Jolida 302 Bias - Need help, no manual!

ttrentt

I just picked up a Jolida 302A from my local jobber. It did not come with a manual, so I am not sure how to bias the tubes correctly! I really can't wait to get this thing up and running, and my jobber doesn't reopen until Monday!

Can somebody please provide a link (I have searched) or a run down on how to bias??? Thank you so much!!! I have a multimeter and familar with electronics.


Trent

Early B.

I have a 502A which is nearly identical to the 302. PM me with a fax number or email address and I will get a copy of the manual out to you ASAP.

BlueMDPicker

40mv plus or minus 4 mV

audiobliss

So, (not having ever seen a tube amp that required biasing) are there little screws or 'knobs' of some sort that must be turned that actually effect the 'biasing'? And then you use that multimeter to check what the setting is? And then you try to get it within a small range based around a manufacturer-suggested rating?

Early B.

Good point, Blue.

My 502 manual says 50mv, but the 302 may be different because of the tubes.

Early B.

audiobliss wrote:

So, (not having ever seen a tube amp that required biasing) are there little screws or 'knobs' of some sort that must be turned that actually effect the 'biasing'? And then you use that multimeter to check what the setting is? And then you try to get it within a small range based around a manufacturer-suggested rating?

Yep. In this case, little screws.

Early B.

Trent, welcome to the Jolida Club. If you have any questions, I'll be glad to help you find an answer. You should know that MadMax is our resident expert on Jolida integrated amps. He has both the 302 and 502. But I gotta warn ya -- don't let Max talk you into trying out the TungSol 6550's. He swears by 'em.

audiobliss

Don't some amps have gauges for the purpose of biasing? Do they take the place of the multimeter? Is there yet another switch to change which tube the gauge is reading?

Early B.

audiobliss wrote:

Don't some amps have gauges for the purpose of biasing? Do they take the place of the multimeter? Is there yet another switch to change which tube the gauge is reading?

I dunno. The only ones I've seen with gauges are self-biasing.

ttrentt

Early B. wrote:

Trent, welcome to the Jolida Club. If you have any questions, I'll be glad to help you find an answer. You should know that MadMax is our resident expert on Jolida integrated amps. He has both the 302 and 502. But I gotta warn ya -- don't let Max talk you into trying out the TungSol 6550's. He swears by 'em.

I really appreciate all the help. I am interested in doing some modifications once I break it it. Will probably be using it with my Monitor 10s, or a set of JBL L26s.

I listen to mostly heavy metal, so I hope you guys don't think its a waste. (Although I am a Jazz guitarist and listen to some jazz)

audiobliss

ttrentt wrote:

once I break it

:eek:

ttrentt

audiobliss wrote:

:eek:

Haha. You left out the other it that was supposed to be "in"

ttrentt

BlueMDPicker wrote:

40mv plus or minus 4 mV

Early is going to fax me the manual. In order to set these, does the amp have to have a load? A tube amp ALWAYS has to have a load right? IF so, does the bias have to do with the load, so I have to re-bias for a set of speakers?

I don't have the info yet, and the fax is at my work, where my JoLida is, but there is no speakers there, but I have my tools there. So I need to know if I need to carry speakers

audiobliss

I'm not sure about your other questions, but a tube amp always needs to have a load. (Thanks for pounding that one into my head, RuSsMaN!) That necessitates that there be a load to bias the amp.

audiobliss

ttrentt wrote:

Haha. You left out the other it that was supposed to be "in"

Oh, that's what the other 'it' was for. I thought maybe you were going to break it twice.

Early B.

ttrentt wrote:

Early is going to fax me the manual. In order to set these, does the amp have to have a load? A tube amp ALWAYS has to have a load right? IF so, does the bias have to do with the load, so I have to re-bias for a set of speakers?

I don't have the info yet, and the fax is at my work, where my JoLida is, but there is no speakers there, but I have my tools there. So I need to know if I need to carry speakers

Manual has been faxed and is waiting for you at work.

According to the manual, step 1 to bias the unit is to make sure the speaker wires are connected to the amp, so this assumes you've got speakers on the other end of the wire.

Why can't you bring the amp home? All you need is a multimeter and a little screwdriver.

ttrentt

Early B. wrote:

Manual has been faxed and is waiting for you at work.

According to the manual, step 1 to bias the unit is to make sure the speaker wires are connected to the amp, so this assumes you've got speakers on the other end of the wire.

Why can't you bring the amp home? All you need is a multimeter and a little screwdriver.

Great, thank you.

As for your question -- uhhh, I shouldn't be spending this money and particular people can't find out.

My multimeter and tool box is at work

audiobliss

ttrentt wrote:

As for your question -- uhhh, I shouldn't be spending this money and particular people can't find out.

ROFL! I predict someone getting pretty perturbed sometime in the not too distant future when this little piece somehow becomes known!

ttrentt

audiobliss wrote:

ROFL! I predict someone getting pretty perturbed sometime in the not too distant future when this little piece somehow becomes known!

My birthday is next month. Somebody doesn't know this is their gift to me! ha!

BlueMDPicker

If there is a input signal present, yes you should load the output stage with a speaker or resistor. Never bias a tube amp with input signal present, your bias setting will be meaningless.

So, to answer your question: back the bias pots off to their lowest setting, power up with no input signal (and no need for a load on the output), monitor the VOM as the tubes heat, adjust bias to 40mv and watch it until the tubes are completely heated (10 minutes or so) and the reading stabilizes. If you can't get within +/- 4 mV with tubes heated, you may have bad resistors in the bias circuit.

audiobliss

BlueMDPicker wrote:

(and no need for a load on the output)

No? Why's that?

BlueMDPicker

Because there is no signal being amplified, hence nothing to dissipate in the output stage. If it keeps your butt from puckering, throw an 8 ohm resistor across the output terminals. But, it's not necessary.

Early B.

ttrentt wrote:

As for your question -- uhhh, I shouldn't be spending this money and particular people can't find out.

I see you like to walk on the wild side. That explains the heavy metal music.

audiobliss

BlueMDPicker wrote:

Because there is no signal being amplified, hence nothing to dissipate in the output stage. If it keeps your butt from puckering, throw an 8 ohm resistor across the output terminals. But, it's not necessary.

Wasn't meaning to question what you said. I just understood otherwise and was curious.

ttrentt

I got it biased up today and the first music through it was Slayer on some old KLH 22s.

Now to get it hooked up to decent speakers and inputs.