(Copied from the Baltic thread as it has a wider relevance for other tube equipment)
As the background of the Melz 1578 tube is somewhat mysterious, unsurprising given its cold war soviet background which predates many of us, I thought I would share what I have learnt.
The Melz 6h8c is analogous to the US 6sn7 tube and was designed for audio use. Its cousin the 1578 was designed for use in demanding industry applications, most interestingly the Soviet nuclear industry to pass a 1578 signal, whatever that is.
Both versions share a similar appearance and both are labelled 6h8c. Some production runs of the 1578 were also labelled ‘1578’, though not all. Conversely, the ‘1578’ label has been added to the regular 6h8c to trick buyers into paying a premium price. My advice is to disregard it and focus in the internal construction.
The 6h8c tubes also used metal bases and drilled holes in the plates in their earlier production runs, which can confuse people into thinking they are 1578. There are however two internal construction differences unique to 1578 which will identify them
- the lower mica (below plates) is rectangular in 1578 but oval in 6h8c
- the upper mica supports (above plates) are large bent silver metal in 1578 but small straight opaque synthetic in 6h8c
I have only ever used the 1578 and not the 6h8c, so I can’t comment on the sonic differences but have read that 1578 is superior. The early production 6h8c might still be quite respectable however don’t be tempted into overpaying for them.
As the background of the Melz 1578 tube is somewhat mysterious, unsurprising given its cold war soviet background which predates many of us, I thought I would share what I have learnt.
The Melz 6h8c is analogous to the US 6sn7 tube and was designed for audio use. Its cousin the 1578 was designed for use in demanding industry applications, most interestingly the Soviet nuclear industry to pass a 1578 signal, whatever that is.
Both versions share a similar appearance and both are labelled 6h8c. Some production runs of the 1578 were also labelled ‘1578’, though not all. Conversely, the ‘1578’ label has been added to the regular 6h8c to trick buyers into paying a premium price. My advice is to disregard it and focus in the internal construction.
The 6h8c tubes also used metal bases and drilled holes in the plates in their earlier production runs, which can confuse people into thinking they are 1578. There are however two internal construction differences unique to 1578 which will identify them
- the lower mica (below plates) is rectangular in 1578 but oval in 6h8c
- the upper mica supports (above plates) are large bent silver metal in 1578 but small straight opaque synthetic in 6h8c
I have only ever used the 1578 and not the 6h8c, so I can’t comment on the sonic differences but have read that 1578 is superior. The early production 6h8c might still be quite respectable however don’t be tempted into overpaying for them.