OT - Firefly squeels when volume 100%

[sir Franc of SOSCASTOA]

I know reading about this somewhere on this forum but can;t find it.
When I set the volume to 100% it starts to squeel.
Anybody knows what causes this and can it be cured?
It's not a bog problem because the amp is way to loud at this volume anyway but I wanna be sure it is nothing seriuos.

Franc.

[Peter Snowberg]

Take it out of the case, turn it up so that it sits on the edge of squeeling, and move the wires around using a chopstick or a piece of totally dry wood (no pencils allowed). As you move the wires you will hear the squeel get affected at some point. Adjust the wiring for the lowest parasitic input at full volume. You might need to shorten wires that are too long or sperate wires that run a log way in parallel. Out of phase wires should cross at right angles if you can make them.

Best of luck,
-Peter

[sir Franc of SOSCASTOA]

Thanks Peter! Wow, I never realized the position of the wires mattered that much!  I moved the kathodewire so it was at at a right angle with plate and grid wires and the squeeling stopped instantly! (would that make sense?)
I am only just beginning to understand about which signal is out of phase with which, but this 'troubleshooting' with a chopstick is fun and great for my understanding

Next thing is to do the same thing with the extra gain stage on, I noticed a squeel at high volume too, but the thing is so darn loud then

[puretube]

yes, makes sense: if wires must cross, best is right angle;
if wires have to go the same direction in parallel: as far apart as possible;

this goals for grid & anode wires, and cathode & anode wires;

grid & cathode wires can be close together;

keep the filament wires away from all, route them as close as possible to the metal chassis, and if you heat with AC, twist them tight together.

[sir Franc of SOSCASTOA]

Thanks for the tips.
I did twist the filament wires and put them close to the chassis as far away from everything as possible (you can see it on the pics on my website).

[Paul Marossy]

When I built mine, I tried to keep all wires as far away from eachother as possible, and where I could, I made them cross at right angles. I also intuitively kept all of the heater wires as far away from everything else as possible and close to the chassis. I had no problems w/ oscillation at all on start-up. I have seen the inside of enough tube amp chassis' to see how they are wired, so that helped when I built mine.

It is very interesting how a couple of wires that are too close to eachother can cause problems like that, isn't it? Some people have experienced this with high gain guitar FX, too. I have never had a problem with this, even though I kind of stuffed a lot of these circuits in a box with wires that are really too long, etc. It's gotta happen to me sometime...  :wink: