Re: Type CA Channel B Gain Adj Problem


Don Black <donald_black@...>
 

The DC is the operating bias voltage for the 536 input stage and should be ignored, it's the peak to peak signal voltage you need to measure.
However I think there's a trap. The TU-2 calibrator only applies the signal to one of the differential inputs to the 536, the other input is AC grounded. That should be 0.1 volt per division according to the TU-2 manual. However if you use the signal through the CA preamplifier. it should enter the 536 as a differential signal, half at each input point but out of phase so they add. It's the total signal between the two inputs that's important so I'd expect to see 50 mV per division on each of the inputs, the grids of V304 and V324 (pins 1 and 3 of the interconnecting socket). They should be identical but of opposite phase, however I'd measure both and add them together in case the CA isn't exactly balanced. If your test scope has differential input you could directly measure the input between the two grids.
Since the error isn't too great if the signals aren't close to what they should be then let me know and I'll double check but I think I'm right. It's a pity they don't have waveforms in the manuals.
Anyone familiar with these models with anything to add or thinks I've made an error, please jump in.

Don Black.

On 01-May-13 11:33 PM, Cliff White wrote:
 

I've been using the calibrator from a different scope, which was calibrated a few weeks ago, so I'm pretty sure it's right. I do have two other working scopes right now, just none of the same series. I'll set the interface to the .1 volt/div and see if that fixes anything. Is the DC voltage it's floating on supposed to be calibrated as well?


Respectfully,
Cliff White, W5CNW
w5cnw@...
On 05/01/2013 01:43 AM, Don Black wrote:
 

I've checked bot the CA and 536 manuals and neither seem to have the usual waveforms that would indicate the signal level from the plugin to the mainframe. However in the TU2 test plugin (attached) it indicates 0.1 volt per division. You should be able to measure this at the mainframe and see if it gives the correct sensitivity. I suggest looking for more than one divisions at 0.1 volts per division. You'll need another scope for this, however any scope will do, you can check it against the calibrator if necessary.
Incidentally, are you relying on the calibrator signal for your measurements? It's always possible that's drifted and may be fooling you. You could measure an AC signal with a meter, calculate its peak to peak voltage (V RMS X 2√2) and see how that agrees with your cal signal.
Don Black.

On 30-Apr-13 12:07 PM, Cliff White wrote:

 

I just finished repairing a Type CA plugin. Everything seems to have calibrated just fine, with the exception of the channel B gain. It won't go low enough. For example, if I apply a .1 volt P-P signal, at .05 volts/div, the lowest the gain will adjust to is about 2.3 divs. It will go higher, but not any lower. Channel A adjusts perfectly. All other adjustments on both channels work fine. Does anyone have any ideas as to how I can fix this?


--
Respectfully,
Cliff White, W5CNW
w5cnw@...



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