tube power supplies, switchmode

[ruffrecords]

Im not suggesting a well designed ,screened smps with extra filtering cant work ,but these wall warts are a liabillity in a live or studio situation .

It i s an unfortunate fact that the huge quantities of poorly designed and constructed SM wall warts, that are fine for charging phones, have given SMPS a bad name. A properly engineered SMPS is good for many applications, including pro audio.

Cheers

Ian

 

[efinque]

The PD-25 is an open frame SMPSU. It is meant to be housed in a screened box. I us the LRS series which are enclosed in a metal case.

Cheers

Ian

Yes the PD-25B is open frame.. I've read people using them (edit : SMPS' in general) for power amplifiers too.

The build also has a pair of output transformers which could be picking up the noise, who knows..

 

[pucho812]

i bought one  8)

Oh yeah, lets see how it goes. I would jump in but money is tight at the moment. Awaiting to sell some things before I make any plunge.

 

[PRR]

> Care to share a link to them?

No. The one I got was 347V!! I did not know there was such a thing; turns out to be the leg of 600V 3-phase, and is commonly used (maybe in Canada) as an industrial supply voltage. Turned out to be an autotransformer to a standard 120V-277V Mvolt LED supply, so I voided my warranty and lost 10 pounds in a instant.

12V LED flood light. Truck store. Snow-plow, off-road, etc. NAPA has a few at high price. Bangor Truck has a whole wall, cuz plows and dumptrucks work dark hours here in the north. This one is 120 Watts. Unless you are lighting a ball-game, probably better to get more this size than look for monsters.

I got a teeny one for a sno-blower on Amazon (sadly my new snoblo lacks any dynamo output- it's optional on Honda-clones).

 

[kambo]

PSU arrived...
will try do some tests this weekend... any specific measurements ?

 

[ruffrecords]

PSU arrived...
will try do some tests this weekend... any specific measurements ?

Output voltage and ripple versus load would what I would measure first.

Cheers

Ian

 

[kambo]

Output voltage and ripple versus load would what I would measure first.

Cheers

Ian

realized most needed stuff (croc cables, resistor box etc) were left at job!
measures 305VDC direct connection.
ripple is 0.2VAC with my jig.

 

[ruffrecords]

realized most needed stuff (croc cables, resistor box etc) were left at job!
measures 305VDC direct connection.
ripple is 0.2VAC with my jig.

Interesting. I think I may get one and have a play.

Cheers

Ian

 

[Bo Deadly]

realized most needed stuff (croc cables, resistor box etc) were left at job!
measures 305VDC direct connection.
ripple is 0.2VAC with my jig.

What is the load? You need a load resistor. But at 300V you need a high wattage part. For example, 305V / 4k7 = 0.065A * 305 = 20 watts. If you have a few different load resistors you can hook them up in parallel and series to see the effect of load on voltage. Specifically does the voltage drop with load or does it stay at 305V until it reaches the current specified as some folks here stated. I would like to know that. Then you can look at ripple with a capacitor (high voltage of course!) to block DC but I would want to know how much low frequency noise there is. High frequency noise is easier to filter.

 

[kambo]

Ian, i wouldnt rush!
found my spare scope cables..... graphs looks like my eurorack scope  :
will grab croc cables/parts etc tomorrow, and hook it to tube pre etc...


edit : add  Ian

 

[kambo]

What is the load? You need a load resistor. But at 300V you need a high wattage part. For example, 305V / 4k7 = 0.065A * 305 = 20 watts. If you have a few different load resistors you can hook them up in parallel and series to see the effect of load on voltage. Specifically does the voltage drop with load or does it stay at 305V until it reaches the current specified as some folks here stated. I would like to know that. Then you can look at ripple with a capacitor (high voltage of course!) to block DC but I would want to know how much low frequency noise there is. High frequency noise is easier to filter.

will try get back tomorrow... it has current adjustment pot underneath... should be able to check that
why cant i use 100K as load resistor ?
i was thinking something else  ;D

 

[Tubetec]

You can use a 100k load ,but the current will only be a few mA, so you wont know much about what happens with higher load currents .

 

[kambo]

found some croc cables, hooked up R-C-R2-C2 with 100k drain resistor. 
ripple cross R2 is still 0.2VAC no change!

same R-C with trx-diode combination,  R2 ripple is  0,004VAC
(edit : 220uf - 1k)

 

[PRR]

Ripple is roughly proportional to load current.

Unless your intended load IS a 100K resistor, you need to suck harder.

 

[ruffrecords]

That is a trx combination??


Cheers

Ian

 

[kambo]

That is a trx combination??


Cheers

Ian

is above question to me  :

 

[kambo]

here some measurements

 

[Bo Deadly]

here some measurements

That's not a realistic SMPS output filter. You definitely don't want to drop across 1K. Use an inductor (aka choke when referring to power filtering) and a capacitor. The capacitor doesn't even have to be that big. Just enough to get the offending frequencies. You're not trying to filter rectified AC like in a linear supply. If the ripple is really 6mV with a 61mA load and no change in 305V out like your measurements say, that's already pretty much awesome.

 

[kambo]

That's not a realistic SMPS output filter. You definitely don't want to drop across 1K. Use an inductor (aka choke when referring to power filtering) and a capacitor. The capacitor doesn't even have to be that big. Just enough to get the offending frequencies. You're not trying to filter rectified AC like in a linear supply. If the ripple is really 6mV with a 61mA load and no change in 305V out like your measurements say, that's already pretty much awesome.

pretty much using what i have ... happy to try ur suggested drawing for measurements!

 

[Tubetec]

6mV at that current sounds very good , by the time you've added in an Rf choke and some Rc decoupling for preamp stages you'd have very very low noise in the plate supply . Be interesting to see how it fares in a small push pull power amp also.