Bias High!!

[grtamp]

I changed bunch of tubes in my D-clone 100w amp , but the minimum current I can take is 45mA with bias-pot to Max....
I put the Svetlana tubes and let burning for 1 hour about , at 45mA , but it's the same.

To get a better range of adjustment and lower the current, I increase the 27K resistor or decrease the 3.3 K resistor in series with the diode?

thanks

[telentubes]

Deleted. Bad advice.

[grtamp]

sorry , but if I decrease to 22K the bias voltage will be low and current will raise!!!!

[ayan]

I changed bunch of tubes in my D-clone 100w amp , but the minimum current I can take is 45mA with bias-pot to Max....
I put the Svetlana tubes and let burning for 1 hour about , at 45mA , but it's the same.

To get a better range of adjustment and lower the current, I increase the 27K resistor or decrease the 3.3 K resistor in series with the diode?

thanks

I think you're saying that the minimum current you can "achieve" is 45mA per tube, correct? Are you using 6L6s? Depending on your plate volatges you should be somehwere in the vecinity of 30mA per tube, give or take, so it sounds like you may be getting ready to cook something.

As you basically said, you will need to make the bias voltage more negative to reduce the idle current. To do this, try using a 2.2K resistor instead of a 3.3K one and see if that gets you where you need to be.

Good luck,

Gil

[grtamp]

Hi Gil, yes, I run with 6L6 power tubes, 45mA is the most low current for tube I can get ! my plate voltage will be around 440/445V( I think to remember when I built)
Compared to the valves that were installed before there's lot of difference!

I hope, whenever I have to change tubes, I don't have replacements somethings in the circuit!

I will try to lower the resistor 3.3 k to 2.2 k.

Thanks very much

[grtamp]

I solved with 1,8K res.
Thanks Gil

[ayan]

I solved with 1,8K res.
Thanks Gil

Glad to hear, and you're very welcome.

Gil

[glasman]

FWIW, the typical 6L6 requires about -47 to -50 volts on the grid to achieve 30 t0 32 mA at 450v. This varies by tube brand.

The bias dividers I use run between -30 and -64 volts (25 turn pot) and covers most tube type I use. Of course, it is a little low for say a KT88.

Gary

[crbowman]

I solved with 1,8K res.
Thanks Gil

Glad to hear, and you're very welcome.

Gil

Gil!
Glad you're still around. I was beginning to think we'd lost you.

[ayan]

I solved with 1,8K res.
Thanks Gil

Glad to hear, and you're very welcome.

Gil

Gil!
Glad you're still around. I was beginning to think we'd lost you.

Well, thanks for that. I have been very quiet for the last...while, mainly due to two reasons:

1. I got a real Dumble...a 2x12 cabinet loaded with EVM 12S speakers. Never heard anything better, I just don't get it, same with the real ODS amps. I think we will never know the real Dumble secrets. BTW, the cabinet weighs a ton and I can't gig with it because of that.

2. I really have the jones for a good Marshall sound, I have OD'd a bit on the Dumble OD tone.

Cheers,

Gil

[Structo]

Wow!

I'm not certain what you got, a Dumble speaker cab or a ODS?
Head and cab?
Sounds like you got the amp too.
Do you think age plays a role in the tone of these amps?

I hope you can still drop by and talk to us mere mortals (I kid).

I do know what you mean, you finally achieve the grail only to want a different flavor.
But I'm sure the Dumble won't go anywhere unless you need the resources.

[ayan]

Wow!

I'm not certain what you got, a Dumble speaker cab or a ODS?
Head and cab?
Sounds like you got the amp too.
Do you think age plays a role in the tone of these amps?

I hope you can still drop by and talk to us mere mortals (I kid).

I do know what you mean, you finally achieve the grail only to want a different flavor.
But I'm sure the Dumble won't go anywhere unless you need the resources.

Tom, I just got a 2x12 cabinet...for peanuts, I might add, not an amp. The reference to the amp was that somehow Dumble seemed to have this ability to make everything sound special. A/B'ing the cabinet with everything else I have is a joke, really - and I really like(d) a couple of my cabinets. The Dumble cab sounds way bigger, about twice as loud, chimier but smoother in the top end, etc. Attached is a teaser.

As far as the Marshall sound, it's been a long time coming for me. As much as I love my amps with a LP and the 335, the Strat is always a problem for one reason or another... and any Marshall will make Strats sound better, IMHO.

Cheers,

Gil

[talbany]

Gil
Congrats on the Big D score.. I too hope you stick around..

Enjoy the amp U deserve it!!

Tony

[jelle]

Congrats! Nice score. Jelle

[crbowman]

Gil,
Can you give us some insight as to what you think makes it sound so special?
I understand that the EVM 12S's are really world class speakers and....well.....I guess that helps ( ) but what else is present that sets it apart???
And by the way......thanks!!