Good morning,
I built (many years ago) an A-370 clone based on the attached schematic diagram. I made a few improvements to it, stabilized +/-12V supply and better components (2SK135/2SJ50, higher quality capacitors across the board, etc.). It did work well, I used it in my system for a while, then moved abroad for work, moved also to a tube (valve) power amplifier and the A-370 clone was stored in my basement in Italy for 30+ years.
I am now thinking to revive it, see how it does perform and possibly improve it.
Re-looking at the schematic diagram, I have a few questions for the (many) experts in this wonderful group.
The main question is about a connection, I have circled it in red. I don't understand its function.
The LM318 output is voltage amplified (VAS) by the couple MPSA43/MPSA93 and from there sent to the couple BC414c/BC416c (emitter-followers for current amplification).
What is the function of the circled connection? It seems it sends the LM318 output to the emitter-followers bases, in parallel to the signal from the VAS stage.
Since this connection is present also in the schematic I found for the MF A-370.2, it should have a useful function, would like to know what this is.
Please note that I am not an expert in this field, it is my hobby. Be gentle if the question has an obvious answer...
Thank you to those who will help.
Regards, Giovanni
I built (many years ago) an A-370 clone based on the attached schematic diagram. I made a few improvements to it, stabilized +/-12V supply and better components (2SK135/2SJ50, higher quality capacitors across the board, etc.). It did work well, I used it in my system for a while, then moved abroad for work, moved also to a tube (valve) power amplifier and the A-370 clone was stored in my basement in Italy for 30+ years.
I am now thinking to revive it, see how it does perform and possibly improve it.
Re-looking at the schematic diagram, I have a few questions for the (many) experts in this wonderful group.
The main question is about a connection, I have circled it in red. I don't understand its function.
The LM318 output is voltage amplified (VAS) by the couple MPSA43/MPSA93 and from there sent to the couple BC414c/BC416c (emitter-followers for current amplification).
What is the function of the circled connection? It seems it sends the LM318 output to the emitter-followers bases, in parallel to the signal from the VAS stage.
Since this connection is present also in the schematic I found for the MF A-370.2, it should have a useful function, would like to know what this is.
Please note that I am not an expert in this field, it is my hobby. Be gentle if the question has an obvious answer...
Thank you to those who will help.
Regards, Giovanni
Attachments
In relation to the LM318 it looks like at type of external filter which can be fitted as advised in the 318 specifications for extra stability .
Thank you duncan2.
If this is to increase stability of the LM318, I will leave it in place.
I am puzzled by the fact that this connection is sort of mixing the LM318 outlet with the VAS amplified signal (above a certain frequency) to the base of the emitter-follower.
Does this affect the voltage amplification in the VAS?
Any other contribution to clarify this matter would be highly appreciated.
Regards, Giovanni
If this is to increase stability of the LM318, I will leave it in place.
I am puzzled by the fact that this connection is sort of mixing the LM318 outlet with the VAS amplified signal (above a certain frequency) to the base of the emitter-follower.
Does this affect the voltage amplification in the VAS?
Any other contribution to clarify this matter would be highly appreciated.
Regards, Giovanni
I think its compensation network to reduce the phase lag at high frequencies (bypassing the phase lag of the VAS)
Incidentally the 2SJ83 and 2SK226 are not complementary, the '83 is 160V and the '226 is 140V, I'd expect
either 2SJ82/2SK226 or 2SJ83/2SK227 (the latter being much much preferred for +/-60V rails).
Incidentally the 2SJ83 and 2SK226 are not complementary, the '83 is 160V and the '226 is 140V, I'd expect
either 2SJ82/2SK226 or 2SJ83/2SK227 (the latter being much much preferred for +/-60V rails).
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Thank you Mark.
I have used 2SK135/2SJ50 (160V), this should be ok with my +/-54Vdc rails.
In the absence of other suggestions, although I still don't have a clear understanding of its function, for the moment I will keep this connection.
Other viewpoints welcome.
I have used 2SK135/2SJ50 (160V), this should be ok with my +/-54Vdc rails.
In the absence of other suggestions, although I still don't have a clear understanding of its function, for the moment I will keep this connection.
Other viewpoints welcome.