too high filament voltage and weird scope reading

[Chiamp]

I am measuring 6,7v at 118v
can this be a reason for an amp producing harsh faint tone riding on the signal or even produce weird cross distortion ( I thought Ihad it go away but its still there when up loud)
I am also experiencing a that one side of my 100w amp is pulling down pretty bad when on full volume, what can be the cause ?

I am measuring two of the four 6l6 over a 1R to ground and on idle at now 35ma on about 450v on the plates, up to just before clipping they are fairly even and nice sine wave
when full vol the other tube draw 220 the other 105ma and the scope shows a rather tilted square clearly showing its something pulling one side down
any ideas what this can be ? the amp is BF fender power amp/ PI - mesa mk2 clean amp with boost and a 100w marshall OT and 6l6

//another related question, currently I used 110R filament balance resistors , would go down to lower value drop it ? if so a suggestion on values, or an other ideas how to lower the filaments to 6,3v

[Tom Phillips]

I am measuring 6,7v at 118v
can this be a reason for an amp producing harsh faint tone riding on the signal or even produce weird cross distortion

To this question I would say no. You probably have a power transformer that is capable of supplying more heater current than you are using so the voltage does not sag much. In any case, high heater voltage should not cause the problem you have described.

Regards,
Tom

[Enzo]

And the hum balance resistors won;t lower it at all, since little current flows through them. Your voltage is 6% high - not worth the concern.

Not sure what you mean a tilted square wave and pulling one side down. If the top line of a square wave tilts down to the trailing edge, that means the filter caps are not up to the load. If you are looking at waveforms, this is a class AB amp, I am assuming, and the output of either tube will not be a complete cycle.

If you are saying the push side and the pull side don;t make the same output, then scope their grids for the input signal. If those are not the same, then neither will the output be.

[loudthud]

Take a look at the scope photos I posted in this thread at the Amp Garage. You will probably have to register to look at them. I recall that unregistered users can't see attachments.

The Amp Garage :: View topic - harmonic distortion

Do the scope photos look like what you are seeing? They were taken using a 70's four input 50W Marshall JMP Mk II converted back to EL34's.

Because the square wave that the amp produces isn't a 50% duty cycle, I would expect each side's current to be different. Also, the collapsing wave on the bottom of the wave would suggest a reduction of current.

[Enzo]

Do you have to register on that forum to see the photos? Your posts there refer to images not in evidence on my screen.

[Chiamp]

Thanks , I checked the pics on ampgarage , could not see the direct likeness to what I have , but I will try to post some pics of how it looks later


Enzo, I posted a question to you regarding lowering filament voltage here

http://music-electronics-forum.com/t7052-post115416/

[loudthud]

Amp Garage: As I remember you can look at some of the sub-forums but you won't see any of the attachments. It happends to me when I forget to log in. You might have to wait for a moderator to approve your membership. There are forums for 'Howard D' and 'Ken F' amps that only members can look at. Lots of boutique builders post there and sometimes the discussions degenerate into flame wars. Not newbie friendly.

[Chiamp]

Ok I switched one of the power tubes to the other side ,, and low and behold it was totally different scope reading now it looks like this much better ,
but one tube draw 39ma the others is 35ma

all readings are with no nfb connected (had one leg in air for testing forgot to solder it in )
but all far better than before for some reason I dont know was it the tubes pulling it down too much ?

sorry for the big pix

belowclean sine


below mid vol


below full vol


------------
below preboost Boost -OD both on full master low


below same as above but more mastervol


below same as above and full master


anything you could diagnose from these pix ?

[Enzo]

What problem are these photos trying to represent? All I see is a signal being overdriven and clipped.

[Chiamp]

What problem are these photos trying to represent? All I see is a signal being overdriven and clipped.

as I wrote just before I took these pix I switched tubes position just for fun and this was the result looked much better ,
before it was clearly tilted on one side I mean really bad ,
but now it looks better compared to before ,
could it have been that tube that did the weird thing,
it is still the same 6l6 tubes inthe amp just different pos and one of them pulled 39 the other 3 tubes 35ma

but I thought I post it for you more experienced scope watchers see anything wrong with it ?
I was thinking maybe the thick vertical clipping might be bad, its actually 3 lines on top of each other in the bottom on the full vol clean clip#3 ,
and also that notch in the bottom on the od clip what does that tell ??

all help appreciated

[Alex R]

Looks normal to me. Dunno about the little notch - but once an amp's clipping it does all sorts of funny things to the waveform. None of that would give me a moment's concern.