Wiring a gz34 rectifier tube with 5v center tapped transformer..

[toobzilla]

Hi all!
I'm trying to finish up a 5f6a clone & am learning that all center tapped windings are not our friend, lol.. wired conventionally, w c.t. to ground, blows fuse after gz34 starts to work. unhooking the ct from ground keeps the fuse from blowing but its got a buzz that it doesnt have when hooked up. My question is what do i do with the center tap? .. is there a different way to wire it?.. any help would be appreciated, particularly in layman's terms as i'm a rookie at this... thanks in advance!
                                                                                                             -Jon

[sluckey]

DON'T CONNECT THE 5V CENTER TAP TO GROUND! Just tape the end of the wire and tuck it out of the way.

[toobzilla]

Ive done that but it seems to introduce hum audible thru speaker even in standby.. that didnt exist in the 10 seconds or so before getting angry, lol.

[HotBluePlates]

... what do i do with the center tap? ...

I will guess you have wired the rectifier socket like the original layout, with 5v wires to Pin 8 and Pin 2, then an additional wire from Pin 8 to the Standby Switch.

Try removing the wire from Pin 8 to Standby.  Instead, connect your 5v CT to the spot on the Standby Switch.  This is a valid use of the 5v CT.



If you still have buzz or hum after this, the 5v winding & the rectifier likely are not the cause.

[sluckey]

That hum is due to some other problem, not due to disconnecting that center tap from ground. At this point you have probably damaged the GZ34 and possibly damaged the PT too. Hope not. Try another GZ34.

[toobzilla]

... what do i do with the center tap? ...

I will guess you have wired the rectifier socket like the
original layout, with 5v wires to Pin 8 and Pin 2, then an additional wire from Pin 8 to the Standby Switch.  You guessed correctly,lol

Try removing the wire from Pin 8 to Standby.  Instead, connect your 5v CT to the spot on the Standby Switch.  This is a valid use of the 5v CT.
 I'll give that a shot...


If you still have buzz or hum after this, the 5v winding & the rectifier likely are not the cause.

Thanks a ton!... much appreciated!
Edit; Fixed quote. Willabe

[tubeswell]

A 5V rectifier tube winding has to be connected the B+, not the ground. If you connect it to the ground (via a center tap), the B+ will short to ground, causing the Mains fuse to blow (hopefully before the PT is damaged). But as sluckey says, it may be too late for that warning.


If a 5V winding comes with a CT, you can connect the CT to the B+ (instead of connecting Pin 8 to the B+).

[Chriscolt]

So, to make sure I understand this correctly, I use the 5V Center tap instead of pin 8 as the B+ supply which then gets connected to the junction of the standby switch and the positive pole of the reservoir capacitor (negative pole to ground). In this case my reservoir capacitor is a 100uf/1.2KV non polarized Film cap.

[tubeswell]

So, to make sure I understand this correctly, I use the 5V Center tap instead of pin 8 as the B+ supply which then gets connected to the junction of the ...reservoir capacitor (negative pole to ground).

yep

[Merlin]

The center tap is only for directly heated rectifiers. The GZ34 is indirectly heated; the output should be taken from the cathode pin. Leave the CT disconnected or you will be putting extra stress on the heater by letting ripple current flow in it.

[tubeswell]

Oops. Missed the bit about the GZ34


Edit: although noting that, I’m not entirely sure why reservoir cap charging current pulses would be that much of a problem for a 1.9A rectifier filament that is connected to the cathode anyway, especially if the rectifier’s maximum reservoir capacitance rating is not exceeded. Interested to hear more about this.