Ticking in one channel [resolved]

[Chris H]

I have recently noticed a light ticking sound in one channel of my SEX amp.
I'm not sure if it is new as I only noticed when listening on headphones.
It is not noticable while music is playing and I have since confirmed that it does come through speakers but is barely audible.

I assumed that it was some interference from electrical device but noticed that SEX is totally silent when first switched on.
Within a minute or so, the ticking starts off very slow but then gets faster until it is a steady 3hz.
It seemed to be as the tubes heat up so I switched the 2 tubes and the ticking switched to the other channel.
But my understanding is that both channels use both tubes so what would cause this?

Some careful listening with headphones reveals that the ticking is still there if music is very low volume (just as music becomes audible) but as volume increases the ticking does seem to stop and not because it is drowned out by the music.

Any suggestions or help appreciated

Chris

[Chris H]

I meant to ask whether my understanding is wrong and that each channel is in fact using 2 halves of a single tube.
If so this would mean it is one of the tubes?

[Chris H]

OK, think I answered my own question.  2 halves of same tube.
Really didn't think it through before asking.

Will assume it is one of the tubes unless told otherwise.


(I really did just have a conversation with myself in public didn't I? - I need to get out more!!!)

[Paul Birkeland]

If it follows a tube, then that helps narrow things down.  What you describe does sound like external interference, so there may be something about that tube in particular that's susceptible to some external source of noise.  It may also help to give the tube some run time if it hasn't been used much.

[Chris H]

Thanks Paul, I hadn't considered one tube being more susceptible to interference than the other though I do have odd tubes (1 x GE and 1 x Syvania)
Intereference was my first thought and is a distinct possibility with wifi receiver near by and various other electronics.
I started to think otherwise due to it starting off slow and speeding up as the tubes warned up.  Also, is unaffected by volume change - same with volume all the way up as all the way down.

Whatever the cause, those tubes don't seem easy to find.

Amp has had plenty of hours put on it since completion earlier this year.
 

[Paul Birkeland]

Often we will pair tubes so they are construction matched, regardless of what the print says. 

You might try the amp in a different room to see if the noise persists. 

[Chris H]

No complaints about the matching of tubes/channels, just noting the different brands if one is indeed more susceptible to interference.

It is barely audible through speakers and I only noiced it on HD800s.
But once heard, I can't unhear it now (between tracks).

Will try it somewhere else though and continue to investigate.

Thanks as always for the pointers.

[Chris H]

A quick update and can put this as resolved.
Repositioning didn't help.

In the end I sourced a couple of NOS GE tubes.
May be easy to source in the US but I could not find any in UK.  Finally found some from a French company.
Ordered 2 so have a spare in case of any future issues (given difficulty in finding them).

Popped in one of the replacements and amp is now dead silent, even with volume all the way up through HD800s.

Have warned the family that I will need to play music louder than normal for at least 100 hours.  You know, just to make sure.