5 watt problem

goldtop0 · Jul 26, 2018

Hi fellas, I've got a 5 watt single input, tone/volume 1 x 6v6, 12AT7, 6Z4 amp.....also has an added a tube/solid state switch.
It farts out(parasitic oscillation) when getting to high volume (12) and I'd like to sort out how to recitify that if possible.
I'm using a G12M20 with it and it sounds okay up to about 7 or 8........above that it goes mushy and dark.
New PT and OT?
What do you guys reckon.

PaulD · Jul 27, 2018

Without a lot more information it is impossible to diagnose what this could be. Is this a commercially built amp? If so what make and model? If it is a home built a link to a schematic and some photos of the inside would help. Has the amp always done this or is it a problem that has just started?

"Farting out" usually refers to blocking distortion (parasitic oscillation is something completely different). Blocking distortion occurs when the grid of the output valve is being driven to the point of conduction. In any case it is unlikely that the problem lies with the transformers.

goldtop0 · Jul 27, 2018

PaulD said:
Without a lot more information it is impossible to diagnose what this could be. Is this a commercially built amp? If so what make and model? If it is a home built a link to a schematic and some photos of the inside would help. Has the amp always done this or is it a problem that has just started?

"Farting out" usually refers to blocking distortion (parasitic oscillation is something completely different). Blocking distortion occurs when the grid of the output valve is being driven to the point of conduction. In any case it is unlikely that the problem lies with the transformers.

Thanks for that.
It's a locally made amp which I don't have a schematic for(cottage industry) but of course can ask the guy who made it to provide me with one, it's been like this since day one.
Interesting that you say it could be to do with the output valve. I'll be taking it to my amp guru to see what is possible.
I bought this one based on the same amp a buddy of mine got which has a far more strident tone all the way to 12, it was a relative bargain and follows the old adage that not all things are created equal.
However it came in a good fender style tweed cab and is just what I like for quieter cafe gigs and playing at home.

CoyotesGator · Jul 28, 2018

Give us a good clear picture of the inside.

goldtop0 · Jul 29, 2018

CoyotesGator said:
Give us a good clear picture of the inside.

Will do this week......... and I appreciate your expertise and perusal:salude

Big Al · Jul 30, 2018

You have the poor thing turned up to vaporise and are suprised it sounds angry? I own a small herd of single ended tube amps and every one of them pups goes from bark and bite to howl and when dimed to woof. I reckon it's the nature of the beast.

You might try a 12AY7 to tame the gain. I've never used that rectamifier thingy and don't know if there is a tighter substitute like I do for overwhelmed 5Y3s to kill the mush.

goldtop0 · Jul 30, 2018

Big Al said:
You have the poor thing turned up to vaporise and are suprised it sounds angry? I own a small herd of single ended tube amps and every one of them pups goes from bark and bite to howl and when dimed to woof. I reckon it's the nature of the beast.

You might try a 12AY7 to tame the gain. I've never used that rectamifier thingy and don't know if there is a tighter substitute like I do for overwhelmed 5Y3s to kill the mush.

Well yes you may well be right with what you say Al...........it's just really frustrating for me.
It goes to weedy and woofy.......a very annoying sound:dang
eg I bet my bottom dollar a 5 watt Fender or Marshall wouldn't fart out like my one.

5 watt problem

goldtop0

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PaulD

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goldtop0

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CoyotesGator

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goldtop0

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Big Al

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goldtop0

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