True, but not the point I was trying to make. The GM-70 (in particular) is more sensitive to loading (in terms of IMD) than many tubes of its ilk (845, 572, 211, etc.) so I don't agree that "4.4K makes more sense" - (you can talk with Jack Elliano of Electra-Print if you need actual test results).
Also, I would say that lowering IMD is the goal of any amp as it's by far the most objectionable form of distortion.
That being said, much of this depends on operating bias (quiescent voltage/current) and you do get wider frequency response (less inductive roll-off) with a 5K winding than w/10K.
All designs are compromises of one sort or another.
Hi
Need some help or advice
Just purchased 4PC GM70 copper plate and the four are not the same
Each two piece were produced in different year
Two has clear top and two has glossy top.
Can someone let me know if those can perform the same or close? I must worried about that or that does not effect the performance
Something similar like on the attached picture
Thank you
Also purchased 4PC graphite plate - those are 100% same
Greetings gabor
Need some help or advice
Just purchased 4PC GM70 copper plate and the four are not the same
Each two piece were produced in different year
Two has clear top and two has glossy top.
Can someone let me know if those can perform the same or close? I must worried about that or that does not effect the performance
Something similar like on the attached picture
Thank you
Also purchased 4PC graphite plate - those are 100% same
Greetings gabor
Attachments
Last edited:
Hard to find a 2 tubes the same.Hi
Need some help or advice
Just purchased 4PC GM70 copper plate and the four are not the same
Each two piece were produced in different year
Two has clear top and two has glossy top.
Can someone let me know if those can perform the same or close? I must worried about that or that does not effect the performance
Something similar like on the attached picture
Thank you
Also purchased 4PC graphite plate - those are 100% same
Greetings gabor
The pointed tube seems has some use as shown this black spot.
That spot is result of alectrons action on the copper plate.
It will increase with tube use, by this copper plates lasting less than the graphite plate version at a considerable more price.
Hi
That type of tube has a ring on the top the others not.
I don't know the function or the name of that ring. Around that ring the tube the glass get like smoked, glossy.
Some tube has that ring on the top some not.
On these picture you can see that ring I talk about.
Greetings gabor
That type of tube has a ring on the top the others not.
I don't know the function or the name of that ring. Around that ring the tube the glass get like smoked, glossy.
Some tube has that ring on the top some not.
On these picture you can see that ring I talk about.
Greetings gabor
Attachments
Thank you!
My question two copper plate tube has that getter on the top and two does not.
All GM70 has two at the side of the bottom but not all has on the top.
Any difference how they perform, do that getter on the top make any difference sound wise.
Take a look at both picture I posted and you can see it. Some does not have that donuts at the top.
Actually the 4PC graphite plate does not have either. At least those has the same structure.
Greetings
My question two copper plate tube has that getter on the top and two does not.
All GM70 has two at the side of the bottom but not all has on the top.
Any difference how they perform, do that getter on the top make any difference sound wise.
Take a look at both picture I posted and you can see it. Some does not have that donuts at the top.
Actually the 4PC graphite plate does not have either. At least those has the same structure.
Greetings
Regarding Ri of GM70, it is around 1k6...1k8 at 800-1000V plate voltages, and around 1k8...2k0 at 1200-1400V. So, for sure, Ra around 8k...10k is a must.
Thank you!
My question two copper plate tube has that getter on the top and two does not.
All GM70 has two at the side of the bottom but not all has on the top.
Any difference how they perform, do that getter on the top make any difference sound wise.
Take a look at both picture I posted and you can see it. Some does not have that donuts at the top.
Actually the 4PC graphite plate does not have either. At least those has the same structure.
Greetings
Among 4 pcs of copper gm70 that I have, from two different manufacturers, all have that getter on the top.
Copper gm70 start to produce "open" sound from 800-1000V plate voltages, while graphite become "open" from 1000V and higher. In my case, with 1200V, finally I got back to graphite, since bass and "sound body" are definitely better with them, at very minor expence at trebles.
I have different copper plate GM-70, with getter rings placed on top or on the sides, and with different rivet numbers on the plate, but they all sound good.
I confirm what Vladimir said, more bass and a more dynamic sound with the graphite plates, but I keep using the copper plates because they are definitely better in the treble.
I confirm what Vladimir said, more bass and a more dynamic sound with the graphite plates, but I keep using the copper plates because they are definitely better in the treble.
I have to add, that my speakers are PMC EB1i, that are "difficult" even for high power SS amps. However, with graphite gm70 I already do not feel any bass limitations (output trafos 40cm2, turns ratio primary/secondary is around 52, output impedance near 0,8 Ohms, fixed bias of gm70, filament heating is via 3A current source, regulated 1200V plate voltage, this also adds to better bass).
If you ask, why not to change speakers, I answer, full-rangers are not for real bass.
Last edited:
HI,
Its said the 211 have a tension swing at B+.
It eat a around 50V more at loud musical passages, usually 900-950V.
Do you think the GM70 Graphite plate also have it?
Or its linear?
Thanks
Yes, for sure, gm70 has similar PS rail voltage swing, as well as any other SE design with classical C-L-C or L-C power supply. In my opinion, this is the main reason of "weak" bass from tube SE. I tried to increase C value up to 2000uF (used 96 pcs of 560uF x 450V lytics, 48pcs per one channel, every 3 cap in series, than all triplets in parallel), with 30H choke before the C. However, regulated plate rail is defiitely better for bass than even a big cap. By the way, L value contributes almost nothing at B+ swing, it serves only for 100Hz ripples suppression. Of course, very special ("light") speakers are needed, if B+ produced by, for instance, 40uF - 10H - 100uF classical power supply.
Last edited:
Thank you VladimirK for the precious information.
Did you designed the regulated or you purchased readily built.
If you designed can you share the schematics with us.
If I knew the difference between the copper and the graphite not that much I could save that $$$ on the 4 copper plate and invest a bit more to the OP transformers or purchase extra 4PC graphite for much less.
Any way the price of the tubes increases almost daily. I do not think it was that bad investment.
By the way now I understand the structure difference between the copper tubes.
All has greeter at the bottom these 2PC has extra on the top.
Greetings
Did you designed the regulated or you purchased readily built.
If you designed can you share the schematics with us.
If I knew the difference between the copper and the graphite not that much I could save that $$$ on the 4 copper plate and invest a bit more to the OP transformers or purchase extra 4PC graphite for much less.
Any way the price of the tubes increases almost daily. I do not think it was that bad investment.
By the way now I understand the structure difference between the copper tubes.
All has greeter at the bottom these 2PC has extra on the top.
Greetings
Saying regulated 1200V B+, I mean simplified approach.
First, I use 5kW mains voltage stabilizer.
Second, after the rectifier, choke and lytics, I put an emitter (source) follower with BUP314 igbt transistor, with its gate connected to C, from RC chain (similar to cap multiplier, few seconds time constant). One should put proper resistive divider before this RC chain, in order that the gate would see 80V less voltage than original 1280V after choke and caps. Counter connected zeners must be on G-E pins, for protection.
The transistor must be very robust, in order to withstand huge power dissipation during transient process at power on/off.
Since such transistor does not belong to audiophile family, I put massive polypropylene after it, just near the tube socket. In my case, they are 80uF x 400V Solen caps, three in series. They are shunted with 1uF film and 0,027uF 1500V silver-mica cap.
First, I use 5kW mains voltage stabilizer.
Second, after the rectifier, choke and lytics, I put an emitter (source) follower with BUP314 igbt transistor, with its gate connected to C, from RC chain (similar to cap multiplier, few seconds time constant). One should put proper resistive divider before this RC chain, in order that the gate would see 80V less voltage than original 1280V after choke and caps. Counter connected zeners must be on G-E pins, for protection.
The transistor must be very robust, in order to withstand huge power dissipation during transient process at power on/off.
Since such transistor does not belong to audiophile family, I put massive polypropylene after it, just near the tube socket. In my case, they are 80uF x 400V Solen caps, three in series. They are shunted with 1uF film and 0,027uF 1500V silver-mica cap.
Last edited:
Have gm70 Copper is not a prob, the prob is if you need some tubes.
Think of GM70 Copper as a investment, its price will increase as stocks go down.
You have just to wait...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.