Welcome Guest! Be sure you know and follow the Phorum Rules before posting. Thank you and Enjoy! (January 12) x

Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5

Model 84 late buzz( 1935 run)
#1

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!


Attached Files Image(s)
       

Finally after 50 plus years I'm back into the hobby again. It's like trying to relearn a second language some of it makes sense and some of it doesn't! Could be fun now considering my son is now into old radios and tube technology!
#2

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.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#3

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...013875.pdf

Finally after 50 plus years I'm back into the hobby again. It's like trying to relearn a second language some of it makes sense and some of it doesn't! Could be fun now considering my son is now into old radios and tube technology!
#4

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.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#5

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.

"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis

Best Regards, 

MrFixr55




Users browsing this thread: 1 Guest(s)
[-]
Recent Posts
AES type of Battery Eliminator has hum in B+
They are trying to use a regulator. Essentially it is an LDO schematic. LDOs are supposed to greatly reduce ripple, so t...morzh — 12:11 AM
AES type of Battery Eliminator has hum in B+
So, I just built a 90 volt 40ma battery eliminator for a farm radio and had to use 1000 mfd for the input filter cap to ...RodB — 10:31 PM
AES type of Battery Eliminator has hum in B+
Caps of 1,000 uF 250V are about $7 in Mouser. C1 could be increased. A NTC inrush limiter could be employed to limit t...morzh — 10:24 PM
AES type of Battery Eliminator has hum in B+
Bruce B — 09:41 PM
AES type of Battery Eliminator has hum in B+
Bruce Could you post the schematic if this power supply?morzh — 09:31 PM
AES type of Battery Eliminator has hum in B+
Hello All, I have built a battery eliminator using the most popular AES K101a. Using plans and all the AES parts  order...Bruce B — 09:27 PM
Need to purchase Old Philco Radio Knobs
Hello Paulo , I have Philco 38-10 too that I am restoring the chassis is almost complete ! Far as my cabinet It is in ...radiorich — 09:00 PM
Need to purchase Old Philco Radio Knobs
HI MORZH Thank you so much for this tip. I will try contacting to him. thanks a lot, Best Regards, Paulo Alo...palonso — 05:27 PM
Refinishing Ideas
We just had the discussion on the GoJo. It is no longer sold, but Goop is, and those two are very close. I use Goop and ...morzh — 11:58 AM
462ron
+1 on what Arran suggested. In my case, my cabinet had the usual scratches and nicks, except the top had water damage pr...462ron — 08:36 AM

[-]
Who's Online
There are currently 1505 online users. [Complete List]
» 1 Member(s) | 1504 Guest(s)
Avatar

>