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I have a couple 30's that I'd like to play with as the VA stage in a preamplifier. Is it a bad idea to use a single battery for both filaments, or should I really be using two?Also, as I place cells in series, what effect does this have on the amp-hour rating of the battery? Do two 1000mAh cells make a 2000mAh battery, or simply a 1000mAh battery with a higher voltage?
Follow Ups:
Hi ,
In series your batteries will be the same mA/H rating . I have built linestages with shared filaments and used a rechargeable battery between filament - and 0V , but I would recommend a supply for each . You could always place your batteries in series and use a resistor between each filament - and 0V , running your battery from filament + to 0V , it's a concept I used when I ran an all battery linestage and it works very well . This way a much lower value bias resistor could be used . I would recommend some 2500-2800mA/H NiMH per 30 , these should give a very reasonable amount of use before recharge .cheers
Thanks for the good word. You have me thinking two cells on each 30,small dropping resistor. 1000mA/hour's give me about a week between charges. 2500mAh gives me much more.As for keeping a charge: I've seen some charger circuits that are intended to run when the power to the amp is switched off. Not sure that I'm comfortable having something I built running 24/7 charging up whatever gets in its path...I think I'll stick with swapping batteries out to an external commercial recharger as the time comes.
I'd like, though, to have some sort of simple low voltage indicator for the flaments (appart from the filaments turning off being their own low voltage indictor). Maybe just an led to light when the voltage drop hits 1.8 over each filament or so. Any thoughts?
Thanks everyone & thanks fatbottle for jumping in on both my questions. (this thread and one from a week or so ago)
Hi ,
Remember the dropper can be incorporated into the bias network ;) I used a DN2540 set to 20mA to charge the batteries in my linestage . I don't know if this is the best way to do it but it works and the batteries never get hot during charge . Whatever form of indicator you use will drain the batteries , maybe the best idea is to buy an LCD voltmeter module and build this into your projectcheers
"the dropper can be incorporated into the bias network" Ummm... what do you mean? Do you have a schematic you could either post or e-mail to me?Thanks!
Like this , remember the 'cathode' resistor has the battery current running through it so will be a much lower value . It takes a bit of adjustment to get it spot on , but maybe worth a play ;)
Ok, it looks like you're using a number of cells to bias the tube & then setting the filament voltage with the dropping resistor. Is that close?I'd like to use as few cells as I can get away with, but you've given me a lot to think about.
Hi ,
Remember Kirchoff's law comes into play with that resistor . You could get away with the cheap 800mA/h Nicads and the 30's 60mA filaments . I bought 25 packs of 4 at £1($1.10) per pack , charging circuit was a LM317 per side . Did the B+ with 70 of the cheap batteries and six per side with a CV1676 . No good with 250mA filament valves such as 3A/109B though , eats the filament batteries flat within a few hourscheers
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