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flysig
diyAudio Member

Join Date: Apr 2009
Quote:
 Originally Posted by PRR If anybody is still unclear how we have >1000V p-p with only 400V supply....
The key point is that the transformer operates on current. That's what makes the magnetic fields that do all the work.

So we can start at the load and the wattage to calculate a current flow. Then we can calculate the current flowing in the primary (assuming no losses). Now we can figure out the voltages necessary on the primary, realizing that the tube is very much a valve allowing current to flow.

Ergo, the voltage on the primary is a byproduct not a cause. Vpp therefore is not some kind of limitation to primary voltage.

PRR
diyAudio Member

Join Date: Jun 2003
Location: Maine USA
Quote:
 Originally Posted by flysig ...transformer operates on current.....
All power systems operate on both voltage and current, sure.

An ideal transformer, no load, draws no current.

Mid-band, a \$50 transformer draws very-little current above load current. (Yes, the bass sucks current.)

It is however perhaps important to use a large enough "envelope" to sketch the WHOLE circuit and annotate all numbers as peak or peak-peak, etc. There's too many loose ends to keep all straight in the head or on a matchbook.

 20th January 2018, 10:51 PM #33 flysig   diyAudio Member   Join Date: Apr 2009 The reason for my comment, hopefully to add insight to the person asking the question, is that people tend to look at the power supply voltage as defining the limits of what will be found within the circuit. Modern semiconductor circuits would normally stay within those voltage boundaries.
PRR
diyAudio Member

Join Date: Jun 2003
Location: Maine USA
Quote:
 Originally Posted by Gnobuddy Are there any 6V6 datasheets that shows plate curves at various different G2 voltages?
Ponder the Triode curves. You know the plate current is hardly affected by plate current. The rise of total current is due to higher voltage on G2.

You can also ponder 7027 sheets, some of which show Vg1 curves for several Vg2 values.

Quote:
 Originally Posted by Gnobuddy ...driving G1 into positive grid voltage territory - but with only 250V on G2 - makes more sense to me than Leo's sky-high voltage on everything.
Positive grid means a POWER driver. The asymmetry means cap-coupling will just grid-block, forcing transformer or followers. The mild grid-block possible (and controllable) in nominal neg-grid cap-coupled overdrive turned out to be very musically useful (see Neil Young).

And tubes LOVE voltage. Vacuum is a terrible conductor. Voltage urges the little electrons along. Yes, high voltage is hard on materials. The 315-350 spec on 6V6 is probably about allowing use of the cheapest plate-metal (or softest oxides) to keep cost down. And when 6V6 was new, nobody had much over 300V in hand. Electrolytic caps don't like >450V, usually run less, and then the Field Coil used 100V-150V. So 300V rating was ample. But as these mild-mannered radios vanished, and hard-worked TV sets dominated, the factories had improved materials in bulk.

dotneck335
diyAudio Member

Join Date: Dec 2012
Quote:
 Originally Posted by Gnobuddy So how did Leo manage it? He didn't put 285 volts on the screen grid, he put something closer to 400 volts on them. .....So now we know the factory datasheet curves are worthless in Leo's world, a world in which you penny-pinch the cheapest output valve you can find till the anode glows dull red, rather than do the right thing and buy the next size bigger valves. In Leo's penny-pinching world, the 6V6 curves have all moved far from where the factory told you to expect to find them. .....How much lower? Again, we can't tell without actually measuring 6V6 curves with 400V on G2. But apparently, Leo found that OT's with a 6600 ohm primary did the trick. Whether Leo did careful testing to find the optimum, or simply bought the cheapest OT he could find that was "a bit less than 8000 ohms", we can only guess. My bet is that it was the latter.
If you can put your incessant Leo-bashing aside for a moment, don't you suppose that maybe the 6V6 with 415v and a 6600Ω load just sounded better? Leo listened to musician's input probably better and more often than did any other manufacturer.

Gnobuddy
diyAudio Member

Join Date: Mar 2016
Quote:
 Originally Posted by dotneck335 If you can put your incessant Leo-bashing aside for a moment
Sigh. I'm not interested in bashing Leonidas. I'm also not interested in worshipping him through rose-coloured glasses.

I am somewhat interested in understanding some of the technical decisions he made. Sixty or seventy years later, the cult of Leo tends to blindly see these as always superior, but let's not forget they were often despised by contemporary instrument manufacturers who saw them as cheap and shoddy shortcuts.

Quote:
 Originally Posted by dotneck335 don't you suppose that maybe the 6V6 with 415v and a 6600Ω load just sounded better?
No, I don't think so, for a few reasons. The most compelling one: put a VVR on a pair of 6V6s and try changing the B+, and listening.

For clean guitar tones - the only kind Leo was interested in - I've found negligible difference in output stage tone over a wide B+ range, most particularly in push-pull output stages, as long as you're not pushing the amp to near its full limits.

Also interestingly, I have two Fender amps with virtually identical power amp sections, both using 6V6 outputs. The Superchamp XD has lower B+ than the Princeton Reverb reissue. And the XD has considerably better clean tone!

I don't think the lower B+ is responsible for the better tone, except indirectly: the 445V B+ in the PRRI more or less mandates the use of JJ 6V6S outputs, which seem to be clean to the point of sterility. So here is a case or more B+ indirectly creating worse clean tone.

When I stand back and look closely at Leo's creations, they always seem to fit the mould of accountant-thinking: the cheapest-made thing that the customer will buy without too much complaint. Essentially the Walmart approach to product design.

Worth noting: the most iconic Fender product - the Stratocaster - was created mostly by Freddy Tavares, after Leo told him he wasn't interested in Tavare's ideas for a new guitar. Leo did let Tavares work for him, for free, while Tavares worked out the design and built some prototype guitars, though.

Without Tavares, Jimi probably wouldn't have played a Fender guitar, and the striking shape of the 'Strat wouldn't have inspired a million kids to learn to play the electric guitar. Without Jimi, Fender Corporations fortunes would probably have taken quite a different turn.

Since the discussion of 6V6 load lines is essentially at an end, and we are now on subjective ground where there is rarely any agreement or useful outcome, I will now tip my hat to all of you, wish you a good day, and depart this thread.

-Gnobuddy

 23rd January 2018, 01:06 AM #37 dotneck335   diyAudio Member   Join Date: Dec 2012 With a tip o' the Hatlo Hat to MIB2: "All Hail Leo!! All Hail Leo!!"

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