EZ81 rectifier noise

[Stixx]

I tried to search, but over 200 results came up, many of them being large threads, so please forgive me for not reading thru all of them...

I am about to finish my second amp (Morgan-Jones headphone amplifier with 3x 6922) after successfully building and de-humming my first one (c3g-headphone amp, see thread somewhere here).
I changed the psu slightly by adding a hybrid tube rectifier with two UF4006 to form the centertap (trans hasn't got one...) and a EZ81.
Now the amp is up and running for testing, voltages are in the ballpark, but upon warming up there is a strange noise coming from the rectifier....hard to describe...it's a tiny somehow mechanical noise but clearly audible (with no headphones over my ears!).
Also I' ve got some 120 Hz hum with headphones on...

Any suggestions?

Thanks in advance,
Oliver

[Sheldon]

Have another rectifier tube to try? Try also switching around the 6922's, just to rule that out.

Picture of the grounding arrangement?

Sheldon

[dsavitsk]

I have experienced this too while the tubes warm up -- if it is the same thing, it sounds like current and or heat rushing trough the tube causing banging and clanging and a sort of rushing noise. It has happened to me with 2 different EZ81's, but it goes away after things are warm. I just ignore it and it eventually (~30 seconds) goes away.

[ivegotmono]

I have an Eico HF81 with two EZ 81. One or both did this during warm up after I replaced the first two electrolytics in the PS ( I went from 30uf to 40 uf) They only did it during warm up and after about three days they no longer did it at all.
Steve

[kevinkr]

Hi Stixx,
I assume you are in Germany so that would be 100Hz buzz.

Also PLEASE cover the terminals on your power transformer. I used similar ones whilst living in Belgium (teenage years long ago) and zapped myself more than once. (And they were usually covered - don't use electrical tape for this except as a temporary thing.) Accidents happen easily!

Clanking and banging of the envelope is not unusual with the EZ81, as doug indicates it should go away once the tube has warmed up.

Safety OT story:
Doing a repair on a Studer Revox G36 as a kid (17 or so) in the 1970's I somehow got a couple of fingers across the power switch. 220V will definitely cause a strong involuntary contraction if the connection is good enough. (It was) I watched my right arm fly into my face with fascinated horror as the muscles contracted. At the same exact moment the sound effects from "the six million dollar man" (tv show) filled my head as my arm moved in what seemed like slow motion... It was all over in less than a second, amazing how long that second was - and it really, really hurt. Left a bruise on my forehead, and burn marks on a couple of my fingers. I was very lucky. My younger brother who witnessed the whole thing thought it was hysterically funny, particularly after I mentioned the accompanying sound effects..

Edit: additional thoughts

[sorenj07]

My 6P14P amp makes a sound like ice cracking for a few seconds as the tubes warm up, and for a few seconds after turning it off. Everything works fine though so I don't mind too much.

[kevinkr]

Hey Sorenj07,
I didn't realize you were in the Boston area. PM me sometime through the board.

[Sheldon]

Originally posted by kevinkr
My younger brother who witnessed the whole thing thought it was hysterically funny

As it turned out well, he was right. Thin line between tragedy and comedy.

Sheldon

[valveitude]

As it turned out well, he was right.

Or "The essence of comedy is other peoples misfortune"

-Casey

[aletheian]

I have a few circuits with 6CA4/EZ81 and they all do that... both old manufacture and new JJ's.