Are these 6L6 numbers safe

[TerryD]

I have some Sylvania 6l6s that came with this vibrolux that are definitely not matched but they still sound better than my perfectly matched Sovtek5881 WXT
My ideal ma is 26.6 to 31.7 according to my book depending if you want to run cool or hot.
But this is my best case scenario with my Sylvania.  At idle, one tube at 38.2 and the other at 20.8  So approximately 17 ma apart whatever numbers I use.  It comes out the same if I switch sockets.
 
Is this safe???
Are there better numbers I could run with my Sylvania?
 
Thanks,
Terry

[TubeGeek]

What is the plate voltage?


5-10mA between tubes is considered by most to be more acceptable for matching.  Your 17mA may not be a big issue unless you're experiencing hum or other issues because of it.

As long as you don't exceed the manufacturer's maximum plate dissipation value, then you'll be ok.

[HotBluePlates]

Safe? Yes.


Worst-case, you might not get quite as much clean power output as you would if the tubes were perfectly matched (which implies more than just their idle current).

[sluckey]

At 450v on the GE spec sheet, the maximum screen current is 210 ma.

With that kind of screen current I would keep a fire extinguisher in my gig bag!

[TerryD]

Well OK.  so I'm running 450-455 volts.  If I understand you folks right, I could jack the one tube up to 45-48ma, which would get the other tube up to about 26 -28 ma and be as safe as could be.  Is that right?
 
Terry

[TubeGeek]

An option would be to install a bias control for each tube, thus you can set the bias of each power tube.

[PRR]

> one tube at 38.2 and the other at 20.8
> running 450-455 volts

Not "ideal", but hardly "bad" or "un-safe".

If it sounds bad, diddle bias.

If it sounds good, stop worrying and PLAY.

[tubeswell]

Well OK.  so I'm running 450-455 volts.  If I understand you folks right, I could jack the one tube up to 45-48ma, which would get the other tube up to about 26 -28 ma and be as safe as could be.  Is that right?
 
Terry

Did you measure both sets of tube current, plate voltage, and screen voltage simultaneously using identically-calibrated meters and bias measurement resistors? Tube amp measurements taken sequentially (at different times) can often slightly different, even on the same tube, because of a whole range of variables affecting tube operation.


What's more the DC-resistance on different sides of the OT primary is different due to one side of the primary being wound over the top of the other side, and thus having a longer length of wire on that side. Not that it matters for load resistance, because its the turns ratio that determines impedance ratio of the OT.


In a guitar amp it hard to really care about exact output tube balance at idle; just so long as its in the ball-park. Up to 5 mA difference either way is not critical. YMMV

[DummyLoad]

450v max. with 5watts max.  is roughly 11mA. where did 210mA come from?

--pete

[DummyLoad]

this seems pointless and you obviously don't know how a pentode works. THERE IS NO WAY A 6L6GC WILL STAND 210mA flowing through G2, PERIOD. it will very likely become dust in the bottom of the valve at much less that that.


--pete