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Hey Joe,
I finally was able to finish the modifications you sent me which were the CAE-MP3 and the CAE-1A modules. When I performed the tests on the CAE-M3P board at the "BD" to Chassis test with the Bias Pot turned counterclockwise I got -63.5 VDC; turned clockwise I got -30.65 VDC. When I checked the "5" to "5" I got 5.5 VAC on the inside pad on the outside pad I got .24 VAC.
I checked the values on both boards and found that R19 on the CAE-MP4 is 4k
when the parts list says it should be 1k/1w. Would this account for the readings I am getting. I checked all the components and found that this is the only issue.
I have not gone any further in the testing, should I?
Thanks
Richard
Follow Ups:
I finally was able to finish the modifications you sent me which were the CAE-MP3 and the CAE-1A modules. When I performed the tests on the CAE-M3P board at the "BD" to Chassis test with the Bias Pot turned counterclockwise I got -63.5 VDC; turned clockwise I got -30.65 VDC.
This is fine
When I checked the "5" to "5" I got 5.5 VAC on the inside pad on the outside pad I got .24 VAC.
There is only one test - you are noting 2 measurements - so this is not clear.
I checked the values on both boards and found that R19 on the CAE-MP4 is 4k
when the parts list says it should be 1k/1w. Would this account for the readings I am getting. I checked all the components and found that this is the only issue.
What is the _actual_ value of the resistor? Is it a 1K resistor or perhaps 3.9K? How are you taking the measurement - in circuit or out of circuit. In circuit resistance tests are generally contaminated with other components impedances.
If you have any further questions - I encourage you to e-mail me for a more expedited reply
Joe,
Thanks, I will email you directly. It might be about a couple of weeks from now as I am going on vacation.
Thanks again,
Richard
I would like to help you but I am not following you all that well with your description.
With the bias turned all the ay counter-clockwise you should see the most negative voltage at pin 5 of the KT88/6550.
To bias your output tubes you have to measure across a resistor of whatever value(most easy is 10 ohm) that goes from pin 8 to chassis or star ground. If it is paired biasing(usually is unless that has been changed)you should get a reading of about 1.2VDC(across a 100 ohm resistor) with one lead of your meter on pin 8(either tube) and the other lead on chassis ground. But that's only if both tubes share one resistor. That means each tube is drawing 60MA of current(120MA combined) which is on the lower side of what a 6550 can draw. Then you can remeasure the negative voltage at pin 5 of the 6550. It should be in the high 30's to low 40's if I am not mistaken. The lower the negative voltage there the more current it draws.
Now if the tubes glow a bit red on the plates back off on the bias setting a bit until it stops. Not all tubes of the same number draw the same. That is why if you ever change the tubes rebias always. And check your bias about an hour or so after biasing the tubes and again a day or so later to make sure they are stable. At that point check them once a month based on use.
Thanks again, but I have the Premium Modification boards for my MK3. It has a potentiometer on the Driver board to set the bias on the unit so I do not have to bias each tube across the pins.
I am now having other problems like no power at all. I have contacted Joe and until I get power back I am at a stand still.
I do want to thank you for the response. I am just a beginner at this so any help is greatly appreciated.
Regards
Richard
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