Sinus Rig Repair

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sinus trouble
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Re: Sinus Rig Repair

Post by sinus trouble » Tue Apr 18, 2017 10:34 pm

Thankyou for confirming Mr Albert! :)
I believe there is a 100 or 220uf cap following after that 47ohm resistor which is a bonus!
Unfortunately I have no 78L09s at the mo! :(

Also the Idq I had (3.11mA) Is not entirely accurate! It turns out that 3mA of that was just current consumed by the regulator itself!! Doh!!! :lol:

Looking on the bright side though I noticed as I approach 3V bias, the Idq starts to rise quite dramatically!!
I am really petrified to go any higher than 3V!!!

I think I will change the 78L05! Although voltage is present? It does not mean it is functioning as it should
I am as stupid as I look! :|

Albert H
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Re: Sinus Rig Repair

Post by Albert H » Tue Apr 18, 2017 11:45 pm

Do you have a solid 5V at the output of the regulator? If you do, the regulator is OK.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

MC Spanner
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Re: Sinus Rig Repair

Post by MC Spanner » Wed Apr 19, 2017 1:07 am

sinus trouble wrote: Tue Apr 18, 2017 10:34 pm Looking on the bright side though I noticed as I approach 3V bias, the Idq starts to rise quite dramatically!!
I am really petrified to go any higher than 3V!!!
This is starting to make sense now. I think I might have mentioned earlier that I thought 3V was a bit high but it's been a good 10 years since I built with this device and the datasheet would appear to support what you're seeing. Don't forget it's the current you're interested in, not so much the gate voltage. Keep a close eye on the current as you adjust, and I would err on the low side, it's not worth overbiasing 30 quid's worth of FET for the sake of a few extra Watts which won't make much difference to your signal.

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sinus trouble
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Re: Sinus Rig Repair

Post by sinus trouble » Thu Apr 20, 2017 2:20 am

Spot on Mr Spanner! :)
I need to weigh up the pro's and con's in this situation? Do I push it and risk failure? Or leave as is?
I have put this rig through some harsh conditions and its still going strong!
Also it seems to be operating more in the class C region rather than B which can only be good for harmonic attenuation!
I am as stupid as I look! :|

Albert H
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Re: Sinus Rig Repair

Post by Albert H » Thu Apr 20, 2017 11:31 am

Not really. Class C has the device switching so there are some sharp edges that the harmonic filter has to deal with. Class B is usually cleaner!
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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