That's all true. Previously you said there MAY be voltage drop. In truth there is always, as you now correctly put it, forward voltage drop.


See the italics:

Previously you referred to the output of the transformer as increased line voltage. Here you refer to the line voltage as "whether DC or AC." Since you have not separated the concepts of transformer input and secondary output, you have here said that a transformer can output DC.

| In order for the B+ to be in the 300VDC+ range, the output from the power transformer's secondary must be increased before it reaches the rectifier, where it may/may not pass through without voltage drop.
I missed a whole other thing here: The output from the power transformer's secondary is already higher than the line voltage by the factor of the windings ratio and "output... must be increased" is not true.

There is NOTHING between the output from the transformer's secondary and the rectifier except a piece of copper wire. And this wire somehow increases that voltage?

Here you are very clearly saying that after going through the transformer, the transformer's  the voltage must be increased in order to get to the 300VDC+ range. After the transformer, what device or occurrence increases the voltage further?

[There is an apparent increase after the rectifier because a sine wave, rectified and filtered, tends to increase from the RMS value of the sine wave up toward the peak voltage of the sine wave, minus, of course, the forward voltage drop of the rectifier. In tube equipment, that voltage drop can be substantial, way more than the drift from RMS voltage to peak voltage. I just looked up the 5U4 and its voltage drop at 275 mA per plate is 50 volts.]

See, you did say something about DC from the transformer, because at that point you were conflating the concept of "line voltage" with "secondary" and not mentioning that there's an entire circuit between the transformer secondary and the DC measurement point.

Your facts are right but they're expressed in a way that they can clearly mean something you did not intend. It's also hard to tell exactly what you do mean because of the way you put things together. I can't believe you actually intended to say that "the output from the power transformer's secondary must be increased before it reaches the rectifier." But it's what you wrote.

I should have written that the voltage from the primary increases in the secondary before it reaches the rectifier.

We know:
-the PT always works with AC and the ratio of secondary to primary winding causes the increased AC voltage at the secondary output (or decreased, since the heaters use AC voltage, too).
-the rectifier and filtering is where AC is changed to DC and the reason I wrote "may be" is because diodes don't drop the voltage much, unless Zener diodes or some other device/network is used to recreate the effect of the original tube(s) in the half or full wave rectifier.
-It's not DC until the filtering has been done.

For all of the precision in line voltage that we would like to see, it's not always necessary unless the equipment is built to similar tolerance and is operating at the upper limits of the device specs. If they leave enough headroom, normal fluctuations don't do much damage but the fast spikes can take their toll.

Here's an example of something that shows what would seem to be sloppy design, or maybe it was just accepting the fact that line voltage and manufacturing tolerances weren't very stable at the time- at the upper right corner, the diagram shows "voltages read to ground with electronic voltmeter values shown are + or - 20%".

In my amp of this model, I have read over 530VDC at the plates with a solid state rectifier that is sold as a direct replacement (pretty irresponsible, considering the fact that many people would never think of/bother with re-biasing), but the filter caps are rated for 600WVDC, so they still had some headroom. When I installed a tube rectifier, the voltage at the various test points was almost exactly as shown.

[Link: ampwares.com]

This writing is clear and correct.

Yeah, but people who don't know that even solid state rectifiers have a forward voltage drop will never understand diodes. It's to their detriment to write "may" have a voltage drop.


I'd vote for" accepting the fact(s)."

AMEN BROTHER! Solid state drops are less than a volt; that 5U4 I looked up had 50 volts of drop, so replacement with solid state would likely increase the B+ by an unacceptable amount.

Excellent, informative, and accurate. Thanks. You'll never get complaints about the facts from me when you write like this.

You would be surprised by the number of people who recommend using a 5U4 to replace a rectifier in a small amplifier that originally had a 5Y3, 5AR4 5V4, 5R4, etc. This may work, but probably not for too long since the 5U4 can draw 3A vs the others, which draw 2A or less. This is particularly problematic when the incorrect replacement goes into a collectible amp, which includes every model made by Fender from the beginning to the late-'70s, although the actual models at the end of this time are debatable- they can usually be improved to be as good as their predecessors and the reason they weren't as good is due to the fact that many of the people who worked for Fender during their hey-day left after CBS bought the company and made these changes to cut costs.

Leo Fender trained as an accountant during the Depression, but he was interested in other things, including radio repair and music. He didn't play an instrument, but he had many friends who did and they had a lot of problems with equipment reliability, so he would repair theirs. As he learned more about electronics, partnered with Doc Kaufman, making small amplifiers & lap steel guitars in the '30s and continuing to make repairs. He would improve what may have been needed and then, eventually started Fender Electric Instruments.

Leo didn't design everything- some tasks were handed of to others once the company grew to a size that required more of his attention. The amplifier in the link above is said to have been designed by Freddie Tavarez, who was a long-time Fender employee who was also a session musician in Los Angeles, playing steel guitar. He's also known for the steel guitar 'sweep' at the beginning of the theme song for those Warner Brothers cartoons most of us grew up with.

Here's one on-stage, played by Scotty Moore, with Elvis-

The parent company of Torus Power brand is Plitron.
They make their own transformers for the medical industry as well as a lot of audio vendors, including Bryston.

I was not aware that Plitron made the transformers for Equi=Tech.
That doesn't surprise me at all.