Rookie bias question

johnpace2

johnpace2

Well-known member
Hey Guys,

I just got a Marshall 2555x re-issue and they say it comes biased very cold from the factory. I'd like to check this myself instead of running it up to a tech, especially since it has these nice external bias points. Can someone recommend a meter for me to buy? I was a little confused about how the sign in the amp says set meter to mV.



Thanks!
 
I have a bias tool that I picked up on eBay a few years ago. Grab one, buy a multimeter and set it to mA. Its got a tube base that goes into the tube socket, and the tube plugs into that. The end of the bias tool has a red and a black lead that plugs into the multimeter. The bias tool I'm talking about is on eBay for 27 bucks, a multimeter is 10 at a hardware store. Yes, the proper way is to measure plate voltage but I know most Marshalls sound good between 35-40 mA so I just shoot for that. Never had an issue.
 
johnpace2":k6w84lbv said:
For example, the meter below has a selection for mA, but not mV

Click to expand...
Get one that has mV, or with this one, set it to VDC and do the conversion. It's pretty easy...

Steve
 
Racerxrated":30fixlnv said:
I have a bias tool that I picked up on eBay a few years ago. Grab one, buy a multimeter and set it to mA. Its got a tube base that goes into the tube socket, and the tube plugs into that. The end of the bias tool has a red and a black lead that plugs into the multimeter. The bias tool I'm talking about is on eBay for 27 bucks, a multimeter is 10 at a hardware store. Yes, the proper way is to measure plate voltage but I know most Marshalls sound good between 35-40 mA so I just shoot for that. Never had an issue.
Click to expand...
Seems ridiculous to add the cost and added time needed with the bias tool when the thing already has external bias points that any multimeter will work with, even one without a mV setting... Unless he has more amps that don't have external bias points that he wants to bias, I'd just grab a decent multimeter and call it a day...

Steve
 
Hung Huy Tran":bjb4k6ox said:
Your probably don't want to hear this, but it might be a good idea to have a tech take the zap for you.
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I see no way to zap yourself with external bias points...

Steve
 
That amp is a no brainer, get a meter from radio shack for example with mV and set it per the chart. Doesn't get any easier than that amp with the bias test points and the trim pots right there like that. Red to red and black to black test each pair and set each side with the trim pot for that pair per the values written on the amp.
 
sah5150":1v0qeu3u said:
Racerxrated":1v0qeu3u said:
I have a bias tool that I picked up on eBay a few years ago. Grab one, buy a multimeter and set it to mA. Its got a tube base that goes into the tube socket, and the tube plugs into that. The end of the bias tool has a red and a black lead that plugs into the multimeter. The bias tool I'm talking about is on eBay for 27 bucks, a multimeter is 10 at a hardware store. Yes, the proper way is to measure plate voltage but I know most Marshalls sound good between 35-40 mA so I just shoot for that. Never had an issue.
Click to expand...
Seems ridiculous to add the cost and added time needed with the bias tool when the thing already has external bias points that any multimeter will work with, even one without a mV setting... Unless he has more amps that don't have external bias points that he wants to bias, I'd just grab a decent multimeter and call it a day...

Steve
Click to expand...
True, and I'm no tech! :doh: But if he wants to bias other amps he can use it. I know that there are better ways to do this but I'm just sharing what I use. Better he listen to people with more experience than I! :D
 
Thanks guys! So far, the meters I've seen done have mV on them, but I probably just need to keep looking.
 
RG955TT":1v67x9gc said:
That amp is a no brainer, get a meter from radio shack for example with mV and set it per the chart. Doesn't get any easier than that amp with the bias test points and the trim pots right there like that. Red to red and black to black test each pair and set each side with the trim pot for that pair per the values written on the amp.
Click to expand...


It's weird, not a single meter at Sears or RadioShack has mV on it. Only mA.
 
Racerxrated":ueiet76e said:
Since I'm a Jube fan, I gotta ask..even biased cold, how do you like it? Make sure you boost it a bit though... :rock:
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Sounds great so far! I've been told I'll get even better results with proper bias so I'm excited to try that. I'm definitely boosting too. :rock:
 
Just order a Fluke meter online. Like Amazon.

Nobody has mentioned this, but the amp's bias setting means nothing if you don't know the amp's actual operating plate voltage.
 
If you want something to do any amp with I recommend the Compu-bias, have one use it for every amp. Gives you plate voltage so you can do proper calculations, little base with wire goes between tube and socket. Works well, easy to use. Costs a few bucks ($200 or so but they do show up cheaper on ebay from time to time) but I use it for every amp I own and never need a tech for tube changes.
ACCURATELY DISPLAYS PLATE VOLTAGE
ACCURATELY DISPLAYS CATHODE CURRENT
ACCURATELY DISPLAYS CALCULATED WATTAGE
AUTOMATICALLY FOR UP TO 2 TUBES

http://www.compu-bias.com/
 
Yep, Flukes are tough to beat, I've used them on the road every weekday for 32 years ;)
I found a 360.00 one at a pawnshop 12 years ago for 50.00 and added it to the stable :D
Its never missed a lick :thumbsup:
 
For that amp with El34's the suggested current draw (per tube) would be 28ma on the low side and not to exceed 34ma on the high side. Somewhere in the middle worked best for me with my jubes for tube life and tone.. and I played loud.. output master on 8 and lead master on 5 or 6.. lol

post a clip if you can
 
FourT6and2":2gn22k33 said:
Just order a Fluke meter online. Like Amazon.

Nobody has mentioned this, but the amp's bias setting means nothing if you don't know the amp's actual operating plate voltage.
Click to expand...
Actually I did earlier. The correct way. But of course I don't do it that way. :LOL: :LOL:
 
The Craftsman meter has a range switch for mv. I have 2 similar to this. One was only 10 bucks in the Sears junk bin and works great.
 
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