Hi Jim,
Thank you for the reply. The amp appears to be working now. Replaced two
failed transistors on the screen board which were biasing the tube on all
the time. Also changed the bias voltage jumper to get the idle current
within spec.
The amp tripped once while doing test tune-ups on each of the bands, so
hopefully the tube is not gassy. I will run it gently for a while until I
am confident in the tube and repairs.
The transformer secondary for the bias circuit is 70vac, so there appears
to be a typo in the manual regarding -130v on RX.
At 04:12 AM 3/23/2017 +0000, you wrote:
Hello OM,
Not familiar with the Titan II, but when my Titan 1 425 failed with
the exact same symptoms, the B- bias diode
in the power supply "opened up" and was not supplying bias to the
tubes.. Chances are that diode is "open".
73, Jim W3KA
On 2017-03-21 05:27, kr7o@vhfdx.com wrote:
> I am repairing an amp that was from a friend's estate and have fixed
several issues, but now when I switch the amp to Operate, considerable
heat is coming out of the exhaust, so it appears the tube is partially
biased on all the time. I have loaded the amp many times up to about 1kw
output, so I am reasonably confident that the tube is OK.
>
> According to the manual, the cutoff voltage is supposed to be -130v,
but with 70vac on the primary into a half wave bridge, I cannot
understand where they are getting -130v from. My bias voltage is only
-80v in RX. I get up to -95v with the bridge unloaded, which is close to
what would be expected from a half wave bridge. The screen voltage
supply appears to be functioning normally.
>
> I will admit, I am not much of a tech, but I DO know how to work around
high voltage and avoid exposed plate voltage unless absolutely
necessary. I have gotten this far, and would love to get this amp
running if anyone has experience with this amp and does not mind helping
me sort this out. I have more history and measurements, but I will spare
the list.
>
> Thanks,
>
> 73, Robert KR7O/YB2ARO, DM07ba/OI52ee (ex. N7STU)
> DXCC 6M #1122
> WAZ 6M #112
> VUCC 6M, 2M
>
> www.vhfdx.com [1] (KR7O/YB2ARO pages)
> Looking for old VHF QSL cards and logbooks.
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
Links:
------
[1] http://www.vhfdx.com
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
-----
No virus found in this message.
Checked by AVG - www.avg.com
Version: 2016.0.8007 / Virus Database: 4767/14164 - Release Date: 03/22/17
73, Robert KR7O/YB2ARO, DM07ba/OI52ee (ex. N7STU)
DXCC 6M #1122
WAZ 6M #112
VUCC 6M, 2M
www.vhfdx.com (KR7O/YB2ARO pages)
Looking for old VHF QSL cards and logbooks.
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|