6550 SE Amplifier

[Paul Barker]

[andrew Ivimey]

I like it ! A grid choke - I like it more. I've got 'a few' 6550s and they are hungry heaters current but apart from a guitar se amp I've only been thinking about I've never made any progress...

[Mike H]

In case you weren't already aware -

"The ECC88 is a VHF double triode with separate cathodes. The ECC88 was designed for service as a cascode amplifier in the front ends of VHF radio receivers. One triode acted as the local oscillator and the other as the mixer (frequency changer)." - (The Valve Museum)

Ergo I would think grid stoppers are advisable.

[Paul Barker]

Thanks for the warning Mike? One of my books might be Rosenblit explains its designed for cascode. If you look at the table there are the numbers for operating casc. I take it, casc. Abbreviated cascode. The book has values. Cascode if I recall, benefits similar to pentode but ? some benefit. Maybe I should find the book, then the page, then the sumary of benefits.

Anyway kiss these days. I may have swallowed too much Sukuma San etc back in the day and passed over simple stuff that worked fine for decades, before the 300b lovers Japanese came to town and westerners knew nothing all of a sudden.

Now its all Mofos and Mosfets era.

Im going back to pre- Japanese are gods with dht’s transformers and specially treated Louthers era. I may have moved too quickly away from RCL etc

Next obstacle; yet more resistors on order for one thing, and other obstacle lockup is in Flixton where the 6550’s are. I tried to ram a railway protecting iron fence with my van. Van right off, fence a little paint on it from van. Im saying Black Ice, because there was black ice around. Reality is Im under too much stress at home and conscentration lapsed. I have a car i sorn about four years ago. It might get an mot.

Meanwhile its combination of Brompton and bus pass to go look for 6550’s. There will be a delay beofore the youtube upload.

Cant spend the money to make high efficiency stuff for 1 watt amps. This design from kef suits my ears.

[Paul Barker]

Sorry about giving up on the 6EM7 all of a sudden. Whats the point in a 1 watt amp if you dont have hundreds of pounds to try making a good high efficiency speaker yet again, even though I never got it quite right before.

[Paul Barker]

The grid choke’s bought via Nick, Amorphous decades ago now, used and found better than resistors.

Coupling cap? Well with a grid choke it could be 0.047 but I have some 2 uF paper in oil I’ll try. Who knows how good they will sound. You all shall if you wait for the youtube short. No reason not to try them.

But if anyone wants enough bass you dont need 2, not even o.1 uF to pass bass signals to an amorphous grid choke load. I have also tried doubling up on the grid chokes 20 years ago. The extra benefit not required. Certainly now my ears wouldnt hear a difference.
According to JJ a 1meg resistor is ok. But Id go conservative and half that.



But I have grid choke’s so I’m OK with any cap. Rosenblit bye the way is a lover of a few microfarrads in his coupling caps. I think one circuit has 4 uF I emailed him to find out why. Didnt get a clear answer. Probably picked up on telepathy “go away little Man.” Its maybe about ‘Poles and zeros’ I am not worthy to comprehend.

[Paul Barker]

Oh yer, the cathode bypass cap. Do you know this has been an old long standing obsession between Mike Lefevre (now a drunk, if he is even alive) and Dave Slaggle.

But ignore all that battle. Do you know, that with a SE opt if you limit the bass signal where human ear cant hear it the dc current is less harmful to the bass abilities of the opt and results in better bass where you can hear it? Im not talking about the parafeed capacitor interaction by the way.

[Paul Barker]

Well I got to Flixton on the bus. Those ones I said were Tungsol are Amperex. They were the ones I liked best 26 years ago. But they are all coming back with me.

[Paul Barker]

Maybe it will fit in this little 6v6 build. Bypass caps might be a problem though. Shame if so.

[Cressy Snr]

So they let you on the bus with valves round Scarborough then.
Must get my bus pass sorted.

[steve s]

Is that the roundabout at staxton Paul?.. Nice valve stash too.

[Ray P]

Must get my bus pass sorted.

Me too, just a shame I done have a stash like Paul's to fetch.

[Paul Barker]

Yes and yes. Steve and Steve

Opts actually measure 4.6 k at 8 ohm. So power out 9.96 watts 2nd harmonic 8.3% at 5 watts 4%.

Most valves General Electric about 16 kt88 4 Sovtec 2 Amperex 6550A shoulder shape about 8 TT21/22 not done exact count of the split of the TT’s. But wont put anode caps in as an option anyway. They are all my KT88 types. No KT66 in there, I had four nos boxed KT 66’s but sold them years ago. Have a few equipment pulls otherwise. The Amperex I called Tungsol earlier in the thread, as that is what they really are. They sound the best to my ears.

Well Ray they arent over expensive today. You only need two. I saw the Tungsols available at £60 something each but thee is a proviso, they looked right in the picture, but they may be made in China now. Mine are made in the UK. That is a modern can of worms a lot of stuff that looks nos Western made isnt made in the west. Id buy the Sovtec’s if there are any left because the chinese wont imitate East European made valves, yet! When I get amp running I’ll see how the Sovtec’s sound.

[Paul Barker]

Must get my bus pass sorted.

Me too, just a shame I done have a stash like Paul's to fetch.

Now Im unable to work because of Dianas condition I am trying to clear the lockup as it costs £190 a month and its purpose is heating sstuff for my work, when I worked. So I’ll start bringing the valves back home on the bus. Then get skips for the heating parts and releave that cost. Most of the parts go back 20 years and never needed with the boilers of today. Now effectively went obsolete over the years and so no value and paid rent all those years for junk. Hay ho. But to be fair the business paid for the lockup. I kept my valves there aswell.

There is also a torroidal winding machine down there. So anyway I have an estate car sorn, I’ll scrap the crashed van and try see if car will mot as there is aswell an ifor williams trailer there and car has a tow bar. So I can clear lockup more efficientty than one box of valves a day rate on the bus. But add into the mix keeping an eye on Diana. Its a slow process beyond measure. Everything takes for ever. It took me 3/4 of a day to convince Diana to get her shoes on and come to the bank with me, and it was a horendously painful process because at such times she is barking mad. I dint think shes long for this world. The last event so nearly killed her icu held her unconscious until she stopped fitting and that took 4 days and nights. I dont think shed survive another episode that bad. But I dare not ask her if she has considered Not For Resus, even though it is time for that. However if the consultant asks my view while shes under that would be my view. She isnt enjoying life and shes a complete stranger to me, and a stroppy child but not a nice one. Its murder on my state of mind. But its not super urgent to clear the lockup because I have a 66k mortgage Santandair flexible, which is paid up but its a type you can keep as a zero balance for the full term and pull down the load again as much as you need aslong as at term you can pay the loan back, that is my financial flexibility if it is needed in the medium term. But youve probably noticed from my comments Im being careful with money. 5 yeaars of flexible mortgage with a zero balance and havent drawn any down yet. And hence why not in a hurry to get mobile again. If and when Diana dies I am still in great demand as a heating engineer, and have the owner of the business based near Castleford who told me if I want my full time job back after such a scenario “call me”. Heating engineers with 22 years experience are rare today. So I can work off the draw down of the mortgage so to speak.

[steve s]

When I first met you Paul you where nursing, how the years have passed !

My mothers just gone in a home, dad's been looking after her (he's 93) but in November started having heart attacks, mum took some time to settle down in the home, dementia sufferers don't like change but my dad's a different person now.. his guilt putting her there is subsiding !

council's don't always put a charge on your house, it's worth contacting the council.
It's not easy what ever way you turn. The 1st 12 weeks fees are usually on the council, they may offer you occasional respite care for her too.