a friend,.. Is it wrong to
tell people you're waiting for parts and just play it for a while? Is
$750 usd out of line for an old amp like this?
It has a bit of hum at idle but you don't notice it with the volume up
past two and a half, which is surprisingly loud. That pot accessible
from the tube side of the chassis is some kind of hum balance for the
bias circuit? If you turn the Reverb all the way up the hum gets a bit
louder. The vibro ticks a little bit when you stop playing for a few
seconds and sweeping the Intensity knob changes the tone and output
level noticeably.
p.s. Was it common with this era Fenders to have a coiled light gauge
wire wrap as some kind of rf shielding on some of the bundles? It's
tied to the brass ground thing that's common to all the pots.
Thanks again.

[jakdedert]

neel & bob wrote:
On Thu, 1 May 2008 11:17:21 +0100, "Gareth Magennis"
wrote:

"fenderhead" wrote in message
...
Hi, I have a '77 Fender Deluxe Reverb with super weak output. You
can't hear it pass any signal until you dial to ten, then you can hear
it but just barely. About as loud as a quiet conversation. It's the
same for any input. I tried swapping tubes around but no difference.
Anybody ever seen this symptom before? The amp was supposedly gone
through by a pro not long ago and has new looking Fender tubes. Newer
Eminence speaker. It looks really clean and not cruddy like a bar room
amp. Thanks for your time.


Amp techs have the luxury of being able to put in a complete new set of
valves. This tells you in one minute whether it is a valve problem or not.
Paul is right that simply swapping around valves is not always going to make
much of a difference if the faulty one is just moved to another critical
position.


What you could try is pulling all the preamp valves except the phase
splitter V6. (Leave the output valves in) Putting your ear to the speaker
means you should hear a quiet hiss and hum. Plugging the other preamp
valves here should give an identical noise. If one results in a much
quieter noise or nothing at all then that will be faulty. Don't assume
there is only one faulty valve though.

But thre are many other things other than faulty vales that can cause this,
but I wouldn't attempt to go any further than this without a decent
knowledge of valve amps. Remember there are VERY dangerous voltages inside
that can stay there long after the amp is switched off. Trust me, you do
not want to experience them first hand, you could die.



Gareth.

Thanks everyone. It was the .001 cap that feeds pin 2 on the phase
splitter. The Optivisor revealed it to be visibly disconnected.
Also, someone removing one of the power tubes had twisted it as if it
were a bayonet type preamp shield and snapped off the locator pin,
which was left stuck in the socket hole so the replacement 6V6 they
stuck in wasn't inserted etc. but did ram the broken stub into the 5
watt resistor that goes across the socket. (grid?) This is the second
one of these I've seen this winter- must be a rock and roll thing.
The amp was completely unmolested, just like a time machine when I
opened it. It does have an Eminence Legend 12" speaker. This is a
replacement, right? It sounds fabulous, with incredible punch- the
reverb makes me weep. I'm fixing it for a friend,.. Is it wrong to
tell people you're waiting for parts and just play it for a while? Is
$750 usd out of line for an old amp like this?
It has a bit of hum at idle but you don't notice it with the volume up
past two and a half, which is surprisingly loud. That pot accessible
from the tube side of the chassis is some kind of hum balance for the
bias circuit? If you turn the Reverb all the way up the hum gets a bit
louder. The vibro ticks a little bit when you stop playing for a few
seconds and sweeping the Intensity knob changes the tone and output
level noticeably.
p.s. Was it common with this era Fenders to have a coiled light gauge
wire wrap as some kind of rf shielding on some of the bundles? It's
tied to the brass ground thing that's common to all the pots.
Thanks again.

Sounds like it only needs a complete recapping in order to function for
another 30 years. Caps might 'not' be the source of the hum, but it's a
good bet.

jak

[RD Jones]

On May 2, 3:59 am, neel & bob wrote:

The amp was completely unmolested, just like a time machine when I
opened it. It does have an Eminence Legend 12" speaker. This is a
replacement, right?

Yes, the original speaker was most likely a Fender labeled Utah MS12G.

I'm fixing it for a friend,.. Is it wrong to
tell people you're waiting for parts and just play it for a while?

Only if you cause him to miss a gig or session with the amp.
You have to check the reliability of your repairs, don't you ? ;-

Is $750 usd out of line for an old amp like this?

A Deluxe in good operating condition will fetch that or more
here in Nashville. Even more for a Black Face.

It has a bit of hum at idle but you don't notice it with the volume up
past two and a half, which is surprisingly loud. That pot accessible
from the tube side of the chassis is some kind of hum balance for the
bias circuit?

Yes.

If you turn the Reverb all the way up the hum gets a bit
louder.

The reverb recovery transducer will pick up some hum from the
power transformer. Check grounds and shields, and possibly
orientation of the tank to the PT.

p.s. Was it common with this era Fenders to have a coiled light gauge
wire wrap as some kind of rf shielding on some of the bundles? It's
tied to the brass ground thing that's common to all the pots.

Yes.

rd