#1
My stock JCA2112 combo (20 watt 12 inch speaker) has to EL84's that when tested, come to around 10mah. This seems really cold to me. I contacted the maker and they said that there should never be a need to bias it, but there is a bias pot for amp techs to have the option.

Should I try and crank these to at least 20mah? Isn't that standard?
#2
What's the plate voltage?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#3
There is no real "standard". It all depends how old the tubes are, what they are, what amp it is, ect ect... But 10mA is very cold, yes.

That being said, Eurotubes says average bias for a Soldano (which a Jet City is effectively a copy of) is 38-44mA with 460 plate voltage.

I'd really recommend going with the plate voltage/milliamp bias formula on this one, which I don't know offhand. This website should be helpful: http://www.webervst.com/tubes1/calcbias.htm

EDIT: Or I could just get ninja'd by Cath, who is a legit amp tech haha
Gibson RD Silverburst w/ Lace Dissonant Aggressors (SOLD)
Electra Omega Prime Ceruse
Fender Franken-Jag Bass

Amps and the like:
Laney VH100R
Seismic Luke 2x12
Dunlop 105Q Wah
Gojira FX 808
Line 6 M9
#5
Quote by TheStig1214
There is no real "standard". It all depends how old the tubes are, what they are, what amp it is, ect ect... But 10mA is very cold, yes.

That being said, Eurotubes says average bias for a Soldano (which a Jet City is effectively a copy of) is 38-44mA with 460 plate voltage.

I'd really recommend going with the plate voltage/milliamp bias formula on this one, which I don't know offhand. This website should be helpful: http://www.webervst.com/tubes1/calcbias.htm


I think it's different for class A only amps running a pair of EL34's.
#6
200V? Really? That low? Did you measure it?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#7
Quote by Cathbard
200V? Really? That low? Did you measure it?

Unless I'm doing this wrong, 250 give or take.
#8
Sounds too low. Measure between pin 3 and 7.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#9
Quote by Cathbard
Sounds too low. Measure between pin 3 and 7.

366? Does that sound right? Maybe I should just take this to a guy who knows what he's doing haha.
#10
Sounds much better. You'll want something between around 20mA to 25mA. It's way too cold atm.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band