Is this datasheet wrong ??

[kagliostro]

I was looking for a 6L6GC datasheet, with the other datasheet appear also the QE06/50

because I was looking for AB1 with 400V B+ data I give it a look

http://www.mif.pg.gda.pl/homepages/frank/sheets/030/q/QE06-50.pdf

I'm confused because I read Ia 2 x 120mA  - total B+ plate consumption is 240mA  ??



Is my mind out of service or there is a typo ??

I'm trying to understand which is the plate current consumption on a 5E5 and 5E5-A





to establish the max current rating for the primary winding of the OT

(I use a small program to compute data to be used for homebuild transformer)

Thanks

Franco

[pompeiisneaks]

This is a good page to see what different voltages for different tubes plate current would be:

http://www.tedweber.com/webervst/tubes1/calcbias.htm

I took a screenshot of the 6L6GC, attaching. (this is per tube so x2 for 2 tube PP) but from the chart 53mA is 70% diss. and 'hot' so max for the two should be 106mA.

That sheet may be talking about at 100% dissipation or something?  I don't know what Vg1g1p means but it has two values 0 and 80V.  Voltage Grid 1 Grid 1 parallel?  making up things now :P

~Phil

[kagliostro]

Ciao Pompeiisneaks Thanks

So if 53mA is 70%

53 : 70 = 0.757

0.757 x 100 =  75.7mA one tube at 100% two tubes = 151.4mA and this data agree with one other datasheet I've read



I think Vg1g1p  corresponds to the input signal on G1, two columns one for 0 (Zero) input and the other, for the max, 80V input

Seems that there is a typo on the QE06/50 datasheet (or not  )

Could that 2x120mA mean 120mA for the two tubes ?

Franco

[HotBluePlates]

... I think Vg1g1p  corresponds to the input signal on G1, two columns one for 0 (Zero) input and the other, for the max, 80V input ...

No typo.  And you are correct that "Vg1g1p" means grid-to-grid driving signal.

When that driving signal is zero, each tube draws 36mA ("2x36mA").  When the driving signal is 40v peak into one grid (or "80v g1-to-g1"), the plate current rises to 120mA per tube (See more below about this), and 240mA to a single tube when the other side shuts off.

This appears to be Class AB2 operation.  Note that "W_ia" is "Watts, anode input" or power applied to the plate.  With zero grid drive, this is given as 14.4w and it happens that 400v * 0.036A = 14.4w (that -28v for Vg1 must be applied from a negative supply for the data sheet condition).

So look at the driven condition:  W_ia = 48w, and 48w/400v = 120mA.  That 120mA must be RMS plate current over a complete signal cycle at the driven condition.  This is a very complete set of conditions on the data sheet, as they give you plate dissipation while the tubes are driven (20.5w per tube).  Note the output power is 55w, and 55w/2 = 27.5w contributed by each output tube.

As mentioned before, "W_ia" is the total power applied to the plate before output power is transferred by the OT to the speaker.  See that 48w - 27.5w = 20.5w of heat left to be dissipated by the tube at full output power.

Since the data sheet stage is Class AB, each tube sees 3700Ω (plate-to-plate) / 2 = 1850Ω if the other side is still on.  Power output per tube is (120mA)² * 1850Ω = 26.64w.  The extra ~1w might be that 2% distortion cited in the condition.  When one side shuts off, the remaining tube sees half the load it did before, or 925Ω, while plate current doubles to 240mA RMS (but only while the other side is shut off).

240mA RMS corresponds to 240mA * 1.414 = ~339mA peak.  The curves on the data sheet show the tube can manage 340mA with the grid driven just beyond +10v, so the 339mA peak plate current when "40v peak drive" - "28v bias" = "+12v peak g1 voltage" seems reasonable.

I think after this you'll see the column you looked at corresponds to the "Max Signal Plate Current" line of the other data sheet fragment you posted.

I drew the blue part of the loadline for 925Ω to establish the slope; 925Ω * 400mA = 370v, so the ends of the line are at (400v, 0mA) and (30v, 400mA).  The red line overlays the blue line, and shows the tube can manage 340mA with 300v on g2 while going just a bit beyond +10v.

An extra check:  The sheet claims the tube's transconductance is 6mA/v.  40v peak input * 6mA/v = 240mA.

[PRR]

> total B+ plate consumption is 240mA  ??

Yes; for 3700 Ohm load at full output.

AND over-driven into AB2 (note 0.2W power at G1).

And note that you found, not 6L6GC, but QE 06/50. Which does seem to be a 807-6L6-like tube, but not exactly. (Like a 2002 Acura's engine is like my 2002 Accord engine, not exactly).

The 5E5 is cathode-bias and can't work this hard.

The 5E5-A is fix-bias, so you need to know the load impedance. I have not seen 3.7K on any stock Fender OT. Even then, the 5E5-A can not put significant power into G1, and can not get into AB2.

[kagliostro]

Many Thanks HotBluePlates & PRR

I didn't consider the exact class (the datasheet say only AB) and also the load (3700ohm)

Looking around I've seen 6Kohm OT suggested for the 5E5, datasheet say 6.6K for 400V B+ and 152mA consumption

so I'm thinking that an OT with primary winding rated for, at least, 160mA will do the job

Am I correct ?

Thanks

Franco

[HotBluePlates]

Looking around I've seen 6Kohm OT suggested for the 5E5, datasheet say 6.6K for 400V B+ and 152mA consumption

so I'm thinking that an OT with primary winding rated for, at least, 160mA will do the job ...

I don't normally see mA ratings for OT's except when it is unbalanced d.c. for a single-ended OT.

[kagliostro]

Yes, HotBluePlates, as you say

but I must establish the required spec in current ratings because a friend (at DIYItalia) would like to wrap by hand

the OT for an amp (5E5) he want to build from scratch

At DIYItalia we collected a good quantity of info about this activity and someone has build his own transformers, we use a small program

called Wintrasfo to establish number of turns, thikness of wires and other, but we need to know the necessity of the circuit (Load and current)

to set properly the program

Looking around I've seen 6Kohm OT suggested for the 5E5, datasheet say 6.6K for 400V B+ and 152mA consumption

I don't know if I expressed badly, the datasheet I mean is the tube datasheet, not the OT datasheet, about the OT the data I found

is only the 6K primary impedance

Franco

[HotBluePlates]

... I must establish the required spec in current ratings because a friend (at DIYItalia) would like to wrap by hand

the OT for an amp (5E5) he want to build from scratch ...

Then yes, you have the right number.  I'm guessing he needs the current more for sizing the core than the wire...  If it's to size the wire, I hope there is some safety factor built in for current overages during a tube failure, etc (and there probably is some such safety factor used).

[DummyLoad]

> total B+ plate consumption is 240mA  ??

Yes; for 3700 Ohm load at full output.

AND over-driven into AB2 (note 0.2W power at G1).

And note that you found, not 6L6GC, but QE 06/50. Which does seem to be a 807-6L6-like tube, but not exactly. (Like a 2002 Acura's engine is like my 2002 Accord engine, not exactly).

The 5E5 is cathode-bias and can't work this hard.

The 5E5-A is fix-bias, so you need to know the load impedance. I have not seen 3.7K on any stock Fender OT. Even then, the 5E5-A can not put significant power into G1, and can not get into AB2.

couldn't we also assume that's AB2 and NOT AB1 in that Vg1 is given at -28V with Vg1g1p at 80V we'd expect to see Vg1g1p with AB1 at 56ish volts peak or less, and that we have a g1 input wattage for full power drive given.

another clue is that in AB1 with a fixed bias no g1 current flows so Vg1g1p usually does not exceed 2x -V bias - if we exceed that then g1 goes positive, so g1 current flows and we enter AB2 state.

--pete

[kagliostro]

Many Thanks my friends

I hope my brain can retain all the precious info you give me 

Franco

[HotBluePlates]

... couldn't we also assume that's AB2 and NOT AB1 ...

Yep, PRR & I both explicitly noted the QE 05/60 condition is operating in Class AB2.

[PRR]

> couldn't we also assume that's AB2 and NOT AB1

"Wig1 = 0.2W" spills the AB2 secret. This condition needs a part-Watt of drive at G1; datasheet AB1 is nominally zero grid power.

You can also guess because the peak G1 signal voltage goes positive. 28V bias, 80V G1-G1 so 40V peak, must go to +12V positive grid. Must be drawing current. Ass-uming a 1K positive grid resistance, we have 12V and 12mA, or 0.144 Watts peak grid power. So it is the right zone, but the true grid impedance seems to be <1K to make the average 0.2W.

When all the common guitar-amp drivers face a load that dips from 100K to <1K on part of the cycle, they crap-out. You won't come close to 55W out for more than a part-cycle, it will grid-block.