Mercury Magnetic PT heater wiring

[grtamp]

Afriend of mine give me some parts for build an D-clone Amp and a PT Mercury Magnetics (Toneclone FBFTP/MT).
Now I don't know if use the Orange wire center tap for heater or not!
I see in Dumble amp that center tap is made with two 120 Ohm resistor to ground.
What is best way?
Thanks

[David Root]

If that PT has a heater winding center tap, you can safely use it. Dumble only used balancing resistors because his PTs didn't have center taps on the heater winding.

[Structo]

Make dead certain you have the proper diagram for that transformer before cutting any wires.
Some companies use different color codes for the secondaries.

Especially the power tube plate wires because sometimes you have to swap those.
I am talking about the primary wires on the OT on this one.

[Bob-I]

The Mercury I used in my amp had an orange for the core ground. The heater was not center tapped.

Easy enough to figure out. Measure the resistance from heater to the orange. if it's open, it's not a CT.

[ChrisM]

Orange is usually transformer shield wire. But double check as Tom said, good advice.

[CHIP]

I have that transformer, FBFTP . The diagram I have shows the orange wire as the heater center tap 6.3V @7A .
300mA
red wires 335V
red/yel CT B+
blue bias

[grtamp]

I check the resistance from green wire - orange , it's a closed circuit.

On the Orange wire a target show : Safety warning! if this CT is not show on your amp's schematic DO NOT USE IT! instead, cut or tape-off and float it.
A short-corcuit may occur if it is connected to ground or a voltage bearing connection

Here the diagram:

[CHIP]

Mine is not the MT version, but Orange wire is still the heater CT.

[martin manning]

The warning assumes that if there was no CT on the original transformer's filament winding, then the circuit has a virtual CT (100 ohm resistor from each end to ground) somewhere, or possibly one side of the filament circuit is connected to ground or some other reference voltage. You have the option to go either way.

[grtamp]

I will use orange wire CT.
Thanks all for helps

[renshen1957]

Afriend of mine give me some parts for build an D-clone Amp and a PT Mercury Magnetics (Toneclone FBFTP/MT).
Now I don't know if use the Orange wire center tap for heater or not!
I see in Dumble amp that center tap is made with two 120 Ohm resistor to ground.
What is best way?
Thanks

Why not call Paul at Mercury Magnetics?

[grtamp]

I sent a mail to Paul , here the answer:


DO NOT ground one of the green wires AND the Orange wire! This will burn up the PT.

If NEITHER of the greens wires is seeing ground, then it is OK to ground that Orange wire.

If in doubt, just cap off and float the Orange wire.


If I understand right ,I can connect the orange to ground?
Thanks all.

[talbany]

I sent a mail to Paul , here the answer:


DO NOT ground one of the green wires AND the Orange wire! This will burn up the PT.

If NEITHER of the greens wires is seeing ground, then it is OK to ground that Orange wire.

If in doubt, just cap off and float the Orange wire.


If I understand right ,I can connect the orange to ground?
Thanks all.

One cool thing about the false CT/resistors is if you ever get a heater cathode short or for what ever reason the heaters begin to draw too much current the resistors will go before the winding acting as a sort of fuse..Keep in mind it's no guarantee just an added layer of protection. I always use the resistors if I can for just this purpose..Good Luck!!

Tony