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Newcomer, Melbourne, Australia

Started by nodz, March 22, 2013, 04:42:53 PM

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nodz

#60
Quote from: RolyA lot of builders make the mistake of miniaturising their board build, then putting it into a large case   - just making life difficult for themselves.

Since I am building modular and probably going to build into 19" racks for ease of use and storage around the home, size is not really an issue, except height that is.

The 2 x 100uF/400V caps that are in the HT supply line, were snap-ins.  I just straightened the pins slightly with a pair of needle nose pliers and soldered them to the board.  I'm a fan because of their half height, although they have a larger footprint.  For some reason this type of capacitor is cheaper new than many of the others.  I bought a packet of 6 for $9.  It means that they fit in a 1U rack easily.  If i need to buy, rather than scavenge, I buy at www.rockby.com.au and they quite often have specials like that.

Years ago when i was regularly building amateur radio projects and when Dick Smith's was not just a home entertainment store, i used to buy in bulk.  I have 200 x 1N4004 diodes, that I think were $5 for the bag, so as I said for the sake of a 2 cent diode to protect a $2 regulator, cheap insurance.

Over the next few days, will be sorting through the junk box to determine what is needed for the preamp.  I think that I have most of the components, just a few pots and resistors needed, I think.

Roly

I rat caps out of CRT TV's at the local dump and I've noticed that the low profile ones get used a fair bit even where they aren't needed, so it might be a bit of a positive feedback thing where high demand produces lower prices produces higher demand ...  Thanks for the tip about Rockby, Oatley are always worth a net browse too.

Quote from: nodzwhen Dick Smith's was not just a home entertainment store

They could be a barrel of laughs in the shop as well;   ::)

"Where do you keep your transformers?"
Blank look from young sales dweeb.
"We don't stock toys" he sneered.  (Thornbury TechStore, now closed)
(By the time I left they didn't stock electrical transformers any more either, armloads at a couple of dollars a pop.)


"I'd like to look at the oscilloscope in your flyer"
Leads way to a reflecting telescope.  When told I meant an oscilloscope, an electronics test instrument with a display screen, he literally threw a tantrum about how he sold a thousand bucks worth of stuff a day and "didn't have time to piss about with this *s!!t*" and stormed off - astonished, I'd been in the store roughly sixty seconds and it was a $100 item.  (Melb city basement store)


Bought a Set Top Box from DSE Northland.  Over the next few weeks it went into a kind of software meltdown the like of which I've never seen before, a kind of creeping cancer of dysfunction (mind you I was mightily unimpressed to discover that the sense of "up" and "down" inverted between different menus, so it wasn't entirely unexpected - "you never find just one roach in a kitchen").  Finally clagged out so took it back for an exchange, and ran into a reasonable and knowledgeable older guy.

"Forget it" he said, "we aren't stocking those any more" (huge wink), "Here, have one of these" and handed over one marked at twice the price.  It also has a bit of a mind of its own, but at least it didn't rapidly sink into premature senile dementia.


As one of the tech's who helped pay for Dick's first helicopter, these days the only time I will darken DSE's door is if, like Hardly Normal, they have a $2 loss leader on USB flash drives, otherwise, may they and their parent company {"Woolworths is selling electronics chain Dick Smith to private equity group Anchorage Capital Partners for a bargain price of $20 million" - SMH}  just die by fire.
If you say theory and practice don't agree you haven't applied enough theory.

nodz

Quote from: RolyI rat caps out of CRT TV's at the local dump...

I get them from CRT too.  Whenever a mate gets rid of one, I get them to drop it over to my place.  I then take various bits and pieces out of them and then dump the rest.

I will be doing that with the old computer PSUs now, so that I can gather together enough hi-voltage caps for voltage multipliers.

Quote from: Roly"Where do you keep your transformers?"
Blank look from young sales dweeb.
"We don't stock toys" he sneered.

Oh you had this problem too. :lmao:  Towards the end of the component stocking days, I'd walk in there and they wouldn't have a clue.  I wanted an electrolytic cap of a specific value, bloke looked on the computer and said they had stock and then tried to sell me a ceramic cap for $20.  What I wanted was a hi capacity one for use in a 13.8V, 10A PSU for amateur radio supply.

Hopefully, I won't need too many bits to get moving on the preamp.  I'll be reviewing over the next couple of days

nodz

#63
Just wondered now, that I have built the PSU by taking the AC output from a wall wart and then multiplied it back to 240V from a back-to-back transformer, whether I need some kind of over-current failsafe to prevent damage to the Wall wart, PSU and preamp.

phatt

I believe they use Fuses for that. 8|
Phil.

nodz

Hahaha yes Phil.  What I meant was, is all I need a fuse of a small value on the ht side of the transformer because I am using an a.c. wall wart multiplied up

Roly

AFAIK just about all low voltage transformers, and wall warts in particular, these days have internal thermal fuses.  I've actually gone for a dig and repaired a couple just out of curiosity.  If you look at the "Euro-glyphs" on the average wall wart (non-switch mode) one of the symbols means it has a thermal fuse, a sort of square-wave I think, like;
   __
_|   |_
If you say theory and practice don't agree you haven't applied enough theory.

nodz

That's good if they have their own fuses. Makes the wiring up much easier.  Just an on off switch and the standby switch to worry about.