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Model 84 late buzz( 1935 run) - Printable Version

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Model 84 late buzz( 1935 run) - Bruce - 03-04-2025

Good Morning Everyone.
Yet another brain teaser at hand. 
This one is a 1935 version of the 84 closest I can figure from the cabinet it definitely has the changes that can be noted from the service bulletins. My dilemma is that area in the pictures regarding the second detector tube. Looking at it closely you can see where the pins should be connected together one end is lifted if I connect it it buzzes as if you were putting your finger on the grid cap of the tube. If I connect those pins that should be as are my other 84's connected together to ground it immediately buzzes. I have already changed all the capacitors in the blocks and the additional 10MFD filter caps and the resistors that were not within 20% of their stated values. I have checked voltages to both the second detector and the audio tube have check grid bias voltages everything is well within reason. Having it on the veriac The buzz remains the same regardless of the voltage setting. The picture of the resistor laying on the brown paper was attached to those two pins and ground prior to my starting on this repair. I have already substituted several different 77s and 42s. Time for some advice
Thanks to All!

RE: Model 84 late buzz( 1935 run) - morzh - 03-04-2025

Bruce

No, I cannot see where the pins should be connected: your first pic is centered on one spot and the other is centered on he different spot.

You could possibly use some red arrows to point to what you mean.

RE: Model 84 late buzz( 1935 run) - Bruce - 03-06-2025

Morzh
In the 1st picture where the red wire on upper left is ,is a silver wire under it normally connected to pin 5 ( heater pin ).5,4,3 usually connect to ground. Ill redo the picture. The second is a general view of the rest that resembles my other chassis's on other radios,just incase visually looking an notice something questionable.

http://www.nostalgiaair.org/pagesbymodel/875/m0013875.pdf

RE: Model 84 late buzz( 1935 run) - morzh - 03-06-2025

In the sch 5 is not GND-ed. In you picture they look connected together.
If the tube is 77 - pin 5 is NOT a heater pin. 1 and 6 are. Pin 3 should be at about 100V. 5 an d 4 are GND-ed.

RE: Model 84 late buzz( 1935 run) - MrFixr55 - 03-16-2025

Hi Bruce,

I am looking at the pic. Seems that the 2 filter caps are sharing a common negative. That common negative appears to be connected to a non-grounded pin of the AC power input filter cap. The common negative of the filter caps should connect to the center tap of the HV winding (rectifier plate winding) of the power transformer. A 325 Ohm resistor connects this center tap to ground. this resistor is bypassed by a 0.015uFcap. In addition, the values of these filter caps should be higher. The schematic states 8uF and 4uF. You can go a little higher. It appears that one of these caps in only 1uF unless a number is covered or backed out

Hope I am right. Hope this helps.