Blown fuse in Majove Plexi 45

[tucky]

Hi All

I imported a second hand Mojave Plexi 45 from a guy here in the emporium from the US to Australia. It was well packed and seemed to arrive OK. The tubes were wrapped up well and taken out of the sockets.

When I put everything in and turned on the mains, the amp gave an audible hum, which I thought was unusual for this quality amp, and then about two seconds later the pilot light went out and the amp was silent....and dead.

Its blown the 2A fuse in the power socket plug. Mojave has a neat arrangement where you can access it easily. I am going to replace the fuse and try again. If it blows it again I had read that you can take all the tubes out and put them back one-by-one to see if it is one of the tubes. I might try this before I take it to a qualified amp tech.

It has 3 x 12AX7's, 2 x KT66 and 1 x GZ34. Which order should I put them back in? When looking into the amp from the back going left to right you have the 12AX7's, the two KT66's in the middle, and the GZ34 over on the right.

If you guys think I should not risk it and just take it straight to a repairer then tell me. I am a noob in this area.

Andrew

[Blue Strat]

Hum followed by blown fuse sounds like a shorted power tube. Try the amp with all tubes except the power tubes and see if the fuse holds. If it does, then try one power tube...then the other. When/if the fuse blows again, you've found the bad power tube.

Lot's of things can cause hum (other tubes, internal items) and others can take out your fuse (rectifier tube, internal items) but for both hum and blown fuse, power tubes first.

Good luck. Let us know how it works out.

[samtheman]

Usa: 120vac
OZ : 240vac

???

I think you just blew your PT?

Or can you change VAC in your amp?

[Blue Strat]

Originally Posted by samtheman

Usa: 120vac
OZ : 240vac

???

I think you just blew your PT?

Or can you change VAC in your amp?

I was hoping he had that covered. Maybe not?

[tucky]

Originally Posted by samtheman

Usa: 120vac
OZ : 240vac

???

I think you just blew your PT?

Or can you change VAC in your amp?

Yes AUS is 240 v AC. Mojave states on their website that ALL there amps are set up to run any voltage from 100 - 240 V AC. There is no switch evident or visible either inside or outside the amp to change the voltage. Hopefully that is covered, unless there is something that I missed about having to change it manually somehow inside the transformer. I hope not!

[samtheman]

Originally Posted by tucky

Yes AUS is 240 v AC. Mojave states on their website that ALL there amps are set up to run any voltage from 100 - 240 V AC. There is no switch evident or visible either inside or outside the amp to change the voltage. Hopefully that is covered, unless there is something that I missed about having to change it manually somehow inside the transformer. I hope not!

Pls contact Victor (Mojave) before you do anything...

victor@mojaveampworks.com

cheers

/sam

[tucky]

Hi All

I am happy to report that the photos I took were while my Dad (who built kit tube amplifiers when he was a teenager) was taking a look at it for me. He realised that the windings from the primary transformer were in parallel and therefore set up to take 110/120V. So I had made the assumption after reading that the amps could run anywhere between 100-240V AC that you didn't have to do anything to them.

Unfortunately I was wrong. The transformers can do that range of voltages, but because Victor Mason who runs Mojave doesn't like switches, it means the transformer in my 2006 model are wired up for the correct voltage for a specific country. Mine was wired for 120V.

After a couple of emails to Victor who was VERY quick to reply, he confirmed what my Dad said, and suggested how we could fix it. Wire them up in series, and you'll get it producing 240V AC. Did that. Put in new fuse.

SWEET!!!

A testament to the quality and build of Victor's amps! It is singing sweetly now with no apparent ill effects.

And what a sound!!

Thank you Victor Mason.

And thanks to Sam and Blue Strat for your input.

Blue Strat - I'll keep an eye out for some GEC Gold Lion re-issue KT66's from your store.

[Blue Strat]

Whew! That was a close one. I can't believe nothing blew up!

[tucky]

Originally Posted by Blue Strat

Whew! That was a close one. I can't believe nothing blew up!

I know! As I said hats off to Victor. His amps are awesome!

[Blix]

Originally Posted by tucky

Mojave states on their website that ALL there amps are set up to run any voltage from 100 - 240 V AC.

The moment I read this I though this couldn't possibly end well, I don't think there is any tube guitar amps with auto sensing voltage transformers.


But seems your fuse did what it's supposed to and Mojave builds sturdy amp...


Glad it ended well.

[Roe]

haha, the lcr caps handles 900v!