Rockerverb 50 White center tap- problem

[Tyguitar]

Hi, i just replaced the Orange Rockerverb 50 ( 2007 ) model Power Transformer to Mercury Magnetics. The Demeter had burning smell and blow fuse ( at IEC plug )! Removed all secondary connections of PT and it stll blow fuse- confirming PT is dead! Can anyone help? The pins 2-7 had continuity beep on 6v6 tibe base. But soon as I connect the filment centre tap ( white wire ) 2-7-1-8 pins exhibited continuity beep! Seems like a circuit shorted! But remove Centre Tap and its all fine, no more beep 2-7 to 1-8 pins! Can anyone assist? Can i not use the Centre Tap??

[Tyguitar]

I am refering to the two yellow filament wires which comes with a White centre tap wire!

[Jondog]

If you dis-connect all the wires amd check for continuity between the center tap and a filament wire you should get a beep because they are connected internally inside the winding. Pin 1&8 are connected to ground, the center tap is connected to ground. The filament wires are connected to pins 2&7 which because are also connected to the center tap, connects pins 1&8. In other words, normal.

[Tyguitar]

Thanks for reply. Yes, i understand. So are you saying it is normal that once all the wires are connected, pins 1-8 has contuinity beeps with pin 2-7 ( filaments pin)...would that be cause of shorting the PT? I checked my other amp, Fender Deluxe....pin 2-7 has contuinity and pin 1-8 has contuinity, but it has no continuity across all the 4 pins! And a pair of 100 ohms resistors connected at the pilot light as center tap! But this Rockerverb 50, only when i do not connect the center tap, the pins 2-7 and pins 1-8 pair have no contuinity across each pair...like the Fender. Would it be better to float the filament white center tap and use resistors pair at pilot light to ground, then?

[Jondog]

Those 100 ohm resistors on the filaments in your deluxe form an artificial center tap. Theres no continuity because of the resistors. You don’t need those resistors in the Rockerverb because you have a center tap. Just hook the center tap up the way it was designed. It goes to a voltage ground connection on the board.
Beyond that, if you don’t know the reason already, you should find out why the original power transformer shorted. Is the output transformer or tubes OK? Any other damaged components on tve board? It sucks to plug in and blow up a $250 transformer. I know from experience!

[Tyguitar]

Thanks. I hve opened up the Demeter and it smell burnt on Primary wire ( Blue) i can only guess the windings shorted. I hve tested the 4 pieces of EH6v6 tubes for shorts it, it was goo! Only two preamp tubes ( 12ax7 ) which had no contuinity within pins 4-5 but 4-9 and 5-9 has continuity! I can say these two preamp tubes are shorted...but unable to link it caused the dead Demeter PT! Not likely. I am worried not to short out the MM replacement PT, thats why I have doubts upon checking! With pins 1-8-2-7 all exhibiting continuity with each other- is that a short? Remove center tap ( white ) and only pins 1-8 beep and not across to pins 2-7- which i thought should be the case.

[Tyguitar]

I hve also changed new 1N4508 on the preamp board and 1N4007 on the power amp board. The originals exhibited faulty diodes. The B+ section of 1N4508 was tested good. Now puzzled by the yellow filment pair with white center tap meant for the power tubes. Ok, will try as you recommended, or maybe power up wuth center tap disconnected and then with center tap connected...see what happens. But if the resistors pair to pilot light is safer, i rather go that route. Yr views appreciated. The white wire on MM PT also has a red Warning Sticker, Do Not Use It and refer to amp schematic before using, a short circuit may occur! All that worrys me!

[Jondog]

[Tyguitar]

Tks for the schematic- yes it shows White centre tap to OV. Because of the burnt transformer...i felt compelled to ask, could it hve shorted out my PT? I hve replaced all the necessary parts to the power board and preamp board- electrolytic caps and diodes. Everything now measured in order! My main worry is, still pertaining to the power tubes pin shorting each other. The 10nf blue caps to reduce diode switching noises i hve also changed out! Some even recommend to remove it, as cause of Orange amp shorting! I will use a Variac and try with and without white wire center tap- see what gives! Pins 1-8 continuity to pins 2-7 dont sound normal to me!

[Tyguitar]

Sir, if you hve same Orange Rockerverb 50 amp, can you continuity test if yours 1-2-7-8 all beep into each other? Thanks in advance!

[Jondog]

Without the center tap you may very well get hum. I have a Rocker 30 which uses the same transformer. I know pins 1&8 have continuity with pins 2&7. You can put the resistors in for an artificial tap and leave the center tap dis-connected, but it’s not necessary. Pins 1&8, the cathode connection, and 2&7 the filaments with center tap all have a direct pathway to ground.

[Tyguitar]

Sir, greatly appreciated your input! I can feel safe to power up and proceed further, now that i know heater pins and cathode follower pin 8 has contuinity beep into each other, with this Orange amp! It first time I come across such circuitry! I hve repaired Vox, Fender and Marshall amps, but those, clearly pin 8 has no continuity with heater pins 2-7! Thanks for the confidence to me. Sadly, i will not exactly know why my Demeter 2007 PT burned! Likely the internal windings enamel layers of wires are faulty and shorted. I did of course found two bad preamp tubes, but cannot be cause of PT blown! Power tubes flyback voltage likely, but those tubes all seem in working order. The internal fuse 500mA at B+ one blew and the IEC plug 2A fuse blew. Thats the only indicator....the two purple HT wires each had a separate fuse, across it was a blue 10nf cap. Suspect that was faulty? Changed the cap to 10nf 3kv instead of the original 1.5kv! The two violet wires have no continuity with each other, now, even with grey centered tap referenced to ground. That blue cap with fused blown had contuinity, until i changed new cap! I read in Forum even Orange recommended to remove that cap completely! There are 3 such caps at all the diodes sections! What is your expert opinion? Thanks