Hi!

One of my penta II:s just started to hum. Only when turned on and always at the same level. Raising volume doesn't affect the humming. When muted or turned off (stand by) it goes away

Any suggestions

regards

Make sure all connections are properly inserted. Unplug/plug.

I had a similar issue on one of my speakers - turned out to be a cabling issue.

Hi again!

I just noticed that the humming doesn´t start at once when the speaker are turned on but after 10-30 minutes. Is this a capacitor thing maybe?

Your problem sounds like the mains transformer laminations are vibrating at mains frequency, not uncommon.

If this is the issue, then it can be resolved quite quickly depending on transformer type (i.e. screwed or bonded)

Ok!

I have penta II. Are there different kinds of transformers in the pentas? Is this a doityourself job or something for my workshop

regards

Is the humming audible from the bottom of the tower or actually played through the drivers ?

Martin

Hi!

It's not from the drivers, sounds more like a resonance from the bottom. It's always at the same frequency but increases in soundlevel when the speaker have been turned on for a while.

Is the cooling fins getting hotter than the other Penta after being powered up for 5-10 minutes ?

Martin

Reason: Too high idle current.

Solution: Replace the idle current trimmer and readjust to factory specs. Worth doing the other tower while at it since it will just be a matter of time before it happens there too.

Martin

Ok!

I guess this is for my workshop. Are these idle current trimmers standard components or do I have to get them first? Also, do you have a capacitor kit ready for the pentas?

Hi again!

The cooling fins don´t seem to get any hotter on the humming one. In fact neither of them a

is particulary hot. The hum is still there and if I had a guitar tuner it probably would be possible to check the freqency on the hum because it´s always the same. Very annoying when playing at low volume.

A quite comprehensive (audiophile) kit is available but let's first see if it's needed. 

Have you tried switching the left/right channel cables to see if the problem follows the amplifier output or one particular speaker ?

Martin

EDIT: Sorry, I must be getting old. You told that the humming was audible from the speaker physically. Of course swapping cables will not help diagnosing then. The humming speaker will have to be checked out. Could be as simply as transformer hum, as Keith suggests, in which case it won't be causing other faults, just plain annoying.

Ok!

Thanks. Also both my displays have stopped working. They stopped gradually, at first they always worked when turned on but died after a while and now they are all black. Is this something for my workshop when he checks the hum. I tried to change display (with one I knew was working in another penta)but no response. Also tried swapping cables and outputs but...

regards

Yes, there's a capacitor or two in the displays too.

Definitely a job for your workshop. 

Martin