Update bias supply won't work

[Batman8]

Have ceriatone Chupacabra 50 bias sucks. So I read about a 25 volt 450ma transformer ,got one ,installed wont bias up at all , checked ok to board 12 volts at a1 and a2 to diodes .only 1bias pot is hooked up and 1/2 of bias parts on the board the lower half by el34 tube maybe I hooked up wrong now I am stuck any one try this small transformer to bias?? So called better.oh I got restless hooked up wrong burned out transformer... If I get a new trans what next ?? Please help

[ToneMerc]

Well, it should not bias up at all if you used that 25V transformer as a bias source. The bias supply as implemented is designed to see 300+ volts, not a 25V input! Where did you read about using a 25V PT as a bias source for this particular model, on the Ceriatone forum?

The values in the bias supply circuit looks it will have enough range for both tube types, but if I could not get some EL34s to bias up I would decrease both 56K resistors to 39K or 43K for starters.

IMHO, a man's got to know his limitations. You should slow down, drop the soldering iron and pick up some books on the basics, if nothing else study a cross section of existing amp layouts or else you will be burning up lots more stuff.

TM

[Batman8]

Found it in Dan Torres inside tube amps page 184 at the end of bias chapter .also on ceriatones web page New to this, but the bias on this amp is so far off .and tried 3 different sets of nos tubes ,resistor changed
3 times... Best I could get is to sound like a 18 watt Marshall....

[TUBEDUDE]

Throw that book away and don't listen to destructo dan.

[M Fowler]

Torres said to build the new bias circuit as a voltage doubler so you don't use the center tap. 470 ohm voltage dropping resistor then diode reversed to get negative voltage and make sure + end of e-cap goes to ground. But you still have to figure out the bias pot and resistor.

Don't need this extra circuit you could have borrowed voltage from one leg of the HT.