Strange distortion when clean

[Schuabber]

Hi everybody,

I have a nice DR504 1978 2 inputs, all original but the large caps.
I was playing it last Saturday with my Strat and it was very clean and perfect like always, but suddenly, in some chords and notes it started being dark and with a very strange "sponge" type of distorted sounds.
The pre-amp was the Bright at 9:00 and the master was at 12:00.
I changed the settings to more pre-amp and less Master ant it was pretty clean again and later I put it back to the first setting and the strange thing was not there anymore.
So, what could be the problem? Bad power tubes?

Thks a lot!

[OldSchoolDave]

If this behavior is sudden and new to the amp, tubes would be the first items to check (assuming your guitar jack and cables are all o.k.).

Dave

[Schuabber]

Thks for replying.
Yes, the guitar and speaker cables are new from Klotz and the speaker is a brand new EV.
The tubes I was told to be in good shape, and worked fine for one year in house volumes. I know that they should be changed sooner or not.
But this strange noise comes from pre-amp or power tubes?

[mhuss]

It would be worthwhile to remove and re-insert each the tubes a couple of times to make sure the pins and socket contacts haven't accumulated a bit of oxide cruft.

[Schuabber]

Thks mhuss.
I will do it some times and check. Unfortunately just on Thursday

[Schuabber]

Hi again,

I removed and reinserted the tubes, but today I turned it on and found the same unpleasant distorted sound.
I tried to play around with the knobs and it happened that some pots are cracking (oxidized maybe).
But after some time it stopped. I've turned the volume down and I played for 30 minutes without a problem.
Ok, I still need to use some DeoxIT D5 in the connections and pots (never done before), but it looks like that is something that apparently after more time playing (heating time) it stops by ti self. FYI, I usually power up in Stand By ON for 5', then more 5' with Stand By OFF with volume at 0 and after these 10' start playing usually at bedroom level. So, could it be that, besides the crackling pots, a or more tube(s) is(are) about to failure?

Thks again!

[OldSchoolDave]

Hi again,

I removed and reinserted the tubes, but today I turned it on and found the same unpleasant distorted sound.

So, could it be that, besides the crackling pots, a or more tube(s) is(are) about to failure?

It's common practice to have a known-good set of spare tubes on hand (if one is going to use vintage valve amps). These don't have to be anything fancy. Grab a set of new JJ's, for example. This allows for trouble shooting one tube at a time (never change more than one item per troubleshooting step!).

Otherwise, it's kinda like the old "change of underwear" joke.

Dave

[Schuabber]

Thks Dave,

I will clean up the old guy here. Change the "diapers" of this old guy, use some spray and maybe give a retube.
I bought it one year ago but I just play it on weekends at home, that's why I never took really care about a good maintenance, and now comes the issues.
It came with new tubes, I've changed the big caps, but I never cleaned it up with spray before. This is gonna be the next step here, a good DeoxIT spray.
I will keep in touch with the news and maybe the solution.

Cheers

[Schuabber]

Hi!
I found the problem!
I was playing today with my Les Paul and nothing wrong with the sound.
I suspected that maybe the Strat was the problem (I got it recently) and there it was.
The sound got sometimes as described before, dirty and distorted from time to time. So I kept playing and I discovered when the bad tone came that if i change the pickup selector the sound come back to normal and then I was playing normal and when I changed to the neck pickup it started the strange sound. I did this for 3-4 times and my 5-way blade is really with corrosion.
So in the end the Hiwatt with dirty pots did nothing bad to my sound! Thanks Dr. Reeves for this indestructible tank.
So I will clean my strat and hiwatt now

Thanks for helping with nice suggestions everyone!

[OldSchoolDave]

Hi!
I found the problem!
I was playing today with my Les Paul and nothing wrong with the sound.

Glad to hear you found the culprit.

Troubleshooting Rule #1: Assume nothing, suspect everything.
Troubleshooting Rule #2: Start with the simple things.
Troubleshooting Rule #3: Change only one thing at a time.

Dave

[mhuss]

Troubleshooting Rule #1: Assume nothing, suspect everything.
Troubleshooting Rule #2: Start with the simple things.
Troubleshooting Rule #3: Change only one thing at a time.

#1 is the hardest rule to follow.