Duncan Designer II - Use of

[richard8976]

Never really used any simulation program. I cannot simulate the circuit in the attachment can I, in Designer II? I don't think so. Do I need to simulate in say, LTspice IV? Thanks.

[dchisholm]

This is the first I ever heard of "Duncan Designer II". I am confident that LTSpice can handle the circuit with ease, provided you can get realistic models for the inductors and you can make a reasonable estimate of the DC output current drawn from the 3 voltage taps. (.It looks like about 10 mA on the 200V tap.)

The component values strike me as a bit unusual. With the transformer secondary of 276-0-276, and an output of only 250V from a capacitor-input filter, there must be a significant DC loss in choke L304. Then again, 20 Henries is a pretty heft piece of iron!

Placing L304 in the negative side of the rectified voltage is a little unusual for a comparatively low voltage valve (vacuum tube) power supply. It's more common to see that when the high voltage gets up in the 500V (or above) range.

There's another clever trick in there: C316 and C317 are selected to resonate with L304 to improve rejection of 100 Hz (second harmonic of the 50 Hz mains frequency, and the dominant AC component coming out of the fullwave center-tapped rectifier). I have wondered how effective this is in practice, since iron-core filter chokes usually have a rather wide tolerance on their inductance value, and it can be expected to vary significantly with the DC current in the winding.

Dale

p.s. - If you try it in LTSpice, you can get some high-quality "Help" from the Yahoo LTSpice User's Group. Do at least a cursory search of the old messages, "Tutorials" section, and other files before you post a question - there really IS a good chance somebody else has already solved whatever problem you may encounter, as well as the NEXT problem (that you haven't thought about yet).

[Elvee]

Ltspice can do it very easily:

[richard8976]

Originally Posted by dchisholm

This is the first I ever heard of "Duncan Designer II". I am confident that LTSpice can handle the circuit with ease, provided you can get realistic models for the inductors and you can make a reasonable estimate of the DC output current drawn from the 3 voltage taps. (.It looks like about 10 mA on the 200V tap.)

The component values strike me as a bit unusual. With the transformer secondary of 276-0-276, and an output of only 250V from a capacitor-input filter, there must be a significant DC loss in choke L304. Then again, 20 Henries is a pretty heft piece of iron!

Placing L304 in the negative side of the rectified voltage is a little unusual for a comparatively low voltage valve (vacuum tube) power supply. It's more common to see that when the high voltage gets up in the 500V (or above) range.

There's another clever trick in there: C316 and C317 are selected to resonate with L304 to improve rejection of 100 Hz (second harmonic of the 50 Hz mains frequency, and the dominant AC component coming out of the fullwave center-tapped rectifier). I have wondered how effective this is in practice, since iron-core filter chokes usually have a rather wide tolerance on their inductance value, and it can be expected to vary significantly with the DC current in the winding.

Hi. Yes, I meant Duncan Amps "PSU Designer II". It's that choke in the negative line that I don't think can be accommodated in the application mentioned.

The original circuit had a thermionic tube containing two rectifiers. I've replaced them with D1 and D2 solid state rectifiers and added the 100 R resistors.

And very good you picking up on that circuit trick to reduce hum. Someone pointed that out to me elsewhere.

L302 is actually quite a small choke physically, rated 18H @ 20mA, 25H @ 7mA. So, most current is supplied BEFORE that choke. L304 does look like PSU choke, it's rated 100mA.

The PSU is not for HIFI, it's for a radio receiver.

Someone mentioned a concern about possible voltage surge, because there is now no soft-start, I mean, we had a soft-start due to the time it took the thermionic rectifier to warm up. But, I've lost that in the modification.

So, I'd like to simulate. Never used Spice though, or any simulator. Have LTspice IV on my PC.

When thinking about soft-start, I was reading about a thermistor placed in PRIMARY circuit. Don't know if that would kill any VOLTAGE surge. Presumably.

[richard8976]

Originally Posted by dchisholm

p.s. - If you try it in LTSpice, you can get some high-quality "Help" from the Yahoo LTSpice User's Group. Do at least a cursory search of the old messages, "Tutorials" section, and other files before you post a question - there really IS a good chance somebody else has already solved whatever problem you may encounter, as well as the NEXT problem (that you haven't thought about yet).

Joined. Thanks.

[richard8976]

Originally Posted by Elvee

Ltspice can do it very easily:

Hi. Thanks. Will use that file in LTspice, when I know how.

Okay, I just got it. Rename the extention, to .asc. Now have Schematic in LTspice.