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Heater voltage in a JTM 60?


 
3/20/2004 10:12 PM
pb
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Heater voltage in a JTM 60?
The schematic says it's 6.3vac. I'm getting 7.1 vac.Could the tranny be getting bad? Thanks
 
3/21/2004 6:21 PM
Bruce /Mission Amps
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quote:
"The schematic says it's 6.3vac. I'm getting 7.1 vac.Could the tranny be getting bad? Thanks"
With all the tubes inserted?  
Bruce
 
 
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3/21/2004 7:18 PM
pb
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Thanks Bruce thats with all the tubes in. Thanks pb
 
3/22/2004 10:13 PM
g1
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What's your applied AC from the wall at? Do you have a variac you could try to see what primary AC voltage will give you 6.3V heaters?  
I did an experiment once on a tube mic that had adjustable heater voltage. Above spec. introduced a lot of noise.
 
3/23/2004 4:02 PM
anonymous
Not a problem.  
Consider: slightly  
excess line voltage  
or 6.3Vac winding  
variance.
 
3/23/2004 4:56 PM
Le Basseur
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In fact,this IS a problem.  
The "slight excess" getting to a "6,3 VAC winding variance" means that the ECC8x tubes' filaments will worn out much faster than they should.This is not happening with the output tubes' filaments though,these being much more tolerant about over-voltage.  
I had enough trouble with stunned customers coming with their freshly-retubed amps wich after 20-30 days (read:a few dozens of hours of playing the amps) proved to have some unexplainable low cathode emission on the preamp/PI tubes.  
If you're using some expensive tubes,be prepared to loose them relatively soon...unless you don't do something and improve the situation.  
Does your amp have a primary voltage selector for the PT?If yes,you'd might want try adjusting (lowering) the filament voltage by choosing the appropriate primary winding.This will also lower the B+ to a certain ammount (20-30 V) and it's up to you to decide what's more important.  
HTH!
 
3/23/2004 10:02 PM
anonymous
Baloney. If this was the case  
every darn amp made in the tweed  
to bF days would eat tubes prematurely.  
(Since line voltage ratings were diff.  
then.)  
Most guys don't "use" tubes long enough  
for this to become an issue anyway.
 
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