[R-390] Re: R-390 Voltage Regulator

Sat Mar 26 14:30:30 EST 2005

Hi

Your point is well made. A lot depends on exactly what the input 
voltage to the regulator is. The assumption I was going on was that the 
unregulated supply was in the 300 to 350 volt range mentioned earlier. 
That and the quoted current drain of 200 ma got me to the roughly 30 
watts.

If the plate current is roughly 100 ma and not 200 ma that also makes a 
big difference. The tube line up is pretty similar to the 390A so the 
current should be in the same general vicinity.

Unregulated B+ of 250 volts and 100 ma of current would get you to 7 
watts (versus 30) in the regulator. If you put a resistor in series to 
dump half of it then you are down to  3.5 watts or less. That's well 
within the simple heat sink region provided you aren't using a marginal 
transistor to start with.

You still have the problem of fold back and dissipation during a short 
or an over voltage on the input. They both scale with the current 
level, but a 25 watt dissipation still seems likely in the event of a 
short and no current foldback. Of course if the parts are cheap enough 
you could just replace them when they fry. Seems like a less than 
perfect design solution on an otherwise bulletproof radio though.

Still hanging on to my box of 6082's ....

	Take Care!

		Bob Camp
		KB8TQ

On Mar 26, 2005, at 12:45 PM, Barry Hauser wrote:

> Hi Bob
>
> The R-391 that turned up with the solid-stated regulator has no real 
> heat sink to speak of, was modded long ago -- so probably run a long 
> time.  It literally runs cold.  There was nothing particularly high 
> tech -- couple of transistors -- small tab mounts, couple of zeners 
> and a few other parts.
>
> As I recall, there was a smudge of heat sink grease and a hole on one 
> side of the 6082 shield where it looked like the modder tried to mount 
> one of the transistors.  That tab mount is just sticking up on the 
> perboard -- with some telltale heat sink grease on it.
>
> This is not to argue -- just what was observed.  It was written up in 
> HSN a couple of years ago.
>
> I'm more than a bit rusty on the theory, but as I recall, when 
> figuring the parameters for a VR circuit, it's has to do with the 
> maximum portion of the power that's being dissipated by the VR -- not 
> the total of the supply.  In other words, if the unregulated coming in 
> is 200 vdc and the VR is set to maintain 180, it's dissipating 20 v X 
> whatever ma's.  Something like that. If I'm not mistaken, the B+ fuse 
> is the same as in an R-390A -- 1/8th amp, so a max of 125 ma?
>
> But, I dunno about that ... but this VR runs cool with no heatsinking, 
> not even mounted to the frame or module.  AC voltage runs high around 
> here - 126-127 v., and when I tested it, I ran it up to nearly 135 
> with the variac. The zeners in the circuit are also small, though I 
> can't tell the wattage by just lookin'.
>
>
> Barry
>
> ----- Original Message ----- From: "Bob Camp" <ham at cq.nu>
> To: "R-390A Receiver List" <r-390 at mailman.qth.net>
> Sent: Saturday, March 26, 2005 10:31 AM
> Subject: Re: [R-390] Re: R-390 Voltage Regulator
>
>
>> Hi
>>
>> If you are going to try the solid state R390 not an A regulator 
>> conversion here's a starting point on the pass device.
>>
>> For a whopping $5.67 you can get a IRFPE30 from International 
>> Rectifier. Data sheet is at 
>> http://www.irf.com/product-info/datasheets/data/irfpe30.pdf.
>>
>> Into an infinite heat sink the part is rated at 125 watts at room 
>> temperature. At 70C the part will handle 75 watts. Since we are 
>> running 20 to 30 watts that seems about right. The heat sink we 
>> attach it to probably will need to be a bit better than a radio 
>> bulkhead, but still smaller than the entire rest of the radio.
>>
>> With an 800 volt rating out to 2 amps overload and over voltage 
>> should not be a major issue. It also has a built in reverse 
>> protection diode so that's one less part you have to wire in.
>>
>> Looks like the only major issue is the power dissipation.
>>
>> Without a lot of work 30 watts seems like a reasonable starting 
>> point. The MOSFET has a lot better saturation characteristics than 
>> the tube. That means that we don't need quite as much headroom on the 
>> regulator. A simple trick is to put a resistor in series with the 
>> transistor to soak up part of the power. If half of the power is in 
>> the resistor that cuts our heat sink down to the 15 watt region. With 
>> a fan on it that can be a fairly small  chunk of metal. With no fan 
>> you will need a fairly large chunk of extrusion. Without going to far 
>> on heat sink design the part should be about 6 X 6 X 3 if it's a 
>> normal multi fin chunk of aluminum extrusion. That will keep the 
>> temperature down to the point that you won't cause burns if you bump 
>> into it. If you don't use the resistor trick then the heat sink goes 
>> to about 10X4X3. That's a pretty big heat sink ...
>>
>> Bottom line is that the tubes run quite a bit hotter than the 
>> semiconductors. That makes them easier in the heat removal 
>> department. For the same margin in the design the volume of the 
>> semiconductor plus heat sink will be at least as large or larger than 
>> the tubes it replaces.
>>
>> Still hanging on to my box of 6082's ....
>>
>> Take Care!
>>
>> Bob Camp
>> KB8TQ
>>
>>
>>
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