Any advantage using DC for filament?

[g1]

I really don't like getting shocks, & nobody but Uncle Fester does as far as I've seen.

Maybe these guys:

[Alan0354]

Question to all the experienced people, anyone actually encounter humming problem due to filament and failed to be fixed by twisting wires, biased up or down from ground? I mean really did try solving the the problem rather than say "well, there is hum, so I put DC supply for filament!!!"

I am not talking about "well it could happen", rather it happened and you really tried solving with simple ways and failed, and you have to have DC filament supply.

My point is DC supply cost a lot more money as you have to have the source voltage that is not there in most of the tube PT. You have to have solid state circuits. If there is a way to bias the filament off ground and solve the problem, why go there.

I used various 12AX7 from different era, brands and used in cascade amps, never once did I notice any hum. As I said, bias the filament only takes two resistors.

[g1]

Why do you think Fender & Marshall etc. use them? It is quite common. Do you think they could make them quieter using other cheaper methods? And they just want to increase their manufacturing costs? That's ridiculous. Of course they have found them to do the job that can't be otherwise accomplished for less cost. Usually only the first few stages of preamp, and for higher gain circuits. If you are not working with high gain stuff, forget about it.

[Enzo]

Plus to someone like Fender or Marshall it is far more important (compared to a home amp builder) that ANY 12AX7 work well in the socket. So maybe some tubes would remain noiseless with AC heaters, but others might not.

[soundguruman]

One challenge is curing an existing hum problem or working with a transformer that doesn't have the higher voltage required to provide rectified 6.3 V. Question, do you need 6.3 volts DC or can it be 5 volts. The Carvin MTS 3200 employed 5 volts DC. But then I didn't really like that amp. Sounded weak to me.

Lower heater voltage shortens tube life. Although, it may not be enough to cause a real headache.

One cure to hum problems is to use ground lift and a hum balance pot. That seems to reduce the noise factor to a very acceptable level. I've seen AC heater feeds placed on a PCB and the previously mentioned solutions use with the result being a very quiet high gain amp.

The only time you need a ground lift is when there is a ground LOOP.

Hum balance pot is used in amps, for the filaments, when there is no filament center tap.

OR Hum Balance control is used on push pull grids, to balance the output, to eliminate HUM.
this is effective because no two tubes are perfectly matched, in the real world. (but there ARE perfectly matched tubes...)

"ACCEPTABLE LEVEL:" the only acceptable level, is NO NOISE AT ALL, AT ANY VOLUME LEVEL.
you can "accept" noise if you want, I DON'T!



If someone could explain the hum balance pot as well as how lifting the ground reduces AC hum that would be great. Is it like putting two loud talkers above floor level in a room so there noise is over head?

Silverfox.

There are "standard methods" as you have mentioned.
There are "special exceptions" because the standard methods DO NOT work on ALL amplifiers.

DEPENDS on the design, layout, AND how high the gain is going to...
sometimes DC filaments are the only solution.

Elevated heaters: you can "borrow" a couple volts from somewhere else in the amp...
to make your voltage reg work properly.

[soundguruman]

Plus to someone like Fender or Marshall it is far more important (compared to a home amp builder) that ANY 12AX7 work well in the socket. So maybe some tubes would remain noiseless with AC heaters, but others might not.

I have noticed that spiral filament JJ tubes can HUM pretty loud in certain circuit.
and works just fine in other circuits...

[soundguruman]

So there is no advantage of DC filament supply?

I am designing an amp, I'm not going to even entertaining the idea of DC filament unless there's a compelling reason for it.

There's lots of compelling reasons, when the amp is HIGH GAIN.

[Alan0354]

Why do you think Fender & Marshall etc. use them? It is quite common. Do you think they could make them quieter using other cheaper methods? And they just want to increase their manufacturing costs? That's ridiculous. Of course they have found them to do the job that can't be otherwise accomplished for less cost. Usually only the first few stages of preamp, and for higher gain circuits. If you are not working with high gain stuff, forget about it.

Plus to someone like Fender or Marshall it is far more important (compared to a home amp builder) that ANY 12AX7 work well in the socket. So maybe some tubes would remain noiseless with AC heaters, but others might not.

I know All the old Fender BF SF, Prosonic, Tonemaster, SuperChamp XD don't use DC filament.

I know the famous old Marshalls don't use DC filament supply. I checked JCM800, JCM900, JCM2000 DSL401 don't use DC filament supply.

I am pretty sure my collection of Fender amp schematics cover most of the famous high end Fenders. I think I name a lot of the famous. Marshalls. I am sure I missed some Marshalls, but this is a pretty complete list of the high end amps of both brands.

I do see Marshall TSL uses DC rectifier for the first tubes. This is very different from regulated DC. All you need is a bridge rectifier and a cap. That's easy and doable. I saw a few newer Mesa has DC rectifiers for first tube. Only one actually use 7805. It is easier to have regulated supply if you already have opamps and pcb. But for all tube amps, it's a lot more components.

Of cause I know you need to have all the tools. My question is did anyone encounter hum problem that cannot be solved by playing with the simple method. OR just go directly to DC filament the moment there is hum?

[soundguruman]

I know All the old Fender BF SF, Prosonic, Tonemaster, SuperChamp XD don't use DC filament.

I know the famous old Marshalls don't use DC filament supply. I checked JCM800, JCM900, JCM2000 DSL401 and TSL100 don't use DC filament supply.

I am pretty sure my collection of Fender amp schematics cover most of the famous high end Fenders. I think I name a lot of the famous. Marshalls. I am sure I missed some Marshalls, but this is a pretty complete list of the high end amps of both brands.

Of cause I know you need to have all the tools. My question is did anyone encounter hum problem that cannot be solved by playing with the simple method. OR just go directly to DC filament the moment there is hum?

I do try all the standard methods first.
I can hook the filaments to a bench DC supply, and that tells me what I need to know.

There are amps with way more gain than Marshall. That's where it comes in handy.
There are amps that were just laid out poorly, like that Vox.
I am not going to re-design and modify the Vox. I am just going to power 3 pre amp tubes with DC filaments.

That is by far, the easiest solution to a poor design.
I tested that with my DC bench supply, and all the hum is GONE.

[tedmich]

really quiet DC supplies are difficult to put together at the amps heaters need, and with regulation its even more involved. I stocked up on LM338's years ago with plans to do this on my amps but I have never needed to. But maybe I don't have "golden ears " (I don't!)

Heres a guy who states he needed 30,000 uF of filtering to quiet his Trainwreck build (!) And that he has a 5 stage uber gain build with all DC heaters and no noise
The Amp Garage :: View topic - DC Heater Supply In A Wreck Build

or maybe he's nutz...

and you can regulate the B+ too, check Gary Pimm's take on the "Swenson" regulator
http://www.pimmlabs.com/web/regulators.htm

I have one for my bench power supply, good to over 500v and a couple amps..

[Enzo]

Look again. I see in my TSL100 drawing a bridge and filter caps for the heater directly below V1 on the page. DC heaters.

DSL401, look right above the speaker jacks, there is your bridge and filters for the DC supply to V1. DC heaters.

If I recall, the JCM900 2100SL-X also has a DC heater on the first tube

Older models are less likely to have DC heaters, and one reason is that there was greater tolerance for hum then. Nowdays it is a bugaboo. And design practices are more sophisticated as well.


If you don;t want to use it, don;t use it, no one is trying to force you.

[soundguruman]

Look again. I see in my TSL100 drawing a bridge and filter caps for the heater directly below V1 on the page. DC heaters.

DSL401, look right above the speaker jacks, there is your bridge and filters for the DC supply to V1. DC heaters.

If I recall, the JCM900 2100SL-X also has a DC heater on the first tube

Older models are less likely to have DC heaters, and one reason is that there was greater tolerance for hum then. Nowdays it is a bugaboo. And design practices are more sophisticated as well.


If you don;t want to use it, don;t use it, no one is trying to force you.

Yes we are trying to FORCE YOU.

We are holding a hot soldering iron, TO YOUR HEAD!!!
Resistance is futile.

[g1]

I know All the old Fender BF SF, Prosonic, Tonemaster, SuperChamp XD don't use DC filament.

I know the famous old Marshalls don't use DC filament supply. I checked JCM800, JCM900, JCM2000 DSL401 don't use DC filament supply.

I am pretty sure my collection of Fender amp schematics cover most of the famous high end Fenders.

As Enzo mentioned, you are mistaken. And I was talking about higher gain amps, so of course old vintage Fender and Marshalls did not use them. When they came out with higher gain amps is when they started using them. Check the first preamp stage when you are checking schematics, not the power tubes.
TSL100 first stage heater supply:

[loudthud]

I added a voltage divider bias network for the heaters on a bass amp I built. Curious to see if it made any difference I shorted it to ground while the amp was on standby, flipped the amp on and took a measurement, then removed the clip lead and measured again. The difference in hum level was 9dB. The hum that it removed was all 60Hz. The level of 120Hz buzz remained constant.

[Enzo]

Cool, so it isn;t ripple, it is indeed 60Hz we are abating with this ploy.