Archeology ..... or, the Holy Grail - Pass style!

[mefinnis]

Somewhere on my website I state that this all started for me with a 20W ClassA amp my father and I built for a friend in the 1970's .......

Well, Nelson's not the only one who can find "interesting" old projects lying around

http://www.users.bigpond.net.au/mefi...ca20_front.jpg

http://www.users.bigpond.net.au/mefi.../ca20_back.jpg

Haven't had a chance to fire it up yet, but hell I smiled when I found it !!!!!!

cheers, mark

[ergo]

"Wear safety glasses...." as Nelson also points in his ZEN articles : )

This one looks like it has been gathering dust for some time and I wouldn't much trust the electrolytics. They might "let out some steam" or literally explode.

I once blew up a much smaller cap, but what a BOOM.

Ergo

[skaara]

Do you still have the schematic?

[Peter Daniel]

I blew a cap once too in 1980. I carry an artificial lens in my eye since then.

Whenever I run any project for a first time now I always wear glasses.

[Nelson Pass]

My experience with the big cans is that the vent plug
blows (watch out for that!) and an ultrasonic whistle
occurs which could deafen you, at least temporarily.

[skaara]

Once I used an old cap, it was dry but I didnt know it was, and i pug it in... BAM!! I was looking like a chicken with all that paper (or something similar..) from the cap on me and it was on the walls, now iam using all new caps, except for the ones I know how old are they...

[mefinnis]

Thanks for the general concern

I will not just "flick the switch" .... I've been around a little longer than that!

No, we will sneak-up slowly on the unsuspecting beast with a variac ..... plus safety goggles and ear plugs !!!!

Schematic ?

http://www.passdiy.com/pdf/classa_amp.pdf

Colleting dust ???

Nope ... rats pooh !!

But in the end ..... it's all good fun.

Regards, Mark

[mrfeedback]

Mark, there was discussion here recently about running up old gear on a variac in short stages over a few days to allow electros to reform safely, elsewise you are risking high leakage currents causing internal heating and gas pressure and explosion.
http://www.vmars.org.uk/capacitor_reforming.htm might help.
Modern electros have a y shaped weakness on the top of the can and this allows these caps to expire gracefully.
Electros with smooth tops can be dangerous, as Peter can testify.
Over the years I have installed caps in reverse and caused cap explosions.
The can really does come off at bullet speed and if it hits a hard surface will mushroom or flatten - I nowadays habitually stand back with my head turned away at switch on - so far I have not been hit but I have had some really close shaves in the past.
Sorry to hear about you learning the hard way Peter, and your advice of safety glasses is good advice.

Eric.

[jh6you]

Boom!!!

I finished wiring. Turned on. Wow…what a nice sound!
Heck…? whenever I stepped up and down the attenuator
for the volume control, I heard the sound, “click!…click!…”
It was funny and strange. It was a new thing.
To fix the trouble, I looked over into the launched Zen V2,
for a close inspection of details of wiring arrangement,
without wearing the safety goggles.
Then, suddenly all happened!

A poor man was lazy in checking the correct polarities
of + and – of the output coupling capacitor.

I however comfort myself.
Even Mr Nelson P…hahaha. Even the artificial-lens-eye Pet…D…hahaha.

JH

[mrfeedback]

Nelson, I can't hear those ultrasonic whistles anymore.

Eric.