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 Post subject: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Mon 30, 2017 5:10 pm 
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Joined: Oct Sat 01, 2011 2:02 pm
Posts: 192
Location: Vulcan Michigan
I recently completed a one tube regenerative radio based on a #27 tube that I had...it play's well, with a 2.5 volt filament Triac ac transformer, and a bunch of 9 volt batteries for the B plus. I have a 40 volt transformer, what determines how many microfarad filter cap to use. being b plus it doesn't matter if it's not regulated correct? I have a bunch of 160 and 450 volt caps around here.trying to get by with what I have thank you.Will send pictures of the radio soon. Perry


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Mon 30, 2017 5:25 pm 
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Location: Maryland 20709, USA
Hi Perry,

Rather than guessing, for now and in the future, I recommend downloading the
free Power Supply Designer II program from Duncan Amps.

http://www.duncanamps.com/psud2/index.html

It's an excellent design program that gives you all the voltages in any ps design.

Once you determine the maximum B+ voltage, I suggest rating the filter caps
at least 2 times that voltage.

- Leigh

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Mon 30, 2017 11:42 pm 
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Joined: Oct Sat 01, 2011 2:02 pm
Posts: 192
Location: Vulcan Michigan
Thanks for your help, I tried to download the program on my phone (Motorola Droid Maxx 2), and our tablet, but I get a "can't open file" message. I would like to use 2N1007 diodes, to rectify, just wondering what value mfd on the filter caps. From what I've read it seems like the values are much higher than what I've seen used in radio schematics...


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Mon 30, 2017 11:54 pm 
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Joined: Jan Tue 16, 2007 7:02 am
Posts: 2209
Location: Lexington, KY USA
Perry,

In order to use the design software, you will need to know how much ripple voltage is a reasonable target. So a guess ends up being at the center of the capacitor choice anyway.

I suggest that you try different capacitors and see how the radio sounds. It would be good to use two capacitors with a resistor between them. Maybe 4.7k or 10k ohms. 10uF to 47uF might be capacitor values to try.

If you have a filter choke, you can try it in place of the resistor. Or an old output transformer primary will do.

Be sure to include a bleeder resistor. 47k or 100k might be good.

If you want more B+ voltage from the same transformer, you can use a voltage doubler or tripler circuit. How much B+ are you getting from your batteries?

It might be good to post a sketch of what you plan to do. If you draw big, a cellphone photo can work.

Ted


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Tue 31, 2017 12:39 am 
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Joined: Oct Sat 01, 2011 2:02 pm
Posts: 192
Location: Vulcan Michigan
Using this phone can be a real pain compared to a personal computer ( wow!) I've been using 7 ,9 volt batteries, but it will play with less just have to turn up the throttle capacitor.maybe I'm overreacting to all of this, I keep thinking that since I don't have a o scope , just would like to get some smooth dc but it should show up as hum , correct. Since I'm using a#27 tube the filament is using a/c just wanted to try something. It's hard sometimes but it's worth it. I'm really happy with the radio itself it's just really neat to use


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Tue 31, 2017 1:00 am 
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Joined: Oct Sat 01, 2011 2:02 pm
Posts: 192
Location: Vulcan Michigan
Some photos


Attachments:
9302017185939.jpg
9302017185939.jpg [ 149.36 KiB | Viewed 512 times ]
930201719018.jpg
930201719018.jpg [ 97.29 KiB | Viewed 512 times ]
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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Tue 31, 2017 1:56 am 
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Location: Maryland 20709, USA
Looks nice.

The 27 tube can handle over 250 volts on the plate if proper bias is available.
At that voltage the plate current is only 5 mA, and lower with lower plate voltage.

So I would not worry about using batteries. 10 9-volt batteries yields 90v on the plate.
After all, real radios of that era were often battery-powered.

- Leigh

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http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Tue 31, 2017 2:05 am 
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ballroad wrote:
Using this phone can be a real pain compared to a personal computer ( wow!) I've been using 7 ,9 volt batteries, but it will play with less just have to turn up the throttle capacitor.maybe I'm overreacting to all of this, I keep thinking that since I don't have a o scope , just would like to get some smooth dc but it should show up as hum , correct. Since I'm using a#27 tube the filament is using a/c just wanted to try something. It's hard sometimes but it's worth it. I'm really happy with the radio itself it's just really neat to use


I've found some regens often work better using lower plate voltages... I had a few that played with less than 18 volts plate.

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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Tue 31, 2017 12:28 pm 
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Joined: Dec Sun 14, 2008 3:33 pm
Posts: 612
Location: Tokyo
From my own experience, I agree with Leigh: a set of 9V batteries will last a very long time in this situation. Regenerative detectors draw very little current, often less than 1mA. I had a 3A5 double triode regen which I ran on 5 9V batteries. About 200~300uA for the detector, a little over 1mA for the audio amp. I scrapped it after a year or so, but the batteries were still fine. Cheap batteries, btw, not alkaline.
In some of the ham radio HBs from the 1930s and 40s, they recommended running the heaters off a small transformer, but using a battery for the B+, claiming the battery would last at least 6 months.

Just mentioning this if you're concerned about battery life.

Rob


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Tue 31, 2017 2:58 pm 
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Joined: Jan Mon 28, 2013 9:35 pm
Posts: 815
Location: Santa Rosa, CA
For driving a regen suggest putting in a bit more effort
and build a variable, regulated supply. Either solid state
or tube. Thats what I've ended up doing and problems
with hum have gone away. Building the supply on a
sperate chassis also helps a lot.

If you don't want to go that route suugest two filter caps
and a healthy choke. When choosing filter caps don't forget
to consider ripple current. I've seen people hang 400 uF
filter caps on a transformer that is rated at 50 mA to try to
get the ripple down. Bad idea!

Look in any older ARRL handbook for a regulated supply and
calculating ripple current.
Steve


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Tue 31, 2017 5:44 pm 
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Location: S. Dartmouth MA 02748-1225 USA
Much about powering a regenerative radio was learned and built into the doghouse supplies for the National SW3 & 5 series. The supply has two chokes and three caps of which are about 10mf. The supply being a separate unit and powering a couple of tubes had a raised filament voltage to account for losses in the connecting cable. Hum control was also addressed by the use of a "triad" of bypass caps connecting to the filament, B+ and power line circuit. Since the caps were not critical in mf, I have found them to be around .01. In a modern application, the use of 600v "safety" caps would be recommended.

Changing to a directly heated filament tube would allow for a battery filament source as well as a positive bias so often recommended for a grid leak detector. Using "Dollar" store "D" cells to create a "B" battery with taps, either soldered together or placed in plastic holders then into a "cigar" wooden box for appearance sake.

Running OFF of any connection or capacitive coupling to the power line has a distinct noise advantage. Though there "may" be some loss of signal if the power line was part of the antenna circuit via a long ground path, that could be remedied by using a short, direct ground not shared by other devices. Getting away from the CATV ground is recommended as even modern TV's generate noises that raise havoc with SW signals...

YMMV

Chas


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 Post subject: Re: Filter cap size on a homebrew b plus power supply
PostPosted: Oct Tue 31, 2017 8:17 pm 
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Joined: Oct Sat 01, 2011 2:02 pm
Posts: 192
Location: Vulcan Michigan
Thanks for everyone's help, well I guess I will stay with 9 volt batteries for b plus power, maybe some neat looking battery box with repro labels, Perry


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 Post subject: Re: Filter cap size on a homebreifw b plus power supply
PostPosted: Dec Mon 04, 2017 4:00 am 
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Joined: Oct Fri 09, 2009 9:25 pm
Posts: 220
Location: Cleveland, Ohio
Perry....would you happen to have a schematic (or link) for this receiver?

Thanks.

Todd
ka8gef

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-Let us never lose the lessons we have learned.


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