How to bias EVH LBXII 15W Head
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- Опубліковано 15 вер 2024
- I wish I had taken the bias down a little further in the video cause it really does make a difference. Maybe next time I'm fooling with it. Pretty darn easy, let me know if you have any questions. Here's the link to the Schematic \m/
support.evhgear... 5150III LBX.pdf
Duuude I’ve been waiting for a tutorial about this ever since I bought my lbx ii used off eBay last year. Thank you so much!
We need a tutorial on the LBX Stealth head
Thanks for the info! Love EVH Gear!!!
I know this is an old video but I can't find schematics anywhere so you know what the test points are for the 5150 lbx with just the red and blue channel or is it the same amp😅
So researching other sources of biasing this series, suggested measuring the voltage drop across R18 as a method of dialing in the bias to 27mv which equals 27ma. With 15.2v at R40, the current is like 45ma across R18. If you go-to -15.0V, the bias current increases. I dialed it in to -16.2v at R40 and the current across R18 ended up around 40ma. Thought it sounded better. Less fizz. May try shooting for 35ma another day. Thanks for the video. Helps me experiment with tones. Maybe 27ma is for LBX III? I'm running LBX I.
I remember there being a common point or two, don’t have the schematic in front me now but ‘Way to Go!’. I find I like the tone of most of my amps biased a bit cooler than recommended, but not all, the Engl I tuned a bit hot.
Awesome, thank you!!
Great video I recently tried a matched pair of Mesa Boogie EL84s (6BQ5) in my EVH 5150 LBX 1 I noticed it was starting to sound a bit fizzy I was told they don't need to be Biased, I was wondering if the test points are going to be the same given its the first model and also is the optimal voltage I'm looking for going to be the same given its a different set of tubes any guidance would be appreciated : UPDATE I went ahead and biased my amp as per video with the mesa boogie power tubes it measured at -16.3 mv way to high I dropped it back to -15.0 mv the tone was so much better, no fizz and a much richer warmer tone with lots of clarity such a difference.
Thanks for the great video. I just got the 5150 LBXiii S 15W ace love it. It has the external bias points but I’m guessing the bias resistor is on the inside like you show in your video. Do you know if that is accurate? I would love to bias the amp myself, but don’t want to take it apart until I find out.
Thanks!!
I can’t say for sure. I have the 50W Stealth and it has the external bias points AND an external adjustment. Seems like if the bias test points were on the outside, the adjustment would be too, know what I mean? Still easier to have the test points on the outside rather than poking probes around on the board. The adjustment is probably inside and very easy to see, probably even labeled. Go for it…
Thanks for getting back to me. The adjustment is definitely not on the outside as there are only the positive and negative test points on the back of them amp. I guess I will take the bottom off and look for the adjustment that you showed in your video.
@@toddknaster9731 - awesome, it should be easy to see.
Sorry to be a pain. Is your multi meter set to Milli amps?
@@toddknaster9731 - no worries, set it to milli volts if you’re using those bias test points.
You're probably not hearing too much difference with the bias changes because much of this amp's tone (and all EVH amps for that matter) comes from the preamp stage, not so much the output stage. Hence the 43 preamp tubes in each model. :-) Gain, gain, and more gain. I swapped out the first preamp tube in mine with a 12AY7 to simmer it down a little bit.
divebomb99 - 43 tubes, lol. I do the same thing with most of my amps, throw an ECC81 in right up front - much better \m/ it did wonders for my Mesa.
Thinking of replacing the tubes in mine. Do i really hvae to bias the amp brother?
NOPE, unless there was an issue with over cooking your tubes you’re fine, but I would recommend you spend the extra dollar to get a matched pair. Once bias is set, there is no reason it will change significantly outside of some sort of catastrophe that requires part replacement.
Thanks for your reply! Merry Christmas!
i have an evh 5150 xlb 15 watt. It seems to have mostly the same layout. Is R40 the correct place to take the reading? The schematics said their BIAS SET TO 28mV AT TP21.
shouldn't it say something like bias test point somewhere? i was told it should be labeled but i can't find it
@@decompression8435 I am not sure. You could have a lead on R40 and, knowing where you started from... move the bias pot and see if your reading changes. It took me a LONG time to find the test point on my board. Can you share the scheet? Sometimes the test point is between components like a cap and resistor, so either location will work.
support.evhgear.com/schematics/EVH®%205150III%20LBX.pdf
Try this, looks like R18 and D10 share the test point, so either will work. If you’re on the ground side of either component your reading will be zero. Good luck \m/
@@oldguyjammin9732 support.evhgear.com/schematics/EVH%C2%AE%205150III%20LBX.pdf
I thought you didn't have to bias el84 tubes?
Michael Mitchell - I used to be under that impression as well but I was wrong, however it is true that a high percentage of EL84 circuits are cathode biased and therefore do not require manual biasing. My error was in thinking that tube type made the determination rather than circuit design.
@@oldguyjammin9732 got ya.... Thank you very much for responding... You have a cool channel and I enjoy the content very much!... Rock on man...
Where did u plug the black cable?
Probably to any ground lug or the chassis somewhere. Any ground connection will work fine.The green wire that comes of the AC plug is excellent.
Can you run el34’s in the LBXii head ?
ricky bobby - do not know, maybe Fender Support can tell you
the tube sockets are much larger for an EL 34 so there's no way
Might be a silly question, but I follow literally everything else in the video so I'll ask! Where do you have the black probe from the multimeter attached to?
chassis ground
@@SeanRussell-KE2CBC hey man, thanks for responding! Hope your channel keeps growing!
anytime. check timestamp 9:30