Nady 1050 Voltages

C

craigmorris74

New member
I'm having problems getting proper voltages on my tube pins on a Nady 1050. I've read amzavareei's thread regarding the problems he was having, but can't exactly determine my problem yet.

Here's what I've done
1. Removed the CF
2. Removed C9 and C10
3. Replaced C1, C2, and C8
4. Replaced the capsule
5. Replaced the transformer

The voltages I'm getting at the tube pins are the following (no tube):
1-72.9
2-0
3-0
4-6.7
5-6.7
6,7,8-0

One of the voltages Marik recommended checking was R5. On one side I get 46.3V and the other I get 0.9V. Way off from what he said I should find there. I also checked pin 3 on the connector and I'm getting about 19V there
I'm know I probably just need to stare at the darn thing till I see the problem, but any tips as to where the problem could lie would be great.

Thanks,
Craig
 
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I don"t know anything about this mic its self but I do know that it uses a 6679/12AT7 Dual Triode tube and from the voltages you have posted it looks like your Plate Voltage (Pin 1) is quite low, It should be in about the 200v to 250v range...also there is no voltage on the Plate of the other Triode (Pin 6) which should also be in the 200v to 250v range but maybe the other Triode isn"t being used in this Mic? but if that was true there also shouldn"t be a connection to the heater of the second Triode (Pin 5)....There is also a Pin 9(Heater Center Tap) which you didn"t post which should be in the 12.6v range if it is being used(Pin 9 isn"t allways used)......

So it looks like you maybe missed connecting something to pin 6 of the tube and/or did something else that caused the Pin 1 Plate voltage to drop to a very low level and cause there to be no voltage on the plate of the other triode(Pin 6).....

Without seeing a schematic of the mic and knowing exactly what modifications you did i couldn"t tell you what you did wrong....

If you post more information (Like a schematic) then it would be easier to help you...
You might also want to check over at "http://www.prodigy-pro.com/forum/" as they can probably help you......

Good luck
 
craigmorris74 said:
Here's a link to the schematic:
http://www.apexelectronics.com/pdfs/smapex460.pdf

I removed the cathode follower circuit by removthing the connections to 6,7,8 of the tube, connecting them together, and to ground.
Click to expand...

Well, that would explain no plate voltage on one side.

I'm trying to figure out this schematic.... That transformer is... is that an output transformer? If so, wouldn't disconnecting that result in... no output? :) If not, what the heck am I looking at there?
 
craigmorris74 said:
The other side of the tube is supposed to be disconnected. The transformer was upgraded, not removed.
Click to expand...

Did you connect that leg of the transformer somewhere else (e.g. pin 3)? Since pin 8 isn't an output from the tube anymore (because you disconnected and grounded those pins), the transformer has to get a signal from somewhere, and unless you connected it somewhere else, the output transistor is just sitting there getting no signal.
 
The output voltage of the power supply is 106V @ B+ and around 20V at the Variable Voltage pin.

I'll check out C2 and see whats there.
 
Looking at your schematic, it looks like everything should be okay. Hopefully you drew your electrolytic caps wrong (curve is the negative side, straight the plus). The only thing I would do would be to remove the wire from pin 5. No sense in heating up the side of the tube not being used, or the mic any more than needed. Plus side of C8 is to pin 1 of the tube?
 
I finally got a glowing tube yesterday, and my voltages seem to be reasonable. However, I knocked a wire or two off the tube socket when putting the body back together. Now I've got no glowing tube again. I'm using a different power supply in case your wondering why the plate supply is higher (at least that's what I think the deal is).
My voltages at the tube are:
pin 1-155V
pin 2-0V
pin 3-0V
pin 4-6.7V
pin 5-6.7V
pin 6,7,8-0V

I'm getting confused and need to take a break.

Thanks for your help,

Craig
 
Looking at your list of pins, noticed one very important thing, there's no pin 9. What is the voltage between pin 9 (joined ends of both heaters) and pins 4/5. If the tube is not lighting up, I bet pin 9 is not attached to ground. I still recommend removing the wire from pin 5.
 
Got everything working! Thanks so much for everone that chimed in and kept me going. mbrebes's tip on the pin 4 to pin 9 voltage solved my problem. Fired it up and initial indications is that it's a nice, thick sounding mic. Will do comparisons later. The schemitic link at the top now reflects all the changes for anyone who needs a visual representation of the cathode follower removal.

Thanks again,

Craig
 
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