Anyone familiar with the SX-117 that could give me a hand?

[K1MNX]

Am stumped diagnosing.  Poor sensitivity and low voltage on the RF gain circuit on V1 and V9.

Thanks.

Mike

[WQ9E]

Hi Mike,

Can you post the exact voltage readings you are getting on all the pins of V1 and V9.  I went through my SX-117 about 15 months ago so I still pretty much remember the basics of it.

Are there any signs of modifications?  I repaired an SX-117 a couple of years ago for another ham and it had additional circuitry added to the gain line to reduce the gain for transmitter monitoring.  According to the owner this was published in CQ or QST sometime in the 60's and was popular with 117 owners.  It required shorting an additional jack on the receiver for full gain-otherwise it had similar symptoms to what you have with your receiver.

Otherwise, as a quick check consider substituting tubes for V1 and V9 if you have spares and haven't done so already.  The voltage on the "gain line" should be very low at maximum sensitivity setting since this would be minimum cathode bias. 

73, Rodger WQ9E

[K1MNX]

Rodger,

Here are the voltages:

V1
2  1.6  8.5
5  154  164
6  121  164
7  1.6  8.3

V9
2  0.1  8.6
5  160  166
6  13.4  59
7  0.1  8.6

I have the connector shorted for receive.  There are no mods that I can see.

Thanks.

Mike

[WQ9E]

Hi Mike,

Check the value of the 39K screen dropping resistor (R-59) and also make sure that the screen bypass C-73 is not leaky.  Your screen voltage for V9 is too low and this will definitely reduce gain; there are other things that could cause this but check the easy ones first!

73, Rodger WQ9E

[K1MNX]

Rodger,  the screen dropping resistor was the culprit.  It had crept up to nearly 1 Meg!  Swapped it out and aligned the IF and it is sounding great.

Thanks again for your help!

73
Mike

[WQ9E]

Mike,

You are welcome and I am glad you fixed it, enjoy!

73, Rodger WQ9E

[Todd, KA1KAQ]

Good job, Rodger - You nailed it!