Twin Regulated Filament Power Supply

[mooreamps]

...

[UR12]

The transformer will not melt down. The 5 volt winding is rated for 3 amperes. The 6 volt winding rated for 6 amperes. Secondly, my design spec required "International" power. Not sure what part of "International" power you don't understand......


-g

Evidently you are the one who is having trouble understanding. I said and I quote again "IF you have a 5 volt winding that is rated at 2 amps and if you try and pull more than two amps either at 6.3v or at 5v you are exceeding the rating of the tranny" I used 2 amps as an arbitrary number. I really don't care what YOUR tranny is rated for. If it's rated at 3 amps and you try and pull more than 3 amps out of it you will be exceeding it's rating. You have made it very clear in your usual condesending and arrogant way that you are shipping an amp over seas. There is nothing different with International power, just an extra winding to handle the 240volts and 50hz operation and your are there.

But I'll tell ya what I will shut up and let you teach everyone here how we should be building amps. There are a few of us here who will sit back and just get a laugh out of your postings and I promise you this will be the last time I interupt while you have your class in session.

oh wait!!! I didn't see the "Put a cork in it" So who do you think you are to go telling people what they can and cannot say on this forum?

[skyboltone]

There is a fair amount of information from self described experts on the net that is just plain wrong. I know when I first showed up here I thought I had a whole lot more to contribute than I really did. My background was in Ham Radio, particularly bringing back to life old transmitters and receivers. I fix them, align them, but I seldom design. When I took the time to pay attention I realized that I had a lot to learn.

Having said that, Dana, this forum needs the spirited interaction between folks otherwise it won't work. Any wacko can submit a drawing but that doesn't mean it's correct. If Mr. Moore or anybody else submits a design here, that the members might be interested in, and then can't take correction or interaction, then he has a problem and should seek out one of the self help forums on self esteem or developing relationship skills. For my part I hope you keep your critical eye and mind on the job.

I don't know all that much about these transformers but I do know that the difference between the wire used in 2 amp windings and that used for 4 amp windings is often not great. In fact from a manufacturing standpoint why stock two sizes of wire? There are things like flux density, core saturation and other stuff to consider besides a winding opening up. Is a 4 amp 6.3V winding only good for 4 amps if the 5 volt winding isn't used at all? Can a 5V 2amp winding even deliver enough additional power to damage itself, or does the voltage just drop off to nothing? Sometimes you can short a winding and nothing happens. Depending on design.

I love the subject of buck/boost because everything you thought you knew about transformers goes out the window when an ordinary door bell transformer is connected in a buck or boost configuration. I can take a 12 volt 24VA doorbell transformer and hook it up for boost and run a 20 amp pump circuit with it when the distance from the panel to the pump is great enough that voltage drop makes the pump not start. I've done it. In the Arctic. The pump ran the heating oil to the boilers, at 50 below.

Dan

[UR12]

Having said that, Dana, this forum needs the spirited interaction between folks otherwise it won't work.
Dan

I love a spirited conversation as much as the next guy. I don't profess to be an expert at anything, I just have fun playing with amplifiers. Having said that I don't think a spirited conversation should include someone talking down to me or being so arrogant that he comes off as a self proclaimed god or has the right to tell someone to "put a cork in it". There is room for Mr Moore and me on this forum I will just go back to ignoring his posts like I did in the past.

[nickt]

In the spirit of spirited conversation I spent some of my employer's time drawing up this in word and paint (I'm such a techo )

Anyway looks to me like there's not much margin on the 12V out. You only get about 2-3V above 12V to stick across the regulator. Assuming there is a sag that would drop yoiur 6.3V down to 5V (say20%) that would mean your regulator would be starved out and I'm assuming do something "funny" - like say pass nothing through.

In any case the circuit would only be usable where you wern't using the 5V winding - don't know if this has been mentioned - because otherwise you'd be sticking say 350V on one end of your 5V winding which would probably be a bad thing (certainly for the 350V winding)

Have I got this right?

cheers
Nick

[paulster]

Anyway looks to me like there's not much margin on the 12V out. You only get about 2-3V above 12V to stick across the regulator. Assuming there is a sag that would drop yoiur 6.3V down to 5V (say20%) that would mean your regulator would be starved out and I'm assuming do something "funny" - like say pass nothing through.

Nick

This is where component choice can help you out, although maybe not down as far as 20% below rated voltage.

There are a good range of what are known as low-dropout or LDO regulators available that only drop say 0.5V at rated current compared with 1-2V for a general purpose regulator. Couple this with some diodes with an extremely low forward voltage rather than an off-the-shelf bridge rectifier (0.45V for certain Schottky ones, and bear in mind the current has to traverse two diodes at a time so you can make a big difference here) and you've suddenly got a lot more headroom available without changing your design but by careful component selection.

For good measure I also filter heavily before the regulator so there is very little ripple at the regulator input. That also provides a little more headroom.

It sounds like a lot of effort but you only need to figure it out once and then it's something you can reuse without modification thereafter.

Paul

[nickt]

hehe - haven't looked at SS components since the 80's when I did it for a living as a service tech.

I guess the point I was trying to make was that the situation where this scheme is a good choice is fairly limited. From what you say LDO's and exotic diodes can make it work but basically only where you
a) need to regulate your filaments in the first place
b) have an unused 5V winding.

Quick question: do you normally regulate your filaments? If so is there a noticeable benefit? (just askin)

Thanks!

[paulster]

Nick

I don't use the 5V winding - I rectify 6.3Vac and then regulate it to get 6.3Vdc for the preamp tubes only. I don't see the point in running the output tubes from DC in a push-pull amp, although I have done it in a single-ended amp when I've had the spare current capacity on my regulator. It means I don't have to get custom transformers wound (which is nice when doing an off-the-shelf build or a modification rather than a ground-up build) and doesn't rely on having a 5V tap spare. It does mean that you have to carefully consider the headroom though as there isn't a lot of room for manoeuvre using 6.3Vac as the source. That's why I found a combination of diodes, filtering, and regulator that I'm happy with and had a batch of PCBs made.

Larry has already summed up the benefit earlier in the thread:

A regulated DC heater supply for the preamp tubes tough is a good thing. In my amps I'm using 12.6V regulated DC for the heaters, fed into all pin 4's, while all pin 5's are grounded and all pin 9's unused. The result is absolutely hum free amps, even dimed not a tad of a hair of hum

I don't like having loads of hum and/or hiss from my amps, as it all contributes to reducing the signal/noise ratio of them. Sure, it'll get lost in the mix eventually, but it's still reducing the available dynamic range and the hum at least is an easy fix. The way I look at it is the less background noise, the more you can hear the amp. It's surprising how many amps suffer from excessive levels of hum when there's an easy fix at no cost whatsoever to sound quality.

Paul

[nickt]

Thanks paulster - I guess you're talking high gain amps here?

One dumb question: couldn't you get away with simply rectifying the 6.3 and adding a cap/dropping resistor/cap pi type filter? Haven't done the sums but feels like it might be cheaper and will certainly degrade gracefully with brown power?

cheers
Nick

[paulster]

Nick

High gain amps, or those with a particularly high gain stage anywhere in the topology, will definitely benefit the most, but I still think the effort is worthwhile, even in something Vox-ey or Fender-ey.

I haven't tried the pi filter method as I went straight to regulated power after trying DC with large filtering in an amp that already had basic (pretty poor actually) DC heaters. Since getting the PCBs made there's no incentive for me not to use regulated DC.

I can definitely get down to 5.5Vac without any problems whatsoever getting a steady 6.3Vdc output, so I'd be more worried about my power tubes if this was representative of the venue voltage (this would be like going from 240 down to 210V, or 120 to 105V in the US).

Paul

[skyboltone]

<bump>

I'm serious about these questions. Anybody know?
"There are things like flux density, core saturation and other stuff to consider besides a winding opening up;
(1) Is a 4 amp 6.3V winding only good for 4 amps if the 5 volt winding isn't used at all?
(2) Can a 5V 2amp winding even deliver enough additional power to damage itself, or does the voltage just drop off to nothing with additional load? Sometimes you can short a winding and nothing happens"

[UR12]

<bump>

I'm serious about these questions. Anybody know?
"There are things like flux density, core saturation and other stuff to consider besides a winding opening up;
(1) Is a 4 amp 6.3V winding only good for 4 amps if the 5 volt winding isn't used at all?
(2) Can a 5V 2amp winding even deliver enough additional power to damage itself, or does the voltage just drop off to nothing with additional load? Sometimes you can short a winding and nothing happens"

Is the teacher out? should we talk amoungst ourselves?

Everything you would like to know about transformers can be found here. Well maybe not everything but I think these pages will answer your questions. Just keep clicking next to delve deeper.

http://www.tpub.com/neets/book2/5.htm

[skyboltone]

Everything you would like to know about transformers can be found here. Well maybe not everything but I think these pages will answer your questions. Just keep clicking next to delve deeper.

http://www.tpub.com/neets/book2/5.htm

Great stuff but it stops well short of answering questions about core saturation and class 2 operation of power transformers. Oh well, as I've said before, hook it up and see if it works.
As I see it the real issue here is the one discussed by NickT and the Paulster. It's about selecting components so as not to loose the free lunch. I agree that there is little point in worrying about DC on output tube filaments. The rectifiers I bought should only loose a volt and we'll see what the regulators do. I'm not buying excess for inventory here as I suspect that the regulator will loose more voltage than Vref. When I've played with this in the past the regulators just drop out. Back to the $7 Xicon 3amp filament transformer.

[Jack]

For 6.3V DC, the simplest approach is to use a 10A bridge and a 1000-10000uF cap. The voltage gain by rectification is compensated by the voltage loss in the diodes and the filtercap. On the marshall JCM900 SLX, that's what they do and it gives a 6.27 V IIRC. If you worry about regulation, get a furman thingny. From my experience, the heater can work equally well between ~ 5.5V and 7.2V without perceivable tone change. The change on the B+ would be much more perceivable IF the bias is fixed. But since the bias voltage will drift accordingly, just like a power scaled amp, you end up with nothing to worry about at all.

IMO, having a voltage regulator in a guitar tube amp is like fuelling your land mower with super.

[skyboltone]

For 6.3V DC, the simplest approach is to use a 10A bridge and a 1000-10000uF cap. The voltage gain by rectification is compensated by the voltage loss in the diodes and the filtercap. On the marshall JCM900 SLX, that's what they do and it gives a 6.27 V IIRC. If you worry about regulation, get a furman thingny. From my experience, the heater can work equally well between ~ 5.5V and 7.2V without perceivable tone change. The change on the B+ would be much more perceivable IF the bias is fixed. But since the bias voltage will drift accordingly, just like a power scaled amp, you end up with nothing to worry about at all.

IMO, having a voltage regulator in a guitar tube amp is like fuelling your land mower with super.

We used to call that brute force regulation. It will depend much on the number of tube filaments etc and is designed by EXPERIMENTATION. Hehe