Tung Sol KT66 and pre-PI cap?

[firemedic]

Yes I'm still tweaking my 40W 5e9 tremolux w/ one tube reverb, tone stack, etc. It's frustrating sometimes but I can't seem to stop. Still messing w/ the tone via cathode bypass caps & preamp coupling caps.
Two questions: can I pop in KT66s in the place of 5881s? I am using pin 1 as a terminal. I also have a pentode/triode switch, will there be issues? They are also huge tubes; possible overheating problems?
2nd, I am using the 5E9 Tremolux driver circuit, with a JAN balanced 5751. It's not a LTP and it's not a split-load driver. I don't know what you'd call it. But it works so I don't want to mess w/ it. I notice that a lot of amps have a coupling cap just before the driver input, but mine does not. Would my amp benefit from one of those caps, or if not, why?

[navdave]

Nope you don't need a cap there it's a paraphase inverter.
Im pretty sure you don't need to to have pin 1 tied to ground when using kt66's.
Kt66's do draw more heater current than 6l6's 0.9 amps verses 1.3 amps so make sure
your PT can handle the extra current.

[firemedic]

I'm seeing a lot of angry reviews elsewhere about the Tungsol KT66. Pin 1 is tied to the metal base which causes shorts across the retaining clips. Guys are melting these things down. I don't have a problem moving the connection off the pin, I hope it pays off in tone. Plus the heaters draw 0.9A like a 6L6, & even though I probably got ripped off, I didn't have the extra filament juice for real KT66s anyway. So there it is.
Does anyone know what to call my driver?   

[navdave]

Well then that sounds like a 6l6's guts stuffed into a bigger shoulder glass bottle a FAKE!
A real KT66 will draw 1.3 amps.
I had a quad of Chinese KT66's from Lord Valve in my 74 Sunn Model T and they were great!

[sluckey]

Does anyone know what to call my driver?

Nope you don't need a cap there it's a paraphase inverter.

[firemedic]

Paraphrase inverter, sounds literary. I thought the term referred to the cap itself going to the driver. My bad.

[jjasilli]

Nope you don't need a cap there it's a paraphase inverter.
Im pretty sure you don't need to to have pin 1 tied to ground when using kt66's.
Kt66's do draw more heater current than 6l6's 0.9 amps verses 1.3 amps so make sure
your PT can handle the extra current.

I checked Frank's Tubes:  the very old specs show NC (no connection); the newer specs show IC - which I interpret as Internal Connection, confirming your post.  The Pin1 connection is always iffy - depending on the tube type.

I have no experience with kt66, but am prepared to believe they are a great sounding tube. 

[firemedic]

I have moved my grid resistor connection off of pin 1 of the sockets. The Tung-sol "KT66"s seem to work fine, & bias a little lower than then the 5881s they replaced. But I have a nagging feeling...

I really don't know WHAT kind of tube this is. If it supposedly draws 0.9A it's like a 6L6. But there is a pin 1 and it's internally connected to the metal tube base. Who knows what else it is connected to in there? I'd like to ground pin 1 now just to be thorough but I really don't know if I should. Or connect it to the cathode? I'm using cathode bias.

I can't report on the tone yet since my test speaker is an old POS w/ no cab. I just know it works & sounds at least as good as a 6L6. Does anybody know more about these Tung Sol KT66s that aren't really KT66s?

[navdave]

I really don't know WHAT kind of tube this is. If it supposedly draws 0.9A it's like a 6L6. But there is a pin 1 and it's internally connected to the metal tube base. Who knows what else it is connected to in there? I'd like to ground pin 1 now just to be thorough but I really don't know if I should. Or connect it to the cathode? I'm using cathode bias.

From Lord Valves catalog:

REFLEKTOR/TUNG-SOL AND SOVTEK KT-66
Neither one of these is actually a KT-66, so I don't carry
either of them.  The Tung-Sol is a set of the Reflektor/
Svetlana 6L6GC guts (albeit with a beefier screen) mounted
in a KT-88 bottle - it neither looks nor sounds like a
KT-66, and does not test like one.  If you need this
particular tone, it's available much more cheaply as the
Reflektor/Svetlana 6L6GC.  As for the Sovtek KT-66, this
is again a set of 6L6 guts mounted in a KT-88 bottle.
(Looks like the 6L6EH got the nod on this one.)  Frankly,
I have no idea whey they even make either of these.
PAIR..................................$NOPE
QUAD..................................$NOPE

[firemedic]

That's what I thought. Thanks navdave.
But they still look cool as hell, and there is a clear difference in the way it passes treble freq., obvious even to me compared to 6L6WXHs anyway. Much less harsh. I'm still tweaking my preamp circuit but am very close to completing this thing, at that point I'll really compare all my power tubes.

[PRR]

phase, not phrase. Very audio, not literary at all.

6L6 was originally metal and the shell was tied to pin 1.

6L6G came soon after, on a plastic base, pin 1 was not connected (often missing). People forgot this, and stole lug 1 for a cheater point.

Using Lug 1 for a tie-point is short-sighted. Yes, Fender got away with it; this is one detail you should avoid.

6L6/6L6G was so very popular that the Europeans had to have one, only better. It isn't easy getting 6L6 performance with just 0.9A heater power, they went for 1.3A and a bit better plate dissipation: KT66. This idea came back around to Newark as the 5881, higher real dissipation than 6L6/6L6G but still on 0.9A heater.

All three tubes are 99% interchangeable, and we often didn't care which we got. Most chassis will bias fine and won't mind the heater current.

6L6GC is a very different tube, an economical TV sweep tube built to work in 6L6 et al sockets but with significantly higher (yet understated) ratings.

What you get today is whatever will work in an amp. I doubt anybody has made separate tooling for 6L6 versus KT66 in decades, though if they have both stampers hanging around from the 1950s they may use both stampers (for either tube). Likewise if they have miles of 0.9A heater-stuff, and can make a good tube with it, why fool with special 1.3A heater wire? Also the technology of TV tubes improves the economics, and I suspect many "6L6GB" and "KT66" are more like 6L6GC than like the originals were in the 1950s.

> look cool as hell

That's the most important thing.

[firemedic]

Paraphrase, paraphase. I have an optometrist appt next month, after that I can learn to read. Baby steps.
This tube sounds pretty good to me, I get the sound I was looking for with it which is all I can ask. It's pretty alive & responsive. And I didn't have to pay for NOS.
I do have some JJ 6L6GCs that I will soon compare, but the JJs always sounded sort of flat while I was tweaking my build. Not holding my breath.
I did discover the world of 12AU7 tonight, I popped one in my preamp today and life is good. Very expressive.