Funny noise. [resolved]

[wetpet]

getting a funny noise. seems like it is from the main transformer. kind of a crackly noise. or a rattling/ vibration. happens on power up. goes away when i remove the tubes. also goes away if I cant the baseplate 45 degrees or more. I found this out when i tipped it up to look under. anyplace I should start?

[Paul Birkeland]

Measure the voltages first and let us know if there are any that don't match what the manual calls for.

[wetpet]

will do. also poked around a little with a plastic pen to see if anything was obviously loose and no love.

[wetpet]

Just to be clear, you don't mean a resistance check with the ac off, but a voltage check with ac? Sorry, been over a decade since I built this. a little rusty.

[Paul Birkeland]

Yes, voltage check with the tubes in an AC on.  Since it's an older SEX amp, it is helpful to post something like:

Terminal 2 should be 100V but is 5V

rather than

Terminal 2 is 5V

I'd also post a photo or two of the amp, just so we can look at the correct manual.

-PB

[wetpet]

ok will do. was a little apprehensive to leave it on with the noise. still can't find my manual so that is slowing me down. Is there an online list of voltages and pin locations? thanks, ed

[Deke609]

Not sure if this is the cause of the problem, but one of the four retaining bolts of the power transformer is unsecured and touching the chassis - it needs a shoulder washer and a locknut.


cheers, Derek

[Paul Birkeland]

That could indeed cause some rattling.

[wetpet]

yes, i noticed that. in fact the bolt and nut are plain missing. there is a nylon washer between the transformer and chassis though. but still may be making contact.

[wetpet]

here are my readings, of course, with the chassis upside down. flipping it back over could cause contact in that corner? above the line are the terminal markings on the transformer, below are my readings from pin to chassis

[wetpet]

After all of the futzing around, the sound went away and the amp is working. just need to play with the headphone jack as I am only getting one channel. oh, and get a new transformer bolt. does bottlehead have them or just use similar?

[Paul Birkeland]

You have the bolt.  You need a #8-32 nut and a #8 shoulder washer.

[wetpet]

found the missing bolt right on my desk. must have fallen out when i inverted the chassis.

[wetpet]

Thanks paul! Now on to my foreplay and paramounts.