radio reception on PI grid

[koen]

So I did a final check of all voltages and solderjoints on my 5E3 before putting the chassis back into the cabinet. Everything looks fine, except that I get a strong radio reception when I touch the grid of the PI (V2 pin7) with the DMM probe (the other probe is connected to the chassis). I also get some radio reception when I move my finger close to the V1 grid wires, but I can understand that, since my body works as an antenna and it is not as strong as the radio at V2. Even with the volumes at zero, touching the PI grid (at the socket and the eyeletboard) gives a strong signal through the speaker.

Is this something I should worry about? And if so, anything specific to look for to fix it?

[Steve Conner]

I don't think this is worth worrying about.

[imaradiostar]

Do you like the station?

Just kidding. As long as it doesn't do it while you're not probing you should be fine. Like Steve said.

jt

[koen]

Good to know!

Lol, just saw your name 'imaradiostar', it's not you, is it?

[imaradiostar]

You never know- but it's more likely some ham radio guy. I'm more of a geek rocker. My output is too low to mention.

You should look up the Presidents of the United States version of "Video killed the Radio Star." It's funny and awesome.

At one point I was building amps and pedals under the name "Radiostar Amplification." That didn't last. I'd much rather build things for fun than make it a job and suck all the fun out of it. I have the freedom to try whatever crazy design I like, which is nice.

jamie

[Bruce / Mission Amps]

Try a 10pF to 27pF cap to ground right at the grid.

[Casey4s]

Back around 1965 I was playing a gig with a Silvertone 1484 (which I still have) and I got Police radio reception loud as hell right through the amp. It never happened again for what ever reason.

[koen]

Isn't there a Jimi Hendrix concert recording where the same thing happens?

But I have no issues with radio reception when I'm playing. Only when I was testing all voltages, and I was touching the PI grid with the DMM probe.

[macdillard]

Back in my other life I had a 500 watt linear amp on a CB. It would bleed over really bad. Could pull up to a club and cover up their in house sound system..This was back in the days of Disco's..Had a lot of fun with it. and made some folks unhappy.

[mooreamps]

It means the input impedance of your PI is very high. So the probe from your DMM acts like an antenna. If you used a lower impedance analog meter, it would load down the circuit and the radio inference would not be a pronounced.


-g

[koen]

It means the input impedance of your PI is very high. So the probe from your DMM acts like an antenna. If you used a lower impedance analog meter, it would load down the circuit and the radio inference would not be a pronounced.


-g

That makes sense. So it should be high, correct?

[mooreamps]

That makes sense. So it should be high, correct?

I'm not so sure. I choose to match the input impedance of the [p/i] to the output impedance of the gain stage that's driving it. I've wired it up both ways, and there is no difference in the sound, except when using the very high input impedance the amp makes more noise.

-g