On 21/03/2017 4:39 AM, wrote:
On Monday, March 20, 2017 at 1:18:00 PM UTC-4, Trevor Wilson wrote:
On 20/03/2017 11:58 AM, Phil Allison wrote:
wrote:



Not very surprisingly I cannot source a replacement
BF472, so I need to find a substitute.


I would try a MJE350(pnp/300V/500ma/20w/TO-126/hFE=30-240).
Anchor Electronics http://anchor-electronics.com/ wants US$0.95
each.


** I have already pointed out that Sydney's biggest spare parts
dealer( WES components) has the BF470 in stock for under $1.

Sylvia lives in Sydney.


**I am VERY wary about buying anything from WES now. From their
****ty electrolytic caps (Jamicon - horrible things, one batch of
100 I purchased had a 30% failure rate - I had to recall half a
dozen units I serviced as a precaution) to counterfeit
semiconductors, I've been caught several times. As have some of my
colleagues. I readily admit that small, cheap devices are likely to
be fine though. I purchased some large, Japanese flatpack (two
screw mounting types) from WES last year. Same type as the ones in
the amp. It failed during bench testing. Subsequent tests on
replacement devices revealed a breakdown Voltage (VCEO) of around
90 Volts. The original devices are specc'd at 230 Volts. I ended up
using single screw mounted devices (same ratings), obtained from an
accredited supplier. No problems. A mate did battle with a TV set
flyback MOSFET a few years back. After many hours chasing his tail,
I suggested he stop buying WES supplied parts and go to Element14
for the MOSFET (less than $5.00). Problem solved. WES were kind
enough to refund his money for the dodgy MOSFETs, but not the
considerable amount of wasted time.

Never again. All my electros are sourced from Element14 or RS
Components. Panasonic is my favourite brand. Phenomenally low
failure rate and well priced. That free delivery from RS is very
nice. My spend with WES has fallen dramatically.


-- Trevor Wilson www.rageaudio.com.au

I learned the hard way about counterfeit semis decades ago. Home
stereo amps that would blow up in a week after repair, horiz/HV
output transistors shorting on power up, hybrid smps ICs that just
didn't work or would cause severe oscillation, vertical output ICs
running hot and failing in days, PTV convergence hybrid modules that
defied alignment...

Here in the U.S., the only suppliers I trust are DigiKey, Mouser, and
B&D Enterprises. I'm sometimes forced to buy parts through
AliExpress. These are carefully tested. If one is bad, the batch
gets scrapped.


**Phil was the first person to alert me to counterfeit semis here in
Australia.



--
Trevor Wilson
www.rageaudio.com.au