@Bluesystems I agree with what you are saying when we have an advanced technology product. But I thought there might be a glimmer of hope in @Rossputin’s case if we consider the pedigree of this Dynaco ST 70 variant.
It is my speculation that Holger Schaarschmidt of Erhard Audio is the creator of the design and PCB that OP bought. I believe topologically it is similar to Roy Mottram’s VTA70 design (tubes4hifi.com) with the incorporation of the full power supply and rectification on the PCM and the addition of Pavel’s “Automatic Bias Supply” module (See https://www.audioamp.eu/automatic-b...i-st70-st120-v2-0-with-isolation-transformer/). Holger had an excellent reputation for customer service, but sold the Erhard Audio PCB business to Miller Audio, where @Rossputin spent some good money to buy this top-of-the-line kit he is now struggling with. It even includes the Zero Temp CCS by Pavel (https://www.audioamp.eu/the-problem...ource-for-tube-phase-inverter-901899217-2-en/). I do not expect there is anything inherently wrong in the the design of the amplifier and components. It is probably an assembly issue, or perhaps an electronic part failure.
Without a proper schematic it is harder to troubleshoot, but we know the parts and this hardly is a case of terminal complexity. The automatic bias control can be tested and if it works correctly it can be rules out as source of the trouble. Or it could be bypassed and replaced temporarily with simple cathode biasing. The rest of the topology can be traced out if OP gets back.
It is my speculation that Holger Schaarschmidt of Erhard Audio is the creator of the design and PCB that OP bought. I believe topologically it is similar to Roy Mottram’s VTA70 design (tubes4hifi.com) with the incorporation of the full power supply and rectification on the PCM and the addition of Pavel’s “Automatic Bias Supply” module (See https://www.audioamp.eu/automatic-b...i-st70-st120-v2-0-with-isolation-transformer/). Holger had an excellent reputation for customer service, but sold the Erhard Audio PCB business to Miller Audio, where @Rossputin spent some good money to buy this top-of-the-line kit he is now struggling with. It even includes the Zero Temp CCS by Pavel (https://www.audioamp.eu/the-problem...ource-for-tube-phase-inverter-901899217-2-en/). I do not expect there is anything inherently wrong in the the design of the amplifier and components. It is probably an assembly issue, or perhaps an electronic part failure.
Without a proper schematic it is harder to troubleshoot, but we know the parts and this hardly is a case of terminal complexity. The automatic bias control can be tested and if it works correctly it can be rules out as source of the trouble. Or it could be bypassed and replaced temporarily with simple cathode biasing. The rest of the topology can be traced out if OP gets back.