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Old 18th April 2003, 01:13 AM   #1
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Default KT81 data sheet?

I've recently acquired four very pretty Emitron (but presumably made by GEC) KT81. A search suggested that they might be equivalent to 6V6, and they look about the right size. Does anyone have a full data sheet?
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Old 18th April 2003, 01:48 AM   #2
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Default KT81.

Hi,

Did you try a search on the the 7C5 yet?
It is a loktal glass-pressed base, isn't it?
EL22/M/N148

This site may be helpful, it's in German but just send me an e-mail whenever you may need translation:

KT81

Cheers,
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Old 18th April 2003, 02:05 AM   #3
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Default This is all very embarrassing

I took your suggestion, and looked for 7C5, which was duly quoted as 6V6 equivalent on one site. I looked further, and finally hit Billington's who said that it wasn't an equivalent to 6V6. (Didn't say it was a "potential audio type," either.) Finally, I did what I should have done in the first place, and looked it up in the Vade-Mecum. It's a KT61 equivalent on a pressed glass Loctal base.

In my defence, it's not in my GEC books!
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Old 18th April 2003, 02:13 AM   #4
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Default KT81

Hi,

LOL.

For Pete's sake don't be embarassed....this type was only produced for a couple of years.

Quote:
It's a KT61 equivalent on a pressed glass Loctal base.
Funny, I'm usually faster at getting results using the net than by looking for my books...

Cheers,
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Old 18th April 2003, 02:23 AM   #5
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Default Frank's site - a worldwide treasure

I agree. Since finding Frank's site, I don't often use my data books. However, today I needed to look up valves that just aren't on Frank's site. Gasp!
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Old 18th April 2003, 10:46 AM   #6
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...I have several tube/valve manuals, some going back to WWII, and find they are often 'generous' it what they assume to be equivalents - especially in finding equivalents for KT series valves. So while they confirm that the KT81 and KT61 are electrically equivalent, some maintain that the KT61 is direct equivalent of the EL33, despite the slight difference in heater current and greater differences in electrical characteristics.

Last year I acquired an AC/DC amp which used KT71s in pp output, and one manual suggested 50L6s as equivalents, despite the differences in electrical characteristics, and not even the heater voltage and current are the same, issues which are of particular importance in AC/DC circuits.
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Old 18th April 2003, 03:09 PM   #7
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Default This is what the fuss is about

Now that I'm reasonably certain the a KT81 is electrically equivalent to a KT61, I can think about how to use them with my pair of dinky Partridge 10ka-a output transformers. The Leak TL/10 is the obvious starting point.
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File Type: jpg kt81.jpg (62.4 KB, 146 views)
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Old 20th April 2003, 01:07 AM   #8
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Quote:
Originally posted by bournville
I have several tube/valve manuals, some going back to WWII, and find they are often 'generous' it what they assume to be equivalents - especially in finding equivalents for KT series valves.
I agree. I've never greatly trusted the "Radio Valve" manuals etc, but I've now decided that I don't trust the manufacturers' manuals either when it comes to equivalents. After all, they had a vested interest in making you "Brimarize" your kit, or use GEC valves. Sadly, the more I look at it, the worse the KT81 looks electrically. Yet it's so pretty.
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Old 20th April 2003, 01:28 AM   #9
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Default SAME, SAME BUT DIFFERENT...

Hi,

When it comes to equivalents I only trust the straight tabels of US to European and vice versa conversions.

Anything else you'd better cross-check very carefully.

Sample: 12Ax7A > ECC83 and than it goes on to the 5751...ah not quite the same thing, is it?

Caveat emptor,

P.S. Brimar? They must have come from Krypton.
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Old 20th April 2003, 03:48 AM   #10
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Hi,

I dont know if this is helpful but I have a GEC valve manual from 1952 that list the KT81 as "Obsolescent type"

Summary data is give as:

Heater 6.3V 0.95A

Va max 250V
Vg2 max 250V
Gm 10.8 ma/V

Typical application

Va 250V
Vg2 250V
Ia 40mA
Ig2 7.5mA
Vg1 -4.4V
Rk 90ohm
Load impedance 6000 ohm
Output power 4.3W

I have socket diagram also but I dont have a scanner but if needed I can take digital picture of the page and post on the Web.

For me KT81 seem to be quite far away from a 6V6, the Gm is more than double and the max Va is very low. It look indeed very similar to the KT61 that is given with typical application data identical to the one given for KT81.


Regards Hans
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