4 ms·

They're not preamps. The amp in the article is definitely not an hybrid. Hybrid would mean it uses both Solid State and Tubes to amplify the audio. The tubes a

by ratww 4y ago

They're not preamps. The amp in the article is definitely not an hybrid. Hybrid would mean it uses both Solid State and Tubes to amplify the audio. The tubes are instead only for decorative purposes, and apparently to "turn the circuit on", albeit in a way that is difficult to detect. The article writer used capacitors to simulate the presence of tubes and the amp kept working as normal.

JohnJamesRambo 4y ago
Googling leads me to believe the tubes are used as a buffer stage, which isn't that wild in audio circles, tons of guitar and microphone preamps do this to sweeten the sound or whatever someone wants to call it. I hate fake products, but this one doesn't set off my fraud alarm. And my apologies if other reviews and discussion are wrong about how the tubes are being used in this amplifier, they could be just repeating incorrect facts they hope are right as well.
- ratww 4y ago
  The person that wrote the forum post made a schematic, you can check it yourself. The tubes are not biased properly and the middle one has the grid grounded and the cathode disconnected, so it doesn't do anything. The third tube is being fed voltage that is tapped from the grid of the first tube, only 2V. That's not only less than their ideal operation point (150V? 200V?), but also probably less than needed for starved plate mode operation. So they're not being used to amplify anything. This means they're not buffers either. I doubt audio would even be passing trough them, since it would get rectified by the third tube which is acting as a diode, which is something you definitely don't want. I'm not familiar with Russian tubes but some of those seem to be power tubes... which makes it even weirder. The article writer suggest that they're used as a timer, probably to simulate how tube amps take a while to turn on. He later "replaced" them with capacitors and the amplifier kept working as intended, which probably means they're being used as diodes to turn the circuit on, for purposes of faking operation. This is all in the forum post. If the schematic is correct, they're not preamps nor buffers.
  - JohnJamesRambo 4y ago
    Interesting. Thank you for the details. Most of the audio world and purchasers are wrong about how this amplifier works haha.
  - fuzzfactor 4y ago
    Fairly good assessment IMHO. Naturally that is a custom transformer, just not the high-voltage range that a normal tube amp requires. Looks like the physical layout might have been originally designed to be fully equipped for high-voltage operation, which would mean two additional audio transformers would be needed in addition to a high-voltage version of the present power transformer. Transformers are probably the most costly components to the BOM. The PCBs would all be different too, and a hobbyist having the proper transformers could discard the present ones and completely rewire for conventional high voltage operation, probably easiest on a point-to-point basis without bothering to design an alternative HV PCB for the proper passive components needed. If HV transformers were ever originally involved I could imagine the supply of the HV units ran out before the supply of tubes & sockets. Therefore it could have been redesigned as a solid state amp more cost-effectively using the tubes mainly for decoration and to maintain a premium pricing cache. Especially if full tube amps were originally issued and gained a decent reputation to begin with.
    - ratww 4y ago
      Output audio transformers would only be required if it also had a tube power amplification section, but it seems it was never advertised as being 100% tube anyway. It would also need 4 output power tubes for Stereo Class-AB operation, plus a couple of triodes for the inverter, so I don't think there's enough room there for it. If it were Class-A it would probably need much bigger tubes to deliver the wattage it promises, and there doesn't seem to be much space in the box.

by ratww 4y ago

JohnJamesRambo 4y ago

Googling leads me to believe the tubes are used as a buffer stage, which isn't that wild in audio circles, tons of guitar and microphone preamps do this to sweeten the sound or whatever someone wants to call it. I hate fake products, but this one doesn't set off my fraud alarm. And my apologies if other reviews and discussion are wrong about how the tubes are being used in this amplifier, they could be just repeating incorrect facts they hope are right as well.

ratww 4y ago
The person that wrote the forum post made a schematic, you can check it yourself. The tubes are not biased properly and the middle one has the grid grounded and the cathode disconnected, so it doesn't do anything. The third tube is being fed voltage that is tapped from the grid of the first tube, only 2V. That's not only less than their ideal operation point (150V? 200V?), but also probably less than needed for starved plate mode operation. So they're not being used to amplify anything. This means they're not buffers either. I doubt audio would even be passing trough them, since it would get rectified by the third tube which is acting as a diode, which is something you definitely don't want. I'm not familiar with Russian tubes but some of those seem to be power tubes... which makes it even weirder. The article writer suggest that they're used as a timer, probably to simulate how tube amps take a while to turn on. He later "replaced" them with capacitors and the amplifier kept working as intended, which probably means they're being used as diodes to turn the circuit on, for purposes of faking operation. This is all in the forum post. If the schematic is correct, they're not preamps nor buffers.
- JohnJamesRambo 4y ago
  Interesting. Thank you for the details. Most of the audio world and purchasers are wrong about how this amplifier works haha.
- fuzzfactor 4y ago
  Fairly good assessment IMHO. Naturally that is a custom transformer, just not the high-voltage range that a normal tube amp requires. Looks like the physical layout might have been originally designed to be fully equipped for high-voltage operation, which would mean two additional audio transformers would be needed in addition to a high-voltage version of the present power transformer. Transformers are probably the most costly components to the BOM. The PCBs would all be different too, and a hobbyist having the proper transformers could discard the present ones and completely rewire for conventional high voltage operation, probably easiest on a point-to-point basis without bothering to design an alternative HV PCB for the proper passive components needed. If HV transformers were ever originally involved I could imagine the supply of the HV units ran out before the supply of tubes & sockets. Therefore it could have been redesigned as a solid state amp more cost-effectively using the tubes mainly for decoration and to maintain a premium pricing cache. Especially if full tube amps were originally issued and gained a decent reputation to begin with.
  - ratww 4y ago
    Output audio transformers would only be required if it also had a tube power amplification section, but it seems it was never advertised as being 100% tube anyway. It would also need 4 output power tubes for Stereo Class-AB operation, plus a couple of triodes for the inverter, so I don't think there's enough room there for it. If it were Class-A it would probably need much bigger tubes to deliver the wattage it promises, and there doesn't seem to be much space in the box.