Rotus,
I guess we are down to component replacement! Let us know if you want want to start replacing components and we can suggest best "cheapest" first.
With power OFF!
One other thing to check is a section called "texture breakaway". It is in series with C144 coupling cap on page 11 of the diagram. Is this a pot on the panel? It is shown as VR11 if it is a preset measure the value of resistance with a meter from one end of the pot to wiper make a note of the value then clean the pot and twist it back and forward then reset to value measured!
Then try the amp!
Components are:
C135 is one of two coupling caps to the output stage! Shown as 47nF at 400V. Also C144 100nF 275V
R1,R2,R5,R6 are the screen grid resistors value shown 330Ohm 2W
Grid input is 1.5K R7, R8, R147, R159.
Regards
M. Gregg
Yeah when I wiggled it with power on it made static, I clipped off the strips and soldered the wires straight to the board and it didn't change anything.
It is a pot. Do you think I should check the components out of circuit first or just start replacing them?
I don't think you will gain anything by measuring with a multi meter because the faults will only show with HT. Meter is 9V.
Rotus remember that the resistors in the screen grids voltage is critical 500V or they will flash over.
Caps (polyprop).
The other "possible" is the bias supply. However you need to be systematic so try Wavebourns idea then the coupling caps.
You know we are all hopeing you don't reach the O/P Tx.
Good luck! Keep safety a first prioritory!
Regards
M. Gregg.
Quick update: I changed out what I had on hand first, R7, R147, R159, R8, R149, R154, and believe it or not, the static did clean up a bit!! There still are some culprits to change. I am going to order C135, C144, R1, 2, 5 and 6 and I'm hoping that will be it. I think that a lot of strain has been placed on the 2w resistors, and am going to change them out to 3w or 5w to prevent it from happening again. Does anyone think that I should order any more parts then the ones I have bolded? I am looking to have one more change out session and then be done with 'er!! And whats with D108 and D109, cant find them anywhere. Should I change those diodes??
Rotus,
D108 / 109 are tube saver diodes. They stop the back EMF from the output Tx. You could change them, they show as
SR2873 2KV, 250MA DIODE D108 D109. You could use 3 BYV96E in series to replace each one, however I would just test them and if OK don't worry. Ill have a think about other components! Time is a bit tight at the moment!
Wavebourn may have a few Ideas!
Regards
M. Gregg
Ok I changed out R1,2,5,6 which I think are the screen grid resistors. Nothing. I really thought these were going to be the culprit. I want to change out R201 but it is very hard to find. I wouldve thought that most suppliers would have something like this, but what do I know!!
Nothing happens Wave, I am really starting to believe that it is in fact R201. I have changed most of the resistors in the power section, some capacitors, and I am pretty sure that this is where the issue is. I am having a hard time finding this part through a "reputable" dealer that I have purchased parts from. I am a little nervous about buying from ebays wheel and deal. If you have a retailer that you recommend that may carry this, please let me know.
Radioshack has a 100ohm 10W resistor, and I thought I could try 4 in series just to see if it works, but the resistors are 350V max and the resistor in the amp is steadily pushing 450-460V, damn...
Hey Wave, in the texture breakaway section, why does pin 1 of p303 connect to nothing on either board? What exactly does that mean??
Nothing, just an extra pin.
I don't think R201 is guilty: it is shunted by capacitor. But you may check anyway: connect 600V multimeter between ground and point P204. What do you read there, when the amp is on & cracking?
Did you check R127 and R128, between that funny "grounds"?
I don't think R201 is guilty: it is shunted by capacitor. But you may check anyway: connect 600V multimeter between ground and point P204. What do you read there, when the amp is on & cracking?
Did you check R127 and R128, between that funny "grounds"?
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Wave, when there is static, if I am tracing it back with my multimeter would the voltage be intermittant?? Also, how do I know if I have a 600V multimeter, just if it goes up that high without OL or overload, right?
Right.
I would expect voltage fluctuating when it is cracking.
Usually multimeters are properly labeled, which voltage is safe to apply to them.
I would expect voltage fluctuating when it is cracking.
Usually multimeters are properly labeled, which voltage is safe to apply to them.
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