23-06-2020, 12:19 PM
Mike Watterson Wrote:Likely that amount of metal degrades a frame aerial, so hardly a fair test. The Zinc of the B cells and F cells in an AD3 would have been differently distributed.
Yes I can see that - though TBH the space occupied by the SLA and chunk of aluminium is probably less than the B136 battery. But its a good point, comparison might not be fair.
Mike Watterson Wrote:Basically, on series or parallel sets operated on mains the simplest thing is to check volts on the DAF91 or DAF96 as it will be the end of the chain. Should be 1.35V +/- 5%. Most decent series sets have taps or a rheostat to set the LT current, usually stated. The 7.5V nominal battery sets typically at 6.8V. Any purely with either HT or LT via a dropper off the mains want to be run off a shaver transformer. 1930s to 1960s concepts of safety and 70 year old insulators between metal panels and live chassis are not good.
I really do not like the idea of series-connected filament chains, with bypass resistors as more electrons, going up the chain, leap off into space. Too variable and flakey IMO. It's parallel every time for me.
I don't use my battery sets for everyday listening when a mains radio is available, and no way would I make a mains adaptor and use as a mains set. Though not eschewing the odd modification, I've always kept to the original design intent which is mains-independent.
However, my Vidor CN420a has still had a lot of use in last 10 years, with stabilised battery-derived power supply. LT is set at 1.38V and varies less than a millivolt till the battery (NiCad in this radio) is at its last gasp. It's clocked-up well over 1,000 hours in that time, with 3 valves the same (DK96 I zapped with a moment's carelessness; replacement S/H 'pull' has run 9 years). It goes on overnight travels with me. It's been used on the roof as I clear leaves from gutters.
I'm confident that the long life is due to LT care, after all, 1.5V from a new dry battery is over 7% above the nominal 1.4V rating which must have a disproportionate impact on valve life and cathode depletion. Also, not being forced to operate at 1.1V again means there's been very little possible damage by filament bombardment.
