"N Cook" wrote in message
...
Arfa Daily wrote in message
...
"N Cook" wrote in message
...
Blown illumination lamp behind the retro analogue VU meter and no other
neon
or LED to show the amp is on. It is marked R51 on the overlay and the
schematic from Ashdown but no V or Watts. I will probably up the
dropper
and
put a blue LED in there. Anyone happen to know what sort of rating and
voltage it was ? Connected to full + to - 15 V dc , so 30V through a
1/3W,
220 ohm dropper to this 1/2 inch long, 1/8 inch diameter wire ended
bulb.
Ohm's law fashion presumably about 30mA, 28 Volt. No chance it was a
neon
or
phospher lamp ? as it is a frosted glass bulb, so cannot see the
inside.
While at it anyone know of a better way of mounting the VU meter so it
does
not push in if touched from the front.
--
Have not had to replace the lamp on one of these, so cannot offer any
more
than you have already worked out, except to say that they are a very
innefficient company to get parts out of, and that one of the music store
owners that I do work for, calls them " Trashdown " ...
I currently have two of theirs in, one which requires an output tranny,
and
the other, a mains tranny. They have both sat here for 6 months now,
waiting
...
Arfa
Seeing the price of one BUZ900 or 906 of 13 to 18 GBP reminded me to start
a
thread for any generic (cheap) power FETs
Back the Trashdown
http://www.diversed.fsnet.co.uk/mag200b.jpg
Because of the mm or so protrusion of the plastic bezel through the
aluminium even seriously side on view is quite nifty.
It looks good in the photo. As far as subbing power MOSFETs goes, I've never
been easy with doing that in the same way as it tends to be done with
bipolars. I've always found mossies to be tricky little buggers, and have
only ever replaced with genuine originals, no matter what the cost. There
are so many different varieties, often having very tiny and subtle, but
often very significant differences.
As an example, I was working on a hybrid band amp a few weeks ago. It was
actually a Traynor YCV40. It had two problems, one of which was that the HT
standby switch for the output valves (tubes) didn't work. Investigation
showed that this was not just a switch in the HT line. It was a double pole
job, one side of which was connected to a bi-colour LED for indication of HT
on / off, and the other side was connected to the gate circuit, via an opto,
of a power MOSFET type IRF830. The FET was short, and there was no signs of
any other problems, so I went ahead and replaced it with a similar one from
the IRF series. I went through three different ones in the end, and finished
up replacing the opto, and checking and rechecking every component in the
gate control circuit - and there's a few - to no avail. I might add that I
was doing this only because the owner needed it quickly for a gig. In all
cases, the FET would not switch. When the front panel switch was set to
'standby', the HT dropped only a few volts.
Eventually, the owner had to have it back with only the main fault fixed so
that he could at least use it that night, and I had him bring it back the
next week, by which time I'd ordered in an IRF830. As soon as this (correct)
device had been fitted, completely normal HT switching had been restored.
Arfa