#1
Alright, If I replace the power tubes with the same type of tubes except them being a different brand I don't need to have it rebiased do I ? The tubes are the EXACT same but a different brand.

I wouldn't think you would need to but I don't want to **** something up because I was wrong. So any help is appreciated.

Thanks in advance
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#2
You will still need to rebias, every tube is different even if it is the exact same brand.
#3
Quote by ibanart300
You will still need to rebias, every tube is different even if it is the exact same brand.


I'm at a loss then. Nobody around my area knows anything of how to rebias. =/
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#4
You can get some great information on how to bias and the tools you need on these forums. The first thing you could do is start by listing the amp and tubes you are using.
#5
Quote by Bryc3e
I'm at a loss then. Nobody around my area knows anything of how to rebias. =/

where are you located, and what type of amp is it?
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#6
Quote by Robbgnarly
where are you located, and what type of amp is it?



I live in North Dakota, it's a 6505+.

Tubes I'm using are Svetlana 6l6's. 12AX7 Preamp tubes.
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#7
does that amp have an external bias point like the XXX/JSX? If it does you can check it with a multi-meter, and it is a relitively simple to do.
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#8
Quote by Robbgnarly
does that amp have an external bias point like the XXX/JSX? If it does you can check it with a multi-meter, and it is a relitively simple to do.



Not quite sure what that is so I'll look it up and tell you in a bit.


Edit : Yeah, I googled it and from reading forums it says it does. So I'll look into that. However, i'm very new to the whole biasing concept so would there be a steep learning curve if I tried to do it myself?
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Last edited by Bryc3e at Aug 25, 2011,
#9
Not really. Once you understand the steps a little of the background as to what you are doing it is really quite simple and is a great way to get you more familiar with your equipment and save some money while your at it.
#10
I do believe the 6505 does not have a bias pot, cause I remember Ryan doing a bias pot mod to his 6505, and warming up the tubes, which sounded excellent. So I'm gonna go with the 6505 is a fixed bias amp, and no, you do not need to bias it, just plug and play.

Someone correct me if I'm wrong.
#11
Fixed bias means it does need to be biased. I've never done one but I understand there is some soldering invilved.
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#12
Quote by tubetime86
Fixed bias means it does need to be biased. I've never done one but I understand there is some soldering invilved.


Oh, then it's the other type where the resistor has the bias permanently set, hence why I call it fixed bias.
#13
Hold on guys.

1. Fixed bias means you DO have to bias it.
2. Do not use different tube brands imo.
3. The 6505+ has a bias trim pot. Unfortunately it only measures voltage at the grid and does not give you the amp's current. Additionally, it has a very limited sweep rendering it almost useless. The mods people do to this amp involve a new variable resister (something below 6k). If you want to measure the amps current on this amp you will need a bias probe - the test points cannot be trusted.

--------------
Fixed Bias - you have to bias manually and there is drift - sometimes immediately after.

Cathode Bias - amp biases for you. Nothing to do (except mod it)

Non-Adjustable Fixed - No need to do anything. 6505/5150s are biased this way I believe.


If you need new power tubes I'd recommend a matched quad of tubes from someone like this:

www.dougstubes.com
www.valvequeen.com
www.tubedeport.com
www.thetubestore.com
www.eurotubes.com (not in europe)
www.hotroxuk.com (in europe)


Anyway, I believe the 6505/5150 is non-adjustable fixed bias similar to a Mesa or a Valveking. Buy a quad of matched tubes and plug n play. With 6L6's you should see something like 35ma - 50ma with 35 being on the cold side. I have no idea what they ship from the factory with but they are way cold.


If you think of 'Fixed Bias' as you must fix the bias yourself when replacing tubes it will help you to remember the differences. But, yeah the naming structure for the types of bias is completely whacked and only adds confusion.

More:

https://www.ultimate-guitar.com/forum/showthread.php?t=1411411&highlight=6505+bias
http://www.google.com/#hl=en&cp=10&gs_id=13&xhr=t&q=6505%2B+bias&pf=p&sclient=psy&source=hp&pbx=1&oq=6505%2B+bias&aq=0&aqi=g2g-m1&aql=&gs_sm=&gs_upl=&bav=on.2,or.r_gc.r_pw.&fp=c313f2edd24fc65d&biw=1843&bih=1020
#14
I think we're missing something highly important in this thread. The TS barely has any idea about his amp and biasing. Given that the 6505 needs to be opened up (unless its modded), that's probably one of the fastest ways to get the TS killed.

I mean, it really sounds like the TS doesn't have the tools or knowledge (or have at least researched the basis of biasing) for him to do it safely.
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#15
Quote by ragingkitty
I think we're missing something highly important in this thread. The TS barely has any idea about his amp and biasing. Given that the 6505 needs to be opened up (unless its modded), that's probably one of the fastest ways to get the TS killed.

I mean, it really sounds like the TS doesn't have the tools or knowledge (or have at least researched the basis of biasing) for him to do it safely.



I've tried researching this biasing business but it's so beyond my level of understanding at the moment. I can't find anywhere that writes it so that a dummy like myself can figure it out.
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#16
You sure there is no amp tech around? You really want this done by a pro.
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#17
Even an electronics/T.V. repair shop will have the nessisary skills and equipment to safely do the job.
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#18
buy a matched quad of tubes and pop them in.

trying to bias this amp as it is (stock) is somewhat pointless as mentioned above.

the bias pot is on top of the chassis right next to the power tubes

i'm not sure what the issue is


Edit: Referring to the 6505+/5150II

v.....I believe that to be correct Cath
Last edited by 311ZOSOVHJH at Aug 26, 2011,
#19
Correct me if I'm wrong, but even on its hottest setting a 6505+ is running the tubes pretty cold aint it? If I am correct you'd get away with just plugging them in and going. Buy a matched pair of SED =C=, they can cope with being run pretty damn hot.
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#20
Yes, the bias is way cold on the 5150 family. Unless the tubes are redplating (which would only likely happen on a bad set), there's no need to bias unless you want to tweak the sound.