Next Single Ended build

[Paul Barker]

Thank you though Nick for averting disaster. it would have been -3db at 5k3hz. To be fair my 56 year old ears might never have known

But as an aside, were I building one of those amps Mark might need for his speaker design, I could harness this mechanism making the amplifier it's own valve based active crossover.

But I am not planning to get that clever with speakers in the near future. Would be worth shelving in the memory banks for the bass helper of an OB.

Roll off the full ranger in the OB by deliberately winding the output transformer as the high pass filter to complement it.

Another time.

[Nick]

Its just me, but it seems that folk are making life very hard for themselves in the name of avoiding a capacitor, and possibly in the process introducing problems that may have more sonic cost.

Maybe an alternative would be to find just what it is about the cap thats causing the problem and find a way of avoiding that while still using a cap, or engineering around it (once the problem is known).

[Cressy Snr]

Its just me, but it seems that folk are making life very hard for themselves in the name of avoiding a capacitor.

Too bloody right, in my case at least.
I used to enjoy the challenge, but I just want a quiet life these days.
Taking the regulation off the screens on the output stage of my amp, would not have been necessary, had I stuck to cap coupling. Now I have probably swapped one problem for another in the shape of fscked up bass.

I shan't do it again.

[steve s]

I once tried a single stage amp, it only made a fraction of a watt but was still at a room filling level using an output valve with a gain of 18 straight from the cd player,
the sound with a driver stage and a cap was not alot different, only louder, my conclusion after that was that coupling caps dont take much away...

Px 4 vs 2a3... I have some twin plate 2a3 that i would never use. And why would i
My best sounding px 4 are 250 vts (the old ones),

I went off coupling cap because good transfomers sounded better, but my views have now changed, i am sure the main advantge of transformers is the smoothing effect on the incoming power supply thats been modulated by the load, ... in the case of my old amps anyway.

The trouble with me is i need inspiration to get on and build a new amp, and thats always on the trail of a better sound than my present amp, other wise there is no point in my eyes,

If it was not for the fact of our meets, i think 2 watts are just fine for the average listener,..( me?) with reasonably efficient speakers

[Paul Barker]

Its just me, but it seems that folk are making life very hard for themselves in the name of avoiding a capacitor, and possibly in the process introducing problems that may have more sonic cost.

Point accepted, it certainly isn't viable for a commercial amp.

Maybe an alternative would be to find just what it is about the cap thats causing the problem and find a way of avoiding that while still using a cap, or engineering around it (once the problem is known).

I suppose it's materials choices.

[Paul Barker]

If it was not for the fact of our meets, i think 2 watts are just fine for the average listener,..( me?) with reasonably efficient speakers

Yes 2 watts is easily enough for my situation at home. 3 + watts will give me headroom.

On the sound of 2a3's I think I might have a monoplate RCA knocking about, certainly have a profusion of bi plate and definitely have a pair of Sovtec monoplates. Have some PX4's also.

So when I build this for PX4 I shall incorporate in the filament transformer I'll make the output valve winding tapped for 2.5v and 4v and make myself a base changer which fits into a BR4 pin base and adapts to UX4. Then we can taste all the 2a3's people want to bring

If people are concerned for their 2a3's at 300v I suppose I could switch in an RC stage to drop the voltage for their precious ones. Someone might have mesh plates for instance. I wouldn't worry for brief tasting about my RCA monoplate (assuming I find it). So that will be a fun presentation for a future Owsters.

I did think about 801a but at 300v it's a non starter without changing the rest of the circuit to accommodate grid current. In A1 at 300v into 4k5 most power I can derive is 0.83 watts with 1.7 % second. It isn't enough power to make the comparison fair. Would probably sound great on Ed's speakers that I bought from him in a smaller room though.

As usual I am talking the talk but not walking the walk, as progress is zilch. But then my only time off in a whole week was spent visiting the mother in law who is a lot worse than Regy Perin's Hippo.

I am afraid that as usual I was unable to avoid being to blame for everything, and the constant butt of and insensant train of criticism. It's great to be back home chewing the fat over the next valve amp at last.

[steve s]

It would need to be a good amp that you build to highlight the differences between the 801a and the px4, i would guess your comments would be fair regarding straight sided px4 vs the 801a, but the drivers, transformers and speakers etc etc all go towards highlighting what the various valves are capable of..
But my view there slightly less loss right across with the px4, but you would know thats my view..
But I'm happy to be proved wrong of course, if i was that wrong i could even convert my amps over if they are better, i have a few 801's in a box somewhere. I only have an allegence with what i think sounds better, my ex used stash is testament to that.
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Have i replied to a post thats now changed paul. ?
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[Paul Barker]

I don't recall doing an AB comparison between 801a and PX4, and as you say it can't really be done because of the different needs. Whereas 2a3 is relatively similar so only the most argumentative hearer would claim it is because the amp is more suited to the PX4. But if anyone does think that let's challenge them to provide the amp which better suits the 2a3 and see how it compares then.

The 801a best stay home. At these voltages it wouldn't turn over the dynamo in a lightning bug's ass.

[cressy]

All these amp projects have me eying up those sv 811s of pauls again.............
i happen to have a 6.3v heater transformer with 3 windings at 6amps each in the el34 amp . Ac heating and loads of hummmmm would probably ensue. Wonder if i could bodge some ux4 sockets onto it........

[Paul Barker]

Trouble is you need to drive it with positive grid voltages and grid current, so needs a re-design. Shucks. It is quite a lot of work.

[Paul Barker]

well it has taken me all evening but I have adapted Stephies 801a spreadsheet worksheet for the PX4.

Unfortunately it has gone wrong. But I have an element of success. The chart draws the grid lines accurately and the loadline is correct. The max power curve is getting the wrong data as voltage goes up, but where it counts it is clear.

It predicts the bias voltage wrongly, though it isn't far adrift on power output. The 2nd distortion is not correct. the 3rd may be accurate but I couldn't tell because I haven't worked it out freehand. At this stage I can't really get the broken elements fixed, because I don't understand the formulas Stephie used for the 801a and therefore can't adapt.

However I did have to make a lot of changes to the data ranges to get this crippled version.

I see I have to clean up the data on the -30v gridline aswell as all the above mountains to climb.



The data calc in the spreadsheet predicts 3.1 watts against my 3.2 watts by hand and the distortion 2nd as 5% against my 2.5% but it must be picking up wrong points (probably those programmed in for the 801a) which I have no idea where in the many squares to change. It is a mash up.

But if nothing else I am on the way to making charts.

It was a very painstaking exercise using a vernier to accurately measure spot points on the characteristic curves and transfer them into the spreadsheet. But the data is there now. Though I have to correct a couple of the lines. bigger problem is finding the fix for the calculation regions of the spreadsheet. Makes you appreciate how clever Stephie is.

Anyone thinks they are clever too, please volunteer I send you what I did and what Stephie did and see if you can fix it?

[Paul Barker]

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Have i replied to a post thats now changed paul. ?
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Happens a lot I change my posts as soon as I view them, because I see all my mistakes.

sorry.

This is where the quote button is invaluable. the point you are answering is in context, should the original poster change his mind about making it.

[steve s]

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Have i replied to a post thats now changed paul. ?
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Happens a lot I change my posts as soon as I view them, because I see all my mistakes.

sorry.

This is where the quote button is invaluable. the point you are answering is in context, should the original poster change his mind about making it.

True, but i dont like to ise the quote button if i can help it,
Im not the man to fix your spreadsheet,, its well out of my league
The curves that are out there are enough for me to find out what will work .. Or do for what i want with the volts i have as long as i feel i have the average valve in use
Cheers

[Paul Barker]

Busted

I came home to 12 Tantalum resistors for this project.

Diana "what are all these?"
"Oh just a few resistors"

"Why do they cost £69 then?"

I'll get my coat.

I just had to sit there and listen to the lecture with no valid defence.

No point offering an explanation. I couldn't even rationalise it to myself let alone to her.

Well and truly busted.

The problem is that the level shifter (which might not even work) requires 2 watt tants, 4 for stereo. Have you seen the cost of tants?

Should have tried Kiwame's I know, I am an obsessive hoarding fool. This amp had better be good!

[Greg]

You need to apply some strategy. I don't open or explore her mail or packages and don't inquire until she wants to share it. Likewise she does not inflict scrutiny on me. At the end of the day, as long as the bills are paid and we have food in our mouths, what's to worry about?