This foxed me today ,built an amplifier during the week which is part of my radiation detector I have been working on,worked OK bit noisy it is very high gain.
Today cut up a coke can to make a little screened box to reduce the noise, it decided it didn't want to be an amplifier any more it was going to be a HF oscillator !
I had this problem before in the past ,it just disappeared on it own?
I tried a few different PP3 batteries ,each one gave me a different frequency?
So I used my bench power supply once I got the thing quiet it was OK ,went back to the batteries ,I noticed it worked with one of the batteries if I held it in my hand ,that made me think.
I have got an ESR meter I made some years ago so I did some checking ,one of the batteries didn't even register on my meter ( I dont actually have ohms on the scale) it must have been over 10 ohms.
The zinc carbon batteries do seem to have quite a bit of internal resistance whereas a Duracell Alkaline battery was more like 0.2 ohms.
Barry Wilkins
Today cut up a coke can to make a little screened box to reduce the noise, it decided it didn't want to be an amplifier any more it was going to be a HF oscillator !
I had this problem before in the past ,it just disappeared on it own?
I tried a few different PP3 batteries ,each one gave me a different frequency?
So I used my bench power supply once I got the thing quiet it was OK ,went back to the batteries ,I noticed it worked with one of the batteries if I held it in my hand ,that made me think.
I have got an ESR meter I made some years ago so I did some checking ,one of the batteries didn't even register on my meter ( I dont actually have ohms on the scale) it must have been over 10 ohms.
The zinc carbon batteries do seem to have quite a bit of internal resistance whereas a Duracell Alkaline battery was more like 0.2 ohms.
Barry Wilkins
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