[Boatanchors] HRO-50T Help Needed

[Ian Wilson]

Hi Joe,

A possibility is that the screen resistor of V-5 changed value,
causing the tube to draw excessive current and fry the primary
of the associated IF transformer.

I have seen quite a few short circuits in the screen bypass
capacitors that have done bad things to the screen resistors.

73, ian K3IMW


On Mon, Nov 17, 2014 at 6:18 AM, Joe Connor via Boatanchors <
boatanchors at mailman.qth.net> wrote:

> I need some help confirming my troubleshooting on this receiver. I
> recapped it and aligned it several months ago. It worked great until last
> night. Here's the Rider schematic:
> http://www.nostalgiaair.org/PagesByModel/395/M0012395.pdf
>
> Last night, it suddenly lost strength and sensitivity. Signal injection
> showed that the problem was in the IF stages. An IF signal injected into
> the grid cap of V-6 (2nd IF/6K7) produced a strong signal. An IF signal
> injected into the grid cap of V-5 (1st IF/6K7) produced a weak signal. An
> IF signal injected into the plate of the 1st IF (V-5) produced a strong
> signal.
> I checked voltages and there was no plate voltage on V-5. The plate
> voltages for V-5 and V-6 are fed through R-17, the plate filter resistor.
> R-17 has plate voltage as does the plate of V-6. A resistance measurement
> from R-17 to the plate of V-5 showed an infinite reading.
> As I interpret those readings, it looks like an open primary in T-6, the
> 2nd IF transformer. Does that make sense? Does anyone have any other ideas?
> What puzzles me is how I can get a strong IF signal through the plate of
> V-5 if the primary of T-6 is open. I'm wondering what could cause it to
> open so suddenly.
> If you all agree with my diagnosis, I plan to remove T-6 and, hopefully, I
> will find a break that I can repair. Of course, if anyone has a spare T-6
> lying around, I would be interested in buying it. I suspect, however, that
> will be like looking for the proverbial needle in a haystack.
> As always, thank you for your help.
>                     Joe Connor
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