ShortScale.org

On Sunday I was jamming with my bandmate and my 1972 Twin Reverb began to whistle or whine. It wasn't too loud, but it was certainly there.
I was using the Vibrato channel, and when the vibrato was on, the whistle would thrum along with it. The whistle persisted when I unplugged the instrument cable from the amp, so testing if it would be there on the Normal channel is kinda moot (it's there whether an instrument is plugged in or not).
I didn't do any testing for microphonic tubes, as we were jamming. I just ended up turning it off and using my bass amp for the rest of the time. The amp is still in our jam space so I haven't gotten to it yet

We were working on new material, so I was recording a bit, and it can be heard on the recording. I recorded on my iPhone, just sitting in the room. It comes though as the very high pitch sound over the track; it's subtle enough that you might think it was just recording room noise, but it's the amp. I edited out most of the track and just have a sample of the intro with constant whine, and the outtro, with pulsing tremolo whine.

http://soundcloud.com/ankhanu/twin-whistle

Any thoughts?

Sounds like the vibrato oscillator tube is microphonic.

I don't know if it's the same as the preamp or reverb tubes, but whichever one is the same see if you can swap it over and leave the place you borrowed it from empty and see if it still whistles.

It's definitely a bad 12ax/at/au/ay7 type tube. Turn the amp on and tap/wiggle them all.
When you get to the one with which the noise interacts in any way (this includes stopping completely) you've found the boo-boo.

That's what I was thinking, thanks for the input. I'll start testing next time we get together to jam. I never use the Clean channel, so I can use the tube from that for the replacement.

Yeah that or you could go to the swap meet, buy $10's worth of old radios and get a fistful of awesome vintage tubes...

Of course, half of them won't work but hey, how much does a single shitty EH 12AX7 run you these days?

Yup.

laterallateral wrote:Yeah that or you could go to the swap meet, buy $10's worth of old radios and get a fistful of awesome vintage tubes...

Of course, half of them won't work but hey, how much does a single shitty EH 12AX7 run you these days?

Yup.

$18.99 when I checked the L&M site earlier

Unfortunately, I've never seen anything remotely interesting/useful at the local flea markets and the like. Sydney is a shit hole for many reasons, and a lack of interesting electronics is one of them ;P

That's a sweet idea. I'll be looking out for some at the next car boot sale - although I highly doubt there'd be many old radios knocking about in the UK that aren't in London vintage shops for £300 not working.