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nina 29th March 2008 04:14 PM

GU-50, GM70 and KT88

I wonder how its linearity is at ~400Vdc in triode mode/single ended. Any one has Triode curve of GU-50?

For single ended operation, how is this GU50 tube compare with KT88 and GM70?


ErikdeBest 29th March 2008 05:59 PM


A google search for GU50 triode will reveal good results! I read somewhere that triode connected, the GU50 can take up to 400V (due to the limitation on G2).

I am also curious how it compares soundwise to a KT88... The GM70 will need some more volts on its plate, Brett (member) said it starts singing from 600V onwards.


nafanja 30th March 2008 09:07 AM

Triod variant is fine
This military tube have a good sound for Se and PP, in triod variant.

Have a big time of work.

Good soud with according 6E6P, 6E6P drive tube.

Tweeker 30th March 2008 10:11 AM

I have Russian datasheet with triode curve, is too large to attach.

80ma 400V is limit as triode.

I suggest 4Kish load.

Tweeker 30th March 2008 10:52 AM

From my running of the curves at 400V 80ma, as you go into high impedances, you start trading off: more 3H, less 2H and less power. Is nice tube.

GM70 needs more volts and has a 60watt filament.

ja2dhc 30th March 2008 11:29 AM

GU50 is a Russian version of Telefunken LS50 whose data sheet
can be down-loaded below.

I purchased a Chinese amp using FU50 Triode Connection
Parallel single ended. FU50 is Chinese version of GU50.
My amp Manufacturer's Web page is below.

The schematics is indicated at the bottom of the Web page.

My amp is introduced in my blog(in Japanese) as below.

nafanja 30th March 2008 11:53 AM

For ja2
I am send You the letter, please look e-mail and my missage

Tweeker 30th March 2008 01:52 PM

The Russian tube, while a copy, is not quite identical to the German.

rdf 30th March 2008 02:22 PM

There's a thread somewhere here concerning G2 limits of the GU50. The rather contentious consensus was G2 is more power than voltage limited at lower B+. Use a screen resistor, monitor G2 current and voltage, watch the product of the two. I've run it up to 600 VDC and heavy A2 on the bench without issue for about 12 watts SE into a 10k load. FWIW, I very much prefered the harmonic signature of the GU50 into that load over a KT100.

nafanja 30th March 2008 08:17 PM

Asd far as i know Russian GU 50 is a copy of Telefunken tube.

But spectral analise may show the difference.
But VA parameters the same.

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