math

[shooter]

 want B+ @400vdc, FWB, so 400 / 1.414 = 280ish? 
0-280 ok if I'm grounding the bridge?

[2deaf]

1.414 is theoretical, but actual is a little less.  So you might want 295V or 300Vac.

[shooter]

Thx, was gonna "round up" 

[drgonzonm]

First couple of pi filters, rc's, LC, RC, or RC, LC?  I believe it makes a difference. 
(I know pi filters only deal with caps and inductors). 

[shooter]

I found a couple PT's that should get me close, one's an Edcor 0-295, the other I think is a 0-320.  The PI filters will be pretty "stiff", 1st tap 2 100uF in series, with a 47uF in || and balance bleeders. Then 2 47uF taps with R's, no L's.  Using a UL OT, but want everyone beefy n spec'd just in case I want to || a 2nd Kt88

Hopefully by the weekend I've got the board laid out and a part# for order.  Pretty much settled on a 17" chassis because of iron size (1628sea), still looking for something like 12" X 8-10"

[66Strat]

Just a question. Why bridge rectifier?

[shooter]

Why bridge rectifier

I'm not a guitar player so I come at it a little different, guitar players do like what I build 'anyway

I like the clarity, if you're trying to swing 80% clean and your supply sags 20%, cleans don't stay clean as much.  Very simple to build with, small footprint, I could probably find more, but the music's to good and the green beers not old

[kagliostro]

Why bridge rectifier?

Is the new wave, also KOC on his books say you really don't need a Vacuum Tube Rectifier or to use a Solid State Full Wave Rectifier

if you want SAG you can add a SAG resistor

Using a 0-300v PT instead of a 300v - 0 - 300v usually is cheaper

Franco

[66Strat]

Why bridge rectifier

I'm not a guitar player so I come at it a little different, guitar players do like what I build 'anyway

I like the clarity, if you're trying to swing 80% clean and your supply sags 20%, cleans don't stay clean as much.  Very simple to build with, small footprint, I could probably find more, but the music's to good and the green beers not old

The common consensus, amongst people that have heard me play, is that I as well am not a guitar player. 

I understand the differences between tube and solid state rectification. I was just interested in the thought process used to arrive at bridge rectification. I know how bridge rectifiers work. I was just curious as to the advantages.

[sluckey]

1. A bridge only needs half the AC input voltage to produce the same B+ as a conventional two diode rectifier.

2. A bridge uses the entire PT secondary winding all the time. A conventional rectifier only uses 1/2 of the secondary winding at any time. The other half of the winding will just be sitting there doing nothing.

3. Common rectifier tubes cannot be wired in a bridge configuration unless you add a couple solid state diodes.

So, a bridge requires a lower voltage transformer and it uses the transformer more efficiently. Some would say these things are advantages. I'm not so sure.

[shooter]

I'm not so sure.

Nor am I, I like the appeal of driving a pre 80's "sports car" 8 track n all, but I gotta say, after owning a couple 2.0L turbo all-wheeler drives with XM radio..........

[bnwitt]

Well you can always take that Pre 80's sports car to Chip Foose

[66Strat]

2. A bridge uses the entire PT secondary winding all the time. A conventional rectifier only uses 1/2 of the secondary winding at any time. The other half of the winding will just be sitting there doing nothing.

So, a bridge requires a lower voltage transformer and it uses the transformer more efficiently. Some would say these things are advantages. I'm not so sure.

This is the aspect that interests me. For a given VA secondary rating, the center-tapped transformer would require twice the number of secondary winding turns as the non-center tapped transformer. Intuitively, the non-center tapped transformer would appear to require heavier gauge wire in the secondary. However, if there were a significant difference in wire gauges, the IR losses in the center-tapped transformer would be higher. If both are properly designed, it's probably a wash from a technical aspect.

[shooter]

Well you can always take that Pre 80's sports car to Chip Foose

Yup, and He'd put in a SS recto or at least an LS something

it's probably a wash

You're probably correct, I don't get to deep into theory if the practical, or already been done, works

[PRR]

> if there were a significant difference in wire gauges, the IR losses in the center-tapped transformer would be higher. If both are properly designed, it's probably a wash from a technical aspect.

The CT plan does force higher IR losses. Not a huge amount, but enough to matter.

Half the number of turns with thicker wire is a big win in the winding room. You can run faster and finish in maybe 1/3rd the time.

For 40+ years, the killer reason was that rectifier tube filaments/cathodes are expensive, and at tube voltages need dedicated windings or heaps of heater insulation. The 2-diode Common Cathode plan economizes a bit on cathode costs by doing one big cathode instead of two smaller ones, and on the same heater winding.

The FWB would need three cathodes and three heater windings (or heaps of heater insulation). There are a few. (Mostly done with four single rects instead of an odd-trio of dual and single diodes.) Lots of heater wiring. Very rarely done in tubes. Crystal diodes changed all that.

[kagliostro]

As PRR say








not a simple architecture


Franco

[PRR]

Your second "100 Watt" plan is not a full wave bridge. It is two diodes making 750V, and two more on taps making 220V. Two heater windings (plus the 6V for audio tubes). Also a crystal diode for a low-volt low-current bias supply.

You can see a small optimization: the two extra heater windings only need one extra lead each, the other may be common with the high-volt lead. So 8 leads, not 10; opposed to 5 for the 2D CT plan.

The top one is FWB and shows the three heater windings.