JMP 440v plate voltage and bias maxed out

[gibsonclassic2001]

Did some quick testing on my JMP 2203.
Put some new jj el34 tubes in and tested bias and plate.
With voltage selector on 240v the plate is low 440v and bias pot maxed out @35ma.
Wall voltage is 227v so I changed the selector to 220v setting and now I get normal 475v plate and maxed out bias is 40ma.

Im about to change all electrolytes but I bet that the "low" wall voltage is to blame .

[danman]

Since you mentioned that you installed a new set of tubes, it could also be that you may need to adjust your bias range resistor to better match those new tubes. Or you could exchange them for a set that more closely matches the bias range of your old set. I have occasionally had to change this resistor myself when installing a new set of tubes that wouldn't bias up properly within the range of my bias pot.

[gibsonclassic2001]

Tested a NIB El34b and its the same.
Could it be those 35 year old Daly's?

I only got 4 new 50/50 cans at home so I cant test it yet

[gibsonclassic2001]

Btw heater voltage is 6.2 standby and 6.0VAC on With 220v mode.
Hmmm

[danman]

Well with 475v on the plates, you would want to be at 36.8ma for a 70% bias setting. Are you saying that you can't get below or above 40ma with your bias adjustment? I may have misunderstood you in the OP. Your heater voltage readings look good.

[gibsonclassic2001]

Well with 475v on the plates, you would want to be at 36.8ma for a 70% bias setting. Are you saying that you can't get below or above 40ma with your bias adjustment? I may have misunderstood you in the OP. Your heater voltage readings look good.

Maxed out JJ el34 is 34-35 in 220v/475v plats
Big bottle el34b shuguang is around 30 in this setting.

In 240v/440v plate big bottle el34b wont reach 27Ma.

[danman]

Did your old set of tubes bias up properly before the switch? I still think you may need to look into lowering your bias range resistor(the one inline with the bias pot) to the next lower value. This will bring up you ma reading on those new tubes your trying to bias. Every so often I try a set that is just out of my bias pots range and I will have to change that resistor to bring the bias within range. Do you know what value resistor you currently have in that spot?

[danman]

I forgot to ask how long have you had the amp and whether or not the older set of tubes were in it when you purchased it? Is it possible that a tech could have altered the bias circuit in the past to properly bias that set?

[gibsonclassic2001]

I forgot to ask how long have you had the amp and whether or not the older set of tubes were in it when you purchased it? Is it possible that a tech could have altered the bias circuit in the past to properly bias that set?

The old set of tubes are factory original
Its bone stock!

But I bet that in early 80s Sweden used 220v.
The 230 rating is more true for the last 15-20 years or so.

Having 227v and 240v setting everything is just out of range.

With 220v setting everything measure as it should.


But I need to swap all e-caps before ill try it again.

[stef]

It's not safe to have your amp set for 220VAC with 230+ from the wall

[gibsonclassic2001]

It's not safe to have your amp set for 220VAC with 230+ from the wall

Ill try and test it With my eco gizmo.
It will show highest and lowest current in the wall socket.
It bet this facility is a little under average.

[gibsonclassic2001]

Tested a 2203x. With 6550 35w.
230v setting 227v Wall current 420v plate 5.8v heater.
220v setting 460v plate and 6.3v heater.

Sounds much better!
227v is way to low for 230v setting.

460-470v really got a sweet spot!