I just got one of these in. It had many problems...
First off, a voltage divider resistor in the 1st detector screen circuit had virtually opened (9K resistor measured around 2.3M). Replacing this brought the screen voltage back from the land of ludicrous.
Second, the primaries of both the antenna and LO coils were open. When I tried to unwind a turn or two so I could reconnect them to their pins, but the coils both came off in pieces no larger than a single turn. I found the thinnest wire I had (removed from tunable loopstick) and wound about 20 turns on each coil (it's an ugly looking job, but it works). This brought the radio to some semblance of life.
The gain on the radio seems reasonably good, RF wise, for a four tube set. However, the volume does not seem to me to be up to par. It's listenable, if you're there by the radio, but room filling it's not.
I've rebuilt the bakelite blocks, and changed out any out of tolerance resistors (amazingly enough, almost all the dogbones were still well within tolerance, some within 5%!). I suspect the 2nd detector circuit is not very efficient, but one would think the set was designed more volume than a pocket radio in mind.
Are these radios normally so limited on volume? Or is there something that I've not yet found?
These radios are not such great performers and if you are not in a strong signal area you won't get a lot of volume. Remember that this set is always operating at full gain, and the volume control just attenuates the antenna signal.
Have you tried adjusting the regeneration control on the back panel? You should be able to bring up the gain of the detector to the point where it goes into oscillation, and then back it off to the point of maximum stable gain. If you can't get it to the point where it starts to squeal, then there is something wrong with the detector circuit.
Marginal tubes also make a big difference in this radio, as there just isn't any reserve gain available.
I have an 80. I rebuilt it some one year ago. Had a thread here I think.
Well, the volume is quite ... voluminous. It is loud on my loca station and I even have to turn it down quite a bit for it to be bearable.
But Hi-Fi it is not indeed. Just take a look at the speakert and it will tell you that it is not HiQ stuff.
It was The El Cheapo of the time, I think 18 bucks it was, and the reason d'etre for it was to l'ure customers and then maybe they buy something more adequate but of not....OK they bough this one, after all 18 bucks back then was something.
But the very solution of using the same tube as detector and regenerator at the same time
and no IF is the evidence of "buck saving ingenuity".
But again, it is not the quiet one.
So check the tubes, the way they are employed in this radio a weak tube will indeed make the difference between loud and not so loud.
Also make sure the IF is on the nose too. A good IF alignment may help. It's important that It's working on fq. I have several of the 4 tube sets and all play good and loud.
Terry
Oh, and the obvious!
The regeneration gain (big hexagon) at the back.
No gain - no play'n.
I've adjusted the regen control. It works fine. Again, there seems to be plenty of gain, just no audio volume. I even have to turn the volume down nearly all the way to keep the stations from overloading the front end. It's just the audio volume that is low. I've replaced the 42 output tube (I actually had an NOS one in stock!), but it made no difference. Could a weak 2nd detector (36) cause this issue, even if the front end gain is good?
Have you looked at the audio level on the grid of the 42 with a scope? It sure seems like an audio problem, but there is not much there to go wrong. I would try and measure the P-P audio level on the 42 grid and compare it to what you have on the plate. About 26V P-P should drive a 42 to full output, so if you have good drive but low output you might then check the output transformer or speaker for problems.
I doubt the problem would be the 36 detector as you can get regeneration, but you can switch it with the converter 36 to check and see if it makes a difference. Maybe a bad coupling cap or detector plate load resistor?
Have found on just about all the 80's and 84's need all of the resistors and caps replace. Most are way out of tolerance or leaky. Also it needs a good ground for the volume control to work properly.
Terry
Are you sure that the field coil on your speaker is good?
The field coil is good. Nothing on this radio would work if it weren't.
That being said, I DID find something in the notes for this chassis about a production change where a .18 cap was added from the 42 screen grid to the positive of the first filter cap. Essentially, this equates to a screen bypass cap. Installing this brought the audio up about 300% or so. Much MUCH better. It did change the timbre of the sound some, but it's not unpleasant, just not as much low end as there was before. If I wanted, I could put another small cap across the input grid of the 42, or across the output transformer.
Now, all it seems that I need is to replace the on/off/volume control, a 20K unit. I'm having a bit of trouble finding a 20K with switch that has the requisite shaft length.
One other question, though: How the devil am I getting double peaks tuning from the middle of the band up, when there is only one tuned stage in the IF? I've been able to reduce this a bit by working the LO and ANT trimmers on the tuner back and forth a bit, but can't seem to completely eliminate it. Otherwise, the gain of the radio is quite good and I can now receive most of my "locals" without any antenna at all.