[Johnson] 3B28 make sense.

[radioman]

just the facts

1. 3B28 is a GAS rectifier.
2. 866 is a Mercury Vapor Rectifier

Both have 2.5 Volt 5 Amp filaments... and have otherwise identical
ratings in all respects.. working voltage, current, max current, and
Peak Inverse Voltage.

In all electrical Respects the 3B28 is a direct replacement for 866 and
866-A.

But, the difference is in how they behave and in thier reliability.

This is how it is:
+AF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBf-866 and 866-A +AF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXw-
1. 866's absolutely require warm up to vaporize their mercury before HV
can be applied.  Skip this and they flash over, and short out the Plate
transformer.
( see 3 below)

2. If moved around much.. they require hours of burning in with only the
filaments on to safely re-vaporize thier mercury.  Fail to do this and
they flash over, and short out the Plate transformer ( yes through the
filament winding+ACE-)

3.  Over time, the mercury in 866's oxidizes and causes slag, which
eventually causes the tubes to arc ( flash) over,and that- well you
know...

4. 866's generate considerable RF noise.

5. 866's are really hazardous to your heath if they break..especially if
they are hot +ACE-

6.  866's wear out. ( see 3).

7. 866's generate a lot of HEAT.

+AF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXw-3B28 's+AF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBfAF8AXwBf-

1 3B28's  do not require any substantial warm up time.  The gas they
contain is ionized by the HV itself, causing them to conduct.

2 3B28's having no liquid metal inside.. are not subject to flashover
due to any reason I know of except being operated at voltages that
wildly exceed thier normal limits.

3. 3B28's seem to last nearly forever. The only limitation to thier
life, is however many thousand hours the filaments will last. ( I have
never seen a bad 3B28 +ACE-)

4.  I cant see how one could possibly cause any damage to a power supply

5.The 3B28 does not generate any noise and very little heat.

6. 3B28's are cheap and have a nice purple glow..whenever B+- is present.

In summary... the 3B28 is the intelligent replacement for the arcane
and toxic 1920's mercury vapor technology of the 866.

IMHO...  rectifier filament winding failures in Kilovolt power supplies
are far more  likely traceable to  uncontrolled high current arc faults
of  bad ( or badly operated) 866's..than to the  25 watts of filament
current demand on a transformer +ACE-

My experience using the 3B28 's to replace 866-A's in Globe King 500's
and Globe Champ 300's has all been Positive.  There is no reason the
same wont be true in Valients, Viking 500's or any other transmitter
designed for 866's.

We all know solid state rectifiers work.. although questions of effiency
and
appropriate application remain.  To do it right require current
balancing resistors, and bypass caps.  And for what ?

Larry W6WUH