Champ with SS rectifier, is this right?

[uki]

Hey guys !

My next build, a Champ with SS rectifier, I did some modifications on the schematic replacing the tube rectifier with diodes.

Not sure if my calculation is right, in the schematic just after the tube rectifier voltage says 355v, I understand the tube rectifier does drop some voltage, and the diodes don't, so the voltage from the PT is reduced to match voltage after the diodes. Is my logic and calculation correct?

355/1.4= 250 approximately ?

Thanks in advance.

[eleventeen]

Looks right to me. 250 * 1.4 = 350, close enough.

[uki]

Why this amp only use one wire for the heaters ?

[sluckey]

Why this amp only use one wire for the heaters ?

Because the other PT filament wire is connected to chassis. And so are one of the filament pins of both tubes. IOW, the chassis acts like the second filament wire. This is an outdated idea. Modern filament wiring is superior as far as hum reduction is concerned.

[uki]

Why this amp only use one wire for the heaters ?

Because the other PT filament wire is connected to chassis. And so are one of the filament pins of both tubes. IOW, the chassis acts like the second filament wire. This is an outdated idea. Modern filament wiring is superior as far as hum reduction is concerned.

I see thanks!

So then I should get an PT with 2x 6.3v plus center tap and avoid grounding the heater wire? And modifications would be needed in the schematic?

[sluckey]

You don't actually need a center tap. You can use two 100Ω resistors to create an artificial center tap. The main idea is to have the filaments referenced to chassis ground without actually flowing filament current through the chassis.

[uki]

You don't actually need a center tap. You can use two 100Ω resistors to create an artificial center tap. The main idea is to have the filaments referenced to chassis ground without actually flowing filament current through the chassis.

How many watts on those resistor, 1w ?

Does this schematic works?

[hesamadman]

So then I should get an PT with 2x 6.3v plus center tap and avoid grounding the heater wire? And modifications would be needed in the schematic?

You wouldnt have to make any modifications to the actual schematic. Especially if you do what Sluckey just suggested. The schematic itself shows two heater wires. The layout however, does not. If you want to modify the layout to accommodate current specifications, just connect the grounded point on the pilot light, 6v6, and 12ax7 to the second heater wire that you will have on a newer PT.

[uki]

So then I should get an PT with 2x 6.3v plus center tap and avoid grounding the heater wire? And modifications would be needed in the schematic?

You wouldnt have to make any modifications to the actual schematic. Especially if you do what Sluckey just suggested. The schematic itself shows two heater wires. The layout however, does not. If you want to modify the layout to accommodate current specifications, just connect the grounded point on the pilot light, 6v6, and 12ax7 to the second heater wire that you will have on a newer PT.

Cool thanks, that is what I was thinking, how about this PT will it work ?

[sluckey]

yes

[uki]

Cool !!

In the following picture, the OT if only the 8 ohms is wanted, which primary impedance isn't needed, 5ohms ?

[drew]

^ They aren't really dependent like that.  You just need to decide to use the 5K or the 8K (or maybe make them switchable); then you can use either the 4 ohm tap or the 8 ohm tap or both.

If you're going to be using an artificial center tap for the heaters, consider implementing the "heater elevation" described here:  http://www.valvewizard.co.uk/heater.html

[uki]

^ They aren't really dependent like that.  You just need to decide to use the 5K or the 8K (or maybe make them switchable); then you can use either the 4 ohm tap or the 8 ohm tap or both.

If you're going to be using an artificial center tap for the heaters, consider implementing the "heater elevation" described here:  http://www.valvewizard.co.uk/heater.html

Cool thanks !! Gonna check that link !