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Good IT's arent that expensive.

Posted by Jim Doyle (A) on October 18, 2005 at 15:35:17

In Reply to: Re: Komuro DC 300B w/ 50 DHT? posted by fred76 on October 18, 2005 at 02:45:21:

$83 gets you into the Electra-Print 3634. It's 30mA rated and is
a 5K:5K (or, 1:1) perfect for the 6V6 family. If you really need
special aesthetics, get it potted by E/P. Remember, decent plate
chokes are $54 (i.e. One Electron PRC-2). So... For the extra 25 bucks... it's a no brainer. I bought the 60mA of the E/P interstages because I "anticipated" the need to do 300B IT 845 at
900V. However, that day has not come and may not come, so I now use
the bigger E/P ITC happily with 6W6.

As far as two-staging, why not? You'll need to feed the 6V6 with
a good 20V to go full power. The 50 needs alot of voltage drive.
The reason I did DC but three tubes is to avoid UHF psychotubes like
the 6C45, avoid an additional capacitor phase shift, but get the
100V of drive I needed for the 845.

A 6C5 or 6J5 / 6V6 combo can easily drive the 845 250Vp-p. I did
this for awhile running the 845 at 830V and lots of current. The Komuro gain stage is capable of driving much bigger stuff than
the 50 or 300B. In fact, it might have too much gain.

If you want to knock down some gain, how about Triode 6AV5GA (mu=4)
and 6C5 (mu=20). This will perfectly drive the 50 or 300B. The 6AV5
in triode looks like a 2A3.... The only downside is you might have to
bias it at 40-50mA or so which means the bigger E/P transformer and more B+ being burned down. The 30mA for the 6V6 is actually a fairer price to pay for the drive. ;)

Further, the Electro-Harmonix 6V6GT has been uprated to work at
400V (where guitar amp heads burn up all their classic RCA's). So,
in the long run, the 6V6 is a nice way to go!

-- Jim

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