Hi Varaita;
would you be so kind to return back to the technical discussion, as soon as you are on this forum? I visit Russian technical forums and see how often some people who offer production repeat propaganda working on public, trying to create an impression of smart inventor fighting against retrogrades. Please answer my question about zero bias, what do you mean, and let's start from there.
According to the Gm70 datasheet I have, running 100 mA idle at 500 Vp would require -32 V on the g1. Or if auto biased, then 470 Vp and -30 V on g1. Swinging down 388 Volts peak (29 Watts) would bring Vp down to 112 V Sat. at 200 mA. Checking the datasheet again, this would require about +30 V on the grid.
Here you go: with zero bias it will be 250 mA on 500V. That means 75W of idle anode dissipation.
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Thanks alot for your time and patience in this thread. It was a pleasure to learn about your innovative amp.
Cordiali saluti, Gustavo
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My pleasure to learn with you on a subject so interesting as this amp. The GM70 tube is a great device for music, and certainly have too few amps on the market that use it.
Regards, Gustavo
That checks out for this amp producing about 10W output.
This amp is SE, no help from the bulb; in fact the opposite.
388V peak into 2700 ohms is about 27.8 watts. The lightbulb at 5K dynamic resistance consumes 15 watts, leaving 12.8 watts at the OPT primary.
12.8 watts "ideal" and 9.75 watts out is not surprising depending on the DCR of the primary and secondary, and whether the 2700 ohm load estimate includes the DCR...
So as a reality check on the claims, based on the information provided so far, the anode efficiency of this amp is 12.8% -- at best -- and it produces about 10 watts of audio power at the speaker terminals
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Now, the question is about 0.1% THD on 25W output in the item description. 😎
Who will pay shipment charges if the item is "Not As Described"?
Who will pay shipment charges if the item is "Not As Described"?
What we learned in this topic Gustavo, is that some sellers fool buyers (does not matter: intentionally, or by mistake), and as the result are getting negative feedback and loosing reputation.
Indeed, GM-70 is a great devices for music, and there are really amps available that use them for much better results than we saw here.
And you still have a chance to learn something useful reviewing all technical details of the amplifier, if choose to follow the technical discussion.
Wavebourn,
Just wondering how would you bias a GM70 SET?
I can see using -25V (100ma at 400VDC).
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I feel Mr.Ciro can not disclosure the secrets of his amp, seems a normal procedure as the amp is a commercial product.
In my town there is a tube amp maker, for some reason I can not figure out he flatly refused do me a GM70-SET !! So who know how to made a GM70 amp have a good sales point with the world wide audiophiles.
Gustavo
It is a big difference between non-disclosure of secrets and wrong descriptions.
I can disclosure all details of what had been drawn already, if you want to.
Let's start?
hey, given the situation I would like to ask fore a few facts on this GM70
Is there a huge stock of NOS GM70, or are still in production ?
and how long will there be a reliable supply ?
and for how long will they be affordable ?
So far I know its a russian military tube, for aircrafts, and exstremely rugged and reliable
and supposedly a very clever design
and more hifi related, I have read that it should be a lot easier to drive than other high power triodes like 845 etc
btw, JAC in Germany is working on a GM70 driving GM70
man, I suspect this thing gets hot as hell
regarding this other GM70 amp and its holy lamp, well friends, its a free world
I prefer to talk about what we could do, rather than what others shouldnt
Is there a huge stock of NOS GM70, or are still in production ?
and how long will there be a reliable supply ?
and for how long will they be affordable ?
So far I know its a russian military tube, for aircrafts, and exstremely rugged and reliable
and supposedly a very clever design
and more hifi related, I have read that it should be a lot easier to drive than other high power triodes like 845 etc
btw, JAC in Germany is working on a GM70 driving GM70
man, I suspect this thing gets hot as hell
regarding this other GM70 amp and its holy lamp, well friends, its a free world
I prefer to talk about what we could do, rather than what others shouldnt
It depends on what you want from it. There may be many criteria of optimization. What are yours?
Do you want a resistive loaded cathode follower, or resistive loaded common cathode amp, or transformer loaded cathode follower, or transformer loaded common cathode amp?
The differences are:
1.) In case of resistive load you can use cheap un-gapped transformer, like toroid, to match load resistance.
2.) In case of transformer load transformer will be much more expensive, but you may obtain more power per distortions, or less distortions per power, that is the same.
3.) In case of common cathode stage you will need about 200 V peak to peak to drive the tube;
4.) In case of cathode follower you will need about kilovolt from driver.
Your choice?
OK, looks good. I wish ask you to send me a PM with this details, for we do not cause trouble to others.
A commercial company does not have to give its secrets away, but in time they will become known anyway. If they are good secrets then people will be impressed.
What no commercial company should do is put, or allow to be put, on its website misleading information and then blame someone else for this. The boss is always responsible. It is also not a good idea to half-engage with criticism of your products: either keep quiet and wait for it all to blow over, or defend your product without questioning the qualifications of your critics. We have a saying in the UK "When you realise you are in a hole, stop digging!".
What no commercial company should do is put, or allow to be put, on its website misleading information and then blame someone else for this. The boss is always responsible. It is also not a good idea to half-engage with criticism of your products: either keep quiet and wait for it all to blow over, or defend your product without questioning the qualifications of your critics. We have a saying in the UK "When you realise you are in a hole, stop digging!".
What others? Why trouble? 😱
There are lot of people here who understand all details that were posted no less than myself. And they were already discussed thoroughly. What I suggest, to put them step-by-step, so you and others who have troubles to understand would not have them anymore.
By the way, here is one very clever design of an amp using GM-70 tube. It looks very simple on schematic, but I have to warn novices: KILovolt KILLS!
Óñèëèòåëü íà ÃÌ 70
Re: Michael
"That checks out for this amp producing about 10W output.
This amp is SE, no help from the bulb; in fact the opposite.
388V peak into 2700 ohms is about 27.8 watts. The lightbulb at 5K dynamic resistance consumes 15 watts, leaving 12.8 watts at the OPT primary.
......
So as a reality check on the claims, based on the information provided so far, the anode efficiency of this amp is 12.8% -- at best -- and it produces about 10 watts of audio power at the speaker terminals "
---------
Ah, right you are. I was assuming the 100 mA idle was correct for the stated 29 Watt power. But 29 Watts output would actually require 150 mA idle due to the bulb losses. 100 mA idle with 388 V peak would work for a CCS loaded design to get 27.8 Watts.
So, let's see: if it used 150 mA idle it would be using 500x.15 => 75 Watt tube idle + 75 Watt bulb idle + 60 Watts for filaments + maybe 10 Watts for the input tubes => 220 Watts per channel => 440 Watts stereo (then 90% efficiency of power xfmr at best) => 489 Watts wall outlet power. Then another 161 watts [(29 Wout + .5*29 Wbulb +29 Wtube at least)/.9)x2 channels] wall input to get 29 audio Watts out on both channels for a grand total of 650 Watts wall outlet draw at full power. Even a bit more when including OT losses (about 33 Watts when worked back out to the wall outlet for both including all the inefficiencies to generate the 3 Watt for each OT loss). So 683 Watts line cord. Overall efficiency 8.5%. Gonna need the AC running too. Add another 1000 Watts. Probably can't hear it over the AC running, so get earphones, and chuck amplifier.
"That checks out for this amp producing about 10W output.
This amp is SE, no help from the bulb; in fact the opposite.
388V peak into 2700 ohms is about 27.8 watts. The lightbulb at 5K dynamic resistance consumes 15 watts, leaving 12.8 watts at the OPT primary.
......
So as a reality check on the claims, based on the information provided so far, the anode efficiency of this amp is 12.8% -- at best -- and it produces about 10 watts of audio power at the speaker terminals "
---------
Ah, right you are. I was assuming the 100 mA idle was correct for the stated 29 Watt power. But 29 Watts output would actually require 150 mA idle due to the bulb losses. 100 mA idle with 388 V peak would work for a CCS loaded design to get 27.8 Watts.
So, let's see: if it used 150 mA idle it would be using 500x.15 => 75 Watt tube idle + 75 Watt bulb idle + 60 Watts for filaments + maybe 10 Watts for the input tubes => 220 Watts per channel => 440 Watts stereo (then 90% efficiency of power xfmr at best) => 489 Watts wall outlet power. Then another 161 watts [(29 Wout + .5*29 Wbulb +29 Wtube at least)/.9)x2 channels] wall input to get 29 audio Watts out on both channels for a grand total of 650 Watts wall outlet draw at full power. Even a bit more when including OT losses (about 33 Watts when worked back out to the wall outlet for both including all the inefficiencies to generate the 3 Watt for each OT loss). So 683 Watts line cord. Overall efficiency 8.5%. Gonna need the AC running too. Add another 1000 Watts. Probably can't hear it over the AC running, so get earphones, and chuck amplifier.
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I have bought some GM70 in Russia, my tube shop say the GM70 is NOS(no more made). Looks there is huge stock in Siberia as the price is low.
I think the GM70 is not a jet plane tube, but a stationary use, the 6C33 is a military jet plane, naval and missile tube.
The GM70 plate is a solid cast graphite plate, it run hotter than the 6C33 indeed. And it is said the GM70 is easy to drive than the 211/845.
I read the 300B is a great drive tube for the GM70(see some Polish links earlier this thread).
You must buy many spare GM70 tubes before you need replace, If you have a GM70 amp.
Regards, Gustavo
GM-70 was designed for plate modulators of AM transmitters. Also, it was used in power amps for audio translation networks, they were called Ty-5. Initially anodes were made of graphite, but also were made tubes with copper and even iron(!) anodes.
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