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A little tube porn: "Gossamer" VT-62 (RAF) SE A2 amp

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pmillett

pmillett

Member
Joined 2005
pmillett.com
Finally built some amps using the VT-62 (RAF) triode (basically 4304CB or DET12, or 834 with a B4 base). Conservatively about 15 watts out. Hot as heck.

Driver is a triode/pentode with the pentode a DC coupled cathode follower to drive the VT-62.

Details at http://www.pmillett.com/gossamer.html

PXL_20240420_190407026.jpg
 
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isaacc7

Member
Joined 2006
isaharr.com
Fuling

Fuling

Member
Joined 2001
Good to see more people using a cathode follower rather than a Mosfet to slap the following grid around. I understand why Fets technically are better but I like the built-in soft start mechanism in a cathode follower.
Congratulations to a very nice amp, I like the paint job!
 
SpreadSpectrum

SpreadSpectrum

Member
Joined 2007
tubeswithatwist.blogspot.com/
Very nice! There are so many of these unique-looking tube types that need to make music.

I acquired some real oddball tubes at great prices (VT-127A and 327A, 100T variants built for pulse duty in WWII ship radars) and am getting ready to build custom sockets/supports for them. I've run them up on a breadboard and got astounding performance so I can't wait to get them in the chassis I just got from Landfall.

I did a two-stage design with a CCS-loaded pentode input and feedback from output tube plate to input tube cathode. I ended up with over 30dB of feedback, keeping the transformer out of the loop. Distortion was quite low, but anything that happens in the output transformer goes uncorrected.

Thanks for sharing, I love how good the final product came out. That finish is really nice.
 
C

CijTele52

Member
Joined 2005
Hello Pete, When I read your article about the driver board VT62, I thought it's 801A / VT62. o_O

Thank you for the design ideas of 6LQ8. I tried the same topology with 6EM7, but it wasn't successful because the triode's GM was too low. The high GM dissimilar triode-pentode has more advantages.
 
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isaacc7

Member
Joined 2006
isaharr.com
pmillett said:
The blue amps are push-pull EML 520B amps. About 50 watts out. D3a triode diff pair, transformer coupled to the 520Bs, running at 500V, 90mA per tube. Lundahl iron. Never got around to publishing anything on them... But likely my best design 😁
Click to expand...
So you’re saying you’ve only shared your junk stuff with us? Lol.

Considering your other designs are so good I’m curious as to why you’re partial to that 520B amp.
 
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