#1
Hey guys my new tubes are on their way for my 6505+ and im caught in a little dilemma. This is my first time replacing tubes and my parents are urging me to allow my uncle to install the tubes. He is an electrical engineer or something similar and they say he can do it. I spoke to him about it and he said he will look up the amp and let me know. But I just have this feeling that I would be better off allowing someone who fixes amps at a guitar store for instance, to install the tubes. I don't know what I should do at this point. I know many of you have experience with tube swapping so any advice would be appreciated.
#2
You pull the old tubes out by pushing down on the metal on each side, and pop the new tubes in the same way, the metal on each side of the tube is a "gasp" thing.

Just remember to use a towel or something so you don't directly touch the tube and get finger ickyness on them as it will wear them out faster (apparently)

It's not hard nor do you need some sort of degree that to do it.
Last edited by BoL7z at Jul 13, 2010,
#3
if he's handy, it would save you the cost of getting someone to do something as simple as replace the tubes. generally, all it takes is replacing the tubes, then re-biasing them (which involves turning some pots inside as well as measurements to get the right voltages etc etc). If he is an electrical engineer, he should be fine as long as he understands what he's doing.
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#4
if your uncle can do it...by all means let him do it. it will save you the time and money to take it to a guitar tech. I don't know much about how the 6505+ works, so i don't know how difficult it would be to change them and make sure everything is biased and all that. My amp has a system that allows me to easily change them and bias them...but then again not sure about yours. If he can do it...let him. If he isn't sure...then you should take it to the tech. Good luck.
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#5
If you're doing it yourself, just remember DO NOT TWIST THE TUBES WHEN INSTALLING THEM OR REMOVING THEM. the pins can get bent, or twisted or snap off
#6
It is not hard. Do it yourself.
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#7
Im not gonna do it myself because I don't have a slight clue on how to bias the thing. That is what im worried about, whether or not he will be able to bias it correctly. If he tells me he can do it and can bias it correctly then it seems like that will be my best bet. Im also wondering whether he can bias it to sound its best. Like is there a way he can bias it to sound better even though he isn't an amp tech?
#8
6505 shouldn't need biasing unless it's redplating. It runs the power tubes rather cold.
#9
Quote by BoL7z

Just remember to use a towel or something so you don't directly touch the tube and get finger ickyness on them as it will wear them out faster (apparently)

That is a fallacy that does not need to be repeated.


Also, is this 6505 tube replacement day this is at least the third thread today on the topic.
#10
Quote by Roc8995
6505 shouldn't need biasing unless it's redplating. It runs the power tubes rather cold.


I've read that the 6505+ is not a fixed bias amp and needs to be re biased when switching tubes
#11
Fixed bias doesn't mean you shouldn't adjust the bias. You certainly can adjust the bias on the 6505 if you want, but like almost all Peaveys, it runs the power tubes cold enough that you don't have to.
#12
Quote by Metallica456
I've read that the 6505+ is not a fixed bias amp and needs to be re biased when switching tubes


Maybe if you're switching tube types, but if you're just putting new 6L6's in, it should not need adjusting. So do it yourself.
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#13
Well im switching the stock ruby tubes to the standard retube kit on eurotubes. The power tubes in the peavey are 6l6s and same in the retube kit. But the preamp tubes in the peavey are 12ax7s but in the kit they are ECC83S's
#14
An ECC83 is the same tube as a 12AX7. Preamp tubes don't ever need to be biased anyway.
#15
So now are you going to do it yourself?
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#16
Well many people have told me that the 6505+ is biased cold from the factory and it sounds better with a warmer bias. Ill prbly just have my uncle install the tubes and set the bias warmer
#18
So your saying I can just take the old tubes out and install the new ones without screwing anything up?
#19
the 6505+ head is supposed to be biased, the 6505 head, 6505 combo, and 6505+ combo do not need to be biased (unless you have them modded).


EDIT: If you're only changing preamp tubes (small tubes) then there is no bias needed but power amp tubes for the 6505+ head should be biased.
Last edited by AkiraSpectrum at Jul 14, 2010,
#20
Quote by Metallica456
So your saying I can just take the old tubes out and install the new ones without screwing anything up?


YES. YOU WON'T HURT ANYTHING, I PROMISE.

Look, if you like the way it sounds, you don't need to do anything. Just change the damn tubes. If you're looking for a radically different sound, then by all means go out and blow some money on a tech.
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Last edited by dale-banez at Jul 14, 2010,
#21
Go out and buy a decent multimeter and find a tech that will explain and show you how to bias it. It is going to sound better if you warm the bias up a little and the tubes will handle it just fine. Just don't over do it. The hotter you bias it the faster the tubes will wear out but as stated peavey tends to bias their amps cold which is why you can buy XXX heads that still have the factory tubes in them.
#22
i'm a firm believer that this forum is way too scared about switching power tubes.


seriously, you don't NEED to bias an amp everytime you stick in new power tubes, unless you're switching the output tubes with another model tube (EL34 to a KT88 or something). if not, you can switch in new ones without biasing, unless your amplifier is going crazy, like redplating as colin said.

bias between two tubes shouldn't change from 40mA to 10mA with just a standard tube swap. (6 month old JJ/Tesla EL34s to new JJ/Tesla EL34s.) should be changing more like 40mA to 38mA.
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#23
Quote by ECistheBest
i'm a firm believer that this forum is way too scared about switching power tubes.


seriously, you don't NEED to bias an amp everytime you stick in new power tubes, unless you're switching the output tubes with another model tube (EL34 to a KT88 or something). if not, you can switch in new ones without biasing, unless your amplifier is going crazy, like redplating as colin said.

bias between two tubes shouldn't change from 40mA to 10mA with just a standard tube swap. (6 month old JJ/Tesla EL34s to new JJ/Tesla EL34s.) should be changing more like 40mA to 38mA.


I followed shot's advice and my amp blue up. j/k. It's really easy to do if you're replacing the same type of tubes as long as its a matched set.
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#24
You could do it yourself, just make sure the god damn thing is unplugged, know a guy that missed an entire episode of star trek because he touched his tubes while his amp was still plugged in. Star Trek was starting when he got knocked out and ended when he woke up :P
#25
haha alright guys thanks for all the advice. I did some reading last night and found that the 6505+ has a bias trim pot. People say the sweep on it is very small but is noticeable. Sometime today I plan on adjusting the pot to a warmer setting. I'm assuming my amp has to be unplugged when I'm doing this am I right?
#26
Quote by Metallica456
haha alright guys thanks for all the advice. I did some reading last night and found that the 6505+ has a bias trim pot. People say the sweep on it is very small but is noticeable. Sometime today I plan on adjusting the pot to a warmer setting. I'm assuming my amp has to be unplugged when I'm doing this am I right?

i wouldn't think so...it needs to be on so you get a reading on the multimeter. the way mine works is i turn it on...let it warm up...switch to play mode...put the multimeter needles (not sure about the exact term) into the test points and adjust the trim pot accordingly. Mine has test points in the back panel of the amp, but i am not sure about the 6505+...you might need to pull the chassis out or something. just remember not to go too high on the bias.
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#27
Yup, you can't measure bias current if there's no current there. The amp must be on.

Please, please be careful. Poking around in an amp while it's turned on is very dangerous if you don't know what you can and can't touch. Get a copy of the board layout (not a schematic, that won't help you) and familiarize yourself with where the bias points and the trim pot are (not sure if the 6505 has bias points - you may need a 1R resistor) and don't touch anything else. Keep one hand in your back pocket, and use insulated tools in good condition.
#29
OK I just finished installing the tubes about an hour ago. I turned the bias trim pot all the way counterclockwise to get the amp to run as warm as possible without modding it. I didnt get to play with it that long but the sound has GREATLY improved from the way it sounded with the stock tubes. The sound has tightened up and overall sounds a lot punchier. I cant wait to play through it some more!
#32
Read this:
http://profile.ultimate-guitar.com/311ZOSOVHJH/blog/

I suggest you read 311's blog, it will explain a lot in layman's terms. If you need it, there is a blog describing how to make a poor man's probe in my profile too. You shouldn't have adjusted that trimpot without measuring the bias current. If you set it too high the plate will melt.
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#33
Nah its ok the 6505+ trim pot only moves the bias from something rediculously cold to something still cold but a little higher. Its perfectly safe to turn the trim pot the whole way on a 6505+
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#34
Ah ok. Still, I wouldn't touch a bias pot without measuring it. It's just bad form - even if it is usually safe. It could have all the value tolerances at one extremity giving you an unexpected result. Better to be safe than sorry, power tubes aren't that cheap.
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#35
IMO, if you have an uncle that can do it, and will show what he's doing and how to do it, then you'd solve any future problem of "who's going to change the tubes?" ('cause it's be you).

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#36
Quote by Cathbard
Ah ok. Still, I wouldn't touch a bias pot without measuring it. It's just bad form - even if it is usually safe. It could have all the value tolerances at one extremity giving you an unexpected result. Better to be safe than sorry, power tubes aren't that cheap.

Yeah good you understood what I meant
I had no way of saying it in a technical way but doing a bit of research before showed results of only a really small increase if the trim pot was turned.

To put in in perspective with the trim pot all the way to the right it would still be considered biased cold
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#37
Then I guess if one wants the brown sound one would have to mod the bias circuit. Not much of an EVH amp if you can't wind it up towards redplating huh?
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#38
well if the bias trim pot is limited fixed no worries. lot's of amps are like that but you never know with the tubes if that's within tolerance though.
Prs se Holcomb is the answer
#39
Quote by Cathbard
Then I guess if one wants the brown sound one would have to mod the bias circuit. Not much of an EVH amp if you can't wind it up towards redplating huh?

Yeah well one of the first mods FJA do to a 6505+ is to put in a new pot that allows you to adjust the bias up to where ever you want. Peavey just put it so low and unadjustable so some kid doesnt put it up at meltdown temperature, stuff up his amp and then complain all over the forums how shit his Peavey product was.

I'll find some info so support the trim pot bias what-ever-you-call-it

EDIT: here we go

Quote by Eurotubes
I'm questioned a lot as to the bias adjustment on the 5150 II and 6505+. This amp does have an adjustable bias but the available sweep is pretty narrow and the only way to get the power tubes out of crossover distortion is to lower the resistance to the circuit and once again this is a very easy mod and well worth it.

Inside the amp there is a small circuit board that has the bias trim pot mounted on it and the final bias resister which is a 12K 1/4 watt resister. All that's necessary is to replace that resister with a 6.8K 1/4 watt resister which will increase the window of available bias adjustment. A final bias setting of between 36 to 40mA of plate current per tube measured with a bias probe is a good setting. You only need to probe one tube, set the bias for it and you’re done.


Hope that makes more sense to you than it did me
Basically you have to mod the circuit to even be able to get the bias up to where it should be.
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Last edited by Guitar-KID125 at Jul 14, 2010,
#40
Yes I understood that perfectly, thanks.
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