[Hallicrafters] HT-37 Bias Adjustments

[Sine Wave]

When all else fails, read the instructions.

At 09:34 AM 8/22/04 +0600, you wrote:

>Hi guys,
>
>Pulled the top cover of the HT-37 and here are the voltage measurements
>for grid bias.
>In standby mode, - 49 volts.  Measuring this same voltage in transmit, -
>46 volts.
>
>Following advice posted here, I put the rig in MOX and while
>transmitting, I attempted
>to adjusted the bias to - 49 volts.  Couldn’t get there but I was able
>to get to ­ 47.5 volts.
>In standby, the bias voltage is now ­ 51 volts dc.  This minor voltage
>changed has resulted
>in a cooler running rig (maybe).  I don’t have actual temperature
>measurements, but it
>does feel cooler.  I will run temp checks to confirm.
>
>Possible reasons for this problem (?).  When restoring the rig, I found
>SR1 bad.
>SR1 was replaced with a standard silicon diode of appropriate ratings.
>Both capacitors
>C98 & C99 were also replaced.  When energized, the bias voltage soared
>and I could not
>get the ­ 49 volts dc.  At this point, I changed R64 (4.7k) to (15k).
>This change
>allowed me to obtain the requisite - 49 volts dc at TP2 in standby mode.
>It is possible that
>I may have to change the 15k to a lower value to be able to get back to
>­ 49 but I do not
>think this will be necessary.
>
>Those are the voltage measurements, I will get back later with
>temperature changes (if any).
>
>Bill (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