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 ..
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 ..
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.
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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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.
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.
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"
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"
There are no "disadvantages" apart from the fact that the output transformer is a bit more complex, and voltage gain of the output tube is diminished as a result of local feedback so it requires more from the driver stage.
Your "additional benefits" 1) and 2) are mutually inclusive.
The text below explains some additional difficulty about cathode winding:
"Output transformers with cathode winding are more expensive than analogous ones without dividing the primary. For a very simple reason - in order for the cascade to be stable and with low distortions at high frequencies, the mutual leakage inductance of the separated windings must be extremely low. For this purpose, the windings are made in two wires, and a more expensive wire with silk insulation or triple lacquer is used to provide the required electrical strength. Accordingly, the filling factor of the window falls, which leads to the need to increase the dimensions of the transformer.
By the way, the cathode winding, regardless of its ratio over the turns with the anode, with the correct phasing, forms the classical sequential NFB by voltage, an example is discussed in RDH (the chapter of Negative Feedback, the edition of 1952)."
"Output transformers with cathode winding are more expensive than analogous ones without dividing the primary. For a very simple reason - in order for the cascade to be stable and with low distortions at high frequencies, the mutual leakage inductance of the separated windings must be extremely low. For this purpose, the windings are made in two wires, and a more expensive wire with silk insulation or triple lacquer is used to provide the required electrical strength. Accordingly, the filling factor of the window falls, which leads to the need to increase the dimensions of the transformer.
By the way, the cathode winding, regardless of its ratio over the turns with the anode, with the correct phasing, forms the classical sequential NFB by voltage, an example is discussed in RDH (the chapter of Negative Feedback, the edition of 1952)."
The reason for building this amplifier was finding an alternative for the 211 amplifier. My current amp's are running on RCA 211 Tubes (@ USD 1000+ a pair nowadays) so the step to make an amplifier with GM-70 @ USD 25 a pair was the logic thing to do. I can tell you that the GM-70 amp is the better sounding amp. Even with the Svetlana 300B, the TCO of this amp is lower than my 211 mono blocks.
I have also used a CFB for my 211 amps iGoliath 211
The 9K primary was well chosen. If you look at the graphics of the THD and Frequency response on the last page of the article, you can see that there is nothing to complain about.
6H30 - a wonderfull sounding and stabile and very quiet tube. A Sovtek or EH tube is good enough here.
The first stage is build around the Alan Kimmel mu-stage, where V1 Triode can be primary a voltage amplifier and V2 delivers the current.
The OPT's are reasonably priced... that is below €300,= a pair. You can inquire about the specs and pricing here: Home - Vlaartronic
The driver setup was copied from the Audio Note Ankoru SE 845 (edition 12, page 10) There's a link to the schema within the article's text.
I have also used a CFB for my 211 amps iGoliath 211
The 9K primary was well chosen. If you look at the graphics of the THD and Frequency response on the last page of the article, you can see that there is nothing to complain about.
6H30 - a wonderfull sounding and stabile and very quiet tube. A Sovtek or EH tube is good enough here.
The first stage is build around the Alan Kimmel mu-stage, where V1 Triode can be primary a voltage amplifier and V2 delivers the current.
The OPT's are reasonably priced... that is below €300,= a pair. You can inquire about the specs and pricing here: Home - Vlaartronic
The driver setup was copied from the Audio Note Ankoru SE 845 (edition 12, page 10) There's a link to the schema within the article's text.
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