All voltages look ok. Bear in mind that tube equipment isn't like transistor gear in that the difference of a 1/2 volt can cause problems. Tube gear is much more forgiving. The measurement made back in '31 where made with a meter that loads the circuit a bit like 1000 ohms between the probes. Your modern meter meter is in the order of 20meg ohms.
The SG voltage on the mixer is unknown as you changed the value of #9. The voltages around the 2nd det are unknown as they don't tell you if they are with the detector is oscillating. According to the tube manual -16v is just dandy for the 42's control grid w/250v on the plate. 4.5v seems pretty low and would cause the 42 to draw more plate current than necessary. It is also possible that your 36 tube has low emission causing not enough current to be drawn though the high value resistors in the circuit. This can be the cause of having the higher voltage readings around the 2nd detector.
In your comments you didn't say of it is working? Is it??
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 09-11-2016, 07:59 PM by Radioroslyn.)
Terry, thanks for the input. Yes, the radio is working and also has plenty of volume. I do believe I do have an alignment issue though. I found that if I touch or barely move the wire running from the plate of the Det-Osc tube to the IF primary condenser #7 the station will cut out. Not much movement is needed with a wooden dowel to make this happen. The compensation condenser was also missing the adjustment nut and insulating washer. I found a nylon washer and nut to fit but I'm not sure how bad my alignment is. See in the photo on the left side. Also I'm concerned as to how warm the #11 and #9 resistors are getting. I may abandon the "fake dogbone" idea.
Hi Mike,
The 36 mixer tube has a lot going on and I'm not surprised that if you fool with the plate or grid leads it conks out. Just leave them be. The trimmer that you show in your pic is not #7 but the sensitivity or regeneration control for the 2nd det. If you have a bit of a wooden dowel (1/4") drill and tap a hole in the end of it to fit the screw on the trimmer. Use this to set the sensitivity. Using a metal nut and driver will detune the circuit. This adjustment doesn't have any effect on the IF frequency so it won't screw up the IF alignment. For best performance you'll need to adjust the IF trimmers using a signal generator. Don't even think about trying to do it "by ear" as some may try. Just makes it worst.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 09-12-2016, 09:54 PM by Radioroslyn.)
Again, thanks for all the help! I have not adjusted anything yet. I do have a signal generator (Precision E200C) and a VTVM (Heathkit V-7A), but I have never checked or performed an alignment before. I had to order test leads for both pieces of test equipment. when I get to that I'm sure I will have more questions.
I am concerned about the heat generated by resistors #11 and #9. The Spec sheet I have, Riders 3-25 shows that resistor #11 (16k) should be rated at 5 watts. In the link earlier Ron Ramirez's site recommended a 3 Watt. Am I over thinking the heat generated? I'm going to try an actual 3w, 16k and not the parallel setup (see earlier post) I had to see if there is a difference. Is the extra heat on #9 due to the increased resistance? That resistor is rated at 1 watt.
I believe I have been bitten by the bug. I just acquired a model 84, cosmetically in good condition. Next after this one is complete.
(09-13-2016, 08:25 PM)Mike L Wrote: Again, thanks for all the help! I have not adjusted anything yet. I do have a signal generator (Precision E200C) and a VTVM (Heathkit V-7A), but I have never checked or performed an alignment before. I had to order test leads for both pieces of test equipment. when I get to that I'm sure I will have more questions.
I am concerned about the heat generated by resistors #11 and #9. The Spec sheet I have, Riders 3-25 shows that resistor #11 (16k) should be rated at 5 watts. In the link earlier Ron Ramirez's site recommended a 3 Watt. Am I over thinking the heat generated? I'm going to try an actual 3w, 16k and not the parallel setup (see earlier post) I had to see if there is a difference. Is the extra heat on #9 due to the increased resistance? That resistor is rated at 1 watt.
I believe I have been bitten by the bug. I just acquired a model 84, cosmetically in good condition. Next after this one is complete.
Sorry I miss your Q. By increasing the resistance of #9 it lowers the current flow through #11 and increases the screen voltage on the mixer tube. This in turn raises the gain of the mixer a bit. If you can't sleep at night over this hot resistor swap them out for 5 or 10w units. Remember in '32 it was all about the money.
The model 84 is an updated version of the 80. Circuit is very similar but the 36's are re[placed w/77's. Same drill to fix all caps and resistors, good chance that the ant and or osc coils are open. Better sounding set as the spkr is about twice the size of the 80.
When my pals were reading comic books
I was down in the basement in my dad's
workshop. Perusing his Sam's Photofoacts
Vol 1-50 admiring the old set and trying to
figure out what all those squiggly meant.
Circa 1966
Now I think I've got!
Terry
(This post was last modified: 09-18-2016, 03:22 PM by Radioroslyn.)
I replaced my fake dog bone resistors, #11 (16k) with a 5 watt resistor. I also replaced #9 back to a 9k resistor, also at 5 watts. After a good warm up , all voltages were relatively the same as before. Both of these resistors also get quite warm, but I feel better not having them hidden inside a painted plastic tube. I also have a 13k 3 watt that I want to try at the #9 position as before to see if there is any "performance' difference.
I have two caps to replace in my VTVM, and then I'd like to re-measure these voltages. The radio is working fine, however, today there is a quick pop, pop, pop sound in the audio every 10 seconds or so. Not sure if this is just interference or not once I get it out of the basement away from the florescent lights.
always,though about them new dogbones,,,,with all that new stuff,(plastic),over the new resistor,,,,does this make the resistor,,overheat ,,because there is no air around the resistor,,,, Does the new plastic hold the HEAT in ????
In my case it turns out that these two resistors get hot anyway, so hiding them in a plastic tube was not the cause. The #11 was hidden in a plastic tube, but the #9 was hidden in some molded epoxy putty. I can see #11 getting quite warm as a 5 watt was what was originally called for in that position. #9 (9k) was originally to be a 1 watt and it gets equally warm, so I now have a 5 watt, 9k (as was original) in that location. Excuse my ignorance, but I'm still learning the theory and trying to understand if there is something else that could be causing #9 to get so warm that a 1 watt could not handle it.
Here are the resistors I made and then removed. #9 is actually a 13k made to look like a 9K. Below that photo are the 5watt resistors I temp installed. I plan to go back and make better connections on these two. Also the 1meg (brown, black, green) in the foreground is a fake too but it is fine. Only a 1/2 watt was required there. I like the idea of keeping the "look" of original, but I may just abandon that idea. This radio isn't going anywhere and only I will know what's underneath it.
Mike, when you make a "dog bone" resistor by placing a modern resistor in a plastic tube, do you pot the resistor in epoxy? I have made several "dog bones" and I use JB Quick or Locktite Weld to pot the resistors. The idea being, the epoxy will transfer the heat to the outer surface to be dissipated.
Here are some pictures of a 13K, 3 watt dog bone that I made. I used six 2.2K, 1 watt resistors arranged in a saw tooth fashion to evenly distribute the heat (I always use 2X the wattage rating for all my dog bones).
Yes that's what Steve used in his tutorial on making dogbones but that was for a 1 watt reproduction. This is a 3 watt and would be larger i think.
I suppose you could also put heat sink compound into the tube with the resistors to help the heat flow away but they are mostly silicone based and you would want to keep that a mile or two away from your cabinets
(10-05-2016, 09:21 AM)Steve Davis Wrote: For the 3 watt resistors I use some plastic tubing that I found. The OD is 1/2 inch and the ID is 3/8 inch.
Steve
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