[TenTec] Titan II Bias issue

[kr7o at vhfdx.com]

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 at 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 at contesting.com
> > http://lists.contesting.com/mailman/listinfo/tentec
>
>
>Links:
>------
>[1] http://www.vhfdx.com
>_______________________________________________
>TenTec mailing list
>TenTec at 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.