110v to 240v PT conversion

[craigslee]

Hi,

I have a question regarding the pending 110v to a Mercury Magnetics 240v PT conversion of my Lonestar Special. (actually two, but I'll get to the second one in a minute).

I have successfully completed this procedure on two previous amps with no problems. I just want to check this one first.

I have all the cables accounted for with my Mercury Magnetics replacement except the 110V primary cluster has a white cable with a black stripe as well? Is that necessary? I have the primary black (MM 240v PT black?) and a white (MM 240v Violet?) covered I think, as they seem to trace to the switch & supply input etc... so I'm guessing they are ok?

I have attached a 4 page pdf ( hi res images) URL if anyone can assist.

http://users.tpg.com.au/9876/Lonestar_110v-to-240v.pdf

OK, second question...

I also want to use high quality spade connectors (or similar) and heatshrink them instead of soldering directly to the board. That way I leave the original board connections untouched and then the original 110v PT can be replaced quite easily if required. Is that a wise move?

Looking forward to some helpful comments!!

John.

[craigslee]

OK, all good.

+ White with black stripe is redundant.

+ Black is active (Violet on replacement MM PT)

+ White is Neutral (Black on replacement MM PT)


Correct me if you believe I am wrong.

Over and out

[Phil_S]

I think the white/black is another tap on the primary that wasn't used. Since someone connected it to the 220 pad on the board, it seems to be for a lower voltage mains. By attaching it to the board, you avoid having a flying lead and this is probably safer.

As for the spade lugs, it's done all the time in new production amps. Just make sure you use pairs that mate properly. I'd suggest you get the kind that have molded insulators/covers. I think you probably intended to do that anyway.

[craigslee]

Thanks Phil,

Good to see I'm on the same page.

Excellent advice and much appreciated that you took the time to reply.

[craigslee]

Part 2:

OK, so I get the PT installed, (nice job if I do say so myself).

Unfortunately there is still a trap for the novice!!

I kept blowing fuses one after the other. No Power at all! I thought I had a ground issue or a bad tube at first. Then, I figured I'd better start doing some homework. .. as it turns out there's no actual schematic available for the LSS however the Lonestar Classic has a schematic floating around on the web. Circuit wise its basically the same deal.



Turns out the Metal Oxide Varistor (MOV) at the primary supply input on my US model is rated at 130V, the export needs a 275V MOV.

I dont actually need it to get the amp running, but with the original one still in place it shut off the 240V supply and blew the fuse.

Fundamentally the MOV is installed to protect the amp circuit from excessive input current. I've now decided to install one in every amp I have now as it costs a pittance for the component and its easy to do. Sort of like cheap but comprehensive amp insurance.

Learn something new every day I do.....