Changing PT without a Bias ???????

[dellinger1988]

Hi first post here been lurking for a while cant find some advice on this anywhere else so I thought I would pick your brains!..

ATM my amp has its stock Sovtek 5881/6L6WGC Power tubes. Now I have read that these are not real 5881's but are rather a 6L6GC's and are rated at 30W.. Now Its time to change my tubes and I don't have an Amp Tech or Guitar shop within 100's of miles to get a Bias done with new tubes. I'm wanting to change from the Sovteks to JJ Tesla 6L6GC's also rated at 30W ( I think ).. So my question Is can I put the JJ's in my amp without having a Bias done and will It run? I know that getting a Bias Is obviously the thing to do but Its out of the question unless I do It myself, and I don't really want to do that. Any advice on this would be great thanks.

[stokes]

It can be done,but it will be a crapshoot.The new tubes may fall within a safe bias range but the only way to be sure is to at least check the current draw.What amp are you talking about?

[dellinger1988]

Krank Revolution .. from what i read on avg its PV is 475 if that helps :S .. I dont mind if the tubes only last a few months, but i dont want to blow my amp up either..

[Wilder Amplification]

Krank Revolution .. from what i read on avg its PV is 475 if that helps :S .. I dont mind if the tubes only last a few months, but i dont want to blow my amp up either..

When you speak of the "rated at 30 watts", you're talking about PLATE DISSIPATION, not output power.

ALL 6L6s have a 30 watt plate dissipation rating. This just governs what load they can safely run into at what voltage. But tubes don't see the same output power that the load is seeing (i.e. the OT and the speaker). This is because output sections work like adjustable voltage dividers.

Basically the long and short of it is that the average dissipated power over a full cycle of your signal cannot exceed the max rated dissipation while controlling the load current it takes for the load to see max output power. This means that while the tube itself may see an average power of 30 watts over a full output swing, the load will see much more.

Typically a 2 x 6L6 amp will put out power in the range of 40-50 watts.

In regards to the bias, I would at least check it to be sure. As was said before, it's a crapshoot. Now if you replace them and the plates in the tubes don't turn red (i.e. the grey metal thing you see in the tube) this means that it's not underbiased and it won't hurt anything. If the plates turn red either at idle or at your normal playing volume, you'll need to have the bias adjusted.

[dellinger1988]

^ .. ahh! not as simple as i thought, thank you for that reply much appreciated!!

[stokes]

All 6l6'S do not have a 30 watt plate dissipation rating.Only the 6L6GC's have a 30 watt rating.The others,6L6,G,GA and GB all have a 19 watt rating.Old stock 5881's have a 23 watt rating.Current production 5881's are more like the 6L6GC and have a higher,usually 30 watt,rating.

[Wilder Amplification]

All 6l6'S do not have a 30 watt plate dissipation rating.Only the 6L6GC's have a 30 watt rating.The others,6L6,G,GA and GB all have a 19 watt rating.Old stock 5881's have a 23 watt rating.Current production 5881's are more like the 6L6GC and have a higher,usually 30 watt,rating.

Sorry...should've stated "all current production 6L6s". I forget there are those who still live in the world of NOS.

[DIY_Guy]

I happen to have a Revolution in my studio. I run Svet =C= 6L6's in mine. bias for sure had to be adjusted when I put them in, but as I recall it was still in safe area, just very cold.

And mine came stock with Sovtek 6550s, odd that yours has 5881s

[Gibsonman63]

Bias Meter

Why not invest a few dollars in a bias meter? For less than the cost of nice set of power tubes, you can get a bias meter and know where you are instead of guessing and if you extend the life of your power tubes, it will pay for itself. Also, biasing really isn't a one size fits all affair, but a range of what it is considered reasonable. You may find that you like your tubes biased a little "hot" or a little "cold", but you won't know the difference if you can't measure it and then experiment.

[dellinger1988]

Thanks guys! great feedback really appreciated!, I will pick up some JJ 6L6GC's and see what happens if they run ok and don't red-plate and sound better than the Sovtek's then i will probably just leave it for now at the current bias. I would like to learn how to Bias an amp so i may pick your brains some more at a later date! Cheers

[stokes]

Sorry...should've stated "all current production 6L6s". I forget there are those who still live in the world of NOS.

You have to be careful on a forum like this.Forget those of us who"still live in the world of NOS",which I do,you get some kid who sees what you've said and gets a set of 6L6's on ebay,pops them in his Boogie and then is cursing that so and so Jon who told me all 6L6's......