Fender Hot Rod DeVille 410 sharp noises with high volume levels

[SpencerK.]

Hi, my name is Spencer.
I am fairly new to the world of tube amps and I recently purchased my first one, a used Fender DeVille 410. I really love the clean sound this amp has and I am completely in love its distortion.

However, today I noticed that whenever I crank the volume up past 2 or 3 (it goes to 12) when I have "more drive" switched on with the drive a good bit of the way up, the amp makes horrible screeching sounds and I am forced to turn the volume back down.

I was wondering what the cause of this may be and if there is a problem, how I can fix it. I know that's alot of distortion, but I also read that a tube amp sounds best when cranked all the way up, and I'd like the settings to remain the same as the volume level rises.

These are the conditions I'm playing the amp in:

Fairly small room, with a 25 foot instrument cable
I'm playing an Epiphone '61 reissue SG through it

I did also think about the amp being used. I thought maybe this was a sign that I needed to get it retubed? Or does it have another problem, if it does indeed have one?

[mac1amps]

One thing that you need to keep in mind is that when you're using an amp/channel with a master volume set low, you need more preamp gain in order to obtain your desired break-up level. That being said, when the master is turned up to higher levels, the power tubes start coming into play, providing their own additional distortion to the sound. BUT, along with that your dynamic range has also expanded somewhat, and if you keep the preamp gain "dimed-out", you'll have squealing, and uncontrollable feedback problems. YOU CAN'T LEAVE THE PREAMP GAIN AT THE SAME LEVEL WHEN YOU TURN UP A MASTER VOLUME! It just doesn't work that way. Honest! (FWIW, I've been a full-time tech [AND player] for 35-years)....with respect to your other issue, the sharp noises. If it's like all of the other DeVille's (or Deluxe's......Hot Rod or Blues series) I've seen, it should have all the soldering gone over (by someone who is experienced with soldering). Between all the "cold" solder joints you see, and the minimal amount of solder at certain critical points, such as the jacks, there's alot of room for improvement with these.

[52 Bill]

the amp makes horrible screeching sounds and I am forced to turn the volume back down.

This could be a number of problems, but I would first check to see if any of the small pre-amp tubes have become microphonic. Sometimes due to use, wear or manufacturing tolerances, the internal elements of the tube become loose and will act like a tiny microphone, and when you turn up the volume they will feedback causing ringing, whistles and other noises.

With your guitar on a stand and plugged into your amp, turn the amp on and set a normal volume level. From the back of the amp take a pencil and lightly tap on the tubes. The small tubes on the right are the pre-amps, the 2 large ones on the left are the power tubes. If your tubes are microphonic, you'll hear a ringing sound as you tap each tube. As you turn up the volume, the ringing will continue to get louder, and may start to feedback. Be careful as the glass tubes will be HOT. If this is the sound that you heard earlier, then it's time to get some new tubes.

Hope this helps.

[SpencerK.]

Thank you both for your help. I will try your method tomorrow, Bill, and I'll respond on here afterwards.

[Chuck H]

I've heard that problem with dirty tube sockets, dirty switching jacks and cold solder joints.

To see if it's a dirty tube socket just turn the amp off standby (so it's ready to play) and gently rock the preamp tubes in a small circular motion. Use a cloth or oven mit for the power tubes or you may get burned. If a socket is intermittantly losing pin contact, you'll know. If you get popping or sharp crackle noises with this test just clean and retention the offending socket. For the jacks you can just plug a male into and out of each FX loop or switching jack a few times. Listen for noises. Clean as needed. If it's niether of these, or a bad preamp tube, it could be a bad plate load resistor. I don't know why but Fender uses 1/4 watt plate load resistors in alot of the PCB amps. This is very close to the circuit current on peaks and when they fail they make crackling noises. If it's none of those then it is likely a cold solder joint. In the case of bad plate Rs or cold solder joints you should have a tech fix it.

Chuck

[Enzo]

Hell, I'd rock the power tubes too, I find more cracked solder on the power tube sockets than I do on the small tubes.

And while you are in there poke at the two 5w resistors that drop the voltage to the zeners making +/-15vS+DC. They like to come loose.

[SpencerK.]

Thanks for the suggestions.
The preamp tubes proved to be non-microphonic, although I didn't rock them with oven mits yet.

I talked to a friend of mine today who owns a tube amp and he said that this negative feedback was a normal thing with preamp gain up and volume up also. He said most any amps would do this. Is this true or should I continue to check for problems?

How do I check for a cold solder joint?

[SpencerK.]

bump

[Chuck H]

"I talked to a friend of mine today who owns a tube amp and he said that this negative feedback was a normal thing with preamp gain up and volume up also. He said most any amps would do this. Is this true or should I continue to check for problems?"

If what your friend is suggesting IS the problem, it would actually be a positive feedback thing.

I don't typically see this kind of instability in production amps. Any mass production company knows better than to sell a design that is by nature unstable at any setting. Modified or homebrew amps sometimes will be unstable at extreme settings. But thats usually accepted in those designs because they sound just right at some other settings and aren't intended to be operated in a manner that makes them unstable. But a mass produced product is generally built as user proof as possible with circuits in place to stabilize the amp no matter how it's operated so that the MFG won't get poor reliability reports and product returns.

I am not intimate with that amp, but I'll bet there is a problem that requires troubleshooting.

Do you know or can you get any history on the amp?

Chuck