6X5GT PS Problem

[sled108]

I'm Building an Amp with a 6X5GT PS. It has 114v at Pins 3 & 5, which is Right, and it's a CLCRC Supply...But it has -.8v at Pin 8...I've tried 3 other Rectifiers, but they all show -.8v at Pin 8....Are my Pin-Outs Wrong??...The Heaters Glow, so at least they're Pinned Right???...

 

[Richard Ellis]

We need a schematic as we don't know the specific amp you have built.
_____________________________________________________Rick....

 

[aardvarkash10]

But it has -.8v at Pin 8...

between pin 8 and where exactly? If Pin 8 is at -0.8v, and your other test point is connected to the signal ground elsewhere in the circuit, the voltmeter is telling you you have a resistance between the rectifier cathode and the signal ground...

 

[HollowState]

Your pin outs are correct. Pin 8 is the cathode and you should have around +150VDC unloaded with respect to DC return/ground. Either all 3 tubes have an open cathode connection, which is unlikely, or your tube socket isn't making a connection at pin 8. Check that very carefully.
Is this a full wave with a center tapped transformer?

 

[sled108]

It is between Pin 8 and the AC Ground..

 

[aardvarkash10]

ok - so now you have a 0.8v drop (or difference) between the AC safety earth and the DC signal earth. Is there a resistor or diode in that path? Or have you direct-connected the two earths?

 

[aardvarkash10]

oops - . What hollowstate said...

 

[aardvarkash10]

would a dead short to earth on Pin 8 do this too? ie load the rectifier so that voltage was pulled close to zero?

 

[sled108]

Oh Well, Live and Learn...It would seem that I've totally Screwed the Poodle on this project...I tried to do the Back to Back 12.6v CT RS Transformer Trick..But I only have 114v between Pins 3 & 5.....Nothing between either of those and Ground...It really looks Nice & Glows Pretty though...

 

[sled108]

How's this for Form Over Function? Maybe I can put a Diode Rectifier inside, and just keep the Heaters on the 6X5G?....

 

[aardvarkash10]

oooookay, think I may have it. Is the output of your second transformer centre-tapped? ie are there THREE wires from the secondary, or two...

 

[aardvarkash10]

I reckon this is what you have done. Can you see the problem?

 

[Tom Bavis]

Just add a pair of 1N4007s or other SS rectifiers to make a full-wave bridge. If your transformer has no center-tap, that's your only choice.

 

[sled108]

Here's the Transformer Layout...

 

[aardvarkash10]

yep - what Tom said. Look for a diagram of a hybrid rectifier using a tube and two semiconductor diodes.

 

[Bas Horneman]

http://www.audiodesignguide.com/my/SE_pwd_new1.GIF

 

[sled108]

Bas...You Are The Man!!! All it took was 2 Little Diodes to Ground and now I have 134.7V B+...ThankYou! ThankYou!...And, I Now also have a Working 6DJ8 Phono Amp...
I have a Thread on this Amp that I'll update after Spinning some Vinyl Today..

 

[sled108]

Sounds Great! Check it Out...

http://www.audiokarma.org/forums/showthread.php?t=233322

 

[sled108]

Oh Yeah, Tom...They were 1N4007's that did the trick...Thank You Too...