6550 SE Amplifier

[Paul Barker]

Finally found a crease in one pio cap, and tiny film of oil on the surface around it. Probably a thump in transit. Sadly I had been swapping the Sovtec’s and 50% arent up to par any more as they arent biasing right. Im reserving the one pair British Made Tungsol’s for when Im sure of all other components.

Ive ordered motor run polyprops 150uF which improves the low pass to 3.8 hz

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Ive also ordered beefier cathode resistors.

So some power valve casualties and a reminder that old stock components can wreak havoc, so best start up a new amp build upside down.

The pio coupling caps have higher voltage tolerance and very sterdy cube shaped thicker walled cases, and those weren’t involved in the cause of runaway.

I’ll wait for the new caps. I’m still trying to solve the old couples heating woes in their Filey bungalow probono, and my wife is still driving me mad. Last night Dragon's Den featured Dementia, I was crying from start to finish.

This wasnt on my mind when I was so happy stood as the star of the show in 1980 Slingsby village church. I was so happy that day. And once again thank you Ray so much for finding me the treet plan from ancient times where I can now see myself proposing to the most beautiful girl in Hull at the time. Even if she has no memory. MS memory loss is the opposite of the common memory loss (or what the medical profession are telling you it is). My father a GP believed it was hidden Siphilis which was never completely eradicated. His sex education to me when I was 16 was to frighten me to death about having sex at all. He said “nobody has convinced me that we can completely cure Siphilis. Lately my Uncle his youngest brother reminded me my father took that stand. I did a little research, there are research papers out there. Its very hard to detect the presence of spirowottsits to prove or deny it is causal fir demensia but it may not be healthy to rule it out. However not a tnhing in Dianas case. MS is known to do this. In 2006 as a gas fitter I attended a lady with MS further down the road than my wife was then. She said to me “My husband has left me, one day you will want to, most men leave their wife when they get like this. One day, youre wife will be a stranger!” Her prophesy whether self fulfilling or otherwise came true. Im fighting the urge to spend the rest of my few resources on another van and ride off to wild camp with a dog.

I have improved my status by staying active at the gym with a coach, and joining my son’s bjj club in town. So I have the toughest crew in town as my bezzy mates. I feel secure. My daughter (a talker) in London phones Diana every day and talks at her the whole time. So she doesnt pick up the truth of whats happening. But my son Sam God bless him see’s my pain yet cant see no blame on my side when he hears arguments from the flat beneath us. But he is quietly beginning to understand. Its a lonely misery but Sam is beginning to see reality. The medical profession completely swerve the subject and leave the spouse to face the music all alone. The benefits system which is broken still havent put Diana on PIP.

That lady with MS in 2006 has helped me. At least I had forknowledge. And one consultant the one who last saved Dianas life in icu holding her intubated 4 days and nights until her fitting ceased. He took me aside with a female staff member to make sure I realised how bad it is. But he never mentioned itnin the discharge letter, so its no use when the twatts who decide not to give pip look at any notes they can find.

Benefits are broken and so is the NHS.

[Nick]

Benefits are broken and so is the NHS.

Instead of looking at whats broken, point your gaze at the ones that broke it.

[vinylnvalves]

Benefits are broken and so is the NHS.

Instead of looking at whats broken, point your gaze at the ones that broke it.

I agree that the current regime is to blame for most of this… however.

I read somewhere that the whole welfare/ heath system was originally costed on people living 3 years after retirement age. So we have an outdated business model for these services. I think I heard on Radio 4 that an average man, only pays enough tax over their full working life to pay for 4-5 years of state pension. ( what’s an average man is another question)

The number of adverts for private health care at £12.99 a month being peddled/ promoted by well known people is increasing. Is this where we are going.

Who ever gets in after the election, has got a hospital pass - ( no pun intended).

[Paul Barker]

Well I vote labour because socialist workers party I sam a funding member and union member dont stand a chance of ever ushering in what they bang on about. But thats how far left I am but not stupid enough to expect it to happen. Their argument is Labour always capitulate once they are in. I just dont want continuationof the Conservative reign. Although the austerity measures were agreed on in a cross party agreement. Its just that the conservatives via Liss Truss took the piss too far. She also is so nervous and stupid nobody even conservative will ever give her the reigns again. Lets hope.

Funnily enough the death of Dave the hairy Biker and the draggons Den on dementia bank account on top of my nice st 6550’s suffering excess current made me somewhat unstable in mental health. But Im coming out of it.

[Paul Barker]

I’m diverting a little. So its about cathode bypass cap involving a cap to b+ to cathode. Now I think that cap was calculated based on mu(or was it mu+ 1?) I recall the concept was to inject into the cathode the noise on the b+ out of phase. As we stand my bypass cap is 90uF polypropylene. There is a slight side story, Ive found a data sheet saying ri of triode connected kt88 is 630 which changes -3db base for 90uF to 5.6hz so I shant require the 150uF polypropylene caps on order but not arrived. So mu is 8 so is the cap to b+ 1/8*90 =11 or 1/9*90=10.

Bare in mind also that the b+ noise is also on the 1/2 ECC88 which is messed with out of phase that way yhe effect of which is a mess in my brain as Im not that cleaver. But is the anti-phase noise amplified to the output valve mu of ecc88 +1. Orbis it by A (actual gain) and in any case neither phase or anti phase =.

Similar issue 2nd distortion of ecc88 antiphase to 2nd distortion of output stage I recall it was lower on the output valve than on the 88. But is it multiilied by mu+1 in bith cases and so

WTF

Thoughts on a post card please?

[Paul Barker]

I guess Andrews distortion meter and a variety of trials would answer my questions.

[Paul Barker]

I suppose I have to seperate the two distotions . The 2nd h is one issue. The poer supply noise is another. Therefore the partial ultrapath cap should be arrived at by minimal 100hz ripple as its not about 2nd h and most power supply noise will be 100hz. But there wont be a firmula as that is also reflected out if phase aswell as the 2nd.

So take the 2nd as is and fix noise with ultrapath cap on the scope.

I vaguely recall the percentage cap was discussed on Triodeel forum before Ultrapath had a name. Our group never gave it a name but it predated Jack Elliano giving a name to his version.

I did like our version in which the ultrapath portion was 1/3rd main bypass cap. But I think though cant remember it was fraction of mu or mu+1 of cathode cap. Anyway that was the starting point we adjusted on test. It sounded better to me.

[Paul Barker]

OK I searched Tube diy asylum and only found one post, by Thorsten, who I didn't like in those days because he plagiarised what I posted as his original thought.

But anyway he is the only person I found in this search to refer to what I recall was discussed on Ned Carlson’s Triodeel forum that was an email group with Stephie and other original thinkers in it. I learned a lot there. But didnt keep that email address so all trace is lost. My closest friend there was Jonathon Noble. But Stephie was the most knowledgeable and always enhanced my understanding.

But in this post Thorsten is on the nail. Though he wasnt a member of the mail list.

upload an album

T is on the nail but he isn’t expressing it in the way it was discussed on Triodeel. The concept was to add a cap, not instead of the cathode bypass cap. So a cap of fraction mu added to bypass cap from cathode to b+. The finding was improved sound of an SE amplifier.

Non of the other posts I found in the search even partially expressed the concept we discussed in the email group. All of them seemed to bang on about parafeed or Western Electrick Ultra Path, which are nothing of the kind. Though perhaps a good thing in their own right.

Remember that diy tube asylum was a battle ground in those days of parafeed vs Series SE, and the battle ground was mudied.

[Nick]

Thorston always was one for his brand. And trying to add a bit of woo by claiming that electrons have no reality is typical of that. The Standard Model may have a view on that

I am with him with the no such thing as ground though

[Paul Barker]

Thanks

[Paul Barker]

So life is slow motion, but Ive fitted the 90 uF bypass caps and ordered two 11 uF 600v polyprops for b+ to cathode. Cathode resistors not yet arrived and with more time available decided it was a stupid number 500, and Ive got that many resistors no longer being used, Ive decided to use the 680 oms parallel with 6k8 ohms for 618 ohms. But Im procrastinating about shall I shant I mount them in heatsinks. Its not as simple as you think. Nothing ever is. They arent made for gold coloured resistors to fit and mount on chassis easily. Unless you slice off one side with an angle grinder first. Nobody said it would be easy!

[Paul Barker]

Oh WOW as if there was nothing more to go wrong. The right channel choke open circuit. Another brand new valve damaged as I put in two brand new USA made military 6550’s.

Lucky I had another grid choke.

Now in 7th heaven. AT last once more.

[Paul Barker]

The power supply is silent. The 11 uF caps from cathode to b+ yet to arive. Probably wont hear any difference. The power is more than enough at home on kef corelli loudspeakers. After Ive permanently fixed it, right now its clip leeded x type coupling cap on right channel 47 nuf, the 2uF pio can go back. The voltage on the grid was 75 when the grid choke was open circuit, and I assumed it was coupling cap beofre I swapped it and found same scenario. So with no continuity to ground anyones guess how come there was music and 75v dc at the grid .p, it found a curious path there. But now with grid choke fixed. No dc. It damaged the valve having abuse like a lot of my other 6550’s.

To recap, it all started with an output transformer fused a shorted primary due to n fuse to fuse it.

Built a 6550 amp, it ranaway. Finally found a pio cap sucking current to ground on one channel. Took me a while to figure the fault. Changed to modern motor run caps. That fixed. Next grid choke dead (note to self use 1 meg parallel to grid choke while testing. Choke dcr is 80k ohm and ac over a meg. So no issues. But would save valves if resisto saves a valve grid from finding voltage a good safety measure.

Bass response great. No issues now.

When all the soldering is done and it can sit valves uppermost. I’ll take it to the room with Quad 57’s in.

[Cressy Snr]

Certainly sounded kick-ass on that video.

[Paul Barker]

Should be 8 watts possibly 9 watts. Erie how there isnt any power supply noise. Maybe there is something in the Jeremy Epstein finding in the Darling Fest write up. Also the triode pair distortion cancelation may work. Even if I cant get my head round it. I’m thinking it may be better done with a driver same as output valve and a pentode first, going really crazy to put 4p1L which Mark prefers. But maybe no need anyway.

I’m thinking of something else. Winding phase splitting interstage driven with 6550 Sowter push pull output Transformers, I bought from John Caswell. Im not against that form of push pull.

You will understand how hard this has been for me. Never used to get many failures, had a few too many and the cost of valve life is rediculous. Good job I had loads, but I yet have to see which are damaged. I know the right channel JAN was damaged with +75v on the grid. Its not biasing as good as the left channel. But you cant hear a difference. At least I tracked down every faulty component, one transformer one choke and one capacitor. Strangeley two sources of over current in output valves. E88cc stage worked perfectly. The gain with unbypassed cathode resistor is excelent. The use of all the b+ to maximise gain in that stage thank’s to Morgans suggestion way back when in Vry’s flat, dominated that success, that and the grid choke, even if it let me down. Grid stopper on e88cc must be working.

The power 630 resistors did get the benefit of a heat sink each and they are not overheating at all. I found a simple way. Good job. The 6k8’s dont need it. Its on about 500 to 510 b+. -44 bias right side -47 bias left channel where valve not given a hard time. I chose the operating point of 450v -46v. Cathode resistor 680r parallel with 6k8 but 5% tolerance, So its about there Formula would say 618 ohm but its about 614, close enough. There are no sounds of stress. But I am including the additional wattage allowance of the grid 2 .

It doesnt have the thick lush sound of the 6080 SE which is heavily 2nd h lush, neither does it have the majic of the 6em7. Its less distorted than both true triodes, but much more powerful in spades. So its a success.