My cat Izzy bought a quad of 6550/KT88's tonight

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Re: My cat Izzy bought a quad of 6550/KT88's tonight

Postby Unit_1 on Tue Feb 09, 2016 3:24 pm

Papa Dog wrote:I have heardm but cannot site authority, that the Svetlana "Red S" tubes are so branded for sale on the American market, but are not made by the Russian Svetlana, but instead at another factory which makes tubes for a variety of vendors.

CE dist./Antique Elec. WAS the US distributor for authentic "Winded =C=" tubes.
Last time I checked there was no more "Winged =C=" and the plant had closed down.
So...if that is the case, and they are still closed, any "new" "Winged =C=" are either pulls or "NOS".

Hope I can get a couple quads of those before they run out.


The new Svetlana group bought all the equipment and rights from =C= when they decided to sell "because the market was dead". What they didn't know was that thanks to eBay, the market was about to explode and tube amps were ready to be the first choice of the serious musician. Oops!

I forget the year, but it was a while ago and what's left is what's left. CEDIST sells for $199 *a pair* at wholesale. Ouch! Just glad the new owners use the S mark instead of the =C= mark so it's easy to tell, 'cus I have some EL34's of each kind and just by looking at them you cannot tell the difference except for that.

I've been reading a lot about KT88's in the past few days and a load of people say the new gold lions are better than the old =C=. Of course it's all subjective...

Others insist the PSVANE KT88 treasure are the even better, but some disagree.

And I have tinnitus, with high C sharp and high E screaming away 24/7, so subtle nuances are lost to me. I can tell I like the KT88's better than the EL34's for super loud grunty chunky rock and the tele clean, but thinking I like the EL34's better for acoustic.

Drats. Who has $1000's of dollars to buy them and compare, certainly not me. Wishin' I did tho.... :blah:
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Re: My cat Izzy bought a quad of 6550/KT88's tonight

Postby Papa Dog on Tue Feb 09, 2016 4:08 pm

Unit_1 wrote:
which means I can go ahead and bias these without worrying about a real short. I just wanna see how they sound. I went back and looked at other winged C's I have and almost all of the exhibit more grid leak than other tubes. maybe it's part 'of their magic???



not sure what you mean by "grid leak" on this context.
maybe we should construct a lexicon?
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Re: My cat Izzy bought a quad of 6550/KT88's tonight

Postby Unit_1 on Tue Feb 09, 2016 7:29 pm

not sure what you mean by "grid leak" on this context


On my tube tester you can test for shorts, emissions, filament lifespan, and grid leakage.

Shorts are what they sound like, unless grid leak is really high and then on the H to K short setting (not sure what H to K means) it will appear as a short after the tube is fully warmed up. If you check before the tube is really warmed up, it does not appear as a short.

WHY they have a light that shows the same thing as another test is beyond me.

But anyway, first you test for shorts. On most tube testers if you get a short you stop there. On mine it has built in protection so you can continue to see what the rest of the tests come out to. Then you test for emissions, mine is rated in percentage going up to 120%. Never seen anything past 98 and that was a mullard 12ax7.

Then you test for filament life span by leaving it on the emissions setting and flipping the life test switch. If the emissions then go into the red, the tube is destined to die soon, so you don't use it, or just use it until a new tube can be obtained.

After that is the grid leak test. This should be very low, but on =C= tubes, even the 12ax7's I have, they all seem to be pretty high but still in the green zone.

I'm surmising that this is the flow of electrons that was supposed to be passed to the grid, but wasn't. Seems logical. But, if the grid leak goes into the red, then you also have a bad tube. I had two that were 100% grid leak, they were both sovtek 12ax7's and in just minutes after testing with 100% grid leak, the emissions went to zero.

The crazy thing, is that I do the grid leak test on the KT88's and it bounces around from 20 to 80, all over the place. I've read that the KT88's don't play nice at low voltage, and in fact one guy said
"don't bother buying my tubes if you're going to test them on a 250v tester because they will fail and I'm tired of paying for freight. I know what I'm doing, I have a 500v tester and they test JUST FINE at 500v. I also have four other testers and they fail on all four"


I'm thinking it would be like trying to use a rocket engine that's designed for 5000 pounds of thrust, with fuel pumps designed to deliver only half the fuel. FLAME OUT!

:dunno: MONGO ONLY SMALL PAWN IN GAME OF TUBE TESTING

All I know is that these sound damn good, except the buzzy hum is kinda loud, but not noticeable while playing. This is even with no input cord attached.

I'm going to try the other pair in my Hiwatt DR504 clone today. It's got PIO caps and is extremely quiet with EL34's. My plexi clone has Mustard caps, and they're a little buzzier than PIO caps.
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The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
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Re: My cat Izzy bought a quad of 6550/KT88's tonight

Postby Papa Dog on Tue Feb 09, 2016 10:44 pm

H to K is Heater to Cathode.
In this context it sounds like "grid leak" is current coming off the grid...I would have to pull out data sheets to learn more.
Gring is SUPPOSED to cause more electrons to go to the plate or anode, and the signal going IN is supposed to "modulate" that flow...in other words, making the grid more or less negative in ration to the cathode. Which is where the concept of a "grid leak" resistor comes from...how far from "ground" potential the grid is...usually, the higher it is the louder you will (within the limits of the tube and the rest of the circuit).

SO...O am still not sure what that really means in terms of your tester.

Now...the issue with hum. With 6550s (those are not true KT88s, but higher voltage rated 6550s) you have to improve the power supply filtering somewhat. Almost anything built for el34s will have less filtering. So, add 200mfd of filter and it should quiet right on down.
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Of cabbages--and kings--"
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Re: My cat Izzy bought a quad of 6550/KT88's tonight

Postby Mr. dB on Sat Feb 27, 2016 1:42 am

Unit_1 wrote:
These look sort of 6L6-ish, does it take much to use them instead of 6L6, or EL34? Those I have....



You'll need more B- voltage to get 6550/KT88 to bias properly. A bias supply designed for 6L6 or 6CA7 will run 6550s way too hot.
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Re: My cat Izzy bought a quad of 6550/KT88's tonight

Postby Unit_1 on Sat Feb 27, 2016 3:18 am

Mr. dB wrote:
Unit_1 wrote:
These look sort of 6L6-ish, does it take much to use them instead of 6L6, or EL34? Those I have....



You'll need more B- voltage to get 6550/KT88 to bias properly. A bias supply designed for 6L6 or 6CA7 will run 6550s way too hot.


Yes Sir, you are correct Sir!

I had to remove a resistor before biasing as for the one/half second that I had it turned on it was at 120% at full b- {{{{yikes}}}}. :shock:

Interestingly, someone just put up an auction for another quad of =c= 6550s on eBay, free shipping for $99 :say_what: . Of course I bought them as fricken quickly as I could, since the price for these wholesale at CEDIST is $400!!!!!!! I don't actually have enough amps to use all these tubes, so just storing them away for now. :ROFLMAO:

and then there's the quad of =c= KT88's that I bought 2 weeks ago for $110 free shipping. I'm like dreaming, right? I have to keep taking them out of the box to make sure it's not a dream..... :mrgreen:

the 6550's sound SO unbelievably awesome in my circa 1967 jtm50 plexi model 1987 I made with mustard caps, mercury iron..... at full volume it's a dream like chunky, grinding thumpy experience beyond compare..........

:highfive:
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The ability to play/make music is a gift that not everyone gets. Those of us who have it should use it.

Asimov:Individual science fiction stories may seem as trivial as ever to the blinder critics and philosophers of today — but the core of science fiction, its essence, the concept around which it revolves, has become crucial to our salvation if we are to be saved at all.
Unit_1
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Joined: Mon Oct 03, 2011 3:29 pm
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