[SBE] Continental 816

[Jon Frank]

Hi Barry:

It's been many years since I worked on an FM transmitter with a tube IPA.
High Screen current is some times caused by the tube not being properly
loaded or matched.  First thing I would check is the IPA plate tuning and
loading. If that is correct (and I believe you indicate it is) then look
at tuning and matching in to the PA. This is where I remember seeing
similar problems in the distant past.  Many times the matching is sliding
line type of adjustment that is not externally adjustable. There may be a
damaged component in the PA input matching or tuning circuit.


On 8/28/14 12:02 AM, "Barry Thomas" <barryt at sbe.org> wrote:

>I haven't seen much activity on this list in a long time. I hope the
>brain trust is still active.
>
>It has been soooo long since I've troubleshot a Continental 816 with a
>tube driver stage i really don't remember the old skill set.  Some advice
>on the first things to look at would be great.
>
>The problem:  I am not getting enough power out of the transmitter ....
>Only 80% with it running at full blast.  The final is new and good and
>tunes well. 
>
>I'm fairly certain it's driver-related.
>At first I thought it was just bad 4cx250b tubes...They were old.  I
>Replaced them but still have the same results. Both tubes are operating
>and seem balanced.  I've got a good match from the exciter into the
>driver stage and the driver plate tunes into the final, although PA grid
>current is low (of course).
>
>Driver and PA Plate and screen voltages are fine. Cathode currents of the
>two drivers are balanced but low. In fact All driver current readings are
>low by 50-70% EXCEPT driver screen current reading which is PEGGED.
>Backing off the power to 40% final output un-pegs the meter but it is
>still at the max scale. I know I should remember exactly what this means
>but it has just been too long.  Or maybe the meds have killed too many
>brain cells. 
>
>I am hoping with your help I can short circuit some of my re-education on
>this old box. 
>
>Any suggestions on the FIRST things I should check in the driver stage?
>
>Thanks for your suggestions.
>
>Barry Thomas, CPBE DRB CBNE
>
>Sent from my iPhone 5
>
>
>Barry Thomas, CPBE DRB CBNE
>barryt at sbe.org
>(323) 841-0682
>
>Sent from my iPhone 5
>
>
>_______________________________________________
>The SBE Roundtable, SBE at sbe.org
>To unsubscribe, go to http://seven.pairlist.net/mailman/options/sbe
>
>http://seven.pairlist.net/mailman/listinfo/sbe