output transformers

andrew Ivimey · Post by **andrew Ivimey** » Tue Dec 04, 2007 8:51 am

Correct me if I'm wrong please but ....

In SE if an output valve is happy with a 5K transformer and I use a 3K trafo, this gives more plate voltage, more distortion and makes the amp louder.

Is this the case with PP?

or, if happy at 5K in PP and I use 8K output transformers, plate voltage goes down, the amp is quieter and less demanding on the PSU / rest of the amp ????

Paul Barker · Post by **Paul Barker** » Tue Dec 04, 2007 9:31 am

plate voltage not significantly affected as dc resistance has such a loose connection with reflected impedance as to be inconsiderable.

In theory 1/2 reflected impedance equals double power but doesn't seem to make much practical difference, remembering that double audible effect requires four times power.

As far as how good things sound with different reflected impedances. People get far too hung up on this, probably because they are also far too hung up on loadlines and theory and other theoretical perfectionisms which are not borne out in a listening test.

But when ordering transformers you have to go with something, so we go with practically meaningles things like geting the reflected impedance exactly right.

Post by **Nick** » Tue Dec 04, 2007 9:33 am

In general yes, I had several goes at posting this, starting to witter about load lines, and needing to see what you actually get before generalising. But the simple answer is yes, I guess

Cressy Snr · Post by **Cressy Snr** » Tue Dec 04, 2007 4:25 pm

Paul Barker wrote:
As far as how good things sound with different reflected impedances. People get far too hung up on this, probably because they are also far too hung up on loadlines and theory and other theoretical perfectionisms which are not borne out in a listening test.

Hi Paul
When I built Rocky I didn't give a monkey's about reflected impedances, then one or two people on the other forum (not you, Nick or JamesD) started wittering on about how my amp couldn't possibly be any good with the trafos I had. So much so that I literally became obsessive/compulsive about it with everything I built after that.

I realise now, how silly that attitude is when you consider that loudspeakers are nothing like the nice resistive loads and totally lack the predictability we need to make the maths work.

Steve

Paul Barker · Post by **Paul Barker** » Tue Dec 04, 2007 4:43 pm

Well it gives ignorant people something to obsess about.

andrew Ivimey · Post by **andrew Ivimey** » Tue Dec 04, 2007 4:46 pm

Yes but one has to start somewhere and reflected load / primary impedance seems sensible.

Perhaps the peeps who wittered on about etc etc were about as knowledgeable as you were then. (I still remember thinking indignantly, 'you can't do that!' to the braver souls who ripped out a 2A3 in the WAD PSE design and said that it was an improvement. Then I did it; it was.

Your Rocky had Sowters didn't it? Supposedly great transformers but if I used a pair of say 211s with 2.5k even Sowter trafos at 1kV, I think I'd be in trouble wouldn't I.

Okay extremes are silly.

The WAD toroids I'm using while waiting for the O-Netics really do sound pretty good (I'm impressed), now wth amp is working properly. But I haven't a clue about what primary impedance they are - they work.

Lots still to be done but now it feels like it is very worthwhile going on.

hasta la huego!

ed · Post by ed » Tue Dec 04, 2007 4:54 pm

Paul Barker wrote:Well it gives ignorant people something to obsess about.

whoaaa you can't say that, here, PB...
how about electronically challenged??

I'm not sure which traffos Steve is referring to but when I built my rocky(again in ignorance) I used ubiquitous 1627 and it sounded great. It still does and the same transformers are still in it...so whats all this tosh about it can't possibly sound right cos of reflected impedance?? Is it implying that you can only put together an amp which is destined for one particular speaker and never must it wander from this pre-determined load??

Post by **Nick** » Tue Dec 04, 2007 4:55 pm

Shou;d be simple enough to measure the TX ratio, just stick some AC in at one end and see what comes out at the other.

andrew Ivimey · Post by **andrew Ivimey** » Tue Dec 04, 2007 5:02 pm

should be, Nick, should be.

I'll try it at the weekend. That gives me a ratio, then assuming the one secondary is 6ohm, I get the ballpark figure for the primary, which I can then promptly forget and build another amplifier.

Hooray!

Paul Barker · Post by **Paul Barker** » Tue Dec 04, 2007 5:49 pm

andrew Ivimey wrote: (I still remember thinking indignantly, 'you can't do that!' to the braver souls who ripped out a 2A3 in the WAD PSE design and said that it was an improvement. Then I did it; it was.

I think you would find if you were able to search the history it was originally my suggestion, and it came up initially with mass opposition until a few people actually tried it to quell the very loud voice on that forum at that time of people who had no practical experience just a fast button for Google.

andrew Ivimey · Post by **andrew Ivimey** » Tue Dec 04, 2007 6:23 pm

Ha! well I never.

I learned from that suggestion, so thanks Paul.

And I didn't even know about Google searches in those days either

Darren · Post by **Darren** » Tue Dec 04, 2007 6:25 pm

That conjours up one word for me Paul,

Begins with an "R"....................

I remember that time well, I also remember talking about it and telling peeps to just B&^%y try it and stop whittling on.
I not sure now, but I think MJ tried it first? and liked the result.

But we already knew that didn't we

Paul Barker · Post by **Paul Barker** » Tue Dec 04, 2007 9:56 pm

Yes because I told him to as soon as he said he was buying one, along with a few other suggestions.

But mostly when I suggested stuff to those guys in those days half of them were thinking "who is this mental bloke? how can we get rid of him?"

richardcooper2k · Post by **richardcooper2k** » Tue Dec 04, 2007 10:25 pm

what makes you think we don't still think that paul ?

steve s · Post by **steve s** » Tue Dec 04, 2007 10:32 pm

Paul Barker wrote:Yes because I told him to as soon as he said he was buying one, along with a few other suggestions.

But mostly when I suggested stuff to those guys in those days half of them were thinking "who is this mental bloke? how can we get rid of him?"

and you've not changed paul..

i'm glad to say

my experiences are the same with triodes, anything will do within reason and it will work.. quite well..

does not apply to a pentode amp, i do belive that the damping factor / feed back combination come into play,
and they are far more critical to speaker impedances.. the feed back is required to correct this failing..

steve

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