[flipper]

On Thu, 16 Feb 2012 11:24:13 +0000 (UTC), Alejandro Lieber
wrote:

Alejandro Lieber wrote:
flipper wrote:
As for 'today' it's probably because people tend to copy what was
common or 'popular' and that's not a bad starting place since there
was probably some good reason why it was. The 6DW5 datasheet also
doesn't give any audio amp numbers so DIYers don't have an 'easy' spec
to go by.

As for 'back then' your comparison doesn't hold because the 6DW5
wasn't less expensive than the 6BQ5 and my 1961 RCA price sheet lists
it as $3.20 vs $2.25, or 42% more expensive. Second, it needs a lower,
regulated, screen and, in the Bogen, that sucks up the cost of a 6CM7
regulator.

The Bogen is also operating them at 435V, when Design Max specs 330V,
and Class B which, assuming one doesn't mind Class B, requires the
added complexity of fixed bias.

http://lieber.com.ar/6DW5.png

There are two errors in Bogen's DB230 schematics......
R105 should be 100 ohms, not 220k ohms.
R107 should be 220K ohms, not 100 ohms.

Yep. Looks like somewhere in the documentation process R107 and R105
got transposed.


In short, it isn't at all clear that's 'better' than a pair of 6L6GCs,
and a plain ole simple B+ power supply, which could go up to 55 Watts
Class AB or around 30 Watts Class AB UL for not much more tube cost
(saving the 6CM7, alone, pays for the cost of one pair over the 6DW5).

At any rate, a plain ole 6BQ5 PP amp would have certainly been less
expensive not only in tube cost but the heater and B+power supplies
and OPTs. Plus, 17/15 Watts is only 3 dB less than 30 Watts which,
from a practical standpoint, doesn't really make all that much of a
difference so the cost benefit ratio definitely favors the 6BQ5, which
is probably why they were pretty common.

Now, another 'not seen very often today' tube is the 6CW5, which can
do 25 Watts 'in spec' Class AB, but it also takes a lower screen
supply. But it's a good sounding tube and, since it uses a 250V plate,
is relatively easy to power with readily available 115/230-115V
isolation transformers operated in reverse. And heater power is .76A
vs the 6DW5s 1.2A, which isn't trivial when running 4 of them.

I did a guitar amp with those and kind of like them. They also come in
a 45V heater version, the 45B5. I did a little stereo SE with those
and a 20EZ7 (20V 12AX7) with series heater string off a single
isolation transformer, so no filament transformer.