Johnson Valiant audio issue

[ka4koe]

Would a partially-done / zorched audio drive interstage transformer cause this type of distortion? Or are dealing with a microphone issue?

Philip

[ka4koe]

Anyway, we're dead in the water until the D104 comes in. I'm gonna put a three prong plug on it and replace all the electrolytics before I go any further. A friend recommended justradios.com.

Went up from the standard values somewhat due to the solid state HV rectifiers, ie 450V to 600V.

With my luck, one of those babies will go KABLOOEY!!!! and take out something expensive while I'm still troubleshooting the audio. I don't like cursing in front of K4SMN and the kids.

Noted about 1 VDC and 1 VAC riding on the chassis/microphone jack. Hopefully the new cord and caps will help eliminate voltage on the chassis. I already got a tingle while trying out my Vibroplex bug with the "Beast".

I had a nasty jolt in the mid 80's whilst playing with a friend's R388. It had either a reversed plug or leaky bypass cap. As a consequence, the booger measured about 90V on the chassis. I grabbed a coax connector while my right hand was on the radio panel and WHAM!!!! I was able to let go, but yelled a 4 letter word I'm not proud of. My girlfriend at the time came running. My hands shook for a couple of days after my first experience with a nasty amount of voltage.

Like a friend of mine later said, and I'll quote this maxim for myself, I am very proud of my 37 year involvement in radios and electronics without a single, fatal electrocution.

Philip
KA4KOE

[Pete, WA2CWA]

Did you ever determine whether it was set up for low or high impedance? Have you tried the 638 with the Flex 5000A (line input connection)?



Also, with some audio input (audio generator or equivalent) into the mike input and a scope, you should be able to isolate the Valiant problem if it's in one of the audio stages.

[ka4koe]

Hi Z, and I used it the other day on the Flex.

[WQ9E]

I already got a tingle while trying out my Vibroplex bug with the "Beast".

Philip
KA4KOE

The CW keying line for the Valiant is the -265 bias supply.   It is sourced through a high value resistor so the current isn't dangerous but it will get your attention.  I got the "tingle" several times touching the wrong terminal of the straight key used with my novice Valiant during early morning operation.  It reminds me of the warning in one of the old Tektronix 500 series scopes concerning the sawtooth output used to drive their 1L series spectrum analyzer plug-in.  As stated in the manual, the sawtooth output provides 150 volts creating a shock which some people will find painful.  It sort of implies that others will enjoy the experience

The PTT line has significant positive voltage so poor microphone wiring techniques (or touching this line) are not good ideas. 

[ka4koe]

Did you ever determine whether it was set up for low or high impedance? Have you tried the 638 with the Flex 5000A (line input connection)?



Also, with some audio input (audio generator or equivalent) into the mike input and a scope, you should be able to isolate the Valiant problem if it's in one of the audio stages.

Ahhh.....didn't realize the Flex would serve as a great signal source.

Philip