[Amps] Ref: 4- 6AG7 Linear

[Bill L. Fuqua]

I ran (4) 6AG7 tubes with about 1100 or 1200 volts on the plate. They were in grounded grid and were pressed into a heatsink I made of a block of aluminim. I had drilled 1"holes in it and using a table saw with carbide tip blade cut slices to make fins. It required some air blown over the heat sink but it worked great and  no steam. 
   It only took a few watts to drive and could run continuously at over 150 watts plate input power maybe more.  
   I have been trying to find the parts for this amp but have only found the heatsink. I had a large TV transformer mounted with a voltage doubler and used a pair of large AC run capacitors for the filters. 
   6L6 tubes are not so good for grounded grid due to the additonal capacitance between plate and cathode. The beam forming plates are internally connected to the cathode.  I once tried a 6DQ6 ing GG but it was not stable on the higher frequencies. 
   I had to condition the tubes by initially bring up the HV lowly and letting them spark. But after getting them up to the full plate voltage I had no problem.  I'd like to do the experiment again and take some real measurements. 
   I did open up a tube to see what had happened inside. It had two parallel plates inside and no glass envelope. I am guessing that there was good black body radiation to the metal shell that allowed it to work at such high power for a tube intended to be a video amplifier for early TV and for low power RF applications such a buffers and oscillators. 

73
Bill wa4lav


73
Bill wa4lav 
-----Original Message-----
From: "Bob Good" <k4bg at planters.net>
To: <Amps at contesting.com>
Date: Sat, 25 Dec 2004 09:34:27 -0500
Subject: [Amps] Ref: 4- 6AG7 Linear


Nostalgia !  I aquired my CE 10-B in 1960 and ran it barefoot (!) beside my PP TZ-40's.  I knew of some hams who built the 4- 6AG7's but they only ran 1kv to the plates at 100 ma.  Perhaps 6L6's would run a bit more.  Now if you only could turn them upside down into a coffee can filled with water like we used to do with the AT-1 ! ( metal tubes required ofcourse.)  Thanks for the memories.  Seasons Greetings....  Bob K4BG
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