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I did a little test to see if I liked LED bias or my fav lead acid batteries. The LED bias is cold in the mids the life of the 801 pre amp was not there AT ALL, it only took 10 minutes to hear that I did not like what they were doing, the lead acid batteries win for me, what do all you nuts that have tried this stuff thing of LED, do an of you like lead acid batteries? LED ARE REALLY FUNKY SOUNDING TO ME.blah BLAH
Follow Ups:
I hope to hear more about people's battery biasing experience since I may go this route.Since battery biasing doesn't take much current (if at all) then any battery should work. The old "super heavy duty" pre-alkaline style is known for sounding good. Cheap too.
Rather than putting the battery in series with the cathode a better solution may be to put it in series with the grid resistor. Also consider using a battery bypass cap of 12uF or so, PIO is nice maybe.
2V 25aH+ lead acid batteries can be obtained fairly cheaply. Check All Electronics, ebay etc. You'll have to build a charger.
Tried nicads and LEDs on both phono and line stage tube cathodes. In the phono stage I use 1.2v infared LEDs and found them better than c size nicads. In the line stage I use 3.6v nicads that function at about 4v with voltage applied. The sound is good. I used to use white 3.6v LEDs in this stage and may go back. The bass may have been better with the LEDs. Other changes in the circuit before I retry though. Because of the low price of components, I suggest you try both and let your ears be the judge.C. -=^v=-
Look for discarded computer UPS (uninterruptible power supplies) in your local computer junkyard. Open them up, and measure the battery voltage with a DMM. Those batteries are usually rated 6 V 8 AH.
If the battery has anything above 5V on it, it is in good shape.
I bought several of those for $2 each. I plan to (eventually, when I find the time), use them to power 26 tube filaments, through a CCS.
I hope this tip helps anyone who needs 6V bias.
Carlos
I have used nicads but still like the leads more it is in the mid were I love them.
My whole system is biased with lead acid batteries right now
That consists of
preamp-801 at 200volts on plate one 12volt lead acid on cathode
Driver -801at 520volts on plate three 12volt batteries at 45 volts on cathode
Output -2A3 320 on plate three 12volt batteries at 49 volts on cathode.
I really like the amp straight out of the CD player the best right now the preamp grounding is fun because I switch over to tran out put
And the grounding I like for cap output do's not work for tran out very good it mellowed out the pre to much, on the amp I just changed for the 826 driver which do's not work with interstages because of plate resistance to the 801 with interstage and I like this change for the moment but the 826 was a fun driver to never have had so good interstages before Intel no I like the sound of tran coupling it has such better tone and the attack of instruments
Is not all the same like caps do.
When I changed the bias of the output tube to battery the mid glare and a mid bass glare diapered which I like I love how the amp sound right now it has a very romantic sound is tone is so pretty, but the pre needs so work now
blah blah blah.
Sorry for the bad post I went to fast and did not read over it.
Some of us are bad at righting.
Please be understanding.
Thank you.
Some words are not what they were Intended TO SAY.
Hello ALL DHT:no apologies necessary whatsoever. I enjoyed reading your post. It is a bit dense (which means I will have to read it more than once)... but it does convey your experience and your enthusiasm.
best of in your projects,
Mike LaFevre
what bad post???everything you say makes sense to me so your intent was proper... if others don't understand its their problem not yours and looking at your offerings you have a lot of passion about this... and thats what its all about.
but i get yelled at for always using lower case letters... oddly enough others get berated for using all upper case letters... there is no pleasing everyone so be yourself and don't worry!
dave
what bias voltage were you trying to get???an interesting aside... the use of a rechargable battery in the cathode is known as "Kotei" bias in an old joenet post from reid welch it stated that the direct heating folks preferred lead acid kotei to nicad.
i found i like nimh batteries (two AA nimh in series for -2.7V on a 6C45) best and high capacity nicads better than Lead acid cells... and once you get past 3-4 seriesed cells i tend to prefer the more traditonal R/C combo... (remember that the 6V lead acid cells are just a bunch of lower voltage (2v?) cells in series...
has anybody else compared the various batteries in kotei bias?
dave
Hi DaveNo the batteries Josh and I use are not a package of small units, like for RC use. These are fully sealed LA type used in emergency lighting. They are labeled YUASA and each measures 5.5" x 3.5" x .75".
See you later
D
I'm planning to use batteries in the cathode to heat the filaments of a 2A3 (driver) and an 845 (output).
Is that not recommended in your experience ?I suppose I'll use 2 NiCd's =2.4V for the 2A3 and lead acid batteries for the 845. Not quite sure about the latter yet. I would need 5 cells for 5x2 = 10V. Can't quite get there with NiCd's as 8x1.2=9.6V.
The idea is to avoid almost anything (i.e. resistors, caps) between the filament and the ground.Should I use an equal number of cells on each side of the filament or should I put them all on one side ? i.e.
/\
| |
= =
| |or
/\
| |
| =
| |
?(hope this comes out ok..)
This is all for RC coupling between stages with fixed bias say.
If I go for direct coupling it will get more complicated. One idea would then be to use gas regulators (stacked for the 845) to achieve cathode bias. (Again then I wonder if I should use one on each leg or not.)It all sounds crazy - that's why I haven't done it yet..
Stelios
heating of the fils is a different situation than using the rechargable battery as a form of fixed bias...i think given the amp hour capacity that will be needed you will have to go with the lead acid cells.... and getting them to hit the proper voltage may be tough... i really like the concept of not introducing resistors...
so for your 2A3... if you go for the high capacity nicads... the dcells are around 4AH so in a perfect world you should get just over an hour per pair of them on a 2A3... so you would probably have to make up some packs of multiple cells to get any length of service out of the 2A3...
the lead acids will get you 10V, but unfortunately i have never seen a 10V cell... so you would need 5 of those 2V (dsized) cells, and then you will have a similar situation to the nicads... lots of cells needed.
it seems like quite an undertaking for me to try these current hungry tubes on batteries, but go for it :-)
as for placement of the cells... i would put them in one leg so there is a clear path to ground from one side of the filament, and pay attention to how the DC effects the overall bias of the tube...
essentially the cells will be in series, and its just a question of where you put your AC return... and i would avoid the "ct" of the batteries, either use the + side or the - side and one side just gives you the filament voltage more in biad for the grid.
dave
Thanks for the reply.Yeah, power hungry is the main issue.. 2V lead acids cost a bomb each ! Plus I keep thinking they will run out in the midst of my dad's party and he won't understand what happened ...
I'm glad you pointed out that batteries will affect the biasing - I hadn't realised.
I don't suppose you can parallel nicads ? I think it's a no - no as far as I know but it would be really convenient to be able to, esp. as I have a few 2nd hand ones lying around...
Stelios
the batteries don't effect the bias any differently than any other DC supply does... depending on which side you reference you get a different bias...to be honest i haven't done much with dc supplies in dht's i just noted the difference in bias and clipping depending on which side you reference... as i recall i like referencing the ground side for outputs so the entire filament is at or above so A2 operation is farther away, but for a driver that has headroom... i'll take the + side to ground for that little extra bias for free... it means the rest of the needed total bias is a little easier to get, you just have to be aware that A2 will start at the filament voltage and not 0 V so keep clear.
this is another one of those things that i would like to see a fuller treatment of... i guess you could look at it as using a -7.5V supply on a 10 used as a driver... why not??? as long as you keep deep class A (has anyone ever done a class A2 driver???) and of course the whole thing is not much of an issue with a 2A3 at 2.5V... but the GM70 at 20V thats a different story.
on the paralleling nicads... not sure... some batteries handle it better than others... and charging/discharging have different requirements... not sure what applies to what type...time to crawl back into the box... man its boring in there!
dave
Why not just use the 6a3 instead of 2a3 and share a 12 volta battery across both valves?Paul Barker
Thanks for the reply.Hmmm, I'm assuming you mean the valves for both channels - is that right ? (I'm designing a pair of SETs.)
In that case wouldn't the signals get mixed up ? I think it would be hard to avoid that - no ?
The thing about 2A3 variants is that most of them are not in production - I wanted sth robust that I can easily replace (robust doesn't mean much in my hands..)
Plus I've already bought some Sovtek monoplates. Aargh!! I'm dying to use them! - maybe I should skip the 845 section for until I have plenty of time to work it out..
I thought they were really a bargain at the price and then realised it's their RRP :)
Stelios
man paul... i like the way you think...the two 6B4's in series will work, but the problem comes when you look at the bias of the tubes...
look at the whole string in series... you have:
12.6+.... fil1 ..AC gnd.. fil2.... 12.6-the AC ground will either be ground if you fixed bias, or the R/c combo for cathode bias in ant event the cathode is at AC ground so there shouldn't be the mixing (of course the cap isn't perfect sooo...) the problem shows up when your two tubes have a difference in DC potential between them... so one tube will start with 6V or so different bias than the other...
its "dumb" ideas like this that get us thinking outside the box though... my next thought was to series the 845 and the 2A3 for 12.5V but the current draws would have to be the same... damn that 3.25A filament... but its still thinking outside the box...and thats where all the good stuff is found.
please note that i used quotes around the word "dumb" because i think it was a great idea... but so often thes good ideas mistakenly get filed into the "dumb" category.... at some point or another about 1/2 the things i like in my amps were labeled as something that "won't work" by those that know better...
dave
Since one can get more than 12V with a 12V lead acid battery then maybe the 2A3 and the 845 filaments can be connected in series. To maintain 3.25A through the battery a resistor of 2.5/0.75 = 3.333R, > 2W could be used in parallel with the 2A3 fil.That is if we can make sure the battery provides constantly 12.5V across it (or 3.25A through it). I think that some 12V batteries can go up to 13-14V when fully charged. So some adaptive solution is needed i.e. regulators or maybe a trimpot and a meter.
Seems complicated and if cathode bias is used it gets worse defeating my original purpose of avoiding resistors in the cathode.
But if using RC coupling and fixed bias then it seems worthwhile.If I do use batteries in the end I think I'll go for either one of two options:
a) work out the max time I'll be likely to be listening to music and get an appropriate battery
b) have two batteries which can be connected alternately and have enough capacity so that one can keep playing for as long as the other takes to get charged. The problem would be how to make the transition.
yes "dumb" but I am doing it, each valve is adjusted accordingly in my amp, that is to say the bias controlled through the driver is altered to get a satisfactory average for each tube the only thing you can't alter unless you monoblock is the B+ to each channel, but working with the bias alone you can get both tubes even.Now I have Anrej's 6a5g's in place though I'm going to try ac heating and this will no longer be a problem. Though I love the sound of lead acid batteries they are an inconvenience. It's all that charging and disconnecting from charger for playing beloney that wears you down in the end, and the fact that only the electrically competent can use the amp. In a house where the 4 year old son has to show the 43 year old mother how to get sound out of the video this is an issue.
Regards
I'll keep chipping away for "dumb" ideas!
Paul Barker
well we have to remember at some point not to long ago a group of folks shunned SET's as dumb for PP pentodes... then those PP pentodes got dumped into the dumb category for solid state...its funny how the whole "dumb" concept is brought to life by engineers, and then the marketing division gets ahold of it and they get their cut and the only people who suffer are those convinced by someone else that everything they spent on their sysrem was right.
some fool once said... two wrongs do not a right make... well i have more than two wrongs and guess what... i think my sound is pretty right...
someday those marketers will realize that three lefts actualy make a right, and that means they can sell 3X the stuff... which will of course require 3X the engineers and everyone will be happy.
oh yeah... i don't care how far apart my tubes are operating... as long as they are not totally screwing up and the sound is good... why worry...
on the 6A5G... i would love to see the whole story on that tube... i have heard autopsy reports that many are just plain old DHT's and the books are wrong... who knows maybe the relabel of the 6B4 was just a marketing ploy to keep the tube base diagram drawers happy :-)
dave
Well Dave,they have the V shaped filament (ok I should call it heater but like I say looks and glows same amount as PX4 V filaments). The cathode is connected at the midpoint and they sound pretty good!!! Whether that cathode connection makes them the same characteristics as a dht but with an equal tap I don't know.
I haven't heard any other idht output valves except the 6EM7 power stage. The 6EM7 is far more clinical, and gets distorted at high output, as a look at the curves would tell (know you don't bother much about curves but they do guide and in practice yes though I prefer 6EM7 to multi grids hooked up as triodes it ain't a dht.) I would like to get hold of some R120's they would be an inetersting listen compared to the 2a3 type and these 6a5g's.
Regards
Paul
when you say the cathode is connected in the center of the VV it is just a CT DHT filament with the CT labeled cathode... the tube is still directly heated, it just has a cathode tap...or thats how i see it.. the tube drawing shows the filament CT connected to a cathode, but i have yet to see the cathode element in any of the tubes... has anyone else???for it to be an IDT like most people call it it would need a cathode sleeve... i suspect you could ignore the cathode connection altogether and wire it with a traditional hum-balance or DC and the tube would function the same... but given that the CT is there you would be foolish not to use it!
dave
That makes sense to me, as I said it sure looks like a filament. I see the centre tap as a gain, though an inconvenienceas it means it's not a plug in replacement for 6B4G. Having said that not a problem to guys like us, I very much like the sound of these so I'll use them until destruction.
RegardsPaul Barker
Hi Guys,I have been following this post partially because I would like to heat my 26s with nicads and partially because I am at the mercy of batteries everyday. Most of our Betacams run off of a BP-90 style pack. They are rated at 12 volts but if the meters in our veiwfinders are at all accurate, a fully charged battery will read well over 12 volts...sometimes over 13! Most use high capacity (either 4 or 5 Ah) Sanyo cells in series. I'm curious if these cells are purposely under-rated or if this might be the result of the chargers that we are using. At any rate, I'm hesitant to try these for fear of putting undue stress on my tubes.
FWIW-you can find these 12(13.2) volt nicad packs on ebay for under $100 with a 3 year warranty from time to time. Look for Anton Bauer brand or Pro Battery. Check out the link below- I called a few months ago and they were selling them outright for $80.
Tom
Not sure where you are doing this.I tried LED on the cathode of input stages is that what you did? Sounded abismal. resistors are much nicer sounding whether bipassed or not. The soundstage from led's shrank right back to the speakers, lost all dimentionality. YUK. threw the lot out (I'd collected some from disposable cameras). No place for them in my amps.
Battery bias I have only tried on the grid, I'm doing that now, seems OK, but I think I'll just make a rectified bias supply when I eventually box this amp for convenience sake.
Paul Barker
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