Express Compression

[DaveWell]

Hi !
I bias the amp at around 24.5mA at 400V on B+

I feel it compression at higher volume...

Any advise ?

Thanks

Dave

[Neeno]

Hi Dave,
I have just finished my first amp, a TW Express, and I went thru the bias just a couple of weeks ago, that means I'm probably not a reputable source of informations but I'll try to help.

For 70% dissipation @400V EL34's should be biased around 40-45mA.
I guess you have biased the amp a bit too cold...

P.S.:Some compression in the Express is just right, that is the reason why you can go from clean to dirty with your guitar volume and the perceived level is almost the same.

[vibratoking]

+2

Yup, bias is very cold.

Compression makes the Express.

[geetarpicker]

Compression is the key thing that keeps an Express fairly even volume wise from clean to mean. Without it the amp would not be nearly as practical in a live setting for control from the guitar knobs as your dirty tones would really bump up way above your clean tones. That said, it shouldn't really sound squashed either, and the compression should be fairly transparent sounding. That said personally I'd bias it much hotter!

[DaveWell]

Thanks!

I will Bias it at -32volt (40mA/42mA)

I think it will be the Sweet Spot !

[rooster]

Here's my numbers: NOS XF2 Mullards/28ma, Siemens EL34s/32ma, JJ KT77s/40mas.

Having run the JJs for a few years and then searching out the NOS tubes, I much prefer the NOS tubes. I know Glen runs at least one pair of Siemens, but hearing my clone amp and a Phillips built clone on 40ms vs. 32ma, it was like burnt toast vs. golden brown. And here the 'golden brown', once you hung out with it for an hour or so, sounded better to my ears and made more sense of the amp's controls and overall character/nature. (Not saying I don't love Glen's sound bites!)