Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: chocopower on May 08, 2010, 04:22:09 pm
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Hello,
I´m working in a Blakface Concert. The owner are not happy with the sound of the amp. Too early breakup, fattiness problems.
The cap job is donne. Power resistor are tested.
Is a 120v amp using a voltage converter to 220v.
The only strange in it is the plate voltage. 380dc with 42mA in the 6L6´s.
Is the lower voltage i´ve ever seen in a Blackface fender. Schematic claims for 440dc.
Could this be the origin of the problem?
thanks in advance.
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Hello,
I´m working in a Blakface Concert. The owner are not happy with the sound of the amp. Too early breakup, fattiness problems.
The cap job is donne. Power resistor are tested.
Is a 120v amp using a voltage converter to 220v.
The only strange in it is the plate voltage. 380dc with 42mA in the 6L6´s.
Is the lower voltage i´ve ever seen in a Blackface fender. Schematic claims for 440dc.
Could this be the origin of the problem?
thanks in advance.
yes.
Pull the tubes and then check,that will rule out the tubes. If it still the same, turn it on standby. That will eliminate anything in the preamp and PI. Still the same disconnect from the diodes to the first filter cap. Check the secondaries for 320vac. If not, take the diodes out of the circuit. Still the same, the PT is gone.
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Thanks for you repply.
Owner want to install a E.U. transformer to avoid the extra weight.
the Fender transformer chart (http://www.el34world.com/charts/transchart.htm (http://www.el34world.com/charts/transchart.htm)) call for a 125P7D, but the guy found this one (http://shop.amppartsdirect.com/Vintage-Fender-Style-50W-Power-Transformer-120-240V-40-18029-40-18029.htm (http://shop.amppartsdirect.com/Vintage-Fender-Style-50W-Power-Transformer-120-240V-40-18029-40-18029.htm)) and the seller told him that it is ok for the Concert.
I´m sure about voltage and current ratings, but afraid about size and mounting...
What do you think?
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Thanks for you repply.
Owner want to install a E.U. transformer to avoid the extra weight.
the Fender transformer chart (http://www.el34world.com/charts/transchart.htm (http://www.el34world.com/charts/transchart.htm)) call for a 125P7D, but the guy found this one (http://shop.amppartsdirect.com/Vintage-Fender-Style-50W-Power-Transformer-120-240V-40-18029-40-18029.htm (http://shop.amppartsdirect.com/Vintage-Fender-Style-50W-Power-Transformer-120-240V-40-18029-40-18029.htm)) and the seller told him that it is ok for the Concert.
I´m sure about voltage and current ratings, but afraid about size and mounting...
What do you think?
Here is the specs for both in question.
http://www.classictone.net/40-18005.pdf
http://www.classictone.net/40-18029.pdf
They will both mount and fit in the same hole. The voltages would be different but that would depend if he likes the result. The higher voltage taps would give him slightly more headroom. I would go with the one he picked as well. He'll have the choice of a lower voltage, around 420Vdc or the higher voltage around 490 Vdc. Plenty of current on the heater winding to go between El34 or 6L6GC's. Just make sure the bolt pattern is the same on the chassis he has now and you should be good to go. Just shrink wrap the ends of the 5v wires and stuff them away just in case if needed later.
Those transformers are of a real nice quality. They took the extra time right down to the potting. I have been impressed by them.