Blues jr Conversion, upgrades, bias

[Russ Fuquay]

Greetings.
My first amp build is a Hoffman blues jr Conversion. I've installed the Allen TP 24 power transformer and OT20 output transformer. Why, you may ask? Well, let's say The Originals had to be replaced out of necessity and leave it at that. I figure
as long as I'm replacing them I would like to get a little more headroom and clean power if possible, but still keep the el84's at least for now.

My question is about the correct bias. Given that I'm using the OT 20 and PT 24 what should the correct bias be? Also, do any of the parts that came in the conversion kit need to be changed due to the different Transformers?

Many thanks.

Russ

[pompeiisneaks]

The bias point isn't based upon the OT, but upon the tubes, and EL84's depend on the plate voltage coming into them.  I don't know the Blues Jr voltages, but if you look at the weber bias calculator you can get a quick check, after measuring plate voltages:

http://www.tedweber.com/webervst/tubes1/calcbias.htm

example for 350 V for EL84 class ab, it's about 24mA for 70%. 

Play with the calculator, it's a great tool.

~Phil

[Russ Fuquay]

Good to know. Many thanks!

[ginger]

..... I do this on Stock Blues Juniors

[sluckey]

I do this on Stock Blues Juniors

That video won't help Russ. His bj no longer resembles an original or a bm modded original.