2. amps-preamps
  3. 1080147154

Amp broken?

Yesterday I was preparing to sit down and have a listen on my tube pre/amp so I turned them all on and let them sit
for about an hour to warm up.

The source CDP was on but I hadn't hit play.
I dozed off for a bit and was awakened by the sound of one of my speaker woofers flapping uncontrollably!
Naturally I jumped up and turned everything off as quickly as possible!

It was similar to a sine wave or something like that being played.

I thought it was very odd because I hadn't changed my setup in a few months and things have been working perfectly for all that time.

I decided to unplug the preamp and cdp and swap the speaker terminals to see if I could narrow down the problem to something upstream or the amp or speakers themselves.

I also took off the shroud covering the amp to see if any of the tubes weren't working.

I started the amp up and after the 2 second warmup the other speaker started to flap (and I also noticed the tweeter was going also, the first time I missed it because I was in shock I think!) Also all the tubes looked like
they were lighting up.

Does my problem ring any bells as to what might be the culprit here?

Should I bother testing anything else? I had already unplugged the unit and let it sit for a considerable time before I did my second test!
geoffgarcia
alrau1's avatar
alrau1
56 posts
 
Geoff,

The woofers flapping is due to an infrasonic oscillation, possibly due to a small-signal tube. The first thing you need to do is power up only the power amp . If the woofers flap, try swapping the input/ driver tubes from one channel to the other (or use a new tube, if both channels use half of the tube). You should NOT have to wait an hour, either--wait a minute or two, and use a potholder to grab the hot little tube. Don't bother worrying about the output tubes--I've never seen them cause an infrasonic oscillation.
If they don't flap, turn off the power amp, wait about a minute, then turn on the preamp and, after it's warmed up for a few minutes, turn on the power amp. If the woofers now flap, swap the tubes in the preamp.
If they didn't flap at all, it's either your CDP, or the problem has disappeared (but it WILL be back sooner or later). BTW, I've been an electronic technician for 30+ years, and have manufactured a tube power amp.

Fatparrot,

DC belongs on every tube plate except a rectifier tube. If you don't know the answer, don't make one up.
geoffgarcia OP
92 posts
 
Thanks, I've already turned just the amp on and the problem is still there.
I tried swapping out 4 of my big tubes (KT88's) and the problem didn't change sides.
But I didn't try swapping sides on the 6 smaller tubes yet.

I'll try that when I get home.
lall
122 posts
 
Geoffgarcia
I had a similar problem as you and thought the problem was with my tube amps but it ended up being a CD player problem.
What is your CD player?
cheers
geoffgarcia OP
92 posts
 
Sorry for not posting this earlier!
It turned out to be the set of small tubes on my amp!
I'm not sure if they are input tubes? or what they are called...anyway, I took the amp to the dealer, they gave me a full diagnostic eval on the amp and preamp that I brought and told me that one of the tubes had simply gone bad!
They gave me a new tube for about 15$, gave me a tour of their factory!
Thanks very much to the staff at Rogue! Very helpful and SUPER friendly!
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