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"The Tsar" GM70 single ended amplifier
"The Tsar" GM70 single ended amplifier
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Old 10th February 2018, 09:19 AM   #1
Vortex is offline Vortex  Hungary
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Default "The Tsar" GM70 single ended amplifier

De Tsaar GM70 single ended versterker

Hi Gentlemen,

has anybody tried or heard this build maybe ? (Click on English at the top-right..) The search function here made no result..

Interesting design. 300B as a driver tube, .. you can imagine ..
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Old 10th February 2018, 05:57 PM   #2
FullRangeMan is offline FullRangeMan  Brazil
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300B in driver position is not new, it is used by Ming-Da and others builders already many years.
Also 6H30 is not a smart choice, it is a rare and expensive tube, 300B and 6H30 are both expensive tubes, 2A3 too may be used in 211/805/GM70 driver if one can impressive looks and less cost.

It would make more sense to use 6AU5GT as DeHavilland or other cheap Russian Pentode connected in Triode. Dont know why he use Primary RA 9K it not efficient, hobbist here are using 7K for more power and less cost, but it could be used 6K primary too.
Nice to have more one GM70 amp its a great tube.
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Old 10th February 2018, 07:37 PM   #3
kaputt is offline kaputt  Germany
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I have some 6H30 from Electro Harmonix here. They measured to spec and were not that expensive.
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Old 10th February 2018, 08:05 PM   #4
kevinkr is offline kevinkr  United States
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"The Tsar" GM70 single ended amplifier
It is an interesting design, and quite valid. I designed and built a much simpler GM70 amp that I completed about 7 years ago, class A1 fixed bias with interstage driven by a triode connected D3A, and all solid state supply with SiC rectifiers for the 1kV supply and CLCLC filtering with the chokes in the negative lead to minimize stress on the insulation.. I can get almost 20W in A1 with 7K primary 100mA/1kV. It remains in service to this point in time.
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Old 10th February 2018, 08:08 PM   #5
euro21 is offline euro21  Hungary
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"The Tsar" GM70 single ended amplifier
Quote:
Originally Posted by kaputt View Post
I have some 6H30 from Electro Harmonix here.
6N30P-DR - for example made by Reflektor in Saratov at 1970-80 - is like as "another tube" compared to currently produced EH tube.
And yes, it's expensive as hell.
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Old 11th February 2018, 01:46 AM   #6
FullRangeMan is offline FullRangeMan  Brazil
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EH tubes are all commercial tubes made to create profit to New Sensor, Russian NOS tube are made to nuke war at cost no object, ie made to last the good sound is a bonus.
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Old 11th February 2018, 03:25 AM   #7
VladimirK is offline VladimirK  Uzbekistan
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The FB choke in GM70 cathode, what inductance could it have? I suppose it serves for decreasing output impedance of the amp.
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Old 11th February 2018, 08:26 AM   #8
euro21 is offline euro21  Hungary
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"The Tsar" GM70 single ended amplifier
Cathode feedback coil is part of some PP transformer. I never saw such type SE OPT.
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Old 11th February 2018, 03:05 PM   #9
kevinkr is offline kevinkr  United States
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"The Tsar" GM70 single ended amplifier
It's a feedback winding on the output transformer. I have seen it in other SE designs, and indeed have done it in some older designs of my own.

You will need to contact the author for details about the output transformer if you are interested in building the design verbatim.
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Old 11th February 2018, 05:21 PM   #10
VladimirK is offline VladimirK  Uzbekistan
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In this industrial amp similar FB winding is used. Since this approach is not so widely used, it must have some disadvantages. Could anybody tell about disadvantages?

sacthailand.com

"These will help generate very high quality bass response unheard from conventional SE amp since the controlled motion of woofer is greatly increased. Minuet, therefore, redefines superb bass response (thus enhances full body) along with its excellent midrange and high frequency response.

Besides from lowering THD figure, Cathode Feedback circuit of Minuet EL-34SE does not introducing typical high order odd harmonic distortion associated with most global negative feedback. This helps maintaining smooth and liquid sound without hint of sibilance.

Additional benefits of using cathode feedback circuit are:
1) Lowering output impedance
2) Increasing Damping factor
3) Extending frequency response at both ends of audio spectrum"
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