Help with GZ34

[daghettoalbanian]

I am building an AD-15 remake and am stuck on the rectification portion of the amp. When the GZ34 is soldered in there is no voltage being drawn from the secondary of my power transformer, but when I replace the gz34 with a bridge rectifier the amp works fine. The circuit is soldered up according to the schematic, so I am baffled as to why it's not working. Could i be overlooking something?

[gingertube]

Do you have the GZ34 heater circuit wired up correctly?
Cheers,
Ian

[daghettoalbanian]

Yes the tubes glow up but it doesn't seem to be drawing any power from the transformer. I have 2 and 8 going to the brown wires of transformer i think its 3.15 volts not the heater though and 4 and 6 to the secondary. I am using the blues junior power transformer replacement as well. The tube isn't supposed to be grounded is it?

[MellowTone]

The heater supply for a GZ34 should be 5V between pins 2 and 8. Said 5V tap should be rated for minimum 1.9 amps.

Is the schematic you're working off this one here (or thereabouts)? http://www.prowessamplifiers.com/sch...s/AD15main.jpg

[cobra]

The Valve Wizard this is good onfo if ..you have 2.5 0 2.5 ht from center tap if not pin 8 is h/k if you have only 6.3 volts then poss an ez81

good luck cobra

[12E1]

Originally Posted by cobra

The Valve Wizard this is good onfo if ..you have 2.5 0 2.5 ht from center tap if not pin 8 is h/k if you have only 6.3 volts then poss an ez81

good luck cobra

"ht from center tap" is NOT correct for a GZ34. The cathode has its connection to pin 8, the heater voltage (5 volts AC) is between pins 8 and 6. The HT current must come from pin 8. If you were to take the HT from a tap on the heater winding then you would superimpose half of the heater AC voltage on the HT output.

To the OP - you say it works with a bridge rectifier. That only tells us that there are some volts from the HT on the transformer. I assume that you do have a center tap on the HT winding on the transformer...? (should be marked for example 350 - 0 - 350, or whatever voltage it is designed to provide). Using the GZ34 as a full-wave rectifier requires that the 0 volt center-tap on the HT winding is grounded. Then you get the +HT out from the cathode (pin 8, as above). Note that the heater winding for the GZ34 is at +HT voltages and should be regarded as hazardous. It must not be connected to other valve heaters in the design.

If you do not have a center tap on the HT winding of the transform, then let us know and we can advise an alternative arrangement,

[mctavish]

[QUOTE=12E1;3047911]"ht from center tap" is NOT correct for a GZ34. The cathode has its connection to pin 8, the heater voltage (5 volts AC) is between pins 8 and 6.



Pins 4 and 6 are the PLATES for the HV secondary. Pins 2 and 8 should have 5 volts applied across them to light the heater. Rectified DC should be taken from pin 8.

[mctavish]

To use a 5AR4 rectifier your transformer MUST have a center-tapped HV secondary which should be grounded. If your secondary does not have a center tap then a hybrid Graetz-bridge is possible which utilizes two solid-state diodes alongside the 5AR4 to form a Full-Wave-Bridge.

[12E1]

[QUOTE=mctavish;3047914]

Originally Posted by 12E1

"ht from center tap" is NOT correct for a GZ34. The cathode has its connection to pin 8, the heater voltage (5 volts AC) is between pins 8 and 6.



Pins 4 and 6 are the PLATES for the HV secondary. Pins 2 and 8 should have 5 volts applied across them to light the heater. Rectified DC should be taken from pin 8.

My apologies for the error re pin 6. I would correct my post, but appear to be unable to do so.

[daghettoalbanian]

@mellowtone that is the exact schematic I am using. And my transfper does not have a center tap. Is there a schematic i can see to utilize the gratez bridge. And also would it be better to just go ahead and use bridge rectification?