How to wire heaters with 12.6volt

[Tone Junkie]

So whats the method with 6.3 we have it split into 2 /3.15 so whats the secret with 12.6 is it split into 2/6.3 I know one is series and one parallel but I dont know the difference.Thanks Bill

[kagliostro]

Don't know if this is what you want to know because don't understand well your question

however

6.3v can be split in 3.15v+3.15v as to reduce hum

if the 6.3v winding has no CT you can connect from each wire a 100-220ohm resistor, the other side of the resistors together than to ground

in some old amp that have 6.3v winding without the CT instead of the two resistors you can see a potentiometer ( ~200ohm ) connected to the winding, the wiper is connected to ground, to have less hum you adjust the position of the wiper (must use a potentiometer that can support the current - don't use a normal pot, use a wire pot)

some tubes, like ecc82 can be connected also for 12.6v, they have 3 connections, is something like a 12.6v winding with CT (when you use 6.3v connection you connect one wire to the CT and the other to both other connections)

sometime 12.6v connection is used for a 12v DC connection, also with 12.6v connection consumption is less

12.6v can be reached also by two 6.3v tubes in series (preferably don't use series filament connection for preamp section)

I think all depends in the Power Transformer you have

in old Geloso amps they connected two tubes (connected as 12.6v) as to have a 25v connection and give supply to that from the bias winding of the Power Transformer

hope someone will give further and better explanations

Kagliostro

[Tone Junkie]

Im interested in wiring the 12volt dc connection Ive been studing high gain amps lately and done a couple builds but Im thinking at some point 12 Vdc will be good to use.Thanks Bill

[jeff]

 In a 12A_7 use 12V between pins 4&5 don't use pin 9. This puts the filliment in series. If it's DC you can ground 4 and put 12V on 5 or vice versa

6.3V use pin 9 and 4&5(connected) This puts the filliments in parallel


      4______           4_5_____
       |        |           | |       |
       9(NC) 12V        | |      6V
       |        |           | |       |
       5_____|            9_____|
(the red lines are the filiments inside the tube, NC means no connection)
 The thing with using a center tap or two 100 ohm resistors to get 3.15V on each wire is to reduce AC hum. The tube still sees 6.3V but it's refrence to ground is changed. Instead of a ground wire and a wire having 6.3V AC you have two wires with 3.15 AC out of phase with each other. Hopefully any noise is canceled out. Twisting them together helps reduce hum.

Think of it this way, because they're out of phase, while one wire is at +3.15V refrenced to ground the other is at   -3.15V refrenced to ground, but the tube sees 6.3VAC

If you use DC hum shouldn't be a problem. Ground 5, apply 12.6VDC to 4

[RicharD]

DC filaments aren't really beneficial in a 'point to point' guitar amp.  12VAC filaments are not used because the higher potential increases the risk of filament hum.  Adding a 12 VDC power supply increases cost and often is another circuit that could fail.  DC filaments become necessary when an amp circuit is built on a PCB.  Now there is no easy way to keep the filament AC away from the audio path nor is it possible to twist the circuit path to increase CMRR, unless you wire the filaments off board.  Skimping on a power supply is verboten, but unfortunately often DC filament circuits are just barely powerful enough.  I've been working on a mic preamp circuit and it uses 12VDC filament for several reasons: it's gonna end up on a PCB, it's studio grade (not a geetar amp), & I need a 12VDC power supply anyway for relays and the meter driver circuit.  Although not really necessary for filaments, I am using a regulator.  It's an LT1084CT12 which is a 7 amp device.  That's a fifteen dollar chip and requires a lot of heat sink.  I've never built a guitar amp with DC filaments.  With a proper layout and grounding scheme, 6VAC filaments are just fine and dandy.

[kagliostro]

I forgot to say that one other way to avoid hum is to have (AC) elevated heaters

see the attached schematic

Kagliostro

[Willabe]

That schemo does'nt have/show the FWB grounded. Thats a typo is'nt it? Has to be grounded at the "9:00" junction to work, can't be a floting B+ supply?


     Thanks,    Brad      

[sluckey]

Sometimes bits get dropped during file transfers. I sure miss zmodem!  

How's this...

[Tone Junkie]

Thanks guys I do understand exactly what your saying in most cases the elevated heaters I use are plenty . they have cut down on my noise greatly.
Also learning good lead dress was probably the most helpful to me so far, but I had a circuit schematic that I could elevate to 12 volt dc from a 5 volt tap. but I didnt know how to wire a heater for 12 volts.
 I dont have a planned use for it but I save it in my pile of information for when i might need it in the future. i just know here when i ask questions even though they might be dumb questions some times.
you guys always teach me something usefull your quick to help and you have a huge amount knowledge to tap into, on top of that you never flame me for a dumb question. that cant be said about other forums.Thanks Bill   

[RicharD]

>a circuit schematic that I could elevate to 12 volt dc from a 5 volt tap.

Attached is a partial schematic showing a 12VDC regulated supply sourced from 6.3VAC and 5VAC secondary windings in series.  You do have to make sure both secondary windings are in phase, otherwise your secondary AC voltage will only be roughly 1.3 volts.  You simply swap 2 leads.  It also shows similar 6.3V tubes with their filaments wired in series.  Your seriesed tubes have to be match filament loads, ie. you can't put a 6SL7 in series with a 6SN7, but you can put 2 6SL7's in series.  If you are using 12 volt tubes such as a 12AX7, just forget about pin 9 and wire your 12V supply to pins 4 & 5.