Ashdown Five-Fifteen 100w combo keeps blowing fuses. Help me?

[Jazz P Bass]

Juan, can you 'zip' the file?
It's not loading.

[J M Fahey]

OK.
Itīs the so labelled Ashdown Backpack which matches the Mod instructions.
Also added the picture of a PCB , labelled "65" which seems to match that schematic and description.
As I said before, itīs common for manufacturers to mix and match a just couple "ingredients" and come out with lots of "different" products.
By the way what Leo Fender and Mc Donaldīs did, with HUGE success

The same Ashdown PCB seems to be used for different power amps, probably 15 and 30W ones with smaller ŋTO220? BDX transistors, 65W ones with larger TIP and *maybe* 80/100W ones with all 4 .
Which is a problem because the TO220 can not dissipate the same power as the larger TIP, yet all 4 have same drive and emitter resistors. What were they thinking?
Mismatching not by chance but by DESIGN

What d Saint Enzo ancient teachings say about not mixing even same brand different batch transistors?

[oc disorder]

Some pictures here so I thought may help to link this page as search doesn't seem to pick this up
"looking for an ashdown five fifteen schematic"

http://music-electronics-forum.com/t33661/

[diydidi]

Does this mod apply to the Perfect Ten 30W combo too??
It also has the Darlingtons in there.

[diydidi]

OK. Its official. Contacted Ashdown...
The mod does not apply to other Ashdown amps with similar circuitry/ boards, but only to the 5-15..

[J M Fahey]

'kay

In fact the Mod is not such a big deal, basically going from .22 to .33r emitter resistors.

What I remember seeing on the schematic (quoting from memory, too lazy/sleepy to open it now, it's 6 a.m. here)was thgat the Vbe multiplier transistor had in parallel with the BC and BE resistors another two, much higher value.

I've seen that on a few amps, they do it so as to save the adjustment trimmer $$$$, so they set the bias to a general purpose correct value, but the board tester (still at the factory) has the option, if he sees bias current way too high or too low beyond a certain range, to clip one of those resistors off.

(Slightly) better than nothing, but it's a one shot gun, if later you replace transistors or simply got it the wrong way, adjustment involves pulling the old resistor leads , fitting a new one (which might not be the required value anyway), etc.

Rising ballast resistor values does not correct this basic flaw but helps a little.

Of course the proper solution is to replace one of the biasing resistors with a trimmer and set the values properly.

[martin@djernaes.dk]

Any of you that can help me get to the "inside" of the amp ?

I've remove the 4 screws on the back (the bottom part becomes a bit loose when I do, but the top is not botching)
I've removed the speaker unit and behind is just an empty box - which the cable coming from the front.

My problem is that it has started to cut off and "scratch" and I'll like to see if this can be repaired, but I have more ideas how to open it!



Martin

[g1]

Are there no screws on the sides?
Sometimes the top will get stuck and just need a bit of prying.
Also, sometimes the handle screws need to be removed, but I don't think this chassis would be that deep.

[nosaj]

Try a paint scraper on the edges also.
nosaj

[martin@djernaes.dk]

Thank you - missed the ones in the side :-(