Just picked up a 1930s Battery operated Coronado

[vortalexfan]

Originally Posted by jr_tech

Did you peak both if transformers to 465 khz?

jr

Yes I did, and when I would try to inject the 1400 kHz signal in through the antenna leads so I could work on the dial tracking/alignment I can barely hear the signal generator coming through at full volume using the attenuated output signal at 50% output (the highest amount of output that my signal generator can do), but then the unattenuated output allows the signal generator to be heard at a somewhat normal volume level.

[vortalexfan]

OK so a little update, I got my NOS 1C6 tubes in today and my radio is now mostly working, it is now definitely oscillating (I did the holding another radio up next to it trick and that second radio was picking up this radio's oscillator signal).

But its still not picking up any stations unfortunately.

I've got the IF cans Aligned to 465 kC the Best I can (seeing as neither of the IF cans in this radio are original to this radio and are not 465 kC cans).

So I'm kind of not sure where to go from here now.

Here's a video showing what the radio is currently doing:

https://youtu.be/e702udS6aiM

[vortalexfan]

OK, so another Update, it seems I had a bit of a dislexic moment because this radio's IF Frequency is 456 not 465 like I had been saying the entire time...

Anyways So I realigned the radio to 456 KC and the tuner seems to be working better with the signal generator, but its still not picking up any stations on its own with a long wire antenna hooked up to it...

So I'm wondering if my 30 Tube is bad as well because that tube controls the Second Detector and the AVC circuit which the AVC is working as it should be but I'm wondering if maybe the detector portion of the 30 tube is bad or at least not in very good shape.

Anyone here have a known good 30 tube they could spare me? If not I guess I could get one from ebay.

[Kevin Kuehn]

The 30 tube is a single triode configured as a grid leak detector. Notice the plate tied to ground. Since you say you have AVC voltage changes you can be sure the 30 is working. Can you see AVC voltage change when tuning on and off a known local radio station? Make sure C8 is .0005uf. If it's too large it will start filtering the audio.

[vortalexfan]

Originally Posted by Kevin Kuehn

The 30 tube is a single triode configured as a grid leak detector. Notice the plate tied to ground. Since you say you have AVC voltage changes you can be sure the 30 is working. Can you see AVC voltage change when tuning on and off a known local radio station? Make sure C8 is .0005uf. If it's too large it will start filtering the audio.

No there is no change in the AVC voltage when trying to tune in a known local station. In fact trying to tune anywhere on the dial the AVC voltage stays pretty constant at around positive 15 mV and doesn't go negative at any point when tuning across the dial with just a long wire antenna attached.

It does however work when using the signal generator but like I said previously I have to use my signal generator's unattenuated high volume output signal output in order for the radio to be able to pick up the signal from the signal generator and be able to affect the AVC voltage.

So I'm not sure what's going on here.

Did you see the video I posted of my radio and what it's doing with just an antenna hooked up?

[Kevin Kuehn]

Originally Posted by vortalexfan

No there is no change in the AVC voltage when trying to tune in a known local station. In fact trying to tune anywhere on the dial the AVC voltage stays pretty constant at around positive 15 mV and doesn't go negative at any point when tuning across the dial with just a long wire antenna attached.

It does however work when using the signal generator but like I said previously I have to use my signal generator's unattenuated high volume output signal output in order for the radio to be able to pick up the signal from the signal generator and be able to affect the AVC voltage.

So I'm not sure what's going on here.

Did you see the video I posted of my radio and what it's doing with just an antenna hooked up?

What you say indicates is that your local oscillator is either not running, or it's running at an incorrect frequency.

When you inject an IF frequency from you signal generator you are forcing the correct signal through the IF transformes, which in turn gets detected by the 30 tube and produces AVC voltage. The key here is you're not relying on the local oscillator to mix with the incoming rf signal to produce that outcome.

In normal operation the rf signal mixes with the local oscillator to create beat frequencies equal to the sum and difference of the two. One of those beat frequencies is the IF signal. You should double check that you didn't replace a cap around the 1C6 tuned circuit with a incorrect value and also verify the two winding's in the oscillator coil(#17484) have continuity.

[old_coot88]

Originally Posted by vortalexfan

...it is now definitely oscillating (I did the holding another radio up next to it trick and that second radio was picking up this radio's oscillator signal).

What is the other radio's dial setting when it picks up the Coronado's oscillator? And what is the Coronado's dial setting? The diff between the settings is the Coronado's IF frequency (assuming both radios' dial calibrations are reasonably correct).

For example, if the Coronado's dial is at 550, its oscillator should be heard around 1010 on the other radio. Or if Coronado's at 1140, you should hear the osc at about 1600.

[vortalexfan]

Originally Posted by Kevin Kuehn

What you say indicates is that your local oscillator is either not running, or it's running at an incorrect frequency.

When you inject an IF frequency from you signal generator you are forcing the correct signal through the IF transformes, which in turn gets detected by the 30 tube and produces AVC voltage. The key here is you're not relying on the local oscillator to mix with the incoming rf signal to produce that outcome.

In normal operation the rf signal mixes with the local oscillator to create beat frequencies equal to the sum and difference of the two. One of those beat frequencies is the IF signal. You should double check that you didn't replace a cap around the 1C6 tuned circuit with a incorrect value and also verify the two winding's in the oscillator coil(#17484) have continuity.

Well I checked all of the original "dogbone" resistors in the radio (which are all 1/4 watt resistors according to the service manual) and they are all within spec.

When I recapped this radio, I used orange drops for all but 2 of the capacitors, (the 2 capacitors that I didn't use orange drops on were the .0005 MFD 600 V caps that I had to use Silver Mica caps for because they didn't have any orange drops that went down that low in value), and I made sure that I put the caps in the right spot, so I don't think its the caps or the resistors.

When I first got this radio (and after I realized that someone had attempted to wire a power cord to the antenna wire terminal strip) I had tested the antenna coil and the oscillator coil to make sure they weren't damaged, and they both tested fine.

But then when I was checking voltages around the power switch (where the battery wires wired into the switch), I had accidentally let out some magic smoke but I couldn't tell where it came from, but all I know is that ever since then the antenna coil and the oscillator coil have been reading O. L. on my multimeter, and I'm not sure why because the coils don't look burnt and they don't look damaged either.

Do you need some pictures of the underside of the radio so you can see what the radio looks like underneath and see if you can see anything out of place?

[Kevin Kuehn]

Originally Posted by vortalexfan

But then when I was checking voltages around the power switch (where the battery wires wired into the switch), I had accidentally let out some magic smoke but I couldn't tell where it came from, but all I know is that ever since then the antenna coil and the oscillator coil have been reading O. L. on my multimeter, and I'm not sure why because the coils don't look burnt and they don't look damaged either.

Well if by O.L. you mean they are reading infinite ohms then I think you've found a problem. Those coils should show a fairly low resistance.

[vortalexfan]

Originally Posted by old_coot88

What is the other radio's dial setting when it picks up the Coronado's oscillator? And what is the Coronado's dial setting? The diff between the settings is the Coronado's IF frequency (assuming both radios' dial calibrations are reasonably correct).

For example, if the Coronado's dial is at 550, its oscillator should be heard around 1010 on the other radio. Or if Coronado's at 1140, you should hear the osc at about 1600.

Well the strange thing is that the Coronado's tuner is set to around 640 AM and the tuner on my Panasonic RF-511 AM/FM transistor radio is set to about the same spot and that's where I hear the Coronado's Oscillator on the Transistor radio is at 640 AM on the dial or very close to that spot anyways and when I go up the dial the oscillator noise kind of dies off the higher up the dial the tuner goes (on both radios).

So I'm guessing my oscillator is working but not correctly...

[Kevin Kuehn]

Originally Posted by vortalexfan

But then when I was checking voltages around the power switch (where the battery wires wired into the switch), I had accidentally let out some magic smoke but I couldn't tell where it came from, but all I know is that ever since then the antenna coil and the oscillator coil have been reading O. L. on my multimeter, and I'm not sure why because the coils don't look burnt and they don't look damaged either.

Well if by O.L. you mean they are reading infinite ohms then I think you've found a problem. Those coils should show a fairly low resistance. Try putting your meter on diode check and see if you get a beep across each winding. If no you have an open winding, that is providing your meter beeps when you touch the two probes together.

[vortalexfan]

Originally Posted by Kevin Kuehn

Well if by O.L. you mean they are reading infinite ohms then I think you've found a problem. Those coils should show a fairly low resistance.

Well I'm guessing this radio is going to have to be a shelf queen I'm guessing, because those coils are probably going to be darn near impossible to find, and I doubt they could be repaired.

[Kevin Kuehn]

Originally Posted by vortalexfan

Well I'm guessing this radio is going to have to be a shelf queen I'm guessing, because those coils are probably going to be darn near impossible to find, and I doubt they could be repaired.

Post us a couple pictures of what they look like. I doubt they're anything too unique. What you have there is a very basic broadcast band only radio.

[vortalexfan]

Originally Posted by Kevin Kuehn

Post us a couple pictures of what they look like. I doubt they're anything too unique. What you have there is a very basic broadcast band only radio.

Ok, here's the Oscillator and antenna coils.

[Kevin Kuehn]

Originally Posted by vortalexfan

Ok, here's the Oscillator and antenna coils.

Looking at the schematic I'm in disbelief that you opened a winding in both by simply taking voltage measurements.
Are you 100 percent positive that both transformers have at least one winding open? Maybe you should post us a couple pictures of the entire bottom side the chassis, just in case you're overlooking something obvious.

These Meissner numbers will replace them. They use to be common as dirt.
14-1010 standard broadcast band antenna coil
14-4034 456kc oscillator coil

I'm sure there's other manufactures numbers that would work, as well as pulling them out of junked radios. The oscillator coil should ideally be for 456kc, but as mentioned you can usually walk the IF's off frequency a small amount.