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.
-- General electronic repairs, most things repaired, other than TVs and PCs
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 ...
This one was false protection cutting in, cured that. I don't know what the illuminated meter looked like as original but I reckon my re-jig would be better, looks quite nifty. Put a 2K , 3W dropper in and a bright blue LED wired-in and moved to vertically under the meter movement when mounted in chassis, so refraction , through the plastic, forms a blue ring around the ali cut out , especially now I've abraided the aluminium in that recess, plus a bright spot under the meter that shows in bright ambient light and it also throws a light on the scale. 2 LEDs would have been better as the static part of the movement shadows part. Fitted a nylon bolt through the pcb to tighten up against the meter when its aligned into the chassis.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I had to replace one of the long shaft pots with a normal one with bush nut against the front panel. Instead of using the same normal shaft ones as the filter ones where the large area of mounting paxolin doess't matter as any strain is taken by the nuts. The long shaft ones just pass through a plastic sleeve in the front panel and any abuse gets passed to the paxolin to break easily. I would have used the normal ones throughout with bush nuts and extended the terminals by 1/2 inch to the pcb, rather than inherently weak unfixed pots with long shafts.
My circular blue ring illuminator mod looked the bees' knees last night when I tried it in subdued light
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
I will bear that little 'mod' in mind in case I get one in the future. I see quite a lot of Trashdowns from this one particular shop, and know exactly the meter and lamp that you refer to, but as I say, I haven't come across an open one yet ...
2 LEDs either side of the static part of the movement would have been better, more even - next time. I suppose some would say it destroys the retro look.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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.
I've not had a play with white LEDs yet. Missed out on a few remnant stock of white LED christmas light strings after last christmas, someone got there before me in the shoddy goods store.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
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