Washrburn

[pbohrs]

Hello folks,

New member here looking for information on a Washburn VGA 15. I specifically need to know what the V+ is. A' schematic would be great but from all the searching I've done I don't hold a lot of hope. There is a Shinko sticker on the chassis and I tried emailing them in Korea (or Japan), but they don't reply.
I have seen an identical amp in a post from the UK that is badged "Drive VGA15".

So any help would be appreciated very much.

[dmeek]

The main filter capacitors are rated at 25V so V+ and V- will be a little less than that.
V+ and V- on pins 8 and 4 of the 4558 IC should be 15V
Here is the service manual:

https://music-electronics-forum.com/...1&d=1567958979

[Jazz P Bass]

Also, be aware that there where amps manufactured specifically for the Japanese market. (100 Volt AC line voltage)
The label should show if that is the case.

[J M Fahey]

So any help would be appreciated very much.

Help yourself and update what Country are you from in your Member info page, so it´s displayed togerher with your user name.
Answers depend STRONGLY on where you live.

EDIT: the 15W amps use a TDA2030 chipamp which runs on +/-14V rails, so you need a 10+10VAC transformer, rated 1 or 1.5 A or 25/30VA.

If no exact match found, you *might* use an 11+11 VAC one, but that´s pushing the limit; if erring it´s safer to err on the low side, so a 9+9VAC transformer will be fine, just slightly reduced output.

Don´t be tempted to use a much easier to find 12+12VAC transformer, you will probably nuke your chipamp; doubly so the current fakes or substandard ones coming through EBay.

[pbohrs]

Thanks to all, especially the actual manual. Also to Mr. Fahey for the warning on the transformer. (I ordered the 12v CT from Ebay). The one in the amp has an open sec. Any thoughts on where to get the transformers you mentioned? I did replace the amp chip already.
I also edited my profile for location.
Many thanks to all....

[dmeek]

According to the TDA2030A datasheet maximum power supply voltage is +/- 22V so the transformer is probably around 24VCT which would be +/- 18VDC
The zener diodes are 15V so the raw DC would be at least a couple of volts above that.

[J M Fahey]

The premium TDA2030A does, the plain vanilla TDA2030 does not.





In principle, unless specifically labelled TDA2030A and coming from a reputed supplier, I tend to consider all others,specially if an EBAY sale, the cheaper generic version ... if that much.

But hey, since you already odered it, use it.

In principle you should have around 16V rails, consiering diode drops.

IF so, use it.

IF you have trouble, search around or maybe add a couple diodes to "waste" a couple volts.

But for now, testing rules ... it may very well work, simply you are working closer to the limit.

Please keep us updated, specially actual rail voltage measured

Plan B: if you have a problem (a.k.a. the Kamikaze chipamp ) use an LM1875 which meets and widely exceeds all specs.
Bought from a recognized supplier of course.

[pbohrs]

OK, as recommended I found a Hammond 20v ct transformer. Installed, worked fine. At the electrolytics, +/- 15.7vdc. at the zeners. +/- 11.3vdc. Only problem was the 1/2amp fuse couldn't handle the inrush on the bigger txfmr, had to go to 1 amp. So far so good. This is a mighty fine little amp, wish it was mine.

[J M Fahey]

Glad you solved it