ecc88 arcing at shutdown problem...
 

Hello Everybody,

I changed a normal concertina input stage to the attached schema.
Problem is, now it's arcing on shutdown of the amp for a few seconds.
It doesnt do it every time, but much to often.:(

I suspect its the voltage in the capacitors, in combination with the constant current source, who tries to keep the set current going, and raises the voltage on the plate.

It also happened on switch on, but I fixed that already by increasing the power-on delay from 15 to 30 seconds.

Anyone a solution?

A second question:
Does a CCS need some break-in time before it sounds best?
Because at first it sounded like :gnasher: , and now, after about 3 days it sounds already better than without CCS.

greetings and thanks already,
Paul

No. Your ears have got used to it.

I was thinking about that too, but... Focus and soundfield/depth was about completely gone.
Maybe it were the old ecc88's. They weren't used for about 15 years... could it be that they need a re-break-in?

it may be the caps weren't fully polarized

if so hope it has not burn any holes in the cap foils

just a may be..........it could be that the caps were just low magnetized

Sorry - asking the wrong guy. Break-in occurs in items that undergo significant physical change in the first period of life - car engines, speakers, girlfriends, that sort of thing.

Electronic components (including cables) don't "break in". Some may undergo some rapid changes in the first few (milli)seconds of operation (caps and the like...) but other than that the only thing breaking in is your hearing. This process takes as long as it takes to talk your brain into liking the new sounds it thinks it is hearing.

Others will disagree.

I'm really sorry, I dont have a clue to wat you're saying.:confused:

The amplifier without the ccs is in use for about a month or two without problems. So I dont think there's aything wrong with the caps.
The arcing is in the tube...if it happens I can see light coming out of the internal structure, and hear a crackling noise out of the speaker.

Pauldune, my guess is...
at turn off the first tube stops conducting...
the constant current source continues to pull current from the charged power supply capacitors...
it *forces* current into the grid of the second tube...
the curent flows in the second tube from the grid to the cathode to ground...
not good!

I have seen a forward biased diode placed from grid to cathode of the second tube to stop this problem. When the amp is operating normally the diode is reverse biased and not conducting.

Ooops, a tad fast off the mark there Mr. aardvarkash10. Although I do not have references to hand, I understand that metal film resistors, electrolytic capacitors and vacuum tube cathodes all undergo small physical changes during the initial period of use. In other words, they do undergo some form of limited but real 'break in'.

We must differentiate this from the 'hype and bull' marketing used by the namby-pamby audiophile companies who use 'extended break in' to cover up simple psychoacoustic aclimatisation. Indeed their lies are shameful.

Example of protection diode: More cathode follower stuff

Credit: J Broskie / TubeCad

The same can be used in your amp.

True on all counts gordy, but the most important words being "small" and "limited" ie not enough to cause any discernable change. Apart from the 'lytics which have well documented learning curves.