Hello,
I have never owned a tube amp (recently picked one up) or a multimeter before and need some help guidance on how to use the multimeter to set the bias. I picked up the following from Home Depot yesterday - MS8260A (http://www.homedepot.com/h_d1/N-5yc1v/R-202353294/h_d2/ProductDisplay?catalogId=10053&langId=-1&keyword=multimeter&storeId=10051)(http://www.homedepot.com/catalog/productImages/300/0e/0e866503-174a-4bc5-97de-ff940182b2b0_300.jpg).
Here are the steps that I followed:
- Plugged the red cable into mA and black one into COM
- Set the dial to 200m under the V on the right side with underline and dots
- Plugged the pointy end of the black cable into common on the amp hole number 3 which is common and the red on into pin/hole 1
- slightly turn the bias dial clockwise until the correct value is shown
When I turn bias dial the value does not change on lcd, which leads me to believe that I am missing some step or have no business using multimeter :duh
Deepak, if its the Jolida...you measure mV, not mA.
Move the red lead to the V.
Quote from: AcidJazz on April 13, 2012, 07:13:02 AM
Deepak, if its the Jolida...you measure mV, not mA.
Move the red lead to the V.
Figures :rofl:
Thanks Martin. Will try that tonight.
Deepak, congrats on your new amp! As you're learning, tube amps can be so much fun! ;)
Since you were flying blind and may have left the bias set too high, connect the voltmeter before start up so you can watch it rise from zero and prevent it from exceeding the recommended value.
Tubes can tolerate a few seconds of too high bias, but if it overheats then it starts drawing more and more on it's own, aka runaway tube, which will not last long. This might occur after 30 seconds or a minute if the bias was double or more of the recommended value.
I like to turn the bias all the way down before changing power tubes. Use a meter to watch, or make sure you remember if down is counter clockwise.
Have fun!!
Thanks Rich. I was watching the meter and only turned it slightly. Was scarred to blow something or getting electrical shock (I am terrified of power tools and electricity)
Wise man! Tubes need some extra respect, but with a little knowledge they are very safe. Even if it breaks, usually a new tube and a fuse is all you need to fix it yourself. It's a good idea to have an extra tube (or matched pair if required,) along with spare fuses so you can fix it immediately instead of waiting for parts to be delivered. But in a pinch you can get tubes at any guitar shop and the fuses at hardware or home center.
Which Jolida? I have the 502 BRC Integrated which has the built in bias (Turn the screw until the red light don't blink no more).
Quote from: Putz on April 13, 2012, 03:42:44 PM
Which Jolida? I have the 502 BRC Integrated which has the built in bias (Turn the screw until the red light don't blink no more).
Response Audio 3205 which has pins bias slots marked 34087.
Quote from: shadowlight on April 13, 2012, 08:07:42 AM
Quote from: AcidJazz on April 13, 2012, 07:13:02 AM
Deepak, if its the Jolida...you measure mV, not mA.
Move the red lead to the V.
Figures :rofl:
Thanks Martin. Will try that tonight.
no luck. someone want to stop by and show me how to bias and use the multimeter :oops: maybe i should just pickup a cheapo one that is easy to use
Deepak with a multimeter and electricity - oh, the humanity!!!! [-o<
http://www.bing.com/videos/search?q=how+to+bias+tube+amp&qpvt=how+to+bias+tube+amp&FORM=VDRE (http://www.bing.com/videos/search?q=how+to+bias+tube+amp&qpvt=how+to+bias+tube+amp&FORM=VDRE)
Quote from: etcarroll on April 13, 2012, 05:35:01 PM
Deepak with a multimeter and electricity - oh, the humanity!!!! [-o<
http://www.bing.com/videos/search?q=how+to+bias+tube+amp&qpvt=how+to+bias+tube+amp&FORM=VDRE (http://www.bing.com/videos/search?q=how+to+bias+tube+amp&qpvt=how+to+bias+tube+amp&FORM=VDRE)
I watched couple of those but the numbers on the lcd does not move away from .000 :x. Maybe the probes are not making the right contact.
The amp is up and running. Thanks everyone. Martin pointed out I need to push the pointy end all the way in until it snaps in, which I was not doing before. ce I did that the numbers started to move but it still took quiet a bit of turn to make it move. All the tubes are glowing around the same brightness so I think I have is set correctly and the numbers were hovering around 34.9 and 35.2 for el34 tubes.
Hey Deepak, good to hear you got it to bias.
Which EL34s are you using? Stock?
Since the amp and tubes are new, keep an 'eye' on the bias levels for the first couple weeks. Sometimes they drift depending on the tube...however I found the stock EL34(Svetlana, as supplied by Bill) to be quite stable.
I have more suggestions in regard to this amp, but you should 'live' with it stock for a while before chasing the tube roll enhancements.
Enjoy the tube sounds. :thumb:
Yep, the EL34 are stock Svetlana.
Hello Deepak,
Sorry I was not around to answer your questions. Things have been a bit touch and go around here with my mom in a hospital 2-1/2 hours away.
Thanks to all those who chimed in to help out.
For tube rolling, I would suggest waiting till the amp breaks in and you have a better idea of "where you are" before making changes. One you have a feel for the amp's sound, you will have a better idea of what dirrection you will want to go in should you decide to make any tube changes.
Evening everyone.
If you are really on a shoestring budget I got this pocket multimeter just for biasing my Jolida JD 502P and for checking batteries.
(http://www.popsci.com/files/imagecache/article_image_large/articles/mm-rs-AA.jpg)
http://support.radioshack.com/support_meters/doc72/72438.pdf (http://support.radioshack.com/support_meters/doc72/72438.pdf)
A word of caution though. If you are crazy enough to put the taller Tung Sol KT-120 tubes in your Jolida along with Pearl PCF tube coolers checking the bias with this kind of meter can be a finger tip burning experience. ;)
Sorry for the stupid question.
If one has speakers with a 6 ohm nominal impedance which tap do you use if your tube amp has 8 and 4 ohm taps only? Is this one of those situations where you try each tap and see which one you like? The amp in question is a Jolida JD-502P. I'm just concerned because I don't want to damage my gear.
Thanks in advance.
Quote from: sleepyguy24 on June 20, 2012, 02:12:34 PM
Sorry for the stupid question.
If one has speakers with a 6 ohm nominal impedance which tap do you use if your tube amp has 8 and 4 ohm taps only? Is this one of those situations where you try each tap and see which one you like? The amp in question is a Jolida JD-502P. I'm just concerned because I don't want to damage my gear.
Thanks in advance.
I used the 4 ohm tap on my Jolida running my Salk Songtowers. Many speakers that report 6 ohm impedance will dip down to 4. It's usually not a flat curve. Might want to check with the speaker manufacturer to confirm.
You can try both, it won't hurt anything. You will find that the bass is tighter and overall sound is cleaner, deader, softer on 4 ohm tap, which has more leverage to convert voltage into current. 8 ohm tap is more open and alive sounding, and a few dB louder, but bass will be "warmer" (looser and less controlled) and probably more pleasant tubular colorings in the midrange too.
My preference is for the highest tap that the speakers will allow, but rock and bass heavy music will prefer more damping from the lower tap.
Exactly. No harm to try both as Rich suggested. The load is not constant meaning it will go above and below [6] Ohms. Our Pipedreams speakers are [6] Ohm as well and the [8] Ohm tap works best overall for us. Have fun trying.
charles
Many thanks gents for the help. I've made note of the info in the posts above. If I do use the 502P with the 6 Ohm nominal KEF speakers I will try both taps. I really had no idea using different taps could really change up the sound. Good to know.
I could have sworn there was a thread for general tube gear hints but I can't find it. I'll just post this hear in the hope that someone finds this thread.
In another thread these words of wisdom were written:
"First thing you look at when having a problem with a tube product is the tubes."
It reminded me of what happened with my Jolida JD-502P amp. I paid a pretty penny for a matched quad of JAN GE 6550 cryo tubes. One morning I turn on the amp I see a flash and the amp shuts down. I thought it was something else and turned the amp back on. It turns on and then shuts off again. I'm pissed and freaking out thinking something has blown up inside because the fuse was ok. So I call my tech and he tells me to relax and change the tubes first before I head over. Luckily I had a spare set of power tubes that I know worked and the amp was back rocking and rolling. I then started yelling out profanities because my matched quad of cryoed JAN GE 6550 had just become a trio and no replacement tube could be found.
Moral of the story. Check the tubes first. If my tech wasn't cool I could have been out at least $50 to have it reviewed.
Dean, you are lucky it was just the tube. A similar thing happened with my VT-200 except the short in the brand new tube also took out 4 bias resistors. Tube amps sound great but when something goes bad in a circuit with 400-500V plate rails it usually goes bad in a big way. :shock:
But if you want the tube sound that is kind of the cost of admission. like they say, "nothin for nothin". :roll: