[600MRG] power supplies

[Larry Molitor]

I sent this direct to Steve, but seems like a good idea to send it to the list as well:

Power supplies can be problematical. Here's some observations based on years of experience designing/build/using them:
Switch mode supplies are attractive because of their size/weight/cost. But this can be a "penny wise, pound foolish" scenario. A couple years ago I started swamping out my linear supplies for switch mode. Am now back to nearly all linear supplies!
Low cost switch mode supplies should be avoided. They are usually unreliable and always produce RF noise in some part of the spectrum. High cost, major brand supplies are OK except they may need additional filtering. I do use some switch mode supplies here but each one is put inside a metal box with additional filtering on both the AC line and DC out. Of course fans are needed to move air through the box.
Linear supplies are big, heavy, and hot. Also suitable transformers are getting hard to find. The old school regulators using pass transistors are as good as you are going to get. That's what I use here for regulated supplies.
The mostly good news is that the typical class D amplifier does not need a regulated supply! A simple transformer/rectifier/filter cap with a variac on the primary works good and is pretty efficient. The bad news part of this approach is that the filter cap needs to be LARGE!!
Class D and Class E amps are very good mixers being non-linear devices. That means that any ripple  present on the supply line is going to be mixed with the RF signal and produce spurs at +/- 120 Hz (or maybe even +/- 60, 180 and 240). If you want to keep your neighbors happy, you will need about 100,000 uF (or more) for a filter cap in the typical supply.
At WH2XGP I use a linear amplifier with a modified server switch mode fixed voltage power supply. The supply has heavy additional filtering and is very clean. Being linear, I can adjust power by simply turning the "PWR" knob on the TS-590S front panel. Just like on the HF bands!
A source of usable transformers for linear supplies are the boost/buck transformers used for power line voltage adjustment. They show up on ebay and other outlets at reasonable prices. They have 120/220 "primaries" and 12 or 24 or 32 volt "secondaries". Look for one rated at 1 to 2 KVA.
73,
Larry - W7IUV / WH2XGP