[Hallicrafters] HT-37 Bias

[Al Parker]

Hi Bill,
    If your HT-37 is running like you say, it has a problem.  The proper
bias of -49v (if I remember correctly) will cut off the finals with no
signal applied from the driver.  If yours has AC on the bias due to bad
filters in the bias supply, it could have those symptoms I expect.  Or if
the coupling cap from the plate of the driver is leaky it could easily
over-ride the bias.  Or if the bias supply isn't working at all.
    If yours is running that way, don't keep doing it.  We'll all do what
we can to help you.  Don't assume a modification is needed when a problem
is suspected, asking questions is a good way to start.
73,
Al, W8UT
New Bern, NC
BoatAnchors appreciated here
http://www.thecompendium.net/radio/
http://www.hammarlund.info


----- Original Message ----- 
From: "Bill" <k2wh at optonline.net>
To: <hallicrafters at mailman.qth.net>
Sent: Wednesday, August 18, 2004 9:43 AM
Subject: [Hallicrafters] HT-37 Bias


Can someone tell me why the finals in the HT-37 are apparently run
100% of the time at full plate dissipation?  This condition occurs even
during
receive and standby periods.  The manual for the HT-37 under the BIAS
section,
states "the final amplifier tubes are operated close to rated plate
dissipation for optimum performance".

Does this mean all the time or just during transmit?  It would seem to
me
that a simple circuit mod to increase the bias to a higher level during
receive
or standby periods would allow these tubes to cool down.  Then again
Hallicrafters may want to tubes hot to allow the rig to stay warm and
stabilize  and also to stop heat cycling of the finals limiting
mechanical
stresses on the tubes.

Anyone have any ideas on why this is the way it is?  I'm inclined to add
a simple circuit to increase the BIAS on these tubes during receive or
standby to cut down on the heat.

K2WH

______________________________________________________________
Hallicrafters mailing list
Home: http://mailman.qth.net/mailman/listinfo/hallicrafters
Help: http://mailman.qth.net/mmfaq.html
Post: mailto:Hallicrafters at mailman.qth.net
----
List Administrator: Duane Fischer, W8DBF **for assistance**
dfischer at usol.com
----
Hallicrafters Collectors International: http://www.w9wze.org