[triod750]

I have been recently reading about tubes that have been used in communications applications (primarily old under sea lines) and there are fascinating documents regarding the development of pentodes used as repeaters in these systems. I’m not sure if such tubes apply directly to the many discussed in this thread but has anyone tried these tubes in audio applications?

You mean tubes like the C3g? Very popular audio tube...

 

[Designsfx]

@triod750
The first discussed was made/sold-as Mazda and was called SP61 and there are a couple of other CV?? that I need to go back and find. The article discusses the amazing amount of R&D that went into these tubes. I was wondering if they had any place in the audio world.

 

[triod750]

@triod750
The first discussed was made/sold-as Mazda and was called SP61 and there are a couple of other CV?? that I need to go back and find. The article discusses the amazing amount of R&D that went into these tubes. I was wondering if they had any place in the audio world.

Could you please link the article(s)? Always interesting to read.

 

[Designsfx]

Could you please link the article(s)? Always interesting to read.

No problem!

http://www.r-type.org/articles/art-279.htm

 

[triod750]

http://www.r-type.org/exhib/acl0254.htm
This is what you find when you look for 6P12. 7.5V heaters.

https://www.radiomuseum.org/tubes/tube_175hq.html 18.2V heater.
Pick your poison

But STC made something else later that @Isaacc7 has been using, I think.

 

[Isaacc7]

http://www.r-type.org/exhib/acl0254.htm
This is what you find when you look for 6P12. 7.5V heaters.


https://www.radiomuseum.org/tubes/tube_175hq.html 18.2V heater.
Pick your poison

But STC made something else later that @Isaacc7 has been using, I think.

Ooh, cv1724? That looks interesting… oh wait, max voltage is so low Which tube do you think I’m using? The only STC output tube I have is the 5b/254m which is lovely.

 

[Designsfx]

The SP61 was the valve I was most curious about as it is a 6.3V pentode. I thought it interesting that some of these were used in submerged telephone systems. I haven’t heard of it being used in an audio application and was wondering what characteristics it might offer- they seem to be a bullet proof tube!

 

[triod750]

Ooh, cv1724? That looks interesting… oh wait, max voltage is so low Which tube do you think I’m using? The only STC output tube I have is the 5b/254m which is lovely.

I mixed you up with someone else. But I know that @mordy has written about one STC tube that seems close to C3g.

 

[Wes S]

I mixed you up with someone else. But I know that @mordy has written about one STC tube that seems close to C3g.

That would be the 5A/152M.

 

[triod750]

The SP61 was the valve I was most curious about as it is a 6.3V pentode. I thought it interesting that some of these were used in submerged telephone systems. I haven’t heard of it being used in an audio application and was wondering what characteristics it might offer- they seem to be a bullet proof tube!

https://www.radiomuseum.org/tubes/tube_sp61.html
Rare, 1925 to 1945 and used for Radio/TV reception according to Radiomuseum...
Have you found any?

 

[mordy]

I mixed you up with someone else. But I know that @mordy has written about one STC tube that seems close to C3g.

That’s the one but the pinout is different than the C3g.

 

[Designsfx]

https://www.radiomuseum.org/tubes/tube_sp61.html
Rare, 1925 to 1945 and used for Radio/TV reception according to Radiomuseum...
Have you found any?

I have seen them for sale on eBay and honestly some of them look to be hammered. One add was for a small lot that looked very un kept, some had chips in the coating and the seller was very forthright in stating that none had been tested. They weren’t expensive but as the tube would require an adapter for use (and I would need a quad) it seemed risky to me.
Has anyone purchased, used or heard this tube in use before? I’ve seen other tubes of this style offered for sale before but have not heard any feedback with regards to sound/performance traits.

 

[triod750]

That’s the one but the pinout is different than the C3g.

Important to be aware of.

 

[triod750]

They weren’t expensive but as the tube would require an adapter for use (and I would need a quad) it seemed risky to me.

Some day you will feel adventurous. Then you can tell the rest of us

 

[Isaacc7]

I mixed you up with someone else. But I know that @mordy has written about one STC tube that seems close to C3g.

Oh, yeah, I’m using the 5a/152m. Sorry, thought you were talking about output tubes. Yup, it’s a great input tube!