#1
Calling 311 and Cathbard!!!

Ok guys, I'm trying to bias my Splawn QuickRod this weekend. I'm running into a problem getting a stable reading. What appears to be happening is the bias keeps running higher and higher the longer the amp is on. After I made some adjustment, I got it up to around 30-31 mA on startup, which is about what Splawn recommends, but the longer the amp stays on, the higher that number goes. I realize the amp needs to warm up a bit in order to stabilize the bias, but mine never seems to stabilize, it just keeps climbing. When I actually play the amp, it shoots up even faster, which I know is normal, but shouldn't the bias start to fall back down once I stop playing? After a few minutes of warmup, the bias rises several mA, but after a few minutes of actually playing through the amp, it shoots up to dangerous levels and won't fall back down. Is this normal or am I missing something here?

EDIT: A little update on what it's doing; starting it up, not playing through it, it reads 31 mA. 2 minutes later, it drops to about 30.5; about 5 or 6 minutes after that, it rises back up to 34-35. I adjusted it back down to 30, and within 4 minutes afterward it's back up to 33 mA, and still rising.
Ibanez UV777 - Carvin TL60 & 727 - Jackson KE3
Splawn QuickRod - Mesa Stiletto & RoadKing - Peavey Ultra+ - Peavey Bandit
Some pedlulz & cabz


7 String Legion
Last edited by BCKRedBaron at Mar 24, 2012,
#2
Sounds a little odd. What is your plate voltage doing during all this?
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
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Marshall 1960A
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Cathbard Amplification
My band
#4
Give the sockets a good clean too.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
#5
Thanks for the responses guys.

The plate voltage did fluctuate, but it didn't appear to have any correlation to the bias rising. I started working on it Friday night, and the plate voltage was 510V. Saturday we had a washer and dryer running, and the fridge kicked on from time to time as well, so it went anywhere from 505V with those appliances off to 490-495V with them on. It even read as low as 480V at one point. But the bias didn't seem to change with these fluctuations.

At one point Saturday, I had the bias set at 30mA on startup, and I played through the amp, and within about 30 minutes, the bias was up to the high 40s. I stopped playing for a moment to see if the bias idled back down, but it didn't. Just kept rising. I shut it off just before redplate and dialed the bias back down, but it would still keep rising. I never let it get above 38 or so afterward before I shut it down. I did this probably 5 times yesterday.

I'm gonna do a bit more work on it today, then call Splawn tomorrow. I'll clean the sockets again. I try to always do that when I pull a tube out. This is the first time I've tried to bias anything, but I felt like I did my homework on it (311, your guide was very helpful) and I can't think of anything I did wrong, but maybe I'm just missing it.
Ibanez UV777 - Carvin TL60 & 727 - Jackson KE3
Splawn QuickRod - Mesa Stiletto & RoadKing - Peavey Ultra+ - Peavey Bandit
Some pedlulz & cabz


7 String Legion
#6
I don't think you've done anything wrong other than playing the guitar with the probe hooked up. Don't do that. Also make sure you never unplug the multimeter while the amp is running. Part of the reason I created that blog is because none of the info I found on the web was really complete and/or left out what I consider important steps. Biasing an amp is actually very easy but you have to follow the steps methodically.

Also, what kinds of power tubes are you running? Did you get new ones or are you just biasing for tone? Have you checked each tube individually? Which probe do you have? I'd hook everything up and let it run for 15 minutes (don't play) and then check. It should be pretty stable at that point. Your bias will drift naturally. It will definitely drift if you are playing the amp. Make sure a cab is hooked up and turn the amp volume off.

A 480 plate voltage is completely normal for EL34s.

If the milliAmps really do climb and don't stop turn it off obviously and send Scott an email. Then, go buy another multimeter and possibly another probe. I've gotten funky readings before from bad testing gear. Maybe put a fresh battery in too.

That is really all I can think of.
#7
I'm using one of Eurotubes' new ET1 bias meters. It's supposed to be designed to allow you to play with the probe installed. It's just a probe and a meter with a display for mA and plate voltage. Maybe it's the meter? I suppose I can buy a probe and use an actual multimeter as well.

I figure the changes in plate voltages were just a result of the line voltage on the house changing due to use by appliances/other houses on the line.

I'm using the Chinese Valve Art EL34s Splawn uses now. I checked them briefly last week when I got the probe and they were way low (below 23 mA), so I wanted to go up on the bias. I checked all 4 tubes. I'm biasing on the highest reading tube (they're all within about 3 mA), the one closest to the power transformer on the inner pair. I'll try it tonight with the volumes off. And I'll post on here what happens. Thanks again for your help.
Ibanez UV777 - Carvin TL60 & 727 - Jackson KE3
Splawn QuickRod - Mesa Stiletto & RoadKing - Peavey Ultra+ - Peavey Bandit
Some pedlulz & cabz


7 String Legion
Last edited by BCKRedBaron at Mar 25, 2012,
#8
Oh - OK. Well, I had one of the cheap $25 probes and I fried the resistor by playing the amp while biasing.

And yes - it sounds like you have a probe with the meter built in. Can't speak to voltages fluctuating because of appliances running - Cath or someone else will probably know. I guess keep us posted.

#9
Ok guys another update: This evening, I gave the sockets/tube pins a good cleaning with some Deoxit. Then, I set the amp up, turned all volume, tone, and gain controls to 0, nothing plugged into input, of course with a speaker load. Probe is still on the same tube, 3rd from left looking at it from the back (the one closest to PT on inner pair). Plate voltage is around 505V. Bias started at about 26.5 mA, then drifted down to about 25 over 5-10 minutes. It's been about 20 minutes now, and it's at 27.7-27.8.

Update: Now it's been about 30 minutes. For a few minutes the bias stabilized between 27.7-28mA, but then it crept up again. Now it's relatively steady at 28.8-29. Plate voltage at about 503V. So does this sound more normal? The amp's not getting any input whatsoever, but the bias is still creeping up, albeit much slower than before.
Ibanez UV777 - Carvin TL60 & 727 - Jackson KE3
Splawn QuickRod - Mesa Stiletto & RoadKing - Peavey Ultra+ - Peavey Bandit
Some pedlulz & cabz


7 String Legion
Last edited by BCKRedBaron at Mar 25, 2012,
#10
Everything seems pretty normal to me. How does it sound? I'm sure you are fine. It won't hurt to leave it on for several hours if you like and then just check it again before bed time or something.
Last edited by 311ZOSOVHJH at Mar 25, 2012,
#11
Phew, thank God! Haha! So now it's been a little over 40 minutes, and the bias has been stable right at 29 mA. It's at 29.1-29.2 right now.

So should it be ok to play for a while, provided the probe's out? My only concern is that playing it will send the bias skyrocketing again, and it'll redplate.

I'll leave it on for a while as you suggest.

EDIT: One other question, probably a dumb one, but I'll ask anyway: Could having the amp flipped upside down affect it? I know in your guide yours was upside down, and of course you have to have it like that to reach the screw, so it may be a dumb question, but right now mine's setting on it's bottom like normal and it's a heckuva lot more stable than yesterday.
Ibanez UV777 - Carvin TL60 & 727 - Jackson KE3
Splawn QuickRod - Mesa Stiletto & RoadKing - Peavey Ultra+ - Peavey Bandit
Some pedlulz & cabz


7 String Legion
Last edited by BCKRedBaron at Mar 25, 2012,
#12
Yeah, I think you are fine. You said it got up into the high 40s while you were playing it? That seems pretty high but I'm not an amp tech. 35mA is probably as high as ever seen mine. Turn the lights out and watch your tubes while you play. If Bob (at Eurotubes) says you can play while probe is in then so be it. But reading the bias while playing is not a good indicator of the amps bias. You want the amp idle.
#13
I played the amp for about 30 minutes just now with the probe out. Turned out the lights and watched the tubes, no redplating that I could see. I should get more time tomorrow or Tuesday. But it sounds mean right now! I'll work with it some more before I box it up, maybe try 31 or 32 mA.

I may need to send ole Bob an email about his meter.
Ibanez UV777 - Carvin TL60 & 727 - Jackson KE3
Splawn QuickRod - Mesa Stiletto & RoadKing - Peavey Ultra+ - Peavey Bandit
Some pedlulz & cabz


7 String Legion