[Milsurplus] DC to DC Converter Comments

[Peter Gottlieb]

You can work around this if you supply the boost converter from a separate isolated LV transformer winding. Of course if you need to add a transformer to do this you could just have a HV one and not need the DC-DC converter, and not have to deal with the RFI. 


Peter

> On Mar 8, 2019, at 3:41 PM, Al Klase <ark at ar88.net> wrote:
> 
> Gang,
> 
> The current crop of DC/DC converters is really attractive in terms of price and convenience.  However, there are some thing you have to consider.
> 
> 1)  As Breck Smith points out, these thing can be quite noisy at RF, and serious shielding and filtering may be necessary.
> 
> 2)  Because these are boost converters, the negative input is connected directly to the negative output.  Sometimes this doesn't matter, but there are a lot of tube radios where the high voltage supply is NOT connected to ground.  Rather, the high voltage is divided to provide B+ (above ground) and C- (Grid bias - below ground).   A prime example is the venerable BC-348:
> 
> <BC-348 Power Feed 2 smallest.png>
> Dyno HV- goes to chassis ground through inductor 101-B, a 20-volt       drop.  Connecting HV- to ground will cause serious audio distortion, and likely eat the 6K6 output tube.  
> 
> We also ran into this issue with the BC-474 receiver.  
> 
> RTFS before you proceed.
> 
> Regards,
> Al
>  -- 
> Al Klase – N3FRQ
> Jersey City, NJ
> http://www.skywaves.ar88.net/
> 
> ______________________________________________________________
> Milsurplus mailing list
> Home: http://mailman.qth.net/mailman/listinfo/milsurplus
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Milsurplus at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/milsurplus/attachments/20190308/acef74ea/attachment.html>