• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

VTL tt25

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#3
vtl tt25

thanks for the reply.. I have changed the filter caps (that was my first
thought) FWB = ? all the rectifier diodes pass the basic diode test
the amp has 3 diode bridges ? it pops fuse with NO VALVES in and
gentle up on a variac

thanks
 
#4
You need to work logically from source to loads. Power up the mains transformer in isolation from the amplifier, all secondary windings disconnected. Does it pop the fuse? If not reconnect the secondary windings one by one and power them up on each reconnection. Hopefully you will find which area of the amplifier is at fault.

Once you have the area at fault it's just a matter of elimination.

Eventually you will find the problem.

Circuit diagram would make this easier, but not impossible without it.

Regards, Aleks
 
#5
what is your line voltage and what size fuse are you using?
you can disconnect all secondary power traffo connections,
then test it again and see if the fuse pops...
what is your power traffo primary set to? if it is set to 120
and then you were tyring to load it 240, then fuses will surely pop...
 
#7
AJT said:
what is your line voltage and what size fuse are you using?
you can disconnect all secondary power traffo connections,
then test it again and see if the fuse pops...
what is your power traffo primary set to? if it is set to 120
and then you were tyring to load it 240, then fuses will surely pop...
Click to expand...

thanks,, they are set up for 240 (I have used them for 6 months)
fuse 1.6amp (as per label on amp, secondary disconnected, 520 volts fuse ok
with ht insulated ,,valves in' heater also ok..
with transformer out off amp, no short to earth on ht, bias or heater
 
#10
vtl tt25

SORRY for slow reply !! with the ht onl,y powers up ok, with bias only also
ok ,with both connected (transformer out off amp, clip leads) pop !
I've taken the transformer out of the working amp, that will power up
both amps, the faulty transformer ( not connected) 520 v ht ,30v bias, 7.5
heater ,, with dmm shows no faults, I presume the trans has a shorted turn
ht to bias ,?
 
#12
cobra said:
SORRY for slow reply !! with the ht onl,y powers up ok, with bias only also
ok ,with both connected (transformer out off amp, clip leads) pop !
I've taken the transformer out of the working amp, that will power up
both amps, the faulty transformer ( not connected) 520 v ht ,30v bias, 7.5
heater ,, with dmm shows no faults, I presume the trans has a shorted turn
ht to bias ,?
Click to expand...

then better check downstream....
 
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