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John Myung Bongo 4

Off Topic Changing amp power tubes

colinboy

colinboy

Well-known member
Joined
Apr 15, 2007
Messages
1,742
Location
Corkcity,Ireland
Hi Guys just looking for a bit of advice from some of you tech experts here. I need to put in a set of new power tubes and get my amp re-biased. Unfortunately there is no decent amp tech in my area and none specifically for blackstar. Is this something that i can do or possibly learn how to do myself?

Thanks in advance for any advice.:)

Cheers
Colin
 
Yes, of course you can. It's not rocket science. You'll need a screw drivers, multimeter, pencil, calculator, and balls of steel for the first attempt or two. It's not a job you should attempt until you are very sure of what you will do. For starters, you may have to open up your amp. If you are not comfortable taking things apart and putting them back together correctly again, you'll have to acquire that skill. :D

And don't go poking around the high voltages inside of a running amp with a metal probe until you know what you are supposed to do (which is the balls of steel bit).

With some amps it's really simple (test points on the back panel, no disassembly required) and some amps need taking apart and making multiple measurement/calculations of the idle plate dissipation (I recommend measuring the DC voltage drop across each side of the Output Transformer, for safety and accuracy). That may sound complicated, but it's not really.

There are lots of resources out there on the interweb that will teach you the basics of what you need to know and I'd suggest trying the blackstar forum for specifics about your amp.

This my go-to reference...

Biasing

and if you need to do additional reading to understand some of the basic terms, then dive in. Knowledge is key, an safer too. You have some homework to do before your practical class, so get cracking. Feel free to drop me a line if you're stuck, I'll be glad to help out if I can.

Of course back in the old days most people just shoved whatever tubes they had in there and didn't worry about bias unless the tube plates were glowing red. That's an option too. :)
 
Last edited:
Hello

Fresh from the factory, most of the amps are biased on the cold side. I don't think that in the factory they lose a lot of time for biasing perfectly each amp.
Thus, most of the time, you can put new tubes without worrying about bias.
Of course, if you want to "optimize" your amp, you can always bias it.
My advice : put new tube, try your amp. If it sound good, then ... it's good !

By the way, how old is your amp ? If I remember well, your Blackstar is not so old ... My tubes on my Fender Blues DeVille are still the factory's ones and this amp is more than 5 years old. Are you sure you need to change the tubes ?

Good luck and be careful if your try biasing ... there are some powerful caps in an amp.
 
Thanks for the advice guys. Yes Francois your right the amp is only 3 and half years old.I replaced the tubes the first time after 18 months but that might of been caused by myself when i turned the amp on without first connecting to the speaker cab.I replaced all 4 tubes exactly 2 years ago and now theres one or two gone again. I never got the amp biased before i fitted the new set. I am just wondering if i got it biased would the tubes last longer?
I checked out this video on youtube on how to bias an amp and it seems straight forward enough.
Replacing and Biasing Amp Tubes - YouTube
Also i was thinking if i bought this device i would be able to do it myself in future.BIASMASTER System BM2 - TAD BiasMaster

Also i did a bit of research and for amps like mesaboogie theres fixed bias so only their tubes can be used on their amps but when i replaced the last set i used the exact same ones that came with the amp when i bought it so it perhaps shouldnt need to biased???

Thanks again for the advice
Colin
fbecir said:
Hello

Fresh from the factory, most of the amps are biased on the cold side. I don't think that in the factory they lose a lot of time for biasing perfectly each amp.
Thus, most of the time, you can put new tubes without worrying about bias.
Of course, if you want to "optimize" your amp, you can always bias it.
My advice : put new tube, try your amp. If it sound good, then ... it's good !

By the way, how old is your amp ? If I remember well, your Blackstar is not so old ... My tubes on my Fender Blues DeVille are still the factory's ones and this amp is more than 5 years old. Are you sure you need to change the tubes ?

Good luck and be careful if your try biasing ... there are some powerful caps in an amp.
Click to expand...
 
Hello everyone! I'm going to ask another type of question, still regarding changing tubes: I want to change tubes in my amp too (FYI an ENGL Invader 100), but I just found out that the same ENGL tube can be labeled with different "grade", and I noticed that the lower the grade, the higher the price..
Can anyone tell me what is this "grade"?
Sorry colin to hyjack your thread..
 
GreyDog said:
Hello everyone! I'm going to ask another type of question, still regarding changing tubes: I want to change tubes in my amp too (FYI an ENGL Invader 100), but I just found out that the same ENGL tube can be labeled with different "grade", and I noticed that the lower the grade, the higher the price..
Can anyone tell me what is this "grade"?
Sorry colin to hyjack your thread..
Click to expand...

Hi GreyDog,
from what I know, Engl categorizes the tubes by the required bias level. If you still have the original tubes in our amp, you can look at the grade of your tubes (little sticker on the socket) and replace them with the same grade. That is supposed to eliminate the need for rebiasing our amp.

Cheers,
Mikey
 
Hi Colin
I am by no means an "electronics" guy and am lucky enough to have a "best mate" who is a pro amp tech.
I buy my valves from him at mates rates, I then take the amp apart and after I put in the new tubes after cleaning the valve bases, he
sets the bias for me, while I watch him and make him a cup of tea (I also save up all the packs of biscuits I get when I'm working away and "dump them on him and his guitar building business partner - bribery works!!)
Ive watched him do it and beforehand read up about it on forums etc. The last one I did was my MM amp and they give full instructions on how to do it.
One of the problems is, that when you take amps out of their cabinets, wheteher they are combos or heads, they are awkward to work on, on the bench. This is because you invariably need to get access to various places on the PCB / valve bases to check the values. When an amp is "naked", you usually find that the tubes/valves protrude more than the transformers , so you need to have blocks of wood on the bench to sit the chassis on - otherwise you will smash the valves.
Some amps "don't need biasing" - like the Mesa Boogies as previously stated. In this case you don't need to buy their valves - you can use valves that are matched. Mesas's can be modded to give you an option to manually change the bias - but that is nothing to do with your query.
Whilst I'm in rambling mode, thare are now amps on the market that are "intelligent" and have a box of tricks built into them so that you could in theory run mis matched valves and tweak the amp quite easily - it's akin to the concept of modern cars that you can interogate via a "plug and laptop".
For peace of mind Col, get it done - see if you can watch it being done? My mate charges £30 an hour bench time and the whole job can take between 30 - 40 mins - strip down, clean valve bases, bias and re assembly.
I generally leave my amp on for a few hours, whilst in his workshop and play my guitar through it - it gives the amp soak time and you are not biasing cold.
 
hi Colin, there is a group on Facebook called guitarist ireland, if you ask on there I'm sure someone will know who to contact to do the job for you.
 
Thanks for the advice Spud your lucky that you have a mate locally that can does this for you. Only problem where i am living is there is no decent tech in any of the few shops here and normally they would try to overcharge you anyway!
Spudmurphy said:
Hi Colin
I am by no means an "electronics" guy and am lucky enough to have a "best mate" who is a pro amp tech.
I buy my valves from him at mates rates, I then take the amp apart and after I put in the new tubes after cleaning the valve bases, he
sets the bias for me, while I watch him and make him a cup of tea (I also save up all the packs of biscuits I get when I'm working away and "dump them on him and his guitar building business partner - bribery works!!)
Ive watched him do it and beforehand read up about it on forums etc. The last one I did was my MM amp and they give full instructions on how to do it.
One of the problems is, that when you take amps out of their cabinets, wheteher they are combos or heads, they are awkward to work on, on the bench. This is because you invariably need to get access to various places on the PCB / valve bases to check the values. When an amp is "naked", you usually find that the tubes/valves protrude more than the transformers , so you need to have blocks of wood on the bench to sit the chassis on - otherwise you will smash the valves.
Some amps "don't need biasing" - like the Mesa Boogies as previously stated. In this case you don't need to buy their valves - you can use valves that are matched. Mesas's can be modded to give you an option to manually change the bias - but that is nothing to do with your query.
Whilst I'm in rambling mode, thare are now amps on the market that are "intelligent" and have a box of tricks built into them so that you could in theory run mis matched valves and tweak the amp quite easily - it's akin to the concept of modern cars that you can interogate via a "plug and laptop".
For peace of mind Col, get it done - see if you can watch it being done? My mate charges £30 an hour bench time and the whole job can take between 30 - 40 mins - strip down, clean valve bases, bias and re assembly.
I generally leave my amp on for a few hours, whilst in his workshop and play my guitar through it - it gives the amp soak time and you are not biasing cold.
Click to expand...
 
ErnieJohn said:
hi Colin, there is a group on Facebook called guitarist ireland, if you ask on there I'm sure someone will know who to contact to do the job for you.
Click to expand...

Thanks for the heads up John i sent a request there to join the group so il see how i get on when they come back to me.
 
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