Hey forum,
I finished up on the 90 a few days ago (all caps, ecaps, and resistors)but have not aligned. Upon turning it on, a low hum from the system was evident - not from the speaker but from the electronics. The set sounds very clear though and all stations come in. However, the volume is about half of what I expected (based on comparing to the 84)... I think I found a tube though that's bad as the bulb was loose in the base so hopefully that is the cause of the low volume. After listening for several hours, I just heard it start randomly making loud crackling/popping noises like fireworks were going off. It only happens for 3-4 seconds and then the reception is normal again. This happened about every 10 minutes. Any ideas as to what could be going on? A picture is attached as well. Thanks,
BDI
forgot one thing...when i swapped the 24 tube that is suspect with another 24 in the set, the volume went up quite a bit which is why I think it needs replacement (..this is a single 47)
unfortunately I don't have that luxury yet. I received another 2-27's and 1-24 today, used but tested good (according to seller). Substituted them and slightly louder. However, still hear a low buzz in the background. I also switched around the 24s and 27s to see if any difference, which there was none. It sounds very clear, but it amazes me how much weaker channels that the 84B picks up that the 90 doesn't. Is that just because the 84 is regenerative? - does that make it amplify weaker channels better?
If you are sure it is not from speaker, then most probably it is the power transformer buzzing. My 70 also has this problem that becomes more pronounced with higher AC voltage. Not sure what could be done, short of tightening the transformer (did not help me) or...don't know.
I don't have an 84B and have never listened to one but I would think the 90 should be a much better radio. I know my 90 works great and gets some really distant stations with ease.
Quick update guys - After swapping out a few tubes, one was weak. However, I've gotten to the bottom of a bigger issue. The reason the volume seemed a little low is that after rechecking the coils again, I found a break in the outside coil of the first detector transformer (#7). Only the first 2 winds were deteriorated, but I'm guessing it's time for my first rewind. I took a high-res pic and counted 95 turns. Anyone know what gauge wire is used ? Can a heavier gauge wire be used with a variation in the number of turns? thanks-
mark
If only the first two turns of the outside winding are bad, I would first try removing these turns and connecting the remaining good wire end to the solder terminal. Two less turns out of 95 will have a negligible effect on the tuning of the coil.
If you do decide to rewind completely, you must duplicate the exact number of turns and the winding length on the form. Both determine the resulting inductance of the coil.
1. You have already done the major part of the job - unsoldering, removing the coil.
2. Under 100 turns will take 15 minutes to wind manually tops.
3. Main reason - if the wire was damaged (you often see how you take 2 turns off and it breaks then) in the beginning it is likely corroded all the way, and it often shows as discolored enamel, it is likely to happen again. And is also hard to solder - you bend the wire a little and it breaks.
I'm with morzh on that one, rewind the whole coil. The rest of the coil will be just as bad and you dont want to have to go back in there when it quits again.
Beyond that, if you want a radio that you can depend on, you might consider rewinding the rest of the RF transformers and the oscillator coil. Sooner or later, they will fail too.
You can pretty much see for yourself about the gauge.
And a regular enameled magnet wire will do.
Gauge is not too critical, but if it is too thin or too thick your winding length will change too much and so the inductance might suffer.
![[-]](https://philcoradio.com/phorum/images/bootbb/collapse.png "[-]")
