heaters in parallel?

[mook]

the "basic" heaters in amps are daisy chained together, but Is it allowable to connect heaters in parallel?

.....say, for argument, I run my heaters off the PT to a point central to the amp, then I run each tube heater off this central point?

I know this example is not practical, and I don't plan on using it, but I just want to know if it's possible and ok for heaters to be connected in parallel.

seems ok, right?


Mook

[trevorus]

Heaters in parallel was pretty much the standard run of things, as far as I was aware. Now, connecting it as a star layout might present some challenges, and for noise control, probably not the best way to go about it.

[daz]

What he said. Parallel is the way most if not all amps are done. I believe the way you are suggesting is technically the same, IE: Parallel, but doing it that way would just be a lot more wire thereby increasing the chance of noise. It would still be parallel, but instead of each tube taking the wire from the tube next to it you would probably quadruple the amount of wire overall if not more. and they'd still be parallel.

[Groover]

Hi Mook. I think you may be mis-interpreting the common heater wiring scheme. The heater wiring in most amps starts at one end - usually the rectifier tube socket or, if there isn't one, at one of the power tube sockets, and runs to each tube socket across the chassis in turn. And this could correctly (IMHO) be referred to as daisy-chained.

But that does not mean the heaters are electrically in series. In fact heaters in most amps are wired to be electrically in parallel. It is hard to describe verbally why that is the case and what would make it otherwise. I don't have time to do any drawings and post them right now. Perhaps I can tomorrow.

[mook]

Thanks guys, as a added (bonus??) questions, how about this:

is it possible to run the first part of the heaters in AC (say, for the power section), then convert to DC for the preamps?


Thanks!


Mook

[Enzo]

Yes, of course, that is in fact common in commercial amplifiers, Marshall does that in a bunch of models.

To your original question, "daisy chain" just means running wires from one to the next of something. They are not wired in series that way though. So one side of your 6v runs to pin 9 of V1, then from there to pin 9 of V2, then on to pin 9 of V3, etc. and the other side of your 6v runs to pins 4,5 of V1, then from there to pins 4,5 of V2, etc. That is your standard daisy chain wiring. They are all wired in parallel that way.

COuld you run a pair of wires from your 6v out to V1, then another pair of wires from the 6v out to V2, and so on? Yes. Electrically that would be no different. But it would serve no purpiose.

[d95err]

is it possible to run the first part of the heaters in AC (say, for the power section), then convert to DC for the preamps?

Yes, BUT:

DC Heaters seem to cause more problems than they solve (at least for amateurs like us). I've seen countless threads of people having trouble with their DC heaters...

A more effective and much simpler way of reducing hum is DC elevation of the heaters. That means referencing the heaters to a DC voltage instead of ground. All that's required is two resistors and a cap.

[mook]

Yes, BUT:

DC Heaters seem to cause more problems than they solve (at least for amateurs like us). I've seen countless threads of people having trouble with their DC heaters...

A more effective and much simpler way of reducing hum is DC elevation of the heaters. That means referencing the heaters to a DC voltage instead of ground. All that's required is two resistors and a cap.

Or, could you simply elevate the heater center tap (CT) with a DC bias, instead?

Mook

[Wilder Amplification]

Or, could you simply elevate the heater center tap (CT) with a DC bias, instead?

Mook

Yep you sure can. I use a 330K and a 47K in series off the screen node, with the 330K being connected to the screen supply and the 47K tied to ground, then I strap a 10uF filter cap across the 47K (the filter cap MUST be there or you'll inject ripple into the heater winding and end up with a very noisy amp...don't ask me how I know this ).

[mooreamps]

Thanks guys, as a added (bonus??) questions, how about this:

is it possible to run the first part of the heaters in AC (say, for the power section), then convert to DC for the preamps?


Thanks!


Mook

This is the way I do it ; and I'll tell you why. The power tube filaments draw a heavy current load. In fact, sometimes I use a separate 12.6 vac transformer just for the this ; and hit the center tap with a filtered dc offset bias. Then, when the lighter current load for only the preamp filaments, I'll use dc. I'll still twist the heater wires pretty tight using a hand drill, and then float both sides 100 ohms above ground. Seems to work very nice and stable for my SE amps.

-g

[mook]

This is the way I do it ; and I'll tell you why. The power tube filaments draw a heavy current load. In fact, sometimes I use a separate 12.6 vac transformer just for the this ; and hit the center tap with a filtered dc offset bias. Then, when the lighter current load for only the preamp filaments, I'll use dc. I'll still twist the heater wires pretty tight using a hand drill, and then float both sides 100 ohms above ground. Seems to work very nice and stable for my SE amps.

-g

So, just to get this right and understand it:

You use 2 filament trannys, one for pres and one for the power section.

You float BOTH filament trannys above ground with matching 100 ohm resistors.

You then continue to float the bias by hitting BOTH trannys with a DC bias.

sounds like a dang good plan!

But let me ask a few follow up questions:

I might be stupid, but if you are using a 12.6 tranny, how do you power 6.3 volt filaments: 6L6, EL34, etc.

Also, how do you rectify for the DC heaters -- a full wave rectifier or 1/2 wave? or a bridge rectifier?


Thanks!


Mook

[mooreamps]

nonononono.......

I use one extra 12 vac transformer for the power tubes. I use the filament winding from the other transformer, just for the preamp tubes ; and I use a full wave bridge using the fast recovery diodes as those only have a 0.1 forward voltage drop across them.

Also, for what this is worth, I only put buss fuses on the line side of the transformer ; not the primary. You just would not believe how hard some of my friends at work laugh when I tell them how some of these "boutique" builders put line fuses off the secondary windings. "Ya, some of them are rocket scientists too !!!!! "



-g

[Wilder Amplification]

nonononono.......

I use one extra 12 vac transformer for the power tubes. I use the filament winding from the other transformer, just for the preamp tubes ; and I use a full wave bridge using the fast recovery diodes as those only have a 0.1 forward voltage drop across them.

Which you can run power tubes as well as preamp tubes off of 12.6VAC. You just wire each pair of power tube heaters in series across the 12VAC winding (pin 7 of one tube to pin 2 of the other). The heaters become a voltage divider and each only see 6.3V in this config. This config is actually known to be quieter because you're only drawing 1/2 the heater current at 12.6VAC than you would be at 6.3VAC, which means 1/2 the alternating magnetic field density.

Also, for what this is worth, I only put buss fuses on the line side of the transformer ; not the primary. You just would not believe how hard some of my friends at work laugh when I tell them how some of these "boutique" builders put line fuses off the secondary windings. "Ya, some of them are rocket scientists too !!!!! "

-g

Well if you don't put them on the primary side and people laugh at us boutique builders who put them on the secondary windings, then which winding do YOU put them on? You mean to tell me that the "line" side is NOT the primary?

Not only do the boutique builders put them on the secondary, but so do the big name OEM manufacturers. Some of these amps with fused secondaries are even UL certified. Come on now, we can't all be stupid now, can we?

[d95err]

I might be stupid, but if you are using a 12.6 tranny, how do you power 6.3 volt filaments: 6L6, EL34, etc.

Just an example - the Peavey Classic 30 uses an AC supply of about 24V for the heaters, with all 4 EL84 filaments in series. This makes them get away with a simpler power transformer with just two windings - one for the anode voltage, and one that supplies bias, opamps, heaters and relays.

[mooreamps]

Which you can run power tubes as well as preamp tubes off of 12.6VAC. You just wire each pair of power tube heaters in series across the 12VAC winding (pin 7 of one tube to pin 2 of the other). The heaters become a voltage divider and each only see 6.3V in this config. This config is actually known to be quieter because you're only drawing 1/2 the heater current at 12.6VAC than you would be at 6.3VAC, which means 1/2 the alternating magnetic field density.

NO !!! The secondary winding is center tapped... and on the center tap is applied the dc bias. There is no "heaters wired as a voltage divider".

"1/2 of the alternating magnetic field density?" It's like, do you even have any clue what you are talking about ?

Not only do the boutique builders put them on the secondary, but so do the big name OEM manufacturers. Some of these amps with fused secondaries are even UL certified. Come on now, we can't all be stupid now, can we?

Well, if you fail to take into account the limited secondary short current current given the impedance of the secondary winding ; "ya, pretty much.."




http://www.schematicheaven.com/fenderamps/princeton.pdf

Oh ya, here is just one example of those

but so do the big name OEM manufacturers

drawings where they

with fused secondaries

.