[FLY135]

I'm working on my first project, which is a reverb amp that I'm trying
to turn into a guitar amp. I'm confused about the rectifier circuit.
It's a 5Y3 tube. The heater goes to pins 2 & 8. Pin 8 is tapped to a
large electrolytic cap. The question is... Is the heater and the
cathode the same, or at least next to each other? If so wouldn't the
tap to the cap be negative? Shouldn't the cathode be negative?

[Güs]

FLY135 wrote:
I'm working on my first project, which is a reverb amp that I'm trying
to turn into a guitar amp. I'm confused about the rectifier circuit.
It's a 5Y3 tube. The heater goes to pins 2 & 8. Pin 8 is tapped to a
large electrolytic cap. The question is... Is the heater and the
cathode the same, or at least next to each other? If so wouldn't the
tap to the cap be negative? Shouldn't the cathode be negative?

The heater is the cathode in the 5y3, and it's bigger brother the 5u4.
It's "pulled" positive by the positive going AC swing at the
plates/anodes. (rather crude explanation, maybe someone will elaborate)
The high voltage winding of the transformer has a center tap that is
usually tied to ground. The alternating rectification of the high
voltage AC becomes pulses of DC at pins 2 and/or 8, smoothed by the cap,
to give you the DC (B+) that makes the magic.

Play Safe!
Paul

[Phil Allison]

"FLY135" wrote in message
ups.com...


** Groper alert !


I'm working on my first project, which is a reverb amp that I'm trying
to turn into a guitar amp. I'm confused about the rectifier circuit.
It's a 5Y3 tube. The heater goes to pins 2 & 8. Pin 8 is tapped to a
large electrolytic cap. The question is... Is the heater and the
cathode the same, or at least next to each other?


** The same.


If so wouldn't the tap to the cap be negative?


** Its all relative.

Shouldn't the cathode be negative?


** It is, relative to the plates when they are conducting current - about
50 volts negative.

But seeing as the plates are *hundreds of volts positive* relative to
ground, the cathode is still very much positive at those times ( at the
maxima of each half cycle of the AC voltage).

The cap charges up to this positive voltage and does it best to hold onto
it.




......... Phil

[FLY135]

Güs wrote:
FLY135 wrote:
I'm working on my first project, which is a reverb amp that I'm trying
to turn into a guitar amp. I'm confused about the rectifier circuit.
It's a 5Y3 tube. The heater goes to pins 2 & 8. Pin 8 is tapped to a
large electrolytic cap. The question is... Is the heater and the
cathode the same, or at least next to each other? If so wouldn't the
tap to the cap be negative? Shouldn't the cathode be negative?

The heater is the cathode in the 5y3, and it's bigger brother the 5u4.
It's "pulled" positive by the positive going AC swing at the
plates/anodes. (rather crude explanation, maybe someone will elaborate)
The high voltage winding of the transformer has a center tap that is
usually tied to ground. The alternating rectification of the high
voltage AC becomes pulses of DC at pins 2 and/or 8, smoothed by the cap,
to give you the DC (B+) that makes the magic.

Play Safe!
Paul

This pic on wikipedia made it a lot clearer to me. Doh!

http://en.wikipedia.org/wiki/Image:VacRect2E.png