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PostPosted: 06 May 2010, 12:49 
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Location: Las Vegas Nevada USA
I'm starting a new project (before finishing my existing ones but what the heck) to design and build a GM70 SET amp. I don't see a whole lot of circuits out there and could use some advice.

I already have the GM70 tubes and power transformer, and I have my OTs picked out. B+ will be about 1.2 to 1.3kV. Fortunately I live in an extremely dry environment and don't anticipate corona problems. I have 10kV rated hookup wire to use inside the amp.

I'm looking for a tube (triode) to drive the GM70s. I've come across several possible Russian tubes that might work although I'm perfectly willing to use any tube that will do a good job.

In my 300B amp I'm using a 6SN7 driver. I haven't yet done the calcs to see if that will work with a GM70. I definitely want something easily capable of driving the GM70 to full power.

I'm not familiar with a lot of foreign tubes out there and don't really know what's available. Any suggestions for a driver tube for a GM70 would be appreciated.

Thanks.

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PostPosted: 06 May 2010, 13:21 
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Location: Vänersborg, Sweden
6E5P!

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PostPosted: 06 May 2010, 14:35 
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Soundbrigade wrote:
6E5P!


Holy smoke! $2 a tube! The noval sockets will cost more than the tubes! The specs look pretty good.

If I want to run these tetrodes as triodes would I connect g2 to the plate, or to the plate using a resistor, or what??? The data sheet I found is sketchy and in Russian.

I also found a link to a way to connect the screen to the plate using zener diodes bypassed with caps, link here:

http://www.t-linespeakers.org/tubes/triode-trick.html

Any comments on the method this guy uses?

Looks like a good suggestion. Thanks.

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PostPosted: 06 May 2010, 14:59 
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You have data for both 6E5P and GM70 as well as schematics here: http://www.pastisch.se/tubes/lampa/Glava%202-3.pdf

Complete book here: http://www.pastisch.se/tubes/lampa/lampa.htm

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PostPosted: 06 May 2010, 15:11 
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Soundbrigade wrote:
You have data for both 6E5P and GM70 as well as schematics here: http://www.pastisch.se/tubes/lampa/Glava%202-3.pdf

Complete book here: http://www.pastisch.se/tubes/lampa/lampa.htm

Thanks, but unfortunately I can't read Russian. I did manage to find a datasheet for the 6E5P that had some English in the description, and I have plenty of good data on the GM70.

What I really need is some information in English on the 6E5P and some schematics in English of some SET amps using the GM70.

I'm sure I could get the 6E5P to work with the limited information I have, or maybe glean something from the books in Russian if I look at them long enough, but a full datasheet in English would be nice. I suppose if that were available the tubes would cost 5 times as much. :(

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PostPosted: 07 May 2010, 00:59 
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Hi sample...

got a useful datasheet:
Attachment:
6E5P.pdf


You will find a "ready to go" circuit on Magnus' attached .pdf (http://www.pastisch.se/tubes/lampa/Glava%202-3.pdf).
I also have another datasheet for the 6E5P, but the filesize is a bit bigger than allowed.. (280k)...

Hope that was a little help ;-).


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Some of my projects: TDA2050 Chip Amp, the LM3886 Gainclone Thread and the Szekeres Headamp Thread.


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PostPosted: 07 May 2010, 05:42 
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I think the gain 6E5P in triode mode /grid to plate, mu <50/ doesn't enough for driving GM70.
6E5P in tetrode mode has very nice sound! /I tried with 6S33S/.

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Projects: OTL 6AS7 Gen, Electric, SEs 2A3 RCA, 300B JJ, 6S4S, 4P1L, EL11 Telefunken, 6AS7 RCA, 6S33S, 6S41S, 6S19P, PP 6005 Gen. Ellectric , headphone ampl. OTL Loftin White 6AS7 RCA....SE E84L& E80CC Siemens&Tel-n.
http://azazello-sound.blogspot.com/


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PostPosted: 07 May 2010, 09:12 
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azazello wrote:
I think the gain 6E5P in triode mode /grid to plate, mu <50/ doesn't enough for driving GM70.
6E5P in tetrode mode has very nice sound! /I tried with 6S33S/.

That's what I was concerned about. I have no problems using it as a tetrode though. The GM70 is all the triode I need.

After looking at the book some more is obvious I should have been looking at the rM-70, not the GM-70 (I assume an "r" is a "G" in Russian).

The circuit looks simple enough. I guess I'll order a few 6E5P (excuse me, 635n).

I actually found a PSPICE model this morning of the 6E5P. If I can find one for the GM70 I can model the amp before I build it.

Thanks.

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PostPosted: 07 May 2010, 09:27 
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Soundbrigade wrote:
You have data for both 6E5P and GM70 as well as schematics here: http://www.pastisch.se/tubes/lampa/Glava%202-3.pdf

Complete book here: http://www.pastisch.se/tubes/lampa/lampa.htm

Nice book. It just took a litle time to get past the Russian.

I'm used to self biasing with a cathode resistor. Looking at the circuit, it appears the grid bias is set by a negative voltage source and the cathode is almost, but not quite, grounded. If I use a DC source for the heater/cathode, can I omit the 10 ohm resistors and diodes and just connect one end of the cathode to ground and the other to the DC heater source?

Thanks.

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PostPosted: 07 May 2010, 09:37 
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The 6E5Ps are on the way. Looking at the curves this looks like a very linear tube. If the curves are any indication it should sound good. And they were LESS than $3 each shipped from Ukraine, NIB, manufactured in the famous (infamous?) "Reflektor" factory.

I'm feeling good about this amp now. Thanks for the help and suggestions.

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