DC Filament Supply

[defaced]

I've been working on a 4 gain stage amp for a while now and found that it is dead quiet, aside from high gain hiss, with elevated AC heaters. There was noise with elevated DC heaters with ~10,000 uf of filtering.

[ETR]

I'm building mostly high gain amps and I'm always using regulated DC heaters on all preamp tubes. I know it's an overkill but for few bucks in parts why not run them all? On top of that my heaters are elevated to 80-90V because some brands of tubes started failing when used as CF.

+1 on regulated DC filaments. All my high gain amps are built with them.

You may want to make sure youre using ECC preamp tubes for cathode follower stages. 12A series tubes aren't rated as high for cathode to filament breakdown.

[Gregg]

You may want to make sure youre using ECC preamp tubes for cathode follower stages. 12A series tubes aren't rated as high for cathode to filament breakdown.

I know the tubes that fail but you can't build and amp for somebody and tell them not to use this or that - it's better to play it safe.

[ETR]

ECC83 for instance isn't a tube brand, it's a tube type. They were rated for series string filament operation so the cathode to filament breakdown voltage is much higher than a 12AX7. It has nothing to do with the brand of tube used.

[Enzo]

And when the customer walks into the store for a new ECC83 and the salesman assures him it is the same thing as a 12AX7?

[Steve A.]

I dont see how it affects heater life span either.My son has been using this unit for over two years with the DC heaters,and the tubes havent failed yet.As far as it being a waste,I cant agree there either,the unit is as quiet as if it werent there.Is it absolutely necessary? Maybe not,but it works,for a couple $$ in parts.

I agree! While a properly laid out low to medium gain circuit can probably work fine with an AC filament supply, sometimes we are stuck with a circuit board that picks up a lot of noise from the filament supply. So we are often faced with the choice of throwing in $5 worth of parts- or spending many hours troubleshooting layout problems and correcting them.

I forget which amp this was about 10 years ago, but I was tearing my hair out trying to quiet it down, rerouting leads, etc. I finally switched the preamp tube filaments to DC and the difference was like night and day. And the extra work in lead dressing made it even quieter...

Yes, it would be optimum if an amp designer could work out the layout problems so that it wouldn't be necessary to use DC for the preamp filaments. That adds maybe 5 to 10 more parts that could possibly fail at some time in the future, and it does make the circuit more complicated than it has to be. But for DIY builders sometimes you decide to cut your losses and do something that a pro builder might not do...

Just my 2 cents.

Steve Ahola

P.S. For just the filaments I don't usually wire up a regulated supply. But if you are running filaments *AND* 3 relays it can get tricky with the voltage drops depending on how many relays are energized. In which case it is probably better to go with a regulated supply.

[yankeerob]

Yes, if you have a heater winding without a center tap, omit the 100 ohm resistors. They are to provide a "virtual" center tap for a winding that does not have one.

That statement - if I'm reading it right - doesn't make sense... I'm presuming you mean 'if you have a heater winding with a CT, omit etc....

I'm not surprised this discussion is 3 pages deep now - whilst not exactly controversial - it still merits discussion. With the help of guys like Steve - I've built a good handful of amps and repaired/modded even more... and while in many cases better lead dress/signal routing can improve noisy amps - sometimes putting in a DC filament supply in conjunction with with improved routing schemes is an absolute winner...

For example we had a Roccaforte HG100 (a very, very well thought out and constructed amp!!) in for a FX loop - being the customer lives in England and didn't fancy the expense of shipping it all the way to CA and back and Doug wouldn't ship the kit or divulge any info we had to shoot in the dark - so we used a well known ECC82 scheme for the 2204 - bearing in mind Doug's 2204 is an extremely gainy amp with one hell of a power supply! Our first attempt was noisy, the second much better but still too noisy for my liking - the third with a DC filament supply to all pre-amp tubes nailed it...

So it's really about what works at the end of the day. I agree - there's no need for a DC heater supply in something like a 5E3 or other tweed clone - it should be easy enough to dress your wires correctly and get superb signal to noise without dampening - even if you hot rod it out - but as Steve and others have said - there are times that installing a properly designed rectifier - even for the first coupla preamp tubes - can be a quicker and thereby less less expensive solution if you've already done your best to insure the wiring is dressed properly or - as is more often the case - it's just too much work to redress someone else's work or poor layout...

[ETR]

And when the customer walks into the store for a new ECC83 and the salesman assures him it is the same thing as a 12AX7?

My point was its not a brand, thats all.

[defaced]

That statement - if I'm reading it right - doesn't make sense... I'm presuming you mean 'if you have a heater winding with a CT, omit etc....

Good catch, thank you. Your correction is right.

[BK-Amps]

...there's no need for a DC heater supply in something like a 5E3 or other tweed clone..

+1

I only consider DC heaters for high gain circuits and custom scratch builds as I can siphon off an isolated source for relays and such. For simple high gain mods, I'll just float the CT of the heater (which can substatially reduce noise in boosted 2203 style circuits).

BK

[FFortin]

Hi Ray,
there may be some time since you put this link because I cannot track it. I would appreciate to see this schematic for the benefit of other users like me, who struggle with hum problems. In my case, it is about an Hammond organ. I already silenced the power amplifier with DC bias for the first stage tube of all section amps(3 amplifiers in this amp) and now the hum comes from the pre-amplifier module (manuals interface). Best regards,
Francois

[FFortin]

This circuit works great IME, as-is - "improve" it at your own risk:

schematicheaven.com

Ray

Sorry (I forgot to insert the quote in reference to this thread).
FFortin

[g1]

Sadly, Ray is no longer with us. (edit: see post #45)
This should be the correct schematic:

[Justin Thomas]

Sadly, Ray is no longer with us.

Justin

[g1]

Um, sorry I may have been mistaken. I thought I had read that Ray had passed, but I can't seem to find any such reference.
So I'll rephrase that to say:
unfortunately Ray does not post on this forum any longer.