TheRadioBoard

I recently built a small half wave power supply to run my 6SN7 breadboard receiver. The components are 2 filament xformers (wired sec. to sec.), one half of a 6X4, a 20 ufd cap, 4.5 h choke, and bleeder of about 25k. On my first go around I wired it as a choke input filter. The voltage output was a bit lower than I expected, so I switched over to a cap-input filter.

I read a pretty high rms voltage across R1 using the cap-input filter, say 90 volts ac, but hardly anything using the choke input filter. I knew the DC output voltage would increase with the cap-input filter, but I wasn't expecting the AC component. Any thoughts?

Is R1 the bleeder resistor?

Do you have any load connected?

Is the choke still in the circuit when you say "capacitor input"?

What are you using to measure the AC voltage?

Is the 6X4 good? Sometimes these develop heater to cathode shorts?

Rich

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Homebrew Radio ex-Silicon Valley

Rich:

Yes, R1 is the bleeder and load (for now).

The choke and capacitor are always in the circuit. The choke is in series with load, the cap is in parallel.

I need to make a correction to my post in that the ac reading is across R1 regardless of the filter configuration.

I am using an rms digital voltmeter, but my analog does the same thing.

I will try another 6x4.

regards,

brian

Downloud the PSUII designer and it will let you know what to expect out of a given configureation .
http://www.duncanamps.com/software.html

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Mark

Not sure an ac voltmeter won't also read dc. IMO the best way to see the ripple is with a scope. It's possible the choke is ringing. Have you tried measuring without the choke? If you want to risk it, try using the analog meter in dc mode and watch for needle flicker. If you really have 90 V of ac at 60 Hz, you should be able to see it. Start out on the 250-300 V range.

73,

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http://kr1s.kearman.com/
http://qrp.kearman.com/

Sure sounds like something shorted to ground or a reversed electrolytic capacitor...

Roger

6sn7 rcvr? If it is a regen such as a Twinplex etc it is impossible to build a power supply that will not have AC ripple. You can come close but because the regen hears in a range not possible with other circuits it can hear the AC componemt a poor ol superhet would never hear. I have got to the place where I had a useable PSs , reasonably quiet, but always I could hear a lot more on Battery power. You will get a lot of advice on "it is this" or that" but its just smoke. Most of them have never built a regen yet. A regen simply needs a quiet power supply and that means batteries. Even on battery power you can pick up the 60 cycle in the house wiring easily in the absense of a strong signal. You may be able to strike a compromise and trade some weak signal performance for the conveniance of a plug in supply. If you are just swl ing shortwave broadcasters then it will be fine but for weak signal Ham work sooner or later you will want batteries. I use a rechargeable 6 volt on filaments and 10 9 volts transistor batteries on B + supply snapped together. The filament 6 volt needs recharging every other day in heavy use but the B plus 9volts will last over 6months. Sometimes even longer. I buy them at the Dollar store. $10 every 6 months is ok by me.
As for those on AC the best Ps I built was back to back 24 volts transformers from the heating industry (cause they were free, throw aways) for isolation then a 10 ohm 10 watt resistor after a single diode in the + line with a 40 UF 450 voltcap on either sde of it going to ground. (PI)
I then built the 6 volt filment suppy seperate 6 volt transformer but used a diode , a toroid high current choke from a choke assortment I had bought and a 3000uf 50 volt cap from the choke to the B- side. because of the RMS deally with rectifying and caps the net voltage was higher than the 6.3 I wanted so I put a vintage 20 ohm heater rheo in series from a 1920s radio and adjust the filament voltage to suit what I am using it on. Currently it is feeding my one tube transceiver and it works OK but not as good as batteries. I have tried all the modern tricky stuff to but this one is the best so far. Sort of a brute force approach I guess.

Don VE3LYX

Putting aside the utility of my efforts, it turns out that my multi-meter(s) are the culprits.

I read the voltage across 10 9v cells in series, result: 90 + VDC, 200+ AC.

Thanks for all the comments.