I really need more to do :-p -- The 6N6G: an amplifier in a bottle?!

mhardy6647

Señor Member
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So: I should be out working on the garden. I really should.
But I have squandered my morning doing useless things like looking at (very) old RCA Receiving Tube Manuals.
Imagine my surprise when I stumbled upon a tube called the 6N6G. It's not exactly unique, but it is one of those tubes, sort of like a 6BM8, with a driver and output tube section in one envelope. What struck me as interesting is that the power output section is a triode. It is also not entirely unique in that it has its own, built in cathode resistor. But just how often does one encounter a tube that's a triode driver and triode output in one bottle, with its own cathode resistor and direct-heated (oops, indirect, derp) filament(s)... with an octal base? OK, I have no idea... but it caught my eye. :)

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source: https://worldradiohistory.com/BOOKSHELF-ARH/RCA-Books/RCA-Receiving-Tube-Manual-1940.pdf

so, I wanted to see a photo of it... so... off to google I went.
The image isn't the interesting part, but here's a photo of one in all of its ST-envelope glory.

1620488256399.png

one of the other images I saw as from wiki-p, and it caught my eye! :)

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sez Wiki-p:
The 6N6G triple-twin tube enabled building a fully-functional audio amplifier with just two parts: the tube and the output transformer.
(as an aside: triple-twin sounds like some sort of a basketball stat to me...)

Well, OK, I guess technically, some sort of B+ power supply is needed, too (batteries?!?)... and an input jack, oh, and a filament supply (more batteries?!?!?)... but... talk about a spud amp (one tuber)!

:confused: :smoke


Now I want to build one...
 

paulbottlehead

Active Member
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You could definitely build a minimalist circuit with something like this, though you'd want to measure how much AC voltage you need to throw at the input to get the desired output.
 

MrEd

Senior Nobody
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I would think a table radio from that era may well have been normal habitat.
Would be a fun project for sure.
 

Thermionics

Post Whore In Training
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believe it or not -- nope! :(
Thanks for the tip, though -- I was wonderin' about cost-effective ;) iron for such a crazy project. :)
You could always use a pair of these cheap & cheerful $15 output transformers from AES: Transformer - Output, 8 W, Single Ended | Antique Electronic Supply (tubesandmore.com). These are the outputs used by Dave Gillespie in his rehab / performance optimization of the Magnavox 8600-series SEP.

For power transformer, it's just a bog-standard 600VCT with 6.3V secondaries.

Edit - fixed my brain-fart where I put 300VCT instead of 600VCT as the transformer has 300-0-300V primaries and I was under-caffeinated
 
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Kyle

Junior Member
Years ago, I built an amp using a 2B6 which is similar to the 6N6. I only had one 5K transformer at the time but the sound quality was quite good. As I recall, it sounded like a 2A3 with less noise, presumably due to heaters instead of filaments.
I bought a half dozen new in box tubes with 4 solid watts of fun for a buck each. Those were the days. You can't buy a foot of wire for a buck now.
 

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paulbottlehead

Active Member
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The 2B6 running into a 5K load will give you a damping factor of less than 1, which will lead to boomy and uncontrolled bass with just about any speaker you use. This wasn't really an issue with radio receivers at the time, as there wasn't really any content down that deep. Some feedback and an extra gain stage would definitely be in order.
 

Kyle

Junior Member
This was 25 or 30 years ago, I don't recall the circuit I used. I'll do a bit of digging and see if I have a sketch.
I recall that it sounded good but that's still a memory.
 
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