18 watt PT filament windings

[panhead]

The PT for an 18 watt style amp I'm building has two 6.3V filament windings - one with a center tap and one without. I assume winding without the CT is for the EZ81 filament and the the center-tap one is for all the others. Is this correct?

[sluckey]

Yes. The recto doesn't need or benefit from having a CT on the filament winding. All the other tubes will like having a CT.

But, are you sure the one winding is a centertap? I ask because many suppliers offer an 18W PT that has two filament windings, but one winding has a 5V tap, not a center tap, allowing you to use an EZ81 or a 5Y3. Kinda like this one from Doug...

[TIMBO]

Hi panhead, You are correct  

[panhead]

Hi, Sluckey

This PT has a separate 5V winding, in addition to the two 6.3V windings mentioned above.

[EL34]

This PT has a separate 5V winding, in addition to the two 6.3V windings mentioned above

That would be 6 wires
A winding is one long wire with two ends and maybe a tap in the middle somewhere

Are you calling two wires two windings?

[panhead]

No - two wires for one winding. See attached pdf.

[Willabe]

1, 6.3v has CT, the other 6.3v doesn't have a CT, 5v doesn't have CT.

one with a center tap and one without. I assume winding without the CT is for the EZ81 filament and the the center-tap one is for all the others. Is this correct?

Yes, the rectifier tube does not need a CT, either 6v rect. or 5v rect.

Altho, you can use a CT on the rect. heater winding. The CT on the heater winding would be where you take the rectified B+ from, it's called a humdinger. The rect. heater is still floating, not ground referenced. The B+ has to go back through the heater winding and this acts as a choke for the rect. B+. Not seen on guitar amps very much, if at all. I think it's a Hi-fi thing.


                Brad      


                      

[Willabe]

Your non CT 6.3v winding is only 1 amp, got to watch what rect. tube you use. 5Y3 is 1 amp.


                  Brad   

[panhead]

EZ81 filament current is listed as 1A. I suspect (I hope) that the transformer ratings are on the conservative side. This PT is sold specifically for 18W Marshall builds.

[Willabe]

Doh, I got that backwards, I ment the 5v @2a, sorry.

If it's made for that amp it'll be fine. Good luck on your new build.


                  Brad        

[sluckey]

Altho, you can use a CT on the rect. heater winding. The CT on the heater winding would be where you take the rectified B+ from, it's called a humdinger.

EZ81 did not get the 'humdinger' option.    

[Willabe]

Thanks Sluckey, I've got this goofed up, I'm going too fast. Sorry for the confusion guys.

I also was not clear in what I wrote. I was trying to say you could use it (CT) if you had one on the heater winding as a humdinger.          


             Brad      

[sluckey]

I knew what you were saying although I've never heard it refered to as 'humdinger'. I thought it was funny and was picking at you.   

Taking the B+ from a center tapped filament winding on the rectifier tube works well if the recto tube cathode is connected to the filament (5AR4) or actually is the filament (5Y3). But the EZ81 has a totally isolated cathode like many other popular tubes, so the B+ is isolated from the filament. (Guess you could tie them together externally.) And that's what prompted my statement "EZ81 did not get the 'humdinger' option." I was trying to be funny.

[Willabe]

Ohhh, I get it now. Thanks Sluckey.

I've heard KOC and Merlin call it that, who knows where they got it, I bet it's an old term?



            Brad    

[sluckey]

I've heard Merlin mention humdinger, but I thought he was referring to a 100-500 ohm pot placed across a filament string with the wiper connected to ground (or elevated to some positive voltage). It's purpose is to reduce filament hum in an amplifier exactly like creating an artificial center tap using two 100 ohm resistors. The pot makes it adjustable and was often called hum balance in old amps that used them. I have a couple old Hammond amps that have that hum balance (humdinger) pot.

You can find a lot of humdinger info over at ax84.com or by doing a google search for "humdinger filament".



Look at this message posted by Merlin...
http://freestompboxes.org/viewtopic.php?f=2&t=12481


 

[Willabe]

Yes your right. I just went back and looked in his book.   

I have too many books and my memory is not as good as it was when I was oh so much younger. Problem is I'm only 53.   

Looked it up in one of KOC's books and he did refer to it as a humdinger.

Thanks for where to look for more info on it.


                        Brad