#1
So I'm figuring my 6505+ is due a retube. It doesn't sound quite as vibrant in the low end any more and at my last rehearsal it even sounded a little muddy.

Anyway, the advice I'm after is this: Since the range of the bias adjustment is so narrow on these amps could I in essence just retube the whole thing now before one of my tubes craps out completely and then worry about the biasing later? Note this particular amp hasn't had the bias mod so it's adjustment range is stock.

Now I do realise that with most amps this would be a big no no but I hear that even when maxed out, the bias on the 6505+ is still really quite cold and can't get hot enough as to even take the tubes fully out of crossover distortion let alone go too far and allow them to red plate. I've read that at stock it's hard to even get it up to 20mA, let alone a comfortable 35mA. So if this is true, would I be right in thinking that if I left biasing until later the only issue I may have to deal with would be a potential loss in sound quality compared to how it would sound after biasing it for the new tubes?
#2
Yeah for the + just crank the bias to full. It will still be cold.


JJ's are a good value. Eurotubes, Tubedepot, Dougstubes and a few others.


Edit:

to clarify- the stock potentiometer swing is very low. Max is around 20mA like you know.

You can put new tubes in, max it out and call it a day.

If you do decide to get it modded then you really need to check the bias and make sure you are not too high.
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Last edited by R45VT at Apr 2, 2013,
#3
yes you can do that and be fine
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#4
On a high gain amp like the 6505 you won't really notice the difference tbh. Where you notice it most is when you crank the output into saturation. You aren't doing that are you?
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#5
Thanks guys, that's great.

Cathbard, nah it's not likely i'll be pushing it that hard. My band mates don't really let me get above around 2 on the post before they tell me it's too loud haha.
#6
It won't matter shit then.
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
#8
I wish I would have done some legitimate recordings before and after I bias modded mine. Then I could have something to compare to.

As has been stated before, you won't need to adjust the bias if it's stock.

Jackson RR3 Rhoads and DK2M Dinky
Peavey 6505+ w/ Avatar 212 cab
Ibanez TS9, ISP Decimator, MXR 10 Band EQ
-Digitech RP1000
#9
Quote by Tremolo Bum
I wish I would have done some legitimate recordings before and after I bias modded mine. Then I could have something to compare to.


I am contemplating doing the bias mod at some point or another, when I have more spare time that is. Would you say it makes much of a difference tonally?
#10
Not really. A bias modded 6505 will still sound like a 6505. Preamp tube selection will do more than bias modding for this amp. I would bet the vast majority of 6505 owners could not tell the difference between a bias modded one and a stock one just from listening. Bias modding seems to be a bit over-rated with this amp.

After bias-modding mine I was all like "LOLWTFBBQ? Hey 6505 y no SLO toanz???". It was a bit disappointing to me as everything I had read online suggested this would completely revamp the tone.

I ended up changing a lot of things on my amp at once though. I redid the preamp, replaced two blown screen resistors ( it was only running on two power tubes), bias modded it, and modded the lead channel all at once. So it's kind of hard to say if the bias mod alone made a huge difference.

Jackson RR3 Rhoads and DK2M Dinky
Peavey 6505+ w/ Avatar 212 cab
Ibanez TS9, ISP Decimator, MXR 10 Band EQ
-Digitech RP1000
#11
Hmm, well I guess I might as well just keep it stock in that case then.

Thanks for the advice guys, got a new set of tubes on the way now so I'll sling them in when they arrive.
#14
Well that's certainly opened things up a bit! Way more low end now, sounding a lot better and will be fun blasting it properly in the studio tonight.

Thanks again for confirming my thoughts, guys.