DSL50 Is This Bias Low? *PIC Included*

[dinkyguitar]

Hi,

I just got my DSL50 and after doing some riffs I decided to check the bias. The previous owner said they are new tubes and were "properly biased by a certified Marshall tech"

I had the amp on for about 10 minutes and checked the bias. This is what I got:

The tubes are JJ el34's. My MM is set right as far as I know....I should be reading 40-45 mV.....right? Or should I have the amp on for longer? After all it is about 60 deg. in my basement..

dinkyguitar

 

[thrawn86]

Did you leave it On and in Standby for about 30 minutes?

 

[dinkyguitar]

No...the standby switch was in the off position for about 10 minutes...so I got no reading on the MM. Then after 10 minutes if flipped the standby to ON, hooked up the meter and it settled at 33.6 - 33.7. It kept drifting or hovering around this figure...Is that normal?


dinkyguitar

 

[dinkyguitar]

So I played it for over 30 minutes, checked the bias and it went up to 34.4 on each side.

dinkyguitar

 

[Larry K]

I set mine at about 41 per side.

LK

 

[diesect20022000]

i'd say 37 per side is alright. that seems a tad cool to me but, it shouldn't hurt it. too high will be mushy, too low will be stiff so if it feels good there it should be okay i think. hard to say not knowing your current readings.

 

[TwinACStacks]

Take it up to about 38.6 You will be Golden.

TWIN

 

[jcmjmp]

If the plate voltage is in the 465 vdc range, you should bring that bias value up a little. Without knowing what the plate voltage is, its hard to tell what you should set it to as the JCM2000 power transformers can have a lot of variance. I've seen plate voltages on those amps vary from 450vdc to 500vdc.

 

[dinkyguitar]

What's involved with getting plate voltage?

From what I've read, you need to take the chassis out, flip it upside down, clip a neg lead on the chassis, and put a probe to pin 3 on "one" of the power tubes..the take 70% of that...Not sure what the formula is to get your mV..

Sound right?

If so, how do you find pin 3 on the tubes?

1 other question, how long does it take for power to drain from the caps?

dinkyguitar

 

[jcmjmp]

Tube pinouts:
http://bustedgear.com/res_Tube_pinouts.pdf

page 17

Pin3 is the one you need to measure. If you are not familiar with electronics and high voltage safety, I would recommend that you get a pro to do this for you.

 

[Ken]

People set the bias all over the map on these, from mid high 30's up to the maximum 45. I have mine on 43. You won't hurt anything at 33 but you'll find the amp come to life if you bias it a touch higher. Play the amp a half hour before making adjustments.

Ken

 

[dinkyguitar]

Thanks guys...

Ken, I originally took my bias reading after 10 minutes...but later that night, I played it for over a half hour, and took a reading again. On the second time I came up with 34.4.

dinkyguitar

 

[Jimmy Bondy]

Bias it to 43 per side

 

[charveldan]

Doesn't it depend on the current draw of the tube as well as plate voltage/disapation.