6L6 Question

[Paul1453]

Can the 6L6 be operated in the horizontal position?

The data sheet does say anything about that like it does for some other tubes.

It's probably a stupid question.   

[shooter]

The RCA data sheet I have says ANY for position
btw, I learned here, tubes care sometimes.

[eleventeen]

As long as you're not lying on the floor when jamming with a 6L6-fired amp, you should be fine. 

[Paul1453]

Thanks guys!

Now I have also found a data sheet that says position any.

The reason for my question was I have a little SS PA housing,
and the 6L6 won't fit standing up in it.

Sticking out the back gives me more room and should also keep things much cooler inside the housing.   

[Paul1453]

EF86 can mount in any position too.
So both tubes will stick out the back.

I got one of my salvaged laptop PTs and my $8 Chinese DC-DC step up PS.
Used the 12 VDC supply with a 5 ohm 8W dropping resistor for the heaters.
Parallel the 12 VDC to the HT supply and tried that on the setup on my BB.
No problems, even with only a 2.5A 12 VDC supply.
Heaters take 1.1 A and HT very little on top of that.

I did make a shocking discovery.
Don't touch the metal 6L6 and the guitar strings at the same time.   
Just a little nip with a +258 V B+, but I wasn't expecting that.
Wanted to see how hot that metal 6L6 was getting.
I'll only use 6L6Gs when sticking out of the case now.   

[PRR]

The shell of a metal 6L6 should NOT be at plate voltage.

Where did you connect Pin 1, Shell?

[Paul1453]

I don't think it was shocking me with full B+.

It was more of a nibble than a bite.
It felt like less than the normal 120VAC bite.
I really only brushed the tube to try to sense it's temperature.
And I didn't do it again to double check. 
I really should get me one of those IR guns.
Since I was using DC heating, I thought it must have been part of the HV?
Could it have been only 6-12 VDC?

Let me recheck the schematic and get back to you PRR.   

I didn't get a clue from the schematic, but I think Pin 1 was just floating with no connection.
I'll have to check when I get home.
I probably should have grounded it, right?
That should eliminate the shock hazard, correct?

[Paul1453]

Yes indeed, Pin 1 is not connected to anything.

When I check the data sheet that would be fine for the 6L6Gs.
Which have NC (no connection) there, but the old metal 6L6s have Pin 1 connected to S (shield).
So I'm guessing those free electrons were finding an easier path to Gnd through the case,
across my body, to the guitar strings, and into the input.
I think I became the grid leak resistor for the 6L6.

Now that I realize this fact about the metal 6L6,
I suspect this was also a significant factor in the oscillation issues I was experiencing
when I was experimenting with other 6L6 circuits on my BB using the metal 6L6s.

If I ensure I Gnd Pin 1 on the metal 6L6s, I think that should eliminate my shock hazard.
Is that correct? 
I certainly hope so, as my plan was to use my metal 6L6s on this EF86 6L6 SE circuit which sounds very good to me.   

[PRR]

Pin 1 on metal-shell or metal-base (6550) Octals should go to ground.

You may have felt stray electrons bounced out of the plate; they have some velocity (voltage).

It shouldn't be any more oscillation-prone than a glass 6L6.

[Paul1453]

I've got Pin 1 grounded now.   

I've almost transferred this circuit from my BB to this housing.
I just need to wire up the EF86.
It should get done after work tonight.

I'm calling these my "6L6 Shooter" amp.
I've got the majority of the parts for 4 more in stock.   

Just a recap of what I've learned on this.
Metal 6L6s need Pin 1 grounded.  Pay closer attention to data sheet info.
Otherwise, if you touch the can and the strings you become the new grid leak resistor?   
And possibly, the metal can (if not grounded) could act as an antenna and contribute to parasitic oscillations? 

[Paul1453]

It's done and working.   
Sounds great with no issues when used for 1 hour with a +250V B+.

No more shocks when touching the 6L6 and the strings with Pin 1 grounded.   

I'm still testing the limits of the Chinese PS.
Cranking up the voltage can cause it to shut down and restart.
I was surprised when B+ was set to +250 V and I put a tube pre-amp gain on the input,
That also caused the PS to shut down and restart when the volume was set at 50% or more.

I might have to change my laptop brick feeding the PS.
The one I used was 12VDC @ 2.5A, I tried my littlest one 1st.
That used a smaller, lower watt, dropping resistor to run the heaters. 5 ohms 8W used.
I have a few more bricks that are 19.5VDC with higher amps output.
The problem with that was the heater resistor needed goes to 12 ohms and 15W minimum.
But I am thinking that the 19.5V might give the Chinese PS,
the boost it needs to prevent it from overloading and restarting with a strong input under heavy load conditions.   
It's input voltage specs list 8 - 35 VDC output 0 - 390 VDC.

There are no problems with this when running the 12VDC input with a +250V B+ and a non-boosted guitar input,
even when dimed and played for 30 minutes. 

[Paul1453]

OK, a new question.

Why do you think my DC-DC converter works just fine with an unboosted input,

but will balk at the volume being turned up with a boosted input?

I tried the 19.5V Dell laptop bricks and it wasn't pretty.
I paralleled a 25W and a 5W resistor to get 11.7 ohms of resistance.
The dropping resistor calculator I used said I needed 15 W min. for this resistor.
I should have been OK, right?
These bricks balk at simply turning on, I guess from the initial current surge from the heaters.
These damn things only have a 2 prong cord.   
So after a few tries I get one to boot up.
My B+ was right on, but I think my heater supply voltage was on the high side around 7.4 VDC.
The amp warms up and starts to play, but now I have a terrible buzz, not hum, from the Dell brick.
In just a few minutes I could smell the dropping resistors cooking.
They are hot as a pistol, and the buzz is completely unacceptable.   

My original 12VDC brick never balked at turn on, has absolutely no buzz,
and plays fine with B+ @ +250 except when I tried to overdrive the guitar input and turn the volume past 4.

I've got the 6L6 cathode biased and it sounds great otherwise.

Does boosting my input signal cause my 6L6 to draw that much more current being cathode biased?
In your opinion, what the hell is going on with this thing?

I was completely satisfied with my original results until I tried to overdrive the input.
How does overdriving the input cause this problem?   

[HotBluePlates]

OK, a new question.

Why do you think my DC-DC converter works just fine with an unboosted input, but will balk at the volume being turned up with a boosted input?

You know what you did as far as hooking things up, as well as what you're trying to accomplish. But I don't know either of those things; you'll have to dumb it down for me so I can follow what's going on... 

[Paul1453]

OK,

The amp is working great with B+ at +250 VDC.

So I tried turning up the board to put +250 at the plate of the 6L6.
Just testing out the board and seeing if the 250 spec on the DS meant 250 on the plate or what?
So it's working at very low volume with 250 on the plate.
I go to crank up the volume and see what she does now.
A little over 50% volume and the LED on the board blinks out,
sound starts to drop, B+ is falling.
The board starts recycling trying to come back up.
With the volume cranked up, it  recycles, B+ and sound begin to come back up until,
it blinks out again, and starts over.

I turn the volume down to 3, it recycles and remains on.
Turn it back above 5 and she blinks out again.
So I figured it had trouble supplying the current with the higher B+
I didn't realize until later just what my B+ was when I got +250 on the plate.
It was well north of 330 V.  Then I realized that my screens get far more Vs thru their resistor than the plate gets thru the OT.
OK, so I'm pushing this little board too hard I figure.

Adjust B+ back down to +250V and play it dimed for 1/2 an hour no problems.
This circuit is very clean at these voltages, just oh so slightly getting the 6L6 to break up when dimed.
So I say let's help it out a little by boosting the input.
I've got a little Bogen 4 mic and 1 phono preamp box.
It has 2 12AX7s and a 12AT7.
When I played with this before it gave a little boost to it's input and then past that it goes to a more fuzz effect.
It doesn't have an OT and basically has a mic cord for the output.  It also came with a 1/4" jack screw on adapter.
So I plug my guitar into this and it's output into my amp, with them both turned all the way down.  Power em up.
Turn my amp V to 3 and then the preamp gets turned up some.  OK, get volume on the pre at between 1-2, slight 12AX7 distortion at 3, and more fuzz above 4.
OK, so now its working as I expected, so I turn the pre to 3 and want to see how the amp now sounds dimed.
Bang the strings to make some noise and start to turn up the amp volume.
Around 5 on the amp the little board bugs out and starts it's recycling thing again.
I'm like why?  It's still using +250 V B+, whats with the recycling?  It keeps recycling with amp volume above 5.
Turn the amp down to 3 and the board stabilizes and holds.  Above 5, board balks again.
Back to 3 on amp PS comes back up.

I take the pre out now, plug the guitar straight in, and she goes to 10 and plays for 20 min, no problem.
Put the pre in at around 3-4 again, and the amp continues to balk when pushed over 5.
No pre, no problems.

Maybe it's just the output of this Bogen somehow, and it wouldn't do it with a simple 9V pedal?
I don't have any pedals to test that theory with.   
I want to make sure this amp can handle pedals before I show it to anyone.
It really sounds good for such a simple amp with only a volume control.

With my Ibanez with humbuckers plugged in and dimed, and the amp also dimed.
Make some noise, let it naturally fade out, and the amp is silent.
You can't even tell it is on, unless you pluck a string.
Then you find it is still dimed, but when the note fades out, the amp is silent.
It's hard to believe that with the guitar and amp dimed, this thing will remain silent if you want it to.
I have some very quiet amps for hum/noise, but I've never heard an amp as quiet as this when dimed.

The thing plays great and will not balk at all when dimed, if I just use the guitar alone.
Tried some single coils on it, and the 6L6 sounds sweet with only a very faint amount of noise now from the single coil.

I'm trying to figure out how feeding my amp the Bogen mic/phono output can cause my PS to act up?
Does that better explain the issue I'm having?

Any ideas about what is happening?

I think I need to buy a cheap distortion pedal.  I just seem to like the tube distortion sound better.

[Paul1453]

I forgot I have an old Ibanez DUE 400.

Plugged it up to the amp and gave it all the gain and level the 400 would.
Dime the amp and she's a dirty girl now, without any of the PS recycling issues.

So it had to be my Bogen pre-amp.  Not sure how, the 12AT7 output is wrong for an input to an amp?
Even if it is, I'm not sure how that causes my PS recycling symptom.   

[Paul1453]

Here's the circuit with the voltage readings.

A very clean little bedroom amp.  6.5 W @ +250V B+

Which can also be a dirty little girl if fed by a proper overdrive pedal on the input.   

[Paul1453]

So the EF86 6L6 is a real clean amp.

I wanted to see if I could get away using my little 2.65K @ 8 ohms SE OT with the EL34 too.

Staying with the lower voltage B+ designs, +250 seems good to me.

I made my own simple 12AX7 EL34 circuit, like the other with just a volume knob.

The pot is between the 12AX7 stages, and I didn't try to maximize the gain of V1.
I didn't bypass their cathodes and used 2.2K cathode resistors.
I had another circuit with this configuration that states a gain of 20 for each side like this.
It can still get plenty dirty like this, much more than the EF86 6L6 circuit.
I started with 60uF and 250 ohms on the EL34 cathode.
I worked my way down to 100 ohms, and am pulling around 70mA from my bench supply.
About the same current demand as the 6L6 circuit.
My little SE OTs I got from little R-R junk, seem to be able to handle this amount of current without problems.

I'm still experimenting with this circuit on my BB now.
It is very different from the 6L6 circuit.
If someone doesn't like how clean the 6L6 is,
they will likely like the sound of this similar circuit better.

Both of these bigger bottles sound better to me than the little tubes these OTs were used with.