Power transfomer without 52 volt bias tap

[mike the dog]

Hi. I have a Carvin VTR 2800 head that has a bad power transformer.I have a few transformers from old organs with the correct HV secondary voltage, but don't have one with a 52 volt bias tap. My question is, can I drop the voltage from the primary side or drop it from one of the 360 volt secondary leads. I'm sure I'm not the first one with this issue, and hoping someone could teach me the correct way to do this. Thanks in advance for any help!

[big_teee]

You can do it the Marshall way.
http://www.ceriatone.com/images/layo...4Ceriatone.jpg
Good Luck,
Terry

[Prairie Dawg]

Or a Princeton Reverb. Same deal, you just gotta juggle the resistances to get where you need to be. I always wondered whether doing this unbalanced the power transformer but it's such a small current draw it shouldn't really matter.

[tedmich]

AX84's take:



which feeds 2x EL34, so I'd boost the wattage's for 4

[mike the dog]

Thanks for all the input! I will try to add a resistor from a HV line this weekend. Thanks again!

[jrfrond]

That works just fine. The series resistor tapped off of the B+ is usually between 100K-220K. The use of the Pi filter is necessary, as it provides stiffer filtering to prevent the bias supply from sagging when the power amp is pushed and the B+ sags. I'd use 50uF caps though.