801a maximised class A2 excursion.

[Paul Barker]

I’ll keep babling to myself.

I’m conscerned about the distortion profile but I have nothing to compare it to. So I started lateral thoughts. I need to calculate the distortions found at the same power output where the 801a has sky rocketing 2nd 3rd and 4th (but the software only shows it as far as 2% but it arrived at that point almost vertically and who knows at what percentage distortion it settles?

So evrything up to the output valve would provide of other triodes with transmitting heritage with an eye on their cost.

I was pleasantly surprised that 801a’s are still going for as little as £70. I found a tripple all test very good <£200 including delivery. Others singly between £80 and £100. I suggest that’s a very fair price.

Double surprise, it turns out now Svetlana 811-10 is back on the nos market. a 211 clone with 65 watts dissipation . If you search back 22 years you’ll probably find enthusiastic posts by me where the SV811-10 completely a d utterly blew away the 300b for me. In between I think the West bombed the Factory I think? Anyway production stopped and Eric Barbour, effectively the US Ambassador for Svetlana. Suddenly shop was shut.

But now they are plentiful supply, there seem to be two looks, straight sided and a sort of plump St shape that was the original and the pair I have bought 22 years ago. And the price point similar to the 801a. If anything, less money than the 801a and more genuin nos than “Tests very good”!

I THOUGHT THE ORIGINAL 4T4C’S/211 would be way out of price range. But actually no, I would avoid the very cheap ones, I have experience of them and I have demonstrated their apauling sound qualiy compared to the originals. The construction is sloppy the suport structures are fed through holes in other structure which is a floppy fit. A friend thta used to match them for one of the big UK valve stockists said its impossible to mathc them becuase light out you can see the structures arking where these bad assemblies contact each other. The resulting sound is vague, not acurate, the antipathy of a true vt4c.
I cant speak for psvane or any other supposed to be better quality, as I haven’t experienced them. But I’m fine with my true valves as original. I don’t suggest anyone considering this project gamble on the new production becuase it’s price exceeds the cost of nos original valves. But that cost is now creaping up, but still reasonable, and an absolute bragain compared to a far more expensive NOS WE 300b.

So there is a pause (althouhg I’m waiting for parts so there is already a pause) the new pause is while I study the the distortion situation of the other possible output valves with the same general objectives.

It is possible that I end up prefer powering a 811-10/211 such that it gives an output power at least past the point where the 801a goes ditsorted with odd harmonics. Just to see what happens there. If at that point I can stay low distortion that alone os a reason to switch valves. But in all things listening is fundamental. Therefore whatever distortion picture this turns up, everything compared graphically shall get auditioned! If thta concludes with an 801a amplifier, all the better. I suspect it might finish up with something different.

Taking into account the comment Nick G gave mentioning the 300b above in the thread, in that it should be seen at the power level its not distorted. That principles supports this new direction. But there is always a limit, or else we’ll all end up with 833 gm100 212 amplifiers. Been there done that had the T shirt, collecting dust in a drawer.

[pre65]

I’ll keep babling to myself.

I'm watching intently Paul.

I seem to remember, years ago, taking my 833a amp to a meet up in Dartford at DTBs gaff.

The 833a was well received, but Mike H took his 801a amp, and the treble was deffo better on his.

I'm not sure if it was the same day, but hearing Dave's 300b amp though (ex Andrew I) silver wound OPT was an eye (or should it be ear) opener.

[Paul Barker]

I’ll keep babling to myself.

I'm watching intently Paul.

I seem to remember, years ago, taking my 833a amp to a meet up in Dartford at DTBs gaff.

The 833a was well received, but Mike H took his 801a amp, and the treble was deffo better on his.

I'm not sure if it was the same day, but hearing Dave's 300b amp though (ex Andrew I) silver wound OPT was an eye (or should it be ear) opener.

yes Peter Q told me silver is another league.

In our case were comparing all else being same just valve is changing.

[ed]

I’ll keep babling to myself.

Double surprise, it turns out now Svetlana 811-10 is back on the nos market. a 211 clone with 65 watts dissipation . If you search back 22 years you’ll probably find enthusiastic posts by me where the SV811-10 completely a d utterly blew away the 300b for me. In between I think the West bombed the Factory I think? Anyway production stopped and Eric Barbour, effectively the US Ambassador for Svetlana. Suddenly shop was shut.

snigger

I have a box of 572s and 811s, all 3s though...I knew I wasn't deluding myself when I kept saying they were the bees. I may have a pair of 811-3b in amongst them....they were the 811s in the 572 bottle. All new, unused.

I'm not 100% sure but I think the problem was the falling out of the US and the Russian factories.....Svetlana and SED were 2 separate entities. Same product but different intellectual ownership or somesuch....very mysterious and complex.

Not sure about the 211 clone bit though Paul. AFAIR the word was that these were the only truly new design valves for many years...except those 1610 things from Yugoslavia?

anyway, keep babbling.

[Cressy Snr]

Yep keep it up!

[Mike H]

I’ll keep babling to myself.

At least you'll get sensible answers!

I keep threatening to put my 801A amp in a wooden box, it's in pieces waiting, back-burner project.

[Max N]

We’re listening Paul - great stuff!
On the Svetlana thing, the American company New Sensor bought the rights to the Svetlana brand name in US and Canada. So tubes made by the Svetlana company in the Svetlana factory in St. Petersburg can’t use the Svetlana name! They now use the winged C logo...

[Paul Barker]

Now you mention it I once read about Svetlana 300b there in that article stated the Winged C is definately made in the Russian Factory, implying or claiming (Ican’t recall) this is the best one. Might well be!

Mine are from USA stock when that’s where the ones sold in the west came from the international ebay market for Eastern block valves hadn’t yet emerged.

[Paul Barker]

It takes hours and hours to do, but I’ve drawn all over the characteristic curves and measured with a dial vernier gauge, writen the formulas for distortion and power and placed the data input area visible.

Firstly, let’s see what would happen if we built an 801a amp at Stephies operating point, and we then simply unpugged it and plugged in a SV811-10.
First thing to note is the similarity between the two valves. I don’t comprehend what happened to the 3rd and 4th harmonic’s, I vaguely recall Stephie stated these apper as a negative number. I can vouch for the better 2nd harmonic of the 811-10 because any fool can see 2nd harmonic in the grid lines. The 811-10 grid lines look more linear throughout this range, i.e. the 811-10 is nowhere nera it’s headroom, the 801a is about to enter the verticla tragectory of all distortions. If you haven’t spotted it the bias voltage is different (thta is adjustable in the driver stage with ease).





A very important takeaway from this first excercise is what Nick brought up using 300b as example. Don’t plan an amp to infringe the last vestegase of power. We need a different mindset.

There is next plan; an intermediate analysis of the SV811-10 still at 500v (where by the way it doesn’t look ta it’s best), but whta I’m wanting to do is change current to bring max dissipation 65w but remain at same power output, in order to discover whether the distortion improves further and later when it’s powered up get the audition sorted out.

Further on the theme it’s planned to measure up the 211 curves at 500v/40mA so all three valves get the same starting point. Ed I know 811-10 isn’t a true equivalent which a clone would be, but it has same grid spacing so behaves similar the plate can’t quite get to the 75watts they held it back to 65 watts, and chose more practical, base for domestic audio. I don’t think Svetlana designed a new valve they took a hugely successful valve which Thomas Mayor says was built more than any other valve in same envelope, and based their design around it’s success. It’s a shame the Chinese emulated the px25 so badly. If Svetlana had done it they’d have got the grid spacing right.

[steve s]

Paul, have you been reading that artical I linked to where the 811 was measured very low distortion.
They also measure various 300b's and most of them where low distortion too

In my view that does not mean that the sound will be equal.. In that artical they state the bass was more 'tubby' on the modern production and I would read into that their replay system and their ears was not up to the obvious differences we have heard

Enough people heard my 300a's in nicks amp at eggy, then a few brought 300b amps to mine. The difference was not just the bass, the old girls where more musical, when the distortions where around same level... excluding the bass where it was much worse in some of those modern valves. I'd speculate the old valves work better into higher impedance loads than modern production provides.
I'm not sure if that aspect would show up in distortion test without changing the load as they test. Quite a failing in the way amps are generally tested as most speakers impedance is way from constant
Theres much more to a good valve than similar stock measurements in my view.

I have heard that 300b/px4 era sound on ( I'm pretty sure was) wills 801 amp. If I remember correctly will said the 801 was a step up on the 801a.

[ed]

Hi Paul
that's a gargantuan effort you're putting in there..way beyond my attitude, which is still firmly based in 'if it sounds good it'll do'...
however, I did do more than a few experiments back in the day and from memory I concluded the best figures came from the 572 but I couldn't tell the difference in sq....

it was a long time ago and I'm not sure if this is any good to you but this is the last set of results I got from 811-3...not sure without finding my notes if this was at 3.5 watts....but I think I got the same sort of result all the time.

there is a later set of distortion figures shown 3/4 way down this page. I think it relates to SV572-3.
http://www.vitalstates.org/diy/amplifiers/vsl-sv572.htm

also

http://www.cityfujisawa.ne.jp/~rsekido/ ... rtion.html

[JamesD]

Fascinating thread!

I do a graphical distortion analysis too but its simpler than Steffie's and based on (I think) on some work Voltsecond did.

I found that the PT15 doesn't like lots of current but does like lots of volts with a higher load for best performance and power out. In triode mode its very happy at 600-700V and 50-60mA with a 8K to 12K load...

Really enjoying the discussion of where to drive the 801 and 811... and A2 as well

James

[Paul Barker]

Yes to all that you all said.

Because of my dyslexia it’s very hard in the event tor me to measure it all up and input the data to my little distortion calculator spreadsheet. Sometimes the reu;t makes you check it and check it you know check what youve done, have you put something in the wrong column. Dyslexia means you make a error while you are fully focusing with all youre attention and in youre mind you areconfident youve got it right, but a normal person would see loads of mistakes. But when it comes to geting the right measurements from the right place and you have’t slipped along the grid lines to the next one in error and all the many other ways to fail. Just for a dyslexic mind that is a half days solid hard work with sweat dripping off you from conscentration.

So no progress yesterday. I got two callouts which were pleased about. Barely any work at all on average ive had one callout a week at worst one a fortnight.

I don’t know about the rest of you but I’m waiting eagerly to see how the 211 fairs in this 801a operating point were using as a base. Don’t forget the 811a and 211 aren’t planned for constraint to 7 watts. The whole excercise began because of the horrific sight of distortion that probably begins ruining things 2-3 watts before clipping, and it seems very sensible to harness instead a valve that costs no more, has pretty similar operating condiiton at the 801a’s various common quiescent points, but bags of headroom, and offers opportunity to tray various current levels. But will give the 7 watts linear to the end of 7 watts but thta won’t be juts prior to clipping, clipping is distant!

[Paul Barker]

sorry that post is hard reading with all those mistakes. Im sick 0f editing everything ive posted straight after its posted . sorry if some people are very anoyed by my literary errors.

[steve s]

Paul, which ever valve you use would be a good choice, good audio is all about the speaker and amplifier combination, one needs the feed the speakers what they need..you need to be happy the output will be sufficient and clean at the levels you need.
The 211 is a good valve, nicks amp always impresses, and I would guess your best transformers are perfect for the job.
But I'm sure the 801a would be great too.

I'm lucky that with speakers at 102 dB each, I'm right at the low end, and let's me explore oddities as far as amps are concerned.

Cheers..