S calibration signal too weak - tone generator issue?

Brand name believed to be KALIBR.
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Joined: Sat Nov 08, 2014 10:24 pm

S calibration signal too weak - tone generator issue?

Post by Arie1111 »

My L3-3 no longer measures transconductance properly. When doing the internal calibration (tuning freq and voltage with the pots behind the left door) I can not get the S calibration signal to the 120 calibration mark on the L3-3 meter. Even with the external calibration pot on the front on max, I can't get past 80....

I guess the following strange behaviour is related to it. Doing the internal calibration, one should normally find the strongest signal around 1400Hz, when the amplitude is set to 0.45 V. In my L3-3, the lower frequency the tone generator can make is around 1260 (pot turned fully left). When I increase the frequency with the corresponding pot, 1373 is the maximum frequency I can reach. Turning the pot any further immediately results in a total collaps of the generator (0 hz readout). So: my generator seems unable the get high enough to reach the frequency at which the signal is both strong and midway the bandpass filter.

When I did measurements about a year ago, I could still get to about 1400Hz (after that , the signal collapsed too, but that was no problem as the S readout on the L3-3 meter was than more than strong enough to calibrate to the 120 level). My hypothesis is therefore that the frequency band the tone generator can do has shifted down, outside of the desired range near 1400. Or is the bandpass frequency the one that shifted down?

Any hints what the cause of the problem is? Are there perhaps parts whose values have run out of spec?

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Re: S calibration signal too weak - tone generator issue?

Post by Aloha »

I have same situation... But i have spend 100+h in restoration all tubes are new all components are in spect and audio board in rebild... My stops at 110 .. IM Close to finish with CAD schematics and full report...
Jac is probably the only one who can help.. Someone should write me in PM.... It is the last thing to be 100% correctly functional..
Note to jac:i find out that are several discrepancys from the book and what is in the meter for 1 my R100 was 490ohm .. I find out there are several types of A - meters for Kaliber.

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Re: S calibration signal too weak - tone generator issue?

Post by Jac »

sorry, but this is a very difficult subject.

Note, the receiving filter has a certain notch frequency which you can not change, and the tone generator should be tuned to that of course, by the calibration procedure.

If you write here it "doesn't work", I don't think somebody can just tell you what's the problem.

If there has already by done some changes to the internal settings, as you write, and "it didn't help", that's may be the cause of the whole problem. This settings are not to be done such that the needle goes up again, but such that it is by the specifications.

Unfortunately the English translations of the Russian manual, seem made by people who speak little English, but when you know what they are trying to tell, you can sure understand it.

The beginning is, you need to understand completely how the circuiz works at first. Once you are through that, you'll be able to do the calibration procedure, and after that, you can do the fault finding quickly. In that order. So when you want to "fix" off-calibration electronics, without know what you are doing, that's not going to work.

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