want to do PP-GM70

[day]

you can see chematics here http://www.htg2.net/index.php?topic=9106.0
this is my next se-gm70 it is smaller

 

[day]

pic

 

[astouffer]

Beautiful work, and you even wound your own output transformers. Gotta give you credit for that.

 

[darkmoebius]

Re: 75th

GM 70 SE
2x6SN7,2 EL 34, 2 GM 70

12au7, 2 12ax7 ,75TH

Could you explain how the GM70 sounds compared to the 75TH as an output tube?

How much power are you getting out of them both?

Which do you like more?

Thanks

 

[day]

Hi darkmoebius
I have no 75TH to try but now se-845.
i may found some different.

 

[pipla]

pp gm70

hello ,
this is my first post on diyaudio, and I make this:

http://xoomer.virgilio.it/valvolandia/GM70/gm70.htm


and here

http://www.audiofaidate.it/forum/topic.asp?TOPIC_ID=4956&SearchTerms=pp,gm70


6c45pi+ 2*EL34 + 2*GM70 with Bartolucci tranformer( for final
relise)

regards

Remigio

 

[Bandersnatch]

hey-Hey!!!,
I've built with transmitting pentodes, with grid chokes on the finals( PP ), and use much larger caps at the grid choke's attachment to the bias pots, 4 uF in fact, in order to thoroughly 'center' the AC ground at that point. Kevin has a good point in wanting to have that node at AC ground...
cheers,
Douglas

 

[thomas-NGU]

Hello,

Could you please share me the PP GM 70 schema? As simple as good.

Thank you & Regards,

 

[pipla]

hi Thomas
the schematic is into the link posted .
I replay it here:
gm70 mono
meybe same little mistake!

Remigio0

 

[kstlfido]

Hi Pipla-

Thanks for schematic. It is a bit pixelated, but I get the idea. I have been thinking of building PPGM70 amps to compliment my copper speakers for Burning Man.

Do you have a power supply schematic? Thanks!

-Kent

 

[pipla]

hi ,
this is the hi-voltage psu:

 

[hoangduongo]

Hello everybody,
Sorry for digging the old topic up, but I'm going to build a ГМ-70 PP amp too, this will be my practice before I go to a higher level, a ГМ-5Б PP one
After some thought, I came up with this schematic, and I'm thinking of putting one more CF stage before the ГМ-70s, using 6С19П-В, is this necessary?
Any comment or suggestion is welcome
Here is the schem:

 

[djn]

I don't know schematics well enough to comment but that should produce a lot of wpc. Do you need all that power? What is the GM56? I can't find any data on the web.

 

[hoangduongo]

I don't know schematics well enough to comment but that should produce a lot of wpc. Do you need all that power? What is the GM56? I can't find any data on the web.

What do you mean "wpc", is it "watts per channel"?
I did a prototype of this schematic and managed to squeezed 85W out of it (@1kHz), the pair of ГМ-70 seemed can put more but the limit was the PT which could only provide 1.1kVDC and the OPT (local made) which is not so big.
This is more like a challenge for me to pass through than a truly need for power, 'cause I've always wanted to try and make something powerful. But I think 85W is not something big, consider that my favorite type of music is metal.
The ГМ-5Б is not GM56, it's GM-5B, somewhat similar to 3CX300A1.
Thanks for your comment

 

[hoangduongo]

No suggestion at all?
Now think of the CF stage again, I find 6С19П is not suitable because it has very low u (around 2), then the CF stage will have gain of only 0.66.
The driver stage can deliver 360Vpp and I dont want to scale down this too much, so any idea for the CF stage?
Regards,
Duong

 

[45]

No suggestion at all?
Now think of the CF stage again, I find 6С19П is not suitable because it has very low u (around 2), then the CF stage will have gain of only 0.66.
The driver stage can deliver 360Vpp and I dont want to scale down this too much, so any idea for the CF stage?
Regards,
Duong

I would definitevely use a CF. I don't like those 220K grid resistors for big tubes....
You have a number of options like 6BL7GT or one 6SN7 (with the two sections in parallel) for each GM70 or a 6L6, for example. It depends on what you want. Class A1 or AB1? Class A2 or AB2?

Finally I would go for 1250V anode voltage.

45

 

[hoangduongo]

I would like to use Russian tubes, as this is my preference. Something like 6Н6П (6N6P) would be suitable?
The power amp would be class A1 or AB1, I'm not sure now.
I will try to increase B+ to 1.2 or 1.3kVDC, but now the PT limits B+ to 1.1kVDC.
Thank you.
regards,
Duong

 

[45]

I would like to use Russian tubes, as this is my preference. Something like 6Н6П (6N6P) would be suitable?
The power amp would be class A1 or AB1, I'm not sure now.
I will try to increase B+ to 1.2 or 1.3kVDC, but now the PT limits B+ to 1.1kVDC.
Thank you.
regards,
Duong

Then you can use the 6H8C (i.e. the russian 6SN7) or the 6P6S (i.e. the russian 6L6). I don't know the 6N6P. However if you don't want class A2 or AB2 6H8C is fine!
You can also reduce the idle current of the GM70's and get some more power in class AB1 with 1.1 KV, also because you have a 10K output transformer.
You stop as soon as you see crossover distortion if max Pout is your main target.....

45

 

[hoangduongo]

Then you can use the 6H8C (i.e. the russian 6SN7) or the 6P6S (i.e. the russian 6L6). I don't know the 6N6P. However if you don't want class A2 or AB2 6H8C is fine!
You can also reduce the idle current of the GM70's and get some more power in class AB1 with 1.1 KV, also because you have a 10K output transformer.
You stop as soon as you see crossover distortion if max Pout is your main target.....

45

The 6П6С is the Russian version of 6V6GT, if you mean 6L6 then it should be 6П3С/6П3С-Е. The 6N6P (6Н6П) is a Russian twin triode, similar to 12BH7A or 5687 (5687 has different pin-out though).
But anyway, got your idea, and maybe something like this will be ok? (I will use coupling capacitor instead of the IT, and no FB):

An externally hosted image should be here but it was not working when we last tested it.

I think I will stop at 85W max per channel, because if I want to increase, I will have to replace the PT and OPT both.

regards,
Duong

 

[kavermei]

With higher B+ voltages (1.2 ... 1.5kV) it's easier to stay out of the grid current region.

A combination of high B+ and DC coupled CF grid drive is really only useful if ultra high power is wanted (or if no compromise on reproducing large transients is acceptable). It's quite a hassle, with the need for two additional voltage rails and all...

Finally, for RC coupling I would be suspicious of a grid circuit resistance of 220k. The GM-70 datasheet does not specify it but for such a big triode I would feel much more comfortable with 100k ohms max.

In case of RC coupling I think 6Н6П is a good choice for a driver: it has good voltage swing and drive capacity.

Keep us informed on your progress!

Kenneth