Hello, i have bought a engl invader last month,
the clean and the high gain sounds are perfect,
butt i want a bit more vintage tone, more definition, more attack in my crunch sounds.
the invader is equipted with 6 EL34 power-tubes, im not shure what make.
i have measured 26,4mA anode current, 440 volt annode voltage.
i think that's a little low, according to tubetown bias-documentation it should be 29-40mA.
i looked everywere but i can not find a bias potentiometer.
i think its a fixed bias like mesa boogie, does anyone know were the bias-pot is located,
or does anyone know how to mod this amp with a bias pot?

i was also wondering if the amp sounds more vintage with the svetlana el34,
i have this tubes in my marshall 100w super lead mk2 ('74) and i am very satisfied with this tubes.
however Dirk have sugsested me to use jj's in a engl, im not very fond of jj powertubes,
butt its my first engl amp and i want to know jour opinion on this one.

and if i use jj's, and i would use the E34L tubes would the annode current be higher so it would be between 29 and 40mA??
in this case its maybe not nessesairly to mod the amp (because of my warranty).

thanks, greetings Gert

Hi,

using the E34L instead of normal EL34 makes no sense if the powertransformer can not supply the extra power needed to drive the E34L at its limits. Anyway, if you have already some Svetlana EL34 you can test them in the Engl as well. Just remove all powertunbes and load the amp with the 4 Svetlanas you got (the outer left and right socket stays empty). Check it out if you like the sound or not.

Best regards, Dirk

hello, i would like to try the vetlanas but are you shure nothing go wrong by letting the outer sockets empty, because this amp is equipted with a tube monitoring system.
i also think the bias would be different with less tubes, because current will chance in the bias section, less current-> (law of ohm) -> higher voltage on the negative grid.

if sombody dont agree, please reply.
greets, Gert

Hi,

Of course you should check the bias but for the bias-voltage itself it is regardless if there are 4 or 6 tubes used. Also the idle current is per tube. That means less tubes less idle current in sum = less power.
I am not sure about the "monitoring system" but it should react only if there is a short. Try it and you will see.

Best regards, Dirk

hi Dirk,
i have some information from the importer, the invader has no adjustable bias, is has a fixed bias.
they promiced me the schematics, but worned my about my warranty.

your right about the tube monitoring system, it does not respond on missing tubes.
however when i remove 2 engl tubes the anode current go's up. (by 10 percent)
like i thought before, removing tubes interferes the bias.
and i also discovered that the amp sounds more thin with less tubes.
i even run it on 2 tubes and then it sounds verry different with the same stock tubes.
when i put in the svetlana's, the amp sounded more open, and less thick, more bright.
but i only had 4 tubes, i think just like the stock tubes that the sound will be warmer with 6 tubes.
i have tried jj e34l tubes (i had only 2 tubes) it sounds warmer then the svetlana's but i'm afraid the sound will get too thick with 6 tubes.(but its still guessing.)

also what is very interesting, is the anode current on these tubes.
in the same amp, with fixed bias, 2 svetlana's had a higher anode current then 2 stock engl tubes.
and 2 jj's had a higher anode current then the svetlana's.
with some calculating, the svetlana's schould have a anode current of 29,5mA with 6 tubes.
and the JJ E34L schould have 37mA anode current. so that means i don't have to mod the amp.
i just have to replace the tubes by svetlana's or jj's.

A frend or mine also have svetlana EL34 tubes,
i have asked him to borrow 2 tubes (together with my 4 tubes that makes 6  ).
so i will be testing that tomorrow
pitty i dont know sombody with jj e34l tubes.

greetings Gert

Zitat von: Invader from belgiek am Mär 23, 2007, 12:36
i have some information from the importer, the invader has no adjustable bias, is has a fixed bias.

Watch out ! What you are looking for is a "Fixed Bias" in your case it is an "Adjustable Fixed Bias". Please search the net for more infos about this.

Zitat von: Invader from belgiek am Mär 23, 2007, 12:36
however when i remove 2 engl tubes the anode current go's up. (by 10 percent)

OK, less load... depends upon the transformer a little bit.

Anyway, it looks like that these days the "Engl" Tubes are relabeld JJ tubes. I guess the amp will not be sounding to warm if you load it with JJ tubes but if it does you can use also a pair of tubes from an other brand like 4 * JJ and 2 * SED. As long as the tubes have the same ratings it will be OK.

Best regards, Dirk