Hello,
I am new to this board and would like to ask for some help for bringing my old Cit12 back to life:
One channel is showing all kind of faulty voltages and my plan is to replace all transistors.
After testing all transistors with the "two-diod-method" I thought that I had located the trouble to the pre-driver, but unfortunately not so.
I wonder if someone has a list of replacement transistors that has proved to work in the original design for this unit?
Regards//lasse
Stockholm, Sweden
I am new to this board and would like to ask for some help for bringing my old Cit12 back to life:
One channel is showing all kind of faulty voltages and my plan is to replace all transistors.
After testing all transistors with the "two-diod-method" I thought that I had located the trouble to the pre-driver, but unfortunately not so.
I wonder if someone has a list of replacement transistors that has proved to work in the original design for this unit?
Regards//lasse
Stockholm, Sweden
Once we establish how to current limit the amp we can start debugging.
Pull the plug in boards and do the diode test again on the output devices.
Next pull Q704.
Jump C-E on the bias transistor Q708.
Do the following tests with no input and no load on the output.
Measure the voltage at the emitters of the input diff pair and across the 390 ohm in
the collector.
Please tell us the voltages at the rails, the output, and at the pins of the driver transistors.
Pull the plug in boards and do the diode test again on the output devices.
Next pull Q704.
Jump C-E on the bias transistor Q708.
Do the following tests with no input and no load on the output.
Measure the voltage at the emitters of the input diff pair and across the 390 ohm in
the collector.
Please tell us the voltages at the rails, the output, and at the pins of the driver transistors.
Last edited:
Do you have the service manual? Here it is in .pdf:
http://manuals.harman.com/hk/Service Manual/Citation twelve sm.pdf
I would not buy any transistors until we discuss them.
I do not consider the 2N3055 a good substitute for the 40636 outputs.
http://manuals.harman.com/hk/Service Manual/Citation twelve sm.pdf
I would not buy any transistors until we discuss them.
I do not consider the 2N3055 a good substitute for the 40636 outputs.
Last edited:
Here is the 1969 Reference design from the RCA transistor manual:
http://www.diyaudio.com/forums/soli...-12-substitute-transistors-3.html#post2355300
http://www.diyaudio.com/forums/soli...-12-substitute-transistors-3.html#post2355300
Hello and thanks for all input.
This nights work is to rig a lightbulb (will 40-60W be ok?) in series with the mains supply to the amp.
Yes, capacitors: That is where all of this started. I replaced all electrolytics and was powering up the amp and was trying to adjust the bias when something happened. Probably, I managed to short something on the board and now, I have rail voltage on the output.
Panasonic FC all over and expensive can-caps in the PS.
Yes, I have the manuals for this amp.
regards//lasse
This nights work is to rig a lightbulb (will 40-60W be ok?) in series with the mains supply to the amp.
Yes, capacitors: That is where all of this started. I replaced all electrolytics and was powering up the amp and was trying to adjust the bias when something happened. Probably, I managed to short something on the board and now, I have rail voltage on the output.
Panasonic FC all over and expensive can-caps in the PS.
Yes, I have the manuals for this amp.
regards//lasse
Looks to me like either the VAS and/or the PNP driver have C-E shorts, probably not
both. This is why pulling the VAS will help debug it.
I don't see a problem with the NPN driver.
There is no reason to remove the NPN driver until the VAS device is removed and
voltages taken.
The diff pair look to be blown based on their B-E voltage.
both. This is why pulling the VAS will help debug it.
I don't see a problem with the NPN driver.
There is no reason to remove the NPN driver until the VAS device is removed and
voltages taken.
The diff pair look to be blown based on their B-E voltage.
Last edited:
Hello guys,
Just a quick word befors I make breakfast (Swedish time...)
I admire you guys who understand what`s goding on in a electronic cirquit like this one.
And I really appreciate the help from you.
I Will be back with results tonight on the feedback basen on post #3 from Pete
Regards// Lasse
Just a quick word befors I make breakfast (Swedish time...)
I admire you guys who understand what`s goding on in a electronic cirquit like this one.
And I really appreciate the help from you.
I Will be back with results tonight on the feedback basen on post #3 from Pete
Regards// Lasse
Those readings are goofy enough to suspect faulty connections from the card to the chassis connectors. I have a Citation 15 tuner with the same connectors and they're sometimes flaky.
G²
Hi, time for some results:
Rail voltage: +/- 35,5V
Output voltage: +33,7V
Emitter voltage on diff pair: +0,9V
Voltage across 390 ohms resistor: 1,9V
Driver Q706: emitter: +33,6V Base: +34,8V Collector: -35,6V
Driver Q710: emitter: +39,0V Base: +34,7V Collector: +35,2V
Best regards//Lasse
Looking very good so far.
Forgot to ask for the base voltages on the diff pair transistors.
I also want to explain that the original output devices used were what is called single
diffused type of homotaxial type which are not made anymore. Using any newer
faster type will require stability debugging so it is best to just keep the originals if possible.
Forgot to ask for the base voltages on the diff pair transistors.
I also want to explain that the original output devices used were what is called single
diffused type of homotaxial type which are not made anymore. Using any newer
faster type will require stability debugging so it is best to just keep the originals if possible.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.