5E3 first stage interference

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harleyboy2112
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5E3 first stage interference

Post by harleyboy2112 »

I have a 5E3 I built for a customer about 4 years ago. It just started having a problem with the first state motor boating.
With either volume up there is a constant ticking. You take the 1st stage out of the equation and it's fine. I can grab the 1st preamp tube and it stops also.
I've tried every type of voodoo I could and cant seem to get rid of it.
The filtering on the amp is 30-30-30. The grounding is the same grounding scheme I use on all my amps without any problem. First filter cap and center taps to a spot and everything else to a separate ground on the other side of the chassis. There is a 12AY in the first position and a 12AX7 in the second.
Anyone with any ideas?

Thanks!!!
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martin manning
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Re: 5E3 first stage interference

Post by martin manning »

Did you try replacing the 12AY7? It may be microphonic. Classic motor boating is feedback through the power supply, usually due to inadequate decoupling. You might test that theory by paralleling a new cap across the existing one that feeds the first stage.
TUBEDUDE
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Re: 5E3 first stage interference

Post by TUBEDUDE »

Your second filter grounds at the "spot"also yes? That is if it supplies your power tube screens.
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harleyboy2112
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Re: 5E3 first stage interference

Post by harleyboy2112 »

<iframe width="560" height="315" src="https://www.youtube.com/embed/afcRAGb_GVM" frameborder="0" allow="autoplay; encrypted-media" allowfullscreen></iframe>

Here's a video of the problem.
The customer said it was doing this while in the cabinet also. I do shield the back panel on the amp.
Still not able to solve the problem. Here's what I've done so far in no particular order
Changed all filter caps
changed 1st stage bypass cap
replaced carbon comp plate resistors with metal film
re-soldered all grounds
replaced preamp tube sockets
tried different tubes.
tried grounding different points with alligator leads.
checked continuity on all grounds.
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pompeiisneaks
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Re: 5E3 first stage interference

Post by pompeiisneaks »

we don't support direct html, you'll want to just take the youtube link and highlight it and click the 'video' button above in the editor to show it, like so:



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ChopSauce
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Re: 5E3 first stage interference

Post by ChopSauce »

Just out of curiosity (1 more time, cos'I still have too many things to learn:)

- any possibility that the culprit lies near the input jacks?
Andy Le Blanc
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Re: 5E3 first stage interference

Post by Andy Le Blanc »

power supply decoupling,.. Mod the power supply,... it could also be wire dress inside the chassis, double check what and where the longest wire paths
are. I use plastic input jack with its own ground to star as well.
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TUBEDUDE
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Re: 5E3 first stage interference

Post by TUBEDUDE »

Can you get acvess to an oscilloscope?
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harleyboy2112
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Re: 5E3 first stage interference

Post by harleyboy2112 »

I've had a bit of a breakthrough with the amp.
While beating my head against the wall trying to figure it out I noticed the ticking also went away depending on where I was standing.
So I turned around to see what might be causing the interference and realized my router and modem were about 7 feet behind me in a little nook in my workshop. I turned them off and no more ticking.
Now the million dollar question how to shield the amp from this? I haven't noticed this in other amps I've built. I also don't think I've built a deluxe since I've upgraded my router to a more powerful one.
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Reeltarded
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Re: 5E3 first stage interference

Post by Reeltarded »

You can't. Check signals from devices are going to tick. They do it worse on dirty power. You might want to consider grounding all local outlets to your shop area on a single spike. I have a floating outlet in my house near all the techy stuff. That outlet is as miserable as it is dangerous.
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harleyboy2112
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Re: 5E3 first stage interference

Post by harleyboy2112 »

I've come to the conclusion that like Reeltarded said, there's nothing I can do to get rid of it.
I did some experimenting and this is what I found.
I tried out about every amp I own, ones I built, Fender, Peavey, etc., in my shop no guitar plugged in at full volume.
All of the amps make the noise. The ones with full tone stacks make the noise at a much lower level, which seems logical since the tone stack throws away a bunch of 1st stage gain. So A person probably wouldn't notice the noise in an amp with a full tone stack since they probably don't normally play at full volume. The Deluxe of course doesn't throw away so much gain and amplifies the noise considerably.
The noise is definitely being picked up by the 1st stage tube itself. I've tried tube sockets with the metal cover, putting wire mesh on the back cabinet cover & none of that seems to help.
With all that being said it only picks up the noise in my shop which is where my router is. Any other place in my house & there is no noise.
My customer has noticed the noise at home and at Church. I suppose his best bet is to be mindful of where he plugs the amp in and where it's located.
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