|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
141.239.172.248
In Reply to: RE: My HK Citation2 meter quit working posted by AJ on June 10, 2015 at 10:15:54
Hi AJ, and thank you for the tip. Putting in an aftermarket milliampmeter might be neat. I will check if there is something close to the size of the original meter. I was thinking of just installling a test jack and using my meter but I am not sure of what the current or voltage that I should be aiming for that corresponds to the stock meter reading.
I was hoping JM had a fix for this. How about it Jim? Is there a replacement in the works that I should wait for? I am sure there must be a great need for it. Cheers, Dak
Follow Ups:
There are no new meters available for the Cit II, and none in the pipeline. It is FAR better to rig up a set of tip jacks and replace the stock meter with your own DMM. It is more accurate and more dependable - and it can be set up to continue to use the selector switch to allow easy checking of all the different tubes' bias settings.
Those little meters were just barely usable when brand new (fine for bias, not so fine for AC balance); many of them read WAY off now. The YOUNGEST Cit II in the world is 50 years old, keep that in mind!
hI Jim, thank you for the tip. If I put in a test jack do I just run the meter supply wire, the grey wire I believe, to the jack? Cheers, Dak
You need one test point for each meter terminal. If you look at the meter you'll see one lead comes from the selector switch and the other lead goes to ground through a resistor.
You need a tip jack to access the lead from the switch and one to connect to the meter lead that goes to ground. The wires go to the jacks and no longer connected to the meter, you are correct. For the best accuracy you need to get a direct ground connection, so bypass or remove the 300 or 330 Ohm resistor that goes from the meter to ground.
Then when you plug in your DMM to the jacks read the bias voltage, the switch allows you to measure any of the four tubes. And it's way more accurate.
Thank you for the help, Jim. I did install the tip jack right next to the meter and soldered the red wire to it. I checked the reading at the cathode of the power tube and compared it to the reading at the tip jack and found the difference to be negligible. So, even with the resistor in place its effect is not very much. Cheers, Dak
That's correct about the resistor. I'm glad to hear it all worked out for you.
The Cit 2 uses 15 ohm cathode resistors on the output tubes.
The meter is just reading a voltage across those resistors so, using ohms law, 1.5 volts would be 100ma of current and .75 volts would be 50ma.
Current in amps = voltage / resistance
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Hi Tre, yeah, I have previously calculated my kt90 power tubes dissipation at nearly 100ma when the meter needle was centered on the "bias indicator line". I guess what I wanted to know was what the design goal of the bias current? I answered my question when I calculated the bias for the kt90 tubes. cheers, Dak
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: