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Engl Powerball II: what are these "mods"? Why can't I bias it?

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Hi, I've bought a used Engl Powerball II. It's fully working except two things:


1) The first "problem" I heard is that channel 3 (lead 1) and channel 4 (lead 2) have the same tone and the same gain. I've red (and heard online, even on Engl site) that channel 4 has more gain than channel 3 and is tonally different but in mine channel 3 and 4 has same sound and gain (if I put gain pot to max it's same gain on both). Why? Maybe last owner done something?


I though was "bad tubes" issue, so I replaced the stock Engl pretubes with TAD and JJ (that I used on my old amp, so I know they are good) and bought a new quartet of JJ 6L6 (replacing the quartet of TAD) to see if was a tube problem. But I had a second problem.


2) I cannot bias the 4 JJ as I want. Done some research online and I saw where I have to put the multimeter to test the current. I got a low value (108 mA on tube socket). So 108/4 = 27 mA each tube. I wanted 6L6 at least 32 mA each but I cannot go higher with bias pot. It stops at 108. Is it right to measure 108 and then divide per 4 (final tubes) in order to obtain the mA of each tube (approssimatively) or am I doing something wrong?

I measure in 6L6 socket, like in the image below.


I only have a multimeter, not bias probe or anything else. I can bias amps, done a lot with Marshall, Fender etc (except Mesa), but I cannot understand why JJ can't go more than 108 mA (even stock TADs were going to 130+ mA with pot). Am I doing something wrong or I have to change bias pot to bias my JJ 32mA each? Or am I counting this wrong?


I saw another thing inside amp, maybe a "mod"? Why are these resistors etc. here? It seems that they are added after. I though.. is it a "mod" to reduce "gain" on channel 3 and 4 or what?

The last owner said that he didn't change anything.. bah. I see thing changed, Here are the images.

RED circles is where I put my multimeter (ground, socket of tube and bias pot). YELLOW circles are the "mods" I saw.


[ATTACH=JSON]{"data-align":"none","data-size":"full","title":"Engl Powerball II","data-attachmentid":32567855}[/ATTACH]


And here the "mods" I see.







If anyone has an idea of what are these resistors etc and what maybe they do can please say it to me?

For the bias problem too :)

Thanks! Sorry for mistakes, I'm italian!







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When you adjust the bias are you actually measuring current flow or are you determining current flow by measuring the voltage drop across a given resistance? Do you measure each tube individually or is their just one adjustment for the quartet?

Your amp definitely looks like it was modified or experienced a makeshift repair so it is difficult to diagnose without being in the same room and getting an up close look.

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