Just Got New Tubes For My DSL 100

[solarburn]

I spoke with Euro Tubes about this and this was their response:

"The plate voltage is a fixed amount of voltage supplied buy your transformer to the plates of the power tubes. It’s not variable and you really don’t need to worry about it.

Thanks,

Eddie"

fwiw

Watch his JCM 800 vid and tell me the plate voltage is a fixed number. I will say that there is not much difference to the bias number even when there is a 20 volt diff in plate voltage from tubes to tubes. I fail to see where plate voltage is fixed in one place. Call Voodoo Amps and tell them the plate voltage is a fixed number. You will get a different answer.

Makes no difference to me if someone biases diffferently. Hey and I'm just learning all about htis too.

 

[steelhorse]

I hear ya solar but being that the dude that put out the 800 vid clip owns the company I got the response from, it stands to reason that perhaps the 800/900 series and older are different animals than the DSL/TSL's.

They seem to be on the ball over there at Euro so no real reason for me to doubt their information.

And I have watched the 800 clip and wondered the same thing but they told me the plate voltage didn't apply with the TSL so I didn't worry about it.

Oh well, we're all learning!

 

[axl2]

It appears my first official thread on here has been put to good use lol

 

[solarburn]

I hear ya solar but being that the dude that put out the 800 vid clip owns the company I got the response from, it stands to reason that perhaps the 800/900 series and older are different animals than the DSL/TSL's.

They seem to be on the ball over there at Euro so no real reason for me to doubt their information.

And I have watched the 800 clip and wondered the same thing but they told me the plate voltage didn't apply with the TSL so I didn't worry about it.

Oh well, we're all learning!

I hear ya bro. I actually learned how to bias my DSL from his site. I thought I was all good until Trace from Voodoo told me alot more about getting these amps (DSL) biased not to mention on tubes. It was info overload. At any rate here is a bias table for EL34's from Jim Jones on Webers website:
EL34 - 25W Hot (70%) Avg (60%) Cool (50%)

300V 58mA 50mA 42mA
325V 54mA 46mA 38mA
350V 50mA 43mA 36mA
375V 47mA 40mA 33mA
400V 44mA 38mA 31mA
425V 41mA 35mA 29mA
450V 39mA 33mA 28mA
475V 37mA 32mA 26mA
500V 35mA 30mA 25mA

With this you can see how little the bias numbers change from plate voltage to plate voltage biased hot or cold. So if you know DSL's run from 450 to 500 plate voltage then you can get in the neighborhood for the bias and just fine tune it to what sounds best. I have a MM OT and my bias is stable. Watch out for run away bias with DSL's stock OT per Voodoo. The bias may wander too hot while adjusting it and the tube can red plate. Make small pot adjustments either way.

 

[steelhorse]

Yeah, see my post above in describing the bias adjustments.

Minute adjustments!

 

[solarburn]

Yeah, see my post above in describing the bias adjustments.

Minute adjustments!

I forgot to tell you that your "how to" post was great. It took time to write all that out and I know guys here will appreciate that.

 

[steelhorse]

Thanks!

 

[RiverRatt]

Make sure you use insulated alligator clips on the test points. I foolishly didn't think of this, shorted them out, and blew the HT fuse the first time I biased my DSL50, which being a tinkerf^cker I naturally did the second day after I bought the amp. I thought I'd ruined my first Marshall! Thankfully a trip to Radio Shack fixed it up.

 

[spaceforlease]

I think Bob realized that with the bias probes and the multimeter setup he used he probably confused a few folks but it's really simple with the DSL100.

All you need is a decent multimeter. I ordered mine form Euro Tubes.

Take the multimeter and set the dial to the 9:00 position which will be in the DCV 200m setting.

Take the black lead and plug that into the COM port at the bottom right side of the meter.

Take the red lead and plug it into the DC port

I have alligator clip adapters so I use one on the black lead which I clip on to the ground post on the amp bias adjustment.

You'll be using the red lead for the readings.

Be sure the amp has been on for a few minutes to get plenty hot on standby.

Take the amp OFF standby like you are going to play.

Take the red lead and touch each test point on the bias adjustment of the DSL to see where you're at.

We're looking for a reading of between 80 and 90 mV.

With an insulated or plastic small head Phillips screwdriver make MINUTE adjustments to 1 side at a time (you'll see what I mean when you adjust yours!). Remember when you make one side hotter it will cool the opposite side down some, so it will be a back and forth venture until the see-saw quits and you get near identical readings on both sides.

I set mine to 86mV. Played with it for a few days, and went back and checked it for drift but it was still very close so I left it.

The things that could make it easier is of course getting another multimeter, clipping both grounds to the ground post and the positive lead of each to one test point so all you need to do is watch the meters while making the adjustment but it's really simple to accomplish the same thing with only 1 meter, it just takes a little time and patience.

I recently read on the Euro site that the factory test points on the JSX heads are unreliable and they had steps to follow to bias it properly. With that head I switched the meter to the 4:00 position (DCA) moved my red lead to the mA port and used a bias probe on 1 of the tubes (it needs to be a matched set to do it this way). It took some time but with the JSX you just adjust the little dial to get the bias set.

Hope this helps!

so you adjust the biasing with the phillips screwdriver?

 

[steelhorse]

a very small insulated or plastic one

remember minute adjustments, you turn it too hot you'll feel the heat!

 

[RiverRatt]

so you adjust the biasing with the phillips screwdriver?

It's a standard tip, not phillips. The adjustment screw on these is plastic, too. I've always used a small metal precision screwdriver. Even if you accidentally touch the hot lead, we're only talking about 40mV or so. You could get a bigger shock touching a 9v battery. You only need a plastic or insulated screwdriver if you're poking around inside the amp.

 

[solarburn]

It's a standard tip, not phillips. The adjustment screw on these is plastic, too. I've always used a small metal precision screwdriver. Even if you accidentally touch the hot lead, we're only talking about 40mV or so. You could get a bigger shock touching a 9v battery. You only need a plastic or insulated screwdriver if you're poking around inside the amp.

Use the same too. I've had no issues.

 

[steelhorse]

Mine is definitely a phillips head adjustment 'screw' you just need to look and check your amp to see what you need flat tip or phillips, it's very simple.

The DSL may come with a flat head type I've not looked at it yet, but my TSL is definitely phillips head and I presumed they were the same.

 

[RiverRatt]

Didn't know that, steelhorse. Learn something new every day.

 

[steelhorse]

Me too River!

 

[axl2]

k i have a problem...Just got the multi meter today. Installed the tubes, But I'm not getting a reading. It's staying at 00.0 when I use the red pin. Set to 200M DCV on the one from euro tubes...Help?

I'm supposed to have the head still plugged into the cab right?

 

[solarburn]

Always have it plugged into a speaker load/cab. You need to take the amp off standby to get a reading.

 

[axl2]

Always have it plugged into a speaker load/cab. You need to take the amp off standby to get a reading.

Yes it's in a speaker cab. and off standby meaning the black switch on "on" but I'm getting no reading using the red peg on any of the 3 pongs...

 

[steelhorse]

Also be sure the leads are connected to the correct inputs.

Black lead connected to the COM port, red to the 10ADC.

 

[solarburn]

You have the black lead hooked up to the center prong on your amp while you are touching the red lead off?