Melz 1578

Sablon Audio

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May 22, 2015
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(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.

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Lowrider75

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Dec 4, 2019
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The early production 6h8c might still be quite respectable however don’t be tempted into overpaying for them.
This is true, the 6H8C shouldn't be expensive. I think I paid about $50 for a pair and they made crackling sounds in my amp.
 

Sablon Audio

Industry Expert, VIP Donor
May 22, 2015
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This is true, the 6H8C shouldn't be expensive. I think I paid about $50 for a pair and they made crackling sounds in my amp.
Sometimes unused tubes do that initially as impurities get burnt off. Should clear by 50-100 hours.
 

Lowrider75

Well-Known Member
Dec 4, 2019
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The early production 6h8c might still be quite respectable however don’t be tempted into overpaying for them.
This is true, the 6H8C shouldn't be expensive. I think I paid about $50 for a pair and they made crackling sounds in my amp
Sometimes unused tubes do that initially as impurities get burnt off. Should clear by 50-100 hours.
That's true, but not in this case. Some of the metal base tubes have poor soldering in the pins. I had tctubes re-solder my crackling 1578s.
Others on the forum can confirm this.
 

Lowrider75

Well-Known Member
Dec 4, 2019
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@Sablon Audio
Sorry, I think the info about re-soldering the Melz is on Audiogon forum.

You may be familiar with the MELZ 6N8S, 1578 shootout thread. Interesting comments.

 

c1ferrari

Member Sponsor & WBF Founding Member
May 15, 2010
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One of my favorites as well. Do you know the year of your tubes? Any flaws such as noise or cracking?
I have quite a few of them, generally from the mid 70's. No issues with noise in my experience.
 
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c1ferrari

Member Sponsor & WBF Founding Member
May 15, 2010
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Thanks. The earlier, the better I'm told. I have 3 pairs from 1980.
You're welcome! It's been a while, but I typically evaluate all valves with an Amplitrex AT1000. Next, I'll screen them using a Tektronix 576 Curve Tracer. At this point, I'm very confident of a tube's performance regardless of the circuit.
 
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Sablon Audio

Industry Expert, VIP Donor
May 22, 2015
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@Sablon Audio
Sorry, I think the info about re-soldering the Melz is on Audiogon forum.

You may be familiar with the MELZ 6N8S, 1578 shootout thread. Interesting comments.

Thanks, I hadn’t previously been aware if this but googled after you mentioned earlier. Tbh I was a bit surprised given the OTK certification but haven’t had any problems myself.
 
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