Fizzy,crackly distortion from speakers on 36watt lite

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phsyconoodler
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Fizzy,crackly distortion from speakers on 36watt lite

Post by phsyconoodler »

I built a 36 watt lite and it has some nasty trailing distortion when cranked up a bit.It's not a cold solder joint or biasing issue and all the usual suspects like tubes and such have been eliminated.
The plate dissipation is 13 watts.
It sounds like an oscillation and it does lessen considerably when I upped the grid stopper resistors from 8.2k to 220k but it's still there.I could go larger on the grid stoppers but the highs are suffering from the increased stopper values.
Is this the dreaded EL84 fizz problem?
I'm using a separate pair of cathode resistors and caps for each pair of tubes so I'm wondering about the Paul Ruby fix and how one would implement it with separate R/C's ?
Any insight would be appreciated.I have built quite a few 36 watters and this is the first one with this issue.
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Re: Fizzy,crackly distortion from speakers on 36watt lite

Post by zaphod_phil »

The plate dissipation is 13 watts.
Yikes. EL84s are rated for 12W max. 8O
Is this the dreaded EL84 fizz problem?
Looks like it probably is.
I'm using a separate pair of cathode resistors and caps for each pair of tubes so I'm wondering about the Paul Ruby fix and how one would implement it with separate R/C's ?
That doesn't make any difference. The Ruby buzz fix involves a zener and regular diode connected to *each* power tube grid - so four grids get the treatment instead of two. You may also want to add a clamping zener across the cathode caps of each P-P pair.
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phsyconoodler
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Post by phsyconoodler »

Thanks Phil,I will try it and see where I get.

I have a lar-mar master on it too that adds to the confusion on where to put in the diodes. Yeah I know,I'm a dummy!
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Post by zaphod_phil »

The Lar-Mar shouldn't make any difference either, as IIRC it sits on the PI side of the coupling caps to the EL84 grids. The Ruby mod diodes are connected directly to each EL84 grid. The only question is what voltage the zeners should be. One rule of thumb is to use a value around 2V higher than the cathode voltage at idle.
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Post by phsyconoodler »

Tried the Ruby Zener fix and it did nothing.So I tried a filter on the plates of the output tubes and it worked perfectly.
Google 'Smooth your Sonic Ride' for an old guitar player tehnical article.
It worked perfectly in my case.No more nasty distortion or crackling.
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