DC Filament Supply

[Bruce / Mission Amps]

Thanks Enzo! I've decided to go with a Weber copper cap on the 375-0-375 (220mA) for the B+ (cheaper than glass in the long run and the right one will allow me to use EL34's, KT66's or 6L6's), 6.3V on the power tubes and a dedicated DC supply from the 5V (3.5A) for a 12AX7 and two 12AT7's... now all I have to do is figure out how to derive that - any suggestions are more than welcome - thanks for posting!!!

Best regards

Rob

If you are going to forgo the 5v rectifier anyhow, why in the world would you blow good money on a copper cap rectifier (with SS diodes built in it) when you can just use $1 worth of 1N4007 diodes and a 100ohm 10w $1 resistor on a terminal strip or the free unused rectifier socket?
And for what it's worth, DC filaments in a guitar preamp is so unnecessary that it astounds me that people are still trying to figure out how to do it using the 5v winding with a FWB and cap filter.
IMHO... a tremendous waste of time and energy.

[MWJB]

"And for what it's worth, DC filaments in a guitar preamp is so unnecessary that it astounds me that people are still trying to figure out how to do it using the 5v winding with a FWB and cap filter.
IMHO... a tremendous waste of time and energy."...Amen to that.

[Steve Conner]

+1! You only need DC filaments if you're trying to make a 5150 gain monster. And even then, I've made gain monsters with AC filaments and the hum ended up below the noise floor with careful tweaking of a hum balance pot.

Also, if the first gain stage of an overdrive amp is sharing a bottle with anything other than the following gain stage, you're asking for oscillation trouble due to capacitive coupling between the plates.

And yes, the Copper Cap is just two diodes and a resistor in a purty looking copper can. Great for filling the rectifier socket of an existing amp with something that looks presentable, but doesn't make much sense in a scratch build.

[yankeerob]

Firstly let me thank you all for posting - I welcome all the comments so far - there are - however - some factors that need clarifying...

If you are going to forgo the 5v rectifier anyhow, why in the world would you blow good money on a copper cap rectifier (with SS diodes built in it) when you can just use $1 worth of 1N4007 diodes and a 100ohm 10w $1 resistor on a terminal strip or the free unused rectifier socket?

Probably because I wasn't aware that that was all a copper cap is - I'm learning as I go... I have a drawer full of 1N4007's and I've ordered some ally clad resistors to experiment with on another project - and there's no existing rectifier socket as it's a complete new build so if what I think you're saying is true - you've saved me some time and expense

And for what it's worth, DC filaments in a guitar preamp is so unnecessary that it astounds me that people are still trying to figure out how to do it using the 5v winding with a FWB and cap filter.
IMHO... a tremendous waste of time and energy.

In most cases I'd agree with you - I've built a 5F6A clone out of HRDv iron that's surprisingly quiet as I'm using a NOS Mullard CV2024 in V1 and a coupla used Brimar ECC83's (that after 30-40 yrs are showing no signs of giving up) in V2&3 - the noise floor is astoundingly low and everything's heated via the standard 6.3V winding from the HR PT - so I take your point...

But the amp in question (which I might add is still on the drawing board) is a higher gain Orange overdrive clone - and has zero negative feedback so that's why I'd prefer - by design - to use DC heaters on the pre-amp tubes as I do the occasional session and hate modellers with a passion - there's just something big and ballsy about a 4 x 12 and a good mic - especially if you have the dynamic range of an overdrive head with ZNF... and can if you desire - incorporate bias range switching so you can safely switch the sag resistor in or out.

As an aside - DC heaters are common practice in many Matamps and similar derivatives (including Orange) that have no feedback loop - I also have access to some info on how they do it/done it in the past from the 6.3V winding but it involves a regulator that I - so far - have found difficulty in sourcing - though the man with the aforementioned info reckons he can get them - that remains to be seen... but I digress..

My thinking was rather than go with a 5U4 (and the expense and reliability issues with another piece of glass in my amp which I plan to gig with too) - why not go for what seemed like a compromise between a FWBR and a tube - ie a copper cap - but if you're telling me that all a copper cap is is a FWBR with a 'sag resistor' then that's the route I shall take when designing the power supply. Perhaps now you get a better idea of why I - having the luxury on this one-off occasion of an unused 5V winding - was thinking of using it for the DC filament supply - as it would seem - from all I've read so far - that this would be an easier route than tapping off the 6.3V supply...

Finally - I really appreciate the posts - and understand why you've said what you've said!

[mooreamps]

I use a twin dc regulator for the pre-amp and power tube filaments. I do to ensure a consistant 6.3 volts regardless of how much the input power voltage varies. Even on my bench without regulation, I've seen the filament voltage swing as low as 5.5 volts up to over 7.0 volts. I do this to ensure long tube life and consistant tone.

-g

[Enzo]

Wow, with 120v mains, meaning a 20 to 1 voltage ratio on the 6v winding, that represents a 15-20v swing either way on your mains.

[mooreamps]

In my lab, all the power is off a 10 amp breaker, and it has other loads on it beside just my bench. This much of a voltage swing may be more common than what you would want to believe....

-g

[milosch]

I wonder, why not a zener diode after your bridge or half-wave? This assumes you need to do this at all.

[jrfrond]

After much experimentation in the past, I have deemed the DC heater scheme to be a waste of time, components and chassis real estate. A good, balanced and tightly-wound twisted pair is really all that is needed for hum reduction, and regulation is highly overrated. Most heaters are within tolerance at rated line voltage. Also, heaters just do not last as long on DC because they are always at peak voltage. AC heaters reach peak voltage 120x per second (at positive and negative swing) and get to rest at the zero crossing at the rate of 60Hz. It's just another high-tech approach for a low-tech "problem".

[mooreamps]

Also, heaters just do not last as long on DC because they are always at peak voltage. AC heaters reach peak voltage 120x per second (at positive and negative swing) and get to rest at the zero crossing at the rate of 60Hz.

The filaments are still "hot" regardless...

-g

[giorgio]

hi ray,one question to you:I see in the schematics the 2 100ohm resistors..what if you have center tap on the transformer,do you simply omit the two resistor??I'd like to do this mod to an express trainwreck clone,which is too noisy!!

[defaced]

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.

[stokes]

The filaments are still "hot" regardless...

-g

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.

[ETR]

Theres a big advantage in using DC heaters with a high gain 0 feedback design. Not just the hum reduction either. You can wire up your build with a lot less hassle/time. Also you don't need regulators, the loaded voltage should be pretty much the same as with AC. If it's a little higher on your bench wait till it gets plugged into the circuit at the bar with the SVT, lights, PA and refrigerator. Where do you think the filament vlotage will be sitting then?

[Gregg]

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.