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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc. |
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Thread Tools |
8th Jul 2017, 10:59 am | #61 |
Triode
Join Date: Apr 2017
Location: Winchester, Hampshire, UK.
Posts: 42
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Re: Setting bias on Tandberg 12
Another thing I've noticed is the sharp 'knee' as the plot goes from attenuation to the bump ( 5kHz @ 1.785ips for example). The eq curve in the service manual is a gentle increase so there must be something else happening.
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8th Jul 2017, 11:47 am | #62 |
Octode
Join Date: Jul 2006
Location: Perth, Western Australia
Posts: 1,971
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Re: Setting bias on Tandberg 12
Agreed. For 1.875ips that sharp dip around 5kHz followed by the rise is odd.
What signal do the plots represent? Left channel? Right channel? Both summed? |
8th Jul 2017, 2:28 pm | #63 |
Triode
Join Date: Apr 2017
Location: Winchester, Hampshire, UK.
Posts: 42
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Re: Setting bias on Tandberg 12
It's the left channel. I'm fairly sure the right channel was the same but I'll do a proper plot when I have the chance.
The plot is done by recording white noise (eq'ed to be flat up to about 18kHz) and then playing back into my Mac via a quality audio interface. |
8th Jul 2017, 3:22 pm | #64 |
Octode
Join Date: Jul 2006
Location: Perth, Western Australia
Posts: 1,971
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Re: Setting bias on Tandberg 12
Ok, just confirming it isn't right and left summed where deep dips such as in your plots would be a possibility especially at the slow tape speeds.
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23rd Sep 2017, 5:50 pm | #65 |
Triode
Join Date: Apr 2017
Location: Winchester, Hampshire, UK.
Posts: 42
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Re: Setting bias on Tandberg 12
Right, had a bit of time off this and am getting back on the horse. Figured I'd start by changing any suspect capacitors. As well as the high frequency roll off there is a lot of low frequency hum so I'll have a look at the two big electrolytics in the power supply as a starting point.
Getting the main audio circuit board out looks like a challenge but I'm actually quite excited about digging a bit deeper into this refurbishing thing! I was thinking of completely disconnecting the speakers and power amp as I do not have any use for them. Will this cause any problem elsewhere? |