Bell and Howell 385 Conversion

[ubxf]

Thanks CJ, i was thinking of salvaging the output transformer instead of the 25L6 tubes but i didn't know what regular tubes would work well with it

 

[CJ]

who knows the name of this particular distortion emanating from the anode node of this Cathodyne phase inversion manipulation process device?

 

[CJ]

the flat top of the shot above is from blocking distortion of the 6V6GT power tube.


various resistors were tried as grid stoppers and 47 K seemed to be the least value that would round that top.

but we still have the bottom half of the waveform displaying that weird distortion.

here is the before and after shot, the pic on the right is with the 47K grid stoppers installed on the power tubes..

 

[CJ]

various values of resistance added to the grid of the phase inverter to try and stop the lower half wave distortion, scope is on the output of the inverter>

 

[CJ]

interesting that the output transformer seems to negate any differences between the various grid stoppers used on the input of the phase inverter,

scope on 8 ohm output>

 

[Bo Deadly]

Maybe the "nipples" are high frequency oscillation? Does a 10M probe make a difference in the shape?

 

[Flatpicker]

who knows the name of this particular distortion emanating from the anode node of this Cathodyne phase inversion manipulation process device?

Your answer may be here (see section "Avoiding Unpleasant Overdrive"):

http://www.valvewizard.co.uk/cathodyne.html

 

[CJ]

Thanks Flatpicker!

will try 10 M probe..

 

[Bo Deadly]

Your answer may be here (see section "Avoiding Unpleasant Overdrive"):

http://www.valvewizard.co.uk/cathodyne.html

Yup. That's definitely it. But if it's a 5E3 push-pull, that power tube will be grid current limiting and therefore the "spike" won't make it through to the output. So don't worry, be happy.

 

[CJ]

5E3 has no NFB which makes fixing the distortion easier.

(stole that from PRR over at EL34 world)

Princeton Reverb also uses the Cathodyne and they don't sound half bad when pushed, there is NFB used on that model.