Trace Elliot Commando MK1

[jondoe]

Schematic ->Trace-Elliot Commando Bass Service Manual.pdf

Hi all, I have one of these brutes in bits at the moment, it had fried both the TIP35/36 output transistors, I've replaced them with good quality parts and it looked fine on a dummy load. When I placed the amp back into the chassis and wired up the existing speaker driver it was OK at low volumes but when I cranked it up it crackled and farted, I turned it off and one of the mosfets was pretty damn hot. The DC resistance on the original driver is a rather low 1 Ohm, although i can't find the original spec of it (no useful label) this is way too low, did the dying fet's fry the original driver?

I've rigged up an 8ohm junk driver and it runs it well, even at high volumes, the fets barely warm up, but it does seem to put out a reasonable amount of DC when powering up, the cone rises sharply before returning back to a resting position for about half a second, is that expected? I've read conflicting accounts of this being the norm on some older style amps, I was wondering what your collective thoughts are?

thanks

[J M Fahey]

S it had fried both the TIP35/36 output transistors, I've replaced them with good quality parts and it looked fine on a dummy load.

Cool, good sign.

When I placed the amp back into the chassis and wired up the existing speaker driver it was OK at low volumes but when I cranked it up it crackled and farted, I turned it off and one of the mosfets (power transistors, not Mosfets here but bipolars)was pretty damn hot. The DC resistance on the original driver is a rather low 1 Ohm, although i can't find the original spec of it (no useful label) this is way too low, did the dying fet's fry the original driver?

Most probably.

I've rigged up an 8ohm junk driver and it runs it well, even at high volumes, the fets barely warm up,

Good, then original driver is toast.
If possible, upload sideways and back pictures, to guess a replacement.

but it does seem to put out a reasonable amount of DC when powering up, the cone rises sharply before returning back to a resting position for about half a second, is that expected? I've read conflicting accounts of this being the norm on some older style amps,

No big deal, as long as it lasts 1 or 2 seconds tops.

Of course, if it goes forward or backwards and stays there, usually accompanied by a loud hum, turn it off NOW.

[jondoe]

Thanks J M Fahey

I can't take pictures of it at the moment, but the driver is a Jesen Special Design, blue/silver label, with "75-LSP-J12-COMM" on a small sticker on the magnet.

No loud hum or constant driver extension on power up so fingers crossed all it needs is a driver.

[J M Fahey]

Thanks J M Fahey

I can't take pictures of it at the moment, but the driver is a Jesen Special Design, blue/silver label, with "75-LSP-J12-COMM" on a small sticker on the magnet.

No loud hum or constant driver extension on power up so fingers crossed all it needs is a driver.

Is that the original TE speaker or the one you added for testing?

"Jensen Special Design with a blue/silver label" SCREAMS old Fender speaker.

It will definitely NOT stand T.E. Commando power output.

[jondoe]

The Jensen was the original speaker, it didn't look like it was fitted at a later date, but who knows. I had taken it out to get some info but have put it back in and put the cab somewhere out the way for now, damn thing takes up half my work space

I tested it with a Celestion Truvox 1525, ran it up and 3/4 volume for 10 minutes, no problems.

[J M Fahey]

The Jensen was the original speaker, it didn't look like it was fitted at a later date

It´s impossible that a modern British made amp carries a 60´s American vintage speaker fitted from Factory.

And that would explain its voice coil blown and shred to pieces, that speaker must stand some 20 W RMS.

[jondoe]

It´s impossible that a modern British made amp carries a 60´s American vintage speaker fitted from Factory.

And that would explain its voice coil blown and shred to pieces, that speaker must stand some 20 W RMS.

That does sound impossible . I've had a read of the Jensen history, in 1996 Sica started to reissue classic Jensen drivers, by 1999 they had a wider range of driver models under the Jensen name. This Trace Elliot was built from 1995, although I don't know the exact date. The schematic is dated 1997, the final page is dated 1999, so maybe they were in production in the late 90's, but I can't find anything concrete on that. With those dates in mind I would say it is possible it could have a new Jensen.

The original screws for the speaker grill and retaining screws were all unmolested and so tight I struggled to remove them and they certainly look molested now, which is what lead me to think they were all original, but I might be wrong!

The driver in the cab looks much like this one I saw on ebay, which I think is fairly modern.

[J M Fahey]

Have a closer look at yours, Jensen does not hide its origin and clearly states "Made in Italy".

In any case, why would it? ... Italians have the most advanced Speaker Industry in the World. (Just bthink RCF, B&C and a ton more ... including SICA)

I bet the SICA Engineers must grind their teeth when forced to make such crude 60´s technology speakers.

When I recover my ADSL (down for 7 days now) I´ll link to a SICA Factory video

[jondoe]

This is a crappy picture of the fitted driver, that label looks fairly modern, I bet the real details are under the top most sticker

[g1]

I'd guess it's OEM and the 'comm' on the label is for Commando.

[J M Fahey]

[ATTACH=CONFIG]55213[/ATTACH]

This is a crappy picture of the fitted driver, that label looks fairly modern, I bet the real details are under the top most sticker

When you said BLUE and SILVER I expected this:

[jondoe]

When you said BLUE and SILVER I expected this:

Top half's blue, bottom half's silver

[J M Fahey]

Oh, no big deal, just rotate it half turn and we´re even