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nigelh 20th Dec 2004 6:11 am

Battery eliminators
With solid state power supplies, used with portable valve radios, the HT and LT are applied to the circuitry virtually immediately, as opposed to a gradual increase in HT as is the case with a valve power supply: can there be any resulting damage to the filaments of the valves?

McIntyre 20th Dec 2004 6:35 am

Re: Battery eliminators
I assume portable means battery receivers? If so the HT would propably be somewhere between 90-120 and LT at 1.5v. These voltages (originally) supplied by two seperate batteries apeared instanstaneously when the set was switched on. The filament voltage always appears immeditaly on the vast majority of of battery receivers I've seen - and propably also true for 6.3V. filaments in paralallel.

Battery eliminators from the fifties used early solid state diodes even in sets such as the Akkord which came with its own transformer for 90 and 1.5V had a switch at the back of the set and gives HT immeditaly.

Not sure exactly but I believe the "Warming up" time of the regular Dx xx type 1.5 battery valve is literaly a couple of seconds. I don't see any reall benefit for gradual HT, I do have a couple of circuits using a EL33 (could be considered a sacrilige for this valve) and another a EL81 for use as a battery elminator if you would like to try them out.

Apart from over running the filament of I don't believe that any damage can occur from immediate HT and LT in portable sets - even if there is the battery valves are so cheap and pleantiful.


Duke_Nukem 20th Dec 2004 8:41 am

Re: Battery eliminators
My only concern re solid state supply is its low output impeadance compared to a battery on the LT supply. The valve heaters are much lower impeadance when cold, so without additional circuitry the solid state version will cause a higher surge current in the delicate little battery valve's heaters.

The solution is not to use a voltage regulator but instead to use a constant current source instead.


nigelh 20th Dec 2004 8:56 am

Re: Battery eliminators
Thanks for the info, Andrew and Jon

GMB 20th Dec 2004 9:00 am

Re: Battery eliminators
Having just has a look at a few spec. sheets for some modern batteries I can't help wondering whether using a modern battery could stress battery-valve filaments. An alkaline cell packs a much greater punch than the old leaky zinc-carbon cells of the 60's!

John M0GLN 23rd Dec 2004 1:24 pm

Re: Battery eliminators
I remember reading somewhere, it might have been in the BVWS Bulletin a few years ago, that 6L6s in some jukebox amplifiers used to have 12v put across the heaters for a short period to warm them up quickly, to make sure you did'nt miss any of the music, depending on how long the amp' stayed on after the record finished, the valves could have been subjected to quite a hard life, but I don't know if they lasted very long.

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