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Post subject: Fender Hot Rod Deluxe Problem
Posted: Fri Oct 18, 2013 11:44 am
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Hey guys, I have a problem with my Drive channel that I am having trouble finding. When in the drive channel now if you turn any of the tone controls past about 5 it starts making the most ungodly rumbling/squealing noise I have ever heard. I also notice if you hit the bright button while in drive channel it goes into a high frequency squeal. I happened to have my multimeter hooked up to the bias point and ground and noticed the bias voltage goes from normal to the sky as it begins the rumble/squeal when you hit the mid point on the tone controls. The tubes are brand new and check out fine on my tube tester, any ideas?

Thanks,
Rad


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Post subject: Re: Fender Hot Rod Deluxe Problem
Posted: Fri Oct 18, 2013 2:32 pm
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Hi Radmaximus,

Although the tubes are new and test fine, you might still have a microphonic tube. Since this only occurs on the drive channel, try another tube in V2 first. It could be any of the tubes, so after trying one in V2, if the problem persists, put the original back in V2 then try the same in V3 and then V1. It's usually a good idea to first rule out the tubes, and most tube testers will not show a microphonic tube, so substitution is the best bet. I suspect the preamp, but it could even be an output tube. There are other possibilities, but try the tubes first and get back to us.

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Post subject: Re: Fender Hot Rod Deluxe Problem
Posted: Fri Oct 18, 2013 5:11 pm
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I post this only as an FYI.

Herbie's makes tube isolators. Normally you'd just replace a tube if it rattled or was microphonic but if that tube happened to cost you an arm and a leg like a NOS Mullard EL34 or a NOS RCA Blackplate 6V6 you might be tempted to try one of Herbie's gadgets. Some guys swear by this sort of thing. Others claim they have very little value. I've never tried one because I never went the NOS route, except one time by accident and the tubes were fine and they were also cheap.

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Post subject: Re: Fender Hot Rod Deluxe Problem
Posted: Fri Oct 18, 2013 6:39 pm
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Good idea BMW-KTM, and those look very cool. 8)

I use these for preamp and power tubes, mostly as a preventative measure in combos, but I have a couple of killer GE preamp tubes that sound great except for the microphonics, which these help stop.

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Post subject: Re: Fender Hot Rod Deluxe Problem
Posted: Fri Oct 18, 2013 11:57 pm
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shimmilou wrote:
Good idea BMW-KTM, and those look very cool. 8)
:lol: I have my moments ... occasionally ....
Load up that software yet?

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Post subject: Re: Fender Hot Rod Deluxe Problem
Posted: Sat Oct 19, 2013 1:18 am
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Yes! RN9 is great, looks like it will replace at least two programs that I have now. I already uninstalled RN7, and after testing the rest of the program I might uninstall Music Maker also. I have yet to try Elements, it's on another computer, but will soon.

Thanks again. :D

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Por favor, disculpe mi español, no se llega a la práctica con mucha frecuencia.


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Post subject: Re: Fender Hot Rod Deluxe Problem
Posted: Sat Oct 19, 2013 8:47 am
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Post subject: Re: Fender Hot Rod Deluxe Problem
Posted: Sat Oct 19, 2013 9:34 am
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" I happened to have my multimeter hooked up to the bias point and ground and noticed the bias voltage goes from normal to the sky as it begins the rumble/squeal when you hit the mid point on the tone controls. "

Sounds like you have a microphonic output tube (6L6GC). This can be dangerous, as you notice the idle bias current (or your measured mV) goes up rapidly along with the ungodly squeal.

You can find which 6L6GC is bad by GENTLY tapping the tubes with the eraser end of a pencil --- have slight volume, no guitar connected. The bad one will make a "tinking" noise. REPLACE the bad one. Do not try to use it --- even with Herbies or some such latex ring. As a microphonic output tube can go ballistic quite quickly, taking out your output tranny.

Usually, when gain stage tubes go microphonic (12AX7 or 12AT7), the bias does not change in the output tubes. Unless you have a bad oscillation/instability issue in the gain stage or phase inverter.

Gotta rule-out bad 6L6GCs first. Good luck!

:D


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