There have been several posts lately about trickle chargers for battery-powered amps, and how to design/build them. Here are some building photos of trickle chargers for a couple of PIMETA's. The chargers are based on the LM317, with 2x9V, powered with a linear regulated 24VDC 500ma walwart (Jameco). The batteries are not pictured, but I'm using some 250mah, 8.4V "9V" batteries I got on e-bay. I will leave the calculations to others. The walwart is linear-regulated only to ensure good sound if the amp is operated under wall power. You will need higher voltage if you use 9.6V "9V" batteries.
The idea started with __redruM and this thread a little over a year ago:
One of the most recent detailed discussions was started by ozshadow here:
__redruM essentially drew from Tangent's design for a charger in the PPA. Since then, what's shown in the schematic below is used in the PINT and the Mini3. The schematic and layout shown in the photos is as follows:
1 - LM317T, TO-92 case
2 - 1N4001 Diodes
1 - 100 ohm 1/8 watt resistor
Protoboard, jumper lead wire
Also added were two Radio Shack 9V battery leads (higher quality versions), and an isolated, 2.1mm walwart socket.
Parts and jumpers placed on protoboard and taped - ready for soldering:
Many thanks to Tangent and __redruM for their comments and ideas in various threads.
Edited by tomb - 10/8/15 at 6:52pm