[Milsurplus] DC to DC Converter Comments

[Al Klase]

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 
<https://en.wikipedia.org/wiki/Boost_converter>, 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:


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/

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