Hi. Keith here in the Great Bergen Swamp of WNY...

I wish that I still had the ARRL "Mobile Manual" that I had back in the
mid-60's. In there was a battery-operated rig called the "Tiny Tim" I
based my first Novice rig on the transmitter from that article, but made
it with a 12AX7 instead of the 3A5 that was used in the original...

I was asked if I had the info on the "Tiny Tim", and I have long since
lost the book, BUT...

Being your basic Pack-Rat, I DO have a copy of the 24th edition of the
Radio Amateur's Handbook (1947), and here are the specs for the 3A5 in
transmitter service:

3A5 - Dual Triode, directly-heated cathode (filament)

Plate dissipation - 2.0 Watts
Maximum plate voltage - 150 Volts
Maximum plate current - 0.030 Amps
Maximum grid current - 5.0 mA
Filament current/voltage - 1.4V (parallel connections)@0.22 Amps
                        2.8V (Series connections)@0.11 Amps
Maximum frequency (Full ratings) - 40 Mc/sec

Here's the typical operating values for Class-C Amp/Osc. service:

Plate Voltage 150V
Plate Current 30 mA
Grid Voltage -35V
D.C. Grid Current 5.0 mA
Input 4.5 Watts
Output 2.2 watts
Efficiency 48.9%

It's a 7-pin miniature tube, the basing diagram is figure 7BC. Pin-out
is as follows:

1 Filament
2 Plate, Triode #1
3 Grid, Triode #1
4 Filament Center Tap
5 Grid, Triode #2
6 Plate, Triode #2
7 Filament

You could run the tube as a MOPA (That's a Master Oscillator/Power
Amplifier) transmitter by using Triode #1 as the oscillator, and Triode
#2 as the P.A. By cutting the plate voltage down to 45 V on Triode #1,
and driving Grid #2 thru a small (100 pF) cap, you should be able to get
about 1 watt out easily, and get a fair note in the process. Keying
would have to be in the Plate line due to the directly heated filament,
so there would be a bit of a shock hazard I am sure. Grid-block keying
would be a possibility, too.

Does anyone have the early editions of the "Mobile Manual" out there?
This might be the next "BIG" project for the QRP-L, the "BATTERY TUBE QRP
RIG"!!!

72/73, Keith, WB2VUO