[Boatanchors] Thanks for Replies: Question: X-Rays from 3B28?

Paul Litwinovich paull at wshu.org
Mon Feb 16 10:33:58 EST 2015

I have always believed that the voltage needed to be above 16kV, and I have
never seen x-ray warnings on broadcast equipment under 5 kW. I have seen it
on klystron TV transmitters in the 35 kW range, but these operate above 20
 I wonder if a standard  Geiger would detect x-rays? I think of Geigers as
detecting particle radiation. It would be interesting to know.

Paul Litwinovich
Director of Engineering
WSHU Public Radio Group
FCC Lic. PGGB 039245

-----Original Message-----
From: Boatanchors [mailto:boatanchors-bounces at puck.nether.net] On Behalf Of
wb3fau55 at neo.rr.com
Sent: Saturday, February 14, 2015 2:51 PM
To: William; boatanchor
Subject: Re: [Boatanchors] Thanks for Replies: Question: X-Rays from 3B28?

There  are SS replacements for the 3B28,  they were made by International
Rectifier, I think the number is IN 2637?  The mercury vapor rectifiers
posed the biggest X ray threat.  But, as William said,  you  are only
running 450volts.  The 3B28s  would  draw 10 amps of filament current.  I
use 5U4s and 5R4s in Apaches and DX-100s
only because they can stand  a huge inrush of power.  Another application, a
Globe King 500B,  I did SS the modulator power supply.  The  stock 816s were
priced out of site.  I used 3B28s in the RF power supply.   866s look nice,
but they are a problem for warming up.  They have X-ray radiation,  but to
what degree of a concern?  I guess you will need to get a Geiger counter-hi.
Don't put  your eyes  next  to them  for any length of time,  you   might
get cataracts.  [hell to get old]  73s Russ.
---- William <w_b_morton at hotmail.com> wrote: 
> Hello All,
> Ok, it appears there is no x-ray risk as the voltage is too low to create
any... or too low to create any strong enough to actually exit the tube.
> As to why not use solid state or 5U4GB:  The only reason I have is my
project uses 807 and 7193 tubes and a non-top cap 5U4GB would look too bald.
I figured what the heck - I found some rectifiers having a top plate cap so
why not use them?  Besides, the tube is filled with xenon.  Such a noble
> True, I now need to get a separate transformer for their filaments and
have to see if I even have sockets and look around for larger plate
connectors and my electric bill will go up and and and...and the whole
shebang might not even work.  But it will still be fun to try.
> If there are any other alternative non-mercury rectifier tubes having top
caps, please let me know.  
> Thanks again for all the responses.
> Best Regards,
> William
> From: w_b_morton at hotmail.com
> To: boatanchors at puck.nether.net
> Subject: Question: X-Rays from 3B28?
> Date: Sat, 14 Feb 2015 03:42:24 +0000
> Hello All,
> Been thinking of using a pair of 3B28 tubes to rectify an output voltage
to around 450VDC.  That value is above the critical anode voltage value of
50V, so that should not be a problem.  Current is less than the 500mA max
listed in the table.  With the output voltage far lower than the ~1000V
values listed in the table, I think these things would not even break a
> Two questions for the experts:
> 1.  Any issue seen operating arund 450VDC?
> 2.  The tubes have a sticker on the base with a warning regarding x-rays.
Why is there a warning on the tube base but nothing shown on the data sheet?
> I had no idea these would present an x-ray risk based on what I saw (and
did not see) on the data sheet, so I picked up a pair.  Perhaps this my
learning experience for the week.
> Have a great weekend!
> Best Regards,
> William

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