Stout build, alternate power supply query

[moody]

Hi all.

I'm new here but have been reading for several week.  I've finished a couple of small guitar amps and have a reasonable amount of experience. 

I'm in the process of making a guitar amp for one of the guitarists in my band (bass player myself) and was looking at the stout as an option.  (he tried a fender based amp that I made but wants a more marshal voice in the same power range).

I am considering making one using the following power supply
http://www.valveheaven.com/Lamington%20Power%20Supply.bmp

Looking at taking this power supply as far as the 2k2 5 watt resistor (which would replace the choke) and having the stout filter chain from that point onward.  From experience HT1 should be approximately 360v unloaded.  Just wanted to confirm with people who know the circuit that there wouldn't be any great problem doing this?

Thanks all

[FYL]

I am considering making one using the following power supply

A quadrupler with two 30V PTs (!). I wouldn't even think about using it.

[moody]

I am considering making one using the following power supply

A quadrupler with two 30V PTs (!). I wouldn't even think about using it.

Don't knock it unless you've tried it.

My question is referring to actual voltage drops and if I've spliced the power supply in at the right point.

[darryl]

Hi Moody,
             Yes it should work.

A quadrupler with two 30V PTs (!). I wouldn't even think about using it.

By way of explanation, Moody hails from Australia, as I do. The cost of transformers here is very high, for a number of reasons - small market, high shipping costs, import duties etc etc. The end result of this is that small DIY builds are not viable unless readily available, low cost transformers can be used - either back-to-back or in voltage multipliers.

[moody]

Hi Moody,
             Yes it should work.

A quadrupler with two 30V PTs (!). I wouldn't even think about using it.

By way of explanation, Moody hails from Australia, as I do. The cost of transformers here is very high, for a number of reasons - small market, high shipping costs, import duties etc etc. The end result of this is that small DIY builds are not viable unless readily available, low cost transformers can be used - either back-to-back or in voltage multipliers.

Hi Darryl, I should have just asked on aggh, but I didn't want to bother them with a schematic that they wouldn't necessarily be familiar with. 

[FYL]

Don't knock it unless you've tried it.

A basic Greinacher doubler and it's quadrupler form are OK when current draw is quite steady but not with a varying load. A Greinacher quadrupler needs 4 cycles to settle properly, even with large caps, and can somewhat modulate the signal.

That's why they aren't used in audio apps, except in the more stable Delon form (think Marshall), and why most people prefer to use back to back transformers when they don't have access to the proper iron.

if I've spliced the power supply in at the right point.

Yes.

[FYL]

By way of explanation, Moody hails from Australia, as I do. The cost of transformers here is very high, for a number of reasons - small market, high shipping costs, import duties etc etc. The end result of this is that small DIY builds are not viable unless readily available, low cost transformers can be used - either back-to-back or in voltage multipliers.

OK.
 

Then what about using 6V 100VA PT's back to back? You've got 240V mains, which would give around 320V B+ thru a silicon recto, lower than the std 350V but perfect for a brown sound.

[moody]

By way of explanation, Moody hails from Australia, as I do. The cost of transformers here is very high, for a number of reasons - small market, high shipping costs, import duties etc etc. The end result of this is that small DIY builds are not viable unless readily available, low cost transformers can be used - either back-to-back or in voltage multipliers.

OK.
 

Then what about using 6V 100VA PT's back to back? You've got 240V mains, which would give around 320V B+ thru a silicon recto, lower than the std 350V but perfect for a brown sound.

100VA is very beefy compared to the 15VA units I am using.  This would probably work and eliminate the need for the third heater transformer, although the B+ would probably be a touch less due to losses, but, I would have to source a cheap 6v transformer with enough current for the job.  I have however used the voltage quadrupler method before without any problems - as have a large number of others (the person who published the schematic runs a valve amp school constructing a 15w amp using that power supply). 

The particular transformer listed was for a time being sold by a large national chain which decided to no longer support electronics, therefore I have 10 or so that were picked up for near nothing.  I would therefore prefer to use them on appropriate sized builds rather than sourcing other far more expensive options.

In a worst case scenario (which I haven't seen) there would be no reason that the transformers couldn't be centre tapped (either each or between the two) and the Delon quadrupler that you mention above could be used.

[darryl]

...but perfect for a brown sound.

A quad-droop-ler provides the same benefit...   

A voltage multiplier can provide a similar effect to the sag of a valve rectifier, although with adequate filtering the supply can still be surprisingly stiff.

For an extreme example of a voltage multiplier in a guitar amp:  http://www.guitargear.net.au/discussion/index.php?topic=17009.0

[PRR]

> Australia, as I do. The cost of transformers here....
> sold by a large national chain which decided to no longer support ... picked up for near nothing

I was gonna say... it makes sense mostly if these transformers are a penny-a-pound. The steep leverage (sag) and odd-lot cap voltage "issues" become moot if you can save several dozen bucks (or already bought the iron).

> 15VA units I am using

How big an amp? Two 15VA, 30VA AC, will give around 20 Watts DC with simple rectification. That's not enough to abuse a two-6V6/two-EL84 amp.

 ... Oh, "Stout" is a one-jug? Then you can fully-toast a 13W tube, sag is not a real issue, and apparently the investment to "just try it!" is small. You can tack-together that diode-cap-lattice and lash it to the nearest 6V6 (or 7K 15W resistor), see what voltage you get.

[moody]

How big an amp? Two 15VA, 30VA AC, will give around 20 Watts DC with simple rectification. That's not enough to abuse a two-6V6/two-EL84 amp.

 ... Oh, "Stout" is a one-jug? Then you can fully-toast a 13W tube, sag is not a real issue, and apparently the investment to "just try it!" is small. You can tack-together that diode-cap-lattice and lash it to the nearest 6V6 (or 7K 15W resistor), see what voltage you get.

How did you get 20v DC?  84v DC from my calculations (2 x 30v x 1.4).  Then through the quadroopler is 336 (usually higher as the wall voltage tends to be a touch over 240v).

As to a one jug amp, this power supply does better than that.  I've yet to hear of a failure on 2 EL84 and 2 12AX7.

I must come from a non-conventional area of the amp making world.  I'd hate to mention the recovered PC power supply caps or 100v line transformers being repurposed for output transformers......

[DummyLoad]

How did you get 20v DC?

20 Watts DC

[moody]

How did you get 20v DC?

20 Watts DC

Ahh my fault.  How is this derived?  I know this power supply can manage 125ma at high tension where the 2xEL84 amp that it was designed for would need approximately 100ma.   I know for a fact that it runs a 15watt 2 x EL84 amp well into overdrive without problem.  Assuming an 18watt circuit rather than 15 watts (20% extra) surely this is still well within the limits of the power supply given?

Looking up, a standard 18w marshal transformer is 290v ac at 120ma rectified to 404 which is with a 5Y3 rectifier dropping aprx 60v = 346ish.  Compared to 60vx4x1.4 = 346v at 125ma with diode quadrupler it seems to be right on target with a touch spare current.  (I didn't expect to get the exact same voltage when I started these calculations  ).

I know this power supply works, but only for 15w 2xEL84 amps.   If there is a good reason why it won't manage the difference between 15 and 18 watts then I will certainly pay attention.

Edit - miscalc.  336v at 125ma.  10v short of 346v.  Still ballpark though.

[Shrapnel]

How did you get 20v DC?

20 Watts DC

Ahh my fault.  How is this derived?  I know this power supply can manage 125ma at high tension where the 2xEL84 amp that it was designed for would need approximately 100ma.   I know for a fact that it runs a 15watt 2 x EL84 amp well into overdrive without problem.  Assuming an 18watt circuit rather than 15 watts (20% extra) surely this is still well within the limits of the power supply given?

Looking up, a standard 18w marshal transformer is 290v ac at 120ma rectified to 404 which is with a 5Y3 rectifier dropping aprx 60v = 346ish.  Compared to 60vx4x1.4 = 346v at 125ma with diode quadrupler it seems to be right on target with a touch spare current.  (I didn't expect to get the exact same voltage when I started these calculations  ).

I know this power supply works, but only for 15w 2xEL84 amps.   If there is a good reason why it won't manage the difference between 15 and 18 watts then I will certainly pay attention.

Edit - miscalc.  336v at 125ma.  10v short of 346v.  Still ballpark though.

125mA @336VDC would require, with a voltage quadrupler supply, 500mA-DC (or better) delivery capability of the transformer used for the base voltage. Power is Power.

[darryl]

The two DSE 2860 transformers Moody is planning to use are rated at 30VAC, 500mA.

Ignoring transformer regulation and diode voltage drops to get an approximate answer:

                                    60 x 1.4 x 4 = 336 volts DC output
                                    500 ÷ ( 1.4 x 4 ) = 89mA DC

It does appear to be under-rated, but as Moody has said, there are a significant number of amplifiers successfully using this transformer arrangement. These amps have all been 2 x EL84 with 2 x 12AX7.

[moody]

The two DSE 2860 transformers Moody is planning to use are rated at 30VAC, 500mA.

Ignoring transformer regulation and diode voltage drops to get an approximate answer:

                                    60 x 1.4 x 4 = 336 volts DC output
                                    500 ÷ ( 1.4 x 4 ) = 89mA DC

It does appear to be under-rated, but as Moody has said, there are a significant number of amplifiers successfully using this transformer arrangement. These amps have all been 2 x EL84 with 2 x 12AX7.

Based on what I have seen of the original design notes on the power supply, 125ma isn't needed, only around 100ma.  I'm going to assume safety factor and over engineering of the original transformers make up the difference from 89ma.

[DummyLoad]

How did you get 20v DC?

20 Watts DC

Ahh my fault.  How is this derived?  I know this power supply can manage 125ma at high tension where the 2xEL84 amp that it was designed for would need approximately 100ma.   I know for a fact that it runs a 15watt 2 x EL84 amp well into overdrive without problem.  Assuming an 18watt circuit rather than 15 watts (20% extra) surely this is still well within the limits of the power supply given?

Looking up, a standard 18w marshal transformer is 290v ac at 120ma rectified to 404 which is with a 5Y3 rectifier dropping aprx 60v = 346ish.  Compared to 60vx4x1.4 = 346v at 125ma with diode quadrupler it seems to be right on target with a touch spare current.  (I didn't expect to get the exact same voltage when I started these calculations  ).

I know this power supply works, but only for 15w 2xEL84 amps.   If there is a good reason why it won't manage the difference between 15 and 18 watts then I will certainly pay attention.

Edit - miscalc.  336v at 125ma.  10v short of 346v.  Still ballpark though.

125mA @336VDC would require, with a voltage quadrupler supply, 500mA-DC (or better) delivery capability of the transformer used for the base voltage. Power is Power.

it is a 500mA device.

http://www.altronics.com.au/index.asp?area=brdp&brd=10&pg=0&list=1

[PRR]

> 500 ÷ ( 1.4 x 4 ) = 89mA DC

The current factor for a cap-input rectifier is closer to 1.6 or 1.8. The HIGH peak currents count for a lot.

As a guide: the VA is multiplied by 1.414/1.8= 0.77. Or say DC Out is three-quarters of VA rating.

I asked the idiot to work it. Idiot didn't have a quadrupler, I used a doubler with 60VAC in (158V DC out) and double your suggested 89mA out, 178mA. This should be the same transformer load.

Idiot's answer below.

Note the Peak current is 2.4 Amps. While this only happens ~~20% of the time, the root-mean-SQuare (heating) value is more than 20% of 2.4A.

The transformer RMS current is 833mA.

This is in excess of the marketed 500mA.

What happens? Trannies over 100VA run hot and die young. Trannies under 10vA cool OK but sag badly.

If you are getting a useful voltage, and you can hold your hand on the tranny, I would not fret.

(It is actually rated to poach your flesh: 120°C insulation. That's the internal hot-spot, the outside is cooler. Still, boiling spit on the top is not an urgent panic, just a long-life issue.)

[moody]

Just to update.  Amplifier is created and working well, though I haven't really been able to test it at any decent volume yet.





Please ignore the scavenged chassis.  This is very much an experimental unit rather than something made to look pretty.

[PRR]

Did the B+ wind up in the 310V-340V range?

Can you leave it run for an hour and still hold the PTs?

Why does it look like a funnel stuck in the side of the chassis??

[TIMBO]

Hi guys, I too am from the land downunder and must disagree with your line of thinking. I agree that components are hard to get and are costly.The general stuff (caps, resistors etc. are as cheep as chips) and the transformers/chokes are well priced if you buy online. I just purchased a 18w PT for $62 Australian ($62 US) delivery about $20 . Buying Three transformer from Jaycar , RS Components will cost about $60 so for the extra cost i'd rather use something that was design for the job. I look at it this way, You say it is an experiment, thats great and when you decided that after the tweaking is done you want to make it a usable amp (i not saying that your idea isn't a good one) and you find that it won't go the distance than it will become costly. In the construction industry the saying goes "right tool for the right job" thanks 

[moody]

Hi guys, I too am from the land downunder and must disagree with your line of thinking. I agree that components are hard to get and are costly.The general stuff (caps, resistors etc. are as cheep as chips) and the transformers/chokes are well priced if you buy online. I just purchased a 18w PT for $62 Australian ($62 US) delivery about $20 . Buying Three transformer from Jaycar , RS Components will cost about $60 so for the extra cost i'd rather use something that was design for the job. I look at it this way, You say it is an experiment, thats great and when you decided that after the tweaking is done you want to make it a usable amp (i not saying that your idea isn't a good one) and you find that it won't go the distance than it will become costly. In the construction industry the saying goes "right tool for the right job" thanks 

The amp is an experiment, the power supply is not.  There are (as far as I know) over 40 amplifiers now out there with the same power supply, and many more with similar designs, no one has problems with them.  The 15 watt amplifier I made before this with a fender preamp and the same power supply is currently rehearsing twice a week and gigging periodically.  I have yet to hear of a complaint about this power supply not going the distance. 

As to the power transformer comparing to $60, I've just costed all four (including output) transformers at $53 plus local shipping.

[moody]

Did the B+ wind up in the 310V-340V range?

Can you leave it run for an hour and still hold the PTs?

Why does it look like a funnel stuck in the side of the chassis??

B+ 311
+1 289
+2 256
+3 254

Haven't done an hour long test yet, will do next weekend, shouldn't be a problem.

[moody]

Did the B+ wind up in the 310V-340V range?

Can you leave it run for an hour and still hold the PTs?

Why does it look like a funnel stuck in the side of the chassis??

Ran for an hour, transformers about the temperature of an electric blanket on medium (maybe 30-35 degrees celcius?? - I don't do farenheit)

The chassis is repurposed.  The pipe out the side was originally where the power came in for 2 flourescent tubes, end of an outdoor light box.