Vox AC30 6TB, 2002

N

N_Cook

Guest
Normal or abnormal ?
Came in for an intermittant problem, fixed, and the following the owner
lives with but is it normal or abnormal?
With feed into a "normal" input and the "brilliant volume" at zero then
there is no control of the bass on the tone control, you need to have a
little advance on the brilliant volume.
Trouble around V7 ECC83 ?
DC voltages cathode,grid,anode
"brilliant half" 0,1.4V, 182V
"tone half" 182,183,290V
all associated pots ,Rs and Cs check out agreeing with schematic as does the
valve and same Vs with a different valve


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
 
On Wed, 14 Jan 2009 14:09:27 -0000, "N_Cook" <diverse@tcp.co.uk> wrote:

Normal or abnormal ?
Came in for an intermittant problem, fixed, and the following the owner
lives with but is it normal or abnormal?
With feed into a "normal" input and the "brilliant volume" at zero then
there is no control of the bass on the tone control, you need to have a
little advance on the brilliant volume.
Trouble around V7 ECC83 ?
DC voltages cathode,grid,anode
"brilliant half" 0,1.4V, 182V
"tone half" 182,183,290V
all associated pots ,Rs and Cs check out agreeing with schematic as does the
valve and same Vs with a different valve
Click to expand...
Assuming I am looking at the correct circuit - the bass control is in the output
of the brilliant circuit only. The "brilliant" and "normal" are mixed at the
junction of the 220k resistors so the bass control will have no effect on the
normal channel.
The brilliant volume control effectively grounds the grid of V7a so I would
expect 0v there and 1.5v ish on the cathode.

--
Geo
 
Geo <hw9j-s5hw@dea.spamcon.org> wrote in message
news:pr1sm4p2jqpk3gg1afubpeqtuc1gjndtn1@4ax.com...
On Wed, 14 Jan 2009 14:09:27 -0000, "N_Cook" <diverse@tcp.co.uk> wrote:

Normal or abnormal ?
Came in for an intermittant problem, fixed, and the following the owner
lives with but is it normal or abnormal?
With feed into a "normal" input and the "brilliant volume" at zero then
there is no control of the bass on the tone control, you need to have a
little advance on the brilliant volume.
Trouble around V7 ECC83 ?
DC voltages cathode,grid,anode
"brilliant half" 0,1.4V, 182V
"tone half" 182,183,290V
all associated pots ,Rs and Cs check out agreeing with schematic as does
the
valve and same Vs with a different valve

Assuming I am looking at the correct circuit - the bass control is in the
output
of the brilliant circuit only. The "brilliant" and "normal" are mixed at
the
junction of the 220k resistors so the bass control will have no effect on
the
normal channel.
The brilliant volume control effectively grounds the grid of V7a so I
would
expect 0v there and 1.5v ish on the cathode.

--
Geo
Click to expand...
So normal, in summary, for this amp?
The "brilliant" half is upper in this section of schematic
http://home.graffiti.net/diverse:graffiti.net/vox1.jpg

There is treble control but not bass control with "normal" input and zero on
brill vol.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:gkkrol$sa2$1@news.motzarella.org...
Normal or abnormal ?
Came in for an intermittant problem, fixed, and the following the owner
lives with but is it normal or abnormal?
With feed into a "normal" input and the "brilliant volume" at zero then
there is no control of the bass on the tone control, you need to have a
little advance on the brilliant volume.
Trouble around V7 ECC83 ?
DC voltages cathode,grid,anode
"brilliant half" 0,1.4V, 182V
"tone half" 182,183,290V
all associated pots ,Rs and Cs check out agreeing with schematic as does
the
valve and same Vs with a different valve


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
Click to expand...


AC30's have always had weird tone circuits that don't do what you think they
should. There may not be any fault at all.



Gareth.
 
On Wed, 14 Jan 2009 16:22:39 -0000, "N_Cook" <diverse@tcp.co.uk> wrote:


So normal, in summary, for this amp?
The "brilliant" half is upper in this section of schematic
http://home.graffiti.net/diverse:graffiti.net/vox1.jpg
Click to expand...
Yes - that is the circuit I have.
There is treble control but not bass control with "normal" input and zero on
brill vol.
Unless there is signal (e.g. from guitar) through the brilliant circuit then
Click to expand...
neither bass nor treble should really have any effect.
The position of the brilliant volume control should not affect the normal path.
Is it possible that C10 - the common cathode decoupling of the first valve is
failing and letting some signal through from the normal to brilliant section?

--
Geo
 
N_Cook wrote:

Normal or abnormal ?
Came in for an intermittant problem, fixed, and the following the owner
lives with but is it normal or abnormal?
With feed into a "normal" input and the "brilliant volume" at zero then
there is no control of the bass on the tone control, you need to have a
little advance on the brilliant volume.
Trouble around V7 ECC83 ?
DC voltages cathode,grid,anode
"brilliant half" 0,1.4V, 182V
"tone half" 182,183,290V
all associated pots ,Rs and Cs check out agreeing with schematic as does the
valve and same Vs with a different valve
Click to expand...
The modern 'copies' are shit.

I have a file full of AC30 schematics fronm the earliest to quite new. Will that
help ?

Often, guitarists compare 'their' AC30 with an well-maintained original and
complain it sounds shit. They're right. It does but there's nothing wrong with
theirs it other than cheapskating.

Graham
 
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