Author Topic: GM-70 tubes  (Read 3761 times)

Offline Tuyen

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GM-70 tubes
« on: January 23, 2015, 03:01:48 PM »
Vintage Russian GM-70 tubes.   What amps have you heard them in and how would you describe their sound?

Cheers!

Offline omodo

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Re: GM-70 tubes
« Reply #1 on: January 23, 2015, 03:09:02 PM »
they make great heaters, not so good in QLD summers!  :P

Offline Tuyen

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Re: GM-70 tubes
« Reply #2 on: January 23, 2015, 03:17:32 PM »
musical heaters..  I like it!

Was given a pair of NOS graphite type tubes.  Wondered if worthwhile looking for suitable iron (most expensive/important part) with the aim to build something for them.     I have to admit I do like the big and clear '211/845' sound.  But then again, I have only heard maybe 5 different amps that use the those tubes and most of them were Chinese :D
« Last Edit: January 23, 2015, 03:19:33 PM by Tuyen »

Offline omodo

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Re: GM-70 tubes
« Reply #3 on: February 05, 2015, 08:33:34 PM »
I wouldn't say mine are overly clear or bright if that's what you mean. I'd say on the warm side of neutral but as always it would depend on the circuit, implementation and voicing. They do sound big, and powerful..


Offline stevenvalve

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Re: GM-70 tubes
« Reply #4 on: February 05, 2015, 09:25:05 PM »
Experience has shown me that in the single ended class A triode world, a lower powered amplifier generally means better sound than a higher powered amplifier. Will a 50 watt GM70 amplifier outperform a 2 watt 45 ?..... Is that true, what do you guys think, does lower power mean better sound.

Offline Peter A

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Re: GM-70 tubes
« Reply #5 on: February 06, 2015, 08:51:16 AM »
Steve,

What did you think of the sound of my STC 4212E amps.

Offline omodo

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Re: GM-70 tubes
« Reply #6 on: February 06, 2015, 09:48:41 PM »
50w would be a slight exaggeration, 15-20w would be closer to the mark, less into a 16-ohm load.

45 SE amps do sound great, are an easy to build and plenty of circuits in the public domain to work from, but as voltage and circuit complexities increase so do the requisite skills. But, better sound or outperform in what respect? there's no perfect amplifier or audio component.

Sure a 45 is able to show great nuance and subtlety, but I feel lacks the scale and dynamic contrasts that higher powered amplifiers bring to the table.

Offline stevenvalve

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Re: GM-70 tubes
« Reply #7 on: February 07, 2015, 01:24:41 AM »
50w would be a slight exaggeration, 15-20w would be closer to the mark, less into a 16-ohm load.

45 SE amps do sound great, are an easy to build and plenty of circuits in the public domain to work from, but as voltage and circuit complexities increase so do the requisite skills. But, better sound or outperform in what respect? there's no perfect amplifier or audio component.

Sure a 45 is able to show great nuance and subtlety, but I feel lacks the scale and dynamic contrasts that higher powered amplifiers bring to the table.
211s and 845s get close to 15-20w, GM70s i think get much more. I had a 211 SE amp that ran 17 watts. SE amps do not have usually have the scale and dynamic contrasts true, unless with say horns, but they do not have the Push / Pull haze either, Great SE amps can really have the illusion of real.
« Last Edit: February 07, 2015, 01:28:03 AM by stevenvalve »

Offline hedalfa

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Re: GM-70 tubes
« Reply #8 on: February 07, 2015, 09:07:13 AM »
Experience has shown me that in the single ended class A triode world, a lower powered amplifier generally means better sound than a higher powered amplifier. Will a 50 watt GM70 amplifier outperform a 2 watt 45 ?..... Is that true, what do you guys think, does lower power mean better sound.

To make an obvious point every valve amp will have then tonal signature of the valves used. Valves that have lower output 45, 50, 300b even el84 have a signature that other types don't have. Yet the ultimate result is still dependent on the design and parts used, so while a single ended 50 or 45 may be excellent in theory, the proof is in the listening. The other problem is being able to effectively drive a speaker. Some even more powerful amps don't handle load well, just talk to Pat Turner about this, poor load handling is poor design however. Just look at how his monster valve amps handle load, just about no body declares the real results of what the amp is doing under load. He has had amps in the workshop with good specified power output but under load they reached high distortion figures after only a few watts. The moral here if there is one, is its the amps actual behaviour that matters. If you have two amps one of 3 watts and one of 20 and they both behave well under load then the 20 watt one will have more real world capability.

I agree with Omono there isn't a perfect amp. Maybe the question is better answered, what is the better amp for? If you have efficient high quality speakers and want to play less complex music with a lot of vocals its hard to go past low power triodes. Yet when you have music that has more scale and complexity low power triode amps have their limits, though by going the extra mile in power supply and output transformers etc this can be offset somewhat.

Push pull fog has no place in serious well implemented push pull design. Sure some push pull amps may sound like they are more foggy, that is due in part for designers being concerned with max power output not controlling the other variables involved. On the contrary a well implemented push pull offers superior load handling and has the possibility to be less foggy than a single ended amp. I own both types of amps so I have no vested interest either way. Though steve is responding to what he has heard, and if shortcuts and poor design are event, in his words id imagine what he hears is a foggy amp.   Its a design challenge, though is no reason why a well designed push pull amp cant sound real, give up some extra power and run in class A.



« Last Edit: February 07, 2015, 03:06:24 PM by hedalfa »

Offline Tuyen

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Re: GM-70 tubes
« Reply #9 on: February 07, 2015, 11:13:41 AM »
From my limited experience with SE amps, I think I would agree with what omodo and hedalfa have written.

I need an amp with balls to drive my 3 way horns.  Mainly due to the 15" woofer.  sometimes I like to play my music at low vol and still be able to hear all the subtleties  (a known strength of high efficiency system) and then sometimes I like to play my music loud   and expect it to stay fully composed!  :)

Offline omodo

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Re: GM-70 tubes
« Reply #10 on: March 03, 2015, 10:00:02 AM »


Ulyanov GM70, WE 300B, Sylvania VT-25/10Y, National Union  45, ordered by rated dissipation, look at the size of the plates on the GM-70 8)

Some of the white/ceramic based 801/#10 were also produced with similar thick carbon plates


Offline hedalfa

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Re: GM-70 tubes
« Reply #11 on: March 03, 2015, 11:31:26 AM »
Big size may for some conjure up for some the image of  big louts of Russian with their jackboots reproducing the music with little finesse or beauty.  Modern Russian valves do have tendency to hard edged and dry sounding. Maybe this is less apparent in vintage models.  Like most things in life there can be exceptions, may be these valves are well behaved ones.
 

Offline zenelectro

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Re: GM-70 tubes
« Reply #12 on: March 03, 2015, 07:10:35 PM »
A few words about the GM70

a/ They take some driving. They are a big tube that will pull considerable grid drive current so often the drive circuit will have a great impact on the overall sound.
If they sound slow and sluggish or hard edged this is not necessarily the OP tube itself. A lot of designs will resort to some sort of cathode follower for driver and
there can be the source of your compromised sound. As always there are plenty of ways to skin a cat

b/ GM70s come in a few different grades which have very different characteristics. From one end of the scale to the other you may as well  be using a different tube.

So I don't think you can generalize about these tubes. A well designed GM70 amp - push pull or single ended can sound spectacular. It's a matter of understanding the
tubes requirements and characteristics.

cheers

T