The schematic is not wrong.
The circuit is not a full wave rectifier, it is a voltage doubler.
That is why you see 140 DC from a 70m VAC transformer.
Gary
> On Mar 25, 2017, at 7:28 PM, kr7o@vhfdx.com wrote:
>
> 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.
>> >
>> > _______________________________________________
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>> > TenTec@contesting.com
>> > http://lists.contesting.com/mailman/listinfo/tentec
>>
>>
>> Links:
>> ------
>> [1] http://www.vhfdx.com
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>
> 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
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