22-06-2020, 04:55 PM
(This post was last modified: 22-06-2020, 05:14 PM by Mike Watterson.)
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.
I've designed and built some SMPSUs ( a Cuk based one was best) with a reed and custom coil in series with the LT to turn it on, so only LT batteries needed. Easier to do for 250mA than 125mA, wrong wire and number of turns and the voltage drop on LT can be too much or it may not turn on reliably.
I decided in the end there was no point to mains adaptors on battery only valve sets. Decent alkaline batteries can have a 5 to 10 year shelf life. So I concentrated on recreation of battery packs with as close to original performance in run time and in original size pack, style of label and type of connector.
There isn't a single one of my valve battery sets I'd consider for everyday listening, though some of the Pye and Philips are very very good, they have their own built in AC. The Hallicrafter's S72 is the only one with BFO and "RF Gain" (it's IF gain really) and though it has a regular speaker it takes 2K + 2K headphones, it has uses a massive battery or 115V mains. The only other one with a phone socket is the McMichael 1929 suitcase model. I've plenty battery valve sets with their own built in mains. Some are more sensible to use on battery and most of the Attache style ones are best used on my shaver transformer in a box with an extra hole drilled for the "earth" pin. Any deemed unsuitable to use on mains either have a USA two blade plug or UK 5A round 3 pin plug, they are sold new here for home lighting.
I have some that take lead Acid and I have one large glass lead acid (NOS never filled from 1970 for a plant room battery backup, so worked when acid added). I've also two simulated Lead Acid packs using parallel and series C cells. The combining diodes add enough voltage drop. The 2V is really almost 2.3V fresh charged (drops quickly to 2.1) about 1.7V when flat, best recharged at about 1.85V. The NiMH are a bit more than the NiCd, but have the same 1V recommended end point. The sets with Lead acid were ALWAYS supposed to have the cell(s) swapped, never charged in place. So the NiMH with even Schottky diodes to combine parallel series can be OK. The original gas vent/ acid inlet becomes a fuse. Separate diodes and resistors split and limit the charging voltage, which should never be in situ.
The continental 1.4V LT models with mains used an NiCd of DEAC brand from the 1940s to regulate the mains. US and UK mostly used serial (impossible with German Y8 metal can family), 7.5V to 12V nominal battery. Some later UK models with mains and 1.4V use a selenium rectifier as a shunt regulator and the LT rises alarmingly if one valve fails or is missing. Some of the 3rd party 1.4V & 9V eliminators would rise to 120V and flash over valves if LT wasn't connected and were either for 250mA or 125mA. Models that did both had a screw to connect a 125mA shunt resistor. They are dreadful, again if one valve is dead/out the LT rises too much.
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've designed and built some SMPSUs ( a Cuk based one was best) with a reed and custom coil in series with the LT to turn it on, so only LT batteries needed. Easier to do for 250mA than 125mA, wrong wire and number of turns and the voltage drop on LT can be too much or it may not turn on reliably.
I decided in the end there was no point to mains adaptors on battery only valve sets. Decent alkaline batteries can have a 5 to 10 year shelf life. So I concentrated on recreation of battery packs with as close to original performance in run time and in original size pack, style of label and type of connector.
There isn't a single one of my valve battery sets I'd consider for everyday listening, though some of the Pye and Philips are very very good, they have their own built in AC. The Hallicrafter's S72 is the only one with BFO and "RF Gain" (it's IF gain really) and though it has a regular speaker it takes 2K + 2K headphones, it has uses a massive battery or 115V mains. The only other one with a phone socket is the McMichael 1929 suitcase model. I've plenty battery valve sets with their own built in mains. Some are more sensible to use on battery and most of the Attache style ones are best used on my shaver transformer in a box with an extra hole drilled for the "earth" pin. Any deemed unsuitable to use on mains either have a USA two blade plug or UK 5A round 3 pin plug, they are sold new here for home lighting.
I have some that take lead Acid and I have one large glass lead acid (NOS never filled from 1970 for a plant room battery backup, so worked when acid added). I've also two simulated Lead Acid packs using parallel and series C cells. The combining diodes add enough voltage drop. The 2V is really almost 2.3V fresh charged (drops quickly to 2.1) about 1.7V when flat, best recharged at about 1.85V. The NiMH are a bit more than the NiCd, but have the same 1V recommended end point. The sets with Lead acid were ALWAYS supposed to have the cell(s) swapped, never charged in place. So the NiMH with even Schottky diodes to combine parallel series can be OK. The original gas vent/ acid inlet becomes a fuse. Separate diodes and resistors split and limit the charging voltage, which should never be in situ.
The continental 1.4V LT models with mains used an NiCd of DEAC brand from the 1940s to regulate the mains. US and UK mostly used serial (impossible with German Y8 metal can family), 7.5V to 12V nominal battery. Some later UK models with mains and 1.4V use a selenium rectifier as a shunt regulator and the LT rises alarmingly if one valve fails or is missing. Some of the 3rd party 1.4V & 9V eliminators would rise to 120V and flash over valves if LT wasn't connected and were either for 250mA or 125mA. Models that did both had a screw to connect a 125mA shunt resistor. They are dreadful, again if one valve is dead/out the LT rises too much.
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.
