8 Sep
2008
8 Sep
'08
12:49 p.m.
Allison wrote:
12AX7 at 12.6V @.15A (1.8VA) or parallel connected
6.3V @ .3a and I consider
that trivial. A transformer sufficient to run 10 of those (18VA) is under
2-3pounds. The average 12V at 1A wall wart can run six of those with a comfortable
margin. We are not talking a lot of power yet. If we are in the realm of 100
or 1000 of those then we have some power needs to deal with.. The solution
there would be to use instead of one 12.6V transformer that can give 150A we
can use ten more readily available transformers of a mere 15A (189VA) which
is more manageable anyway.
...
Another example is 40 years ago I had a Beckman EPUT (events per unit time)
counter that used the then typical tube era 5mhz ring counter decades with
neon readout (0-9 with NE2 type neon behind them) (6 ofthem) plus timebase
for a whopping 42 tubes mostly of the 12AX7 types and it was big (19" rack
width by 11" high) but I distinctly remember it as barely 40 pounds
considering it was fully enclosed in a steel case and each decade
was in its own case that plugged into a matching socket in the cabnet.
On the other hand, the HP524 8-digit 10MHz counter (just shy of 100 tubes) I
have is well over 100 lbs. Due to the combination of size and volume I can
just barely wrangle it up and down the stairs without assistance. (As much as
I like them they are boat anchors and a PITA.)
Aluminum chassis, I expect the 2 power transformers account for well over
half the weight.
Powering tubes in that class (ECC83s) is trivial
compared to the day of the
ABC where typical dual triode was maybe in the class of 6SN7 (6.3V at .6A) or
worse. Early tubes where power hungry for heater power.
This is not an issue of early vs later tube developments. The 6.3V @ 0.3A
'standard' for signal tubes goes back to the early 1930's and the
introduction
of the first series of 6.3V tubes (75,78,6A7..). The 12V at 150mA of the the later
12V tubes follows directly from this (double V,half I,same heat).
The distinction between the 12AX7/ECC83 and 6SN7 regarding filament
requirements is one of capability not age.
The 6SN7 is a significantly higher power tube (5W/plate max dissipation) than
the 12AX7 (1.2W).
The ABC used 6C8 duo-triodes which are 6.3V @ 0.3A. The 12AX7 and 6C8 are more
similar in terms of characteristics than the 12AX7 vs 6SN7.