How tall are kt66 tubes in real life?

[deci belle]

The GEC KT66 datasheet says that the tubes are 135mm tall including the key.

That's 5-3/8"!! Dang!

That means I can't use kt66s in any of my fender amp heads.

How tall are KT66 tubes in real life?

[martin manning]

JJ's data sheet shows 125mm (4.92") from the key to the top.

[deci belle]

Oh— yeah, the data datasheet I saw was for the old production ones that cost a zillion $$. Thank you Martin!

Are the old style kt66s really as tall as they say @ 135mm?

[martin manning]

It seems so, although Genalex's sheet says overall length 125-135mm, seated length 111-121mm, which is quite a range!

[deci belle]

OK!

[Tom Phillips]

It seems so, although Genalex's sheet says overall length 125-135mm, seated length 111-121mm, which is quite a range!

I measured the seated length of the one real Genalex KT66 that I have and it was 112.5mm.

[deci belle]

Hi Tom!

If you ever get around to it, I'd love to know what the total length of that tube is— that way when s'body is selling one on ebay, I'll have an idea of what length I can specify that works for my amp, like I already do when buying short-bottle 5u4gbs to clear my tweed twin head!!

I say that because I need to have a figure to give to the man who is going to make a custom-height Fender tweed-style head-cab for me that will clear real GEC kt66s without looking weirder (too tall) than necessary.

[Tom Phillips]

...I'd love to know what the total length of that tube is...

The contact pins are 11.5mm long and the center key pin is 15mm long so the overall length of my sample of one is 112+15=127mm.

I'm not really sure of your approach but I'd expect that you would plan for tubes at the max limits of the specification range if you are going to have a custom cab made. (Plus room for cooling air circulation. Another issue is that current manufacturers are not very good about adhering to the original tube specs. Because of that you are on the right track in checking lengths before buying.

[Justin Thomas]

I learned the hard way - use the TOTAL unseated length for heads, then add a bit of wiggle room. I've had tubes that didn't fit the head unless I pulled the chassis out and installed the tubes, then reinstall. Kinda annoying!

Justin

[deci belle]

Thanks, you guys!!

The man who already spec'd my new tweed head (JD Newell) wanted to be sure. My current tweed head is 10" overall with almost 4" room for inserting tubes (100mm).

So, as it stands now, it'll be 11.5" overall height for a custom tweed head to clear KT66 tubes, weird-looking or not… that's 1/4" to spare over the CEG max length.

Thanks everyone for helping me decide what height I need to make my new tweed head. The bf-style will be easy to figure out now!!

That was an important consideration we had do work out, Tom (cooling). The front of the cab will be open behind the grill-cloth and the back-panel won't be there at all …just a 2" strip along the bottom of the cab so stuff won't roll out when transporting

[Justin Thomas]

TONE is more important than whether an amp "looks funny..." Just sayin'!

Justin

[Jammin'John]

KT88

They are tall.
I gave them a lot of room in my amp.
The 66 is the one in the middle.

JJ

[WesG]

Somebody (Tung Sol?) makes short-bottle 6550s if you're interested. We use these in Leslie 222 and 247, any taller and the horn won't clear.

[deci belle]

Yow! that is tall, JamminJohn— thank you for posting the picture for me!

I still don'tknow anything about 6550 tubes, Wes. I'll find out about how those sound— thank you for the suggestion!

[Leo_Gnardo]

I still don't know anything about 6550 tubes, Wes. I'll find out about how those sound

6550 was conceived as TungSol's build-up of 6L6 - at least as they were in the early/mid 1950's. And TungSol did a creditable job, the originals are a favorite in Leslie amps for instance. By the time GE released their 6550A in the early 70's, crisp & clean was the goal, and GE certainly met it. A sextet of these in SVT is formidable.

Of course the current TungSol is a bought-and-paid-for marque used by New Sensor to sell their Saratov Russian made tubes. Whether they match the original item in performance, well I'll leave it to others to report. The painted-on logo sure looks good!