TUBES

[Victorinox]

Changing preamp tubes do not need biasing. Single ended (meaning operating on only one power tube) like champs etc do not need biasing. Chaging power tubes on other amps need rebiasing depending on whether it is cathode baised(cant remember the exact term) or fixed biased. Fixed biased needs to be biased because when they use the term fixed, it means the bias is set by a variable resistor and doesn't adjust to the tubes like a cathode biased does. So you need to set it.

 

[Reth]

So that means for the valbee, no biasing is required at all in changing the power tube?
Just pop out the old and pop in the new one ah? Cool!

suckasucks; have you changed your tubes in your valbee yet?

 

[MrBukka]

Now I am really confused.....I was about to re-tube my Blackheart Little Giant (a single end class A amp with one EL34 and one 12ax7) with the Mullards I bought. Well i read through the user manual and it said that it needs biasing........so please help me out here really confused after reading the forum that no biasing is needed for single ended class amps.

Cheers.

 

[celahircelebrindal]

Btw if you guys wanna buy tubes @Burlington Sq get it from Martin Electronics....nice elderly couple running it.The other one nearby...err...not recommended lah.
As for tubes been using tungsol 12AX7 and Svetlana EL34's....the best pre-amp tubes imo would be the Holland made Phillips 12AX7...sweeeeettt!!!
No more in production but you can try in eBay.....the US made one are cheaper but cant be compared to the Holland made...

 

[Ratboy]

Now I am really confused.....I was about to re-tube my Blackheart Little Giant (a single end class A amp with one EL34 and one 12ax7) with the Mullards I bought. Well i read through the user manual and it said that it needs biasing........so please help me out here really confused after reading the forum that no biasing is needed for single ended class amps.

Cheers.

Fact one .. if manual says must bias, please bias else if explode = warranty void : )

theoritically, all tube amps should be biased
but since some circuit designed or the tube used have a wide tolerance
you can get by without biasing
this is especially true for a single ended amps based on 1 power tube.

If the amp runs more than 1 tube ( esp power section )
then you would prefer the tubes to be properly biased
so that they are running similar and will not cause unplanned "distortion"
more so for push-pull design where you want the push and pull to be equal.

 

[seekz]

The number of tubes does not determine the bias lah.

Only cathode bias is self biasing, no need to re-bias.

Push-pull also can self bias

 

[MrBukka]

Thanx guys for the advice! Although I am really tempted to just change the tubes without rebiasing, but I am glad that I waited. I do not want my new amp to BLOW UP in my face lol. Since my Little Giant needs to be biased any idea where can i get it done, and roughly how much will it cost?

 

[lightice]

Cathode bias amps never need to be biased when changing tubes, I've ever only experienced EL84 amps being cathode bias.

Others; KT66, EL34,6V6, 6L6 require so.

 

[MrBukka]

So is the Blackheart Little Giant cathode bias? I couldn't find any info about cathode bias in either their website or the user's guide, and they haven't return my email for quite sometime......Please help anyone?

 

[seekz]

yes it is. or at least thats what the people at some forum is saying

by the way, when switching from pentode to triode or vice versa
you gotta do it when the amp is off, or will damage the power tubes.
just a lil fyi.

I just changed my tubes from wat i can hear, the JJ EL84 is remarkably fatter, and shimmery.
but for the 12AX7, can't really tell the diff, just buy an EH 12AX7. Cheaper.

 

[wasabe19]

will the amp really explode? i thought it might just sound bad if the bias is too hot or cold?

 

[lightice]

I doubt it'll ever explode. Probably just damage the tubes.

Anyhow, you'd need to insert the tubes and switch them on before you can bias it.

So I doubt anything will happen to ur amp if it isn't biased properly, just that it won't sound good and the tubes will need to be changed faster/wear unevenly.

 

[MrBukka]

Thanx alot Seekz for your advice, btw are JJ tubes really good? I heard alot of good reviews about it but never tried it myself. Really tempted to buy them to retube my Little Giant but I got the reissue Mullards instead, hope that they live up to my expectations.........If not I will try the JJs next

 

[seekz]

So to me its just so-so lor, the JJ is as good as an EH, I think maybe the rave reviews you hear about are the JJ "Gold" ones. MUCH more expensive. Haven't tried it.
Only tried the regular JJs.
Btw only refering to the 12Ax7s,

I've yet to try so many brands, and also don't intent to.
My conclusion is that a change in tube can bring about changes in many ways than one, although subtle, but still quite audible. But i still thing that theres really no need to seive tru so many just to find the right one.
for me its its "Just mod the amp lor"

 

[MrBukka]

Just went down to Martins at Burlington Square to day and got myself a JJ EL84 and a Sovtek EL84 military grade and a reissue Mullard 12ax7 that the shop owner reccommended. Will be doing a comparison soon, and perhaps post my findings for all you peeps!

Oh and a little fyi for those Blackheart amp owners, they are actually factory fitted with Shuguang tubes.

 

[Whitestrat]

oh, and is there a difference between 6L6 and 6L6gc. becauase AFAIK, a normal 6L6 puts out way more than 5 watts of power.

Tubes have something to do with power output, though not as much as you think. A lot of it is also due to amplifier class circuitry. If it's using a Class A, then it'll have the lowest output. a Class D will have the highest output in most classes (if I remember correctly) but sound like shit. Best compromise today are Class AB amps...

I tend to think of tubes more about the way they sound rather than the output you get from them.

 

[Ratboy]

will the amp really explode? i thought it might just sound bad if the bias is too hot or cold?

Just kidding about the amp exploding

worst case scenario is that the amp runs too hot, tube melts,
shorts and blows the tranny
which in turn trips your MCB/ELCB causing black out
in the meantime, the amp catches fire
but the fire prevention circuit is down due to power failure
and the building burns down to the ground : )

 

[MrBukka]

Btw Seekz, do you own a Little Giant too?

 

[seekz]

I use a Epi VJR head.

btw, power is not determined by class.
The class only determines the "way" the signal is amplified.
class A is plain amplification
small signal go in big one come out.

class AB is where the signal is split into two.
and re-amped back into one. two amps involved one amplify the positive another amp the neg, thats why louder. but not as harmonically rich as Class A

Class C is for radiowave.
Class D amplifies waves in the form of pulses.
Both not very applicable to guitaring.

The easiest way to get more power/loudness is to use a high
sensitivity speaker, with SPL of 95 and above. Then next is the
efficency of the output transformer. Then the power tubes then
the input tranny.

 

[MrBukka]

I see......good info for future modifications!!!

Lots of people from other forums have been saying that the Little Giant is just a hot rodded VJR, construction wise I may agree since its designed by the same guy, but tone wise they are worlds apart........IMO I think they are more like cousins rather than siblings......lol. Both are still undoubtly very good amps!