I am still new(2 AA5, 2 AC sets, a Zenith 8S661, and Victor R32) But this is the first radio with FM. So I am not familiar with the limiter and discriminator. I started at the output and worked my way back. Almost every thing is right excpet for the plate voltage on the 6SH7 limiter (schematic says 60v, meter reads 9v) I replaced R99(68K drifted to 200K) and C38(.01 measured .138). But even with that problem it seems like AM should work. I can put modulated IF into 1st IF and it sounds good (AM or FM), but back up before the converter or RF and only modulated IF (AM) goes through...I do not see a tank so I suppose that is correct. Tuning cap position does not make a difference with IF input to the AM antenna, so maybe that is not right?

I ran out of .01's so most of those have not been replaced. Holding off on alignment until I get the rest of the .01s replaced. Unless you think that is the issue, then I'll align now and align again after the replacement.

I could not make a clear enough picture of the schematic that would fit in the 800x800 limit. Here's a link if it will help you help me.
http://www.nostalgiaair.org/Resources/362/M0010362.htm

Any ideas? Thanks in advance.
Doug

Replace the caps then do the alignment.

If you can force an I.F. signal of 455 kHz through the RF and converter stages, but not an RF signal, then it sounds to me like the oscillator might not not oscillating. When it is, a negative voltage of about -10v will appear on the oscillator grid at pin 1 of the 6BE6 converter. There will be nothing much there if it's not oscillating.

Could be a bad 6BE6 converter or a number of other things. There are separate oscillator coils for AM & FM and it doesn't seem likely that both are bad. Maybe you made a mistake in replacing caps in the oscillator section, 21, 33, 18?

I doubt alignment is the issue unless someone has been in there messing with the adjustments.

Thanks Oldbear. Looked longer around the 6BE6. I had not replaced the caps 18,21,33. Those are mica I thought those were generally OK? But I did find R94 connected from pins 1-3 vice 1-2(per the schematic). I moved that and replaced C21. I do not see much if any improvement.

The miswire was not my doing. The radio came out of a hoarders house (coworker's wife is involved with the clean up). I do not know the history, but it appears to have been worked on in the past. Most of the .01uf measure out as .01 they are black plastic SPRAGUES so it should work without replacing them, there were a couple of wax coated "orginals?" in there.

I think the OSC is working but I only measure -1V on 6BE6 pin 1. As I tune through the dial most of it is silent (I expect static) I hear a couple of pops. I can set it on that noise 1160-1200ish on the dial (kind of a buzzing static...is that motorboating?) and then if I sweep the siggen I can hear my modulation faintly-but the noise is loud. Same thing at a couple other points on the dial ~900 and 650ish. I also notice a VHF scanner picks up a signal at ~156Mhz when this happens. I put a scope on pin 1 and in FM I see a 50MHz signal...must be the 3rd harmonic setting the scanner off. When I have it tuned so that I hear the noise the OSC trimmer makes a difference, but in the silence it has no effect.

Tried two 6BE6. The OSC coils are not opens. I do not see any shorts in the tuning cap (bent plates), but it would be odd to have that problem except for 2-3 specific points.

So what would cause the OSC to oscillate only at a few sharp tuned spots on the dial?

Hate to let this beat me...works fine with the W-C model 156 phono(I expexted the cartridge to need to be replace but it seems to work) and TV input.

Thanks again
Doug

UPDATE

AM OSC coil was not good as I had thought...or at least it developed a break. I unwound and repaired that.

AM works fine. I had FM for an afternoon, but moved the chassis out of the way for the evening. Back on the bench the next day had nothing..then intermittant AM
I'd have AM there when I turned it on, but it faded away. Switch to FM and back to AM and I'd get AM back for a few minutes. the lower freqs would fade away faster than the local station up at 1450. Currently have the radio back to solid AM across the dial.

But I can not figure out why the oscillator is not working in FM. I was hung up on the plate voltage on the limiter it is 5V vice 60V. But I injected a modulated IF signal after the 1st IF transformer and with the rest of the circuit working the limiter plate voltage came up to 50ish volts, still low, but I am using a digital multimeter not VTVM. I was hung up there so much that I muched up the discriminator coil and ended up have to rebuild it along with the two caps creating the electrical center tap.

Now I am pretty sure it is an OSC problem.
I have chased the signal path and seem to have a good DC path, but something is wrong.

Any suggestions?
Thanks
Doug

http://www.nostalgiaair.org/Resources/362/M0010362.htm

Maybe you already did, but use a toothpick to drop some contact cleaner on the bandswitch contacts (best not to soak the phenolic wafer) and work the switch back and forth a number of times. Also drip cleaner into each tube socket terminal hole and tube pins and plug in and out while still wet.

This chassis is incredibly picky with 6BE6s. You will find that one that works fine in another radio will not work in the CR-216; try a different 6BE6 and see what happens. You may also find that the local oscillator quits at the higher end of the FM band but if you just touch one of the trimmer screws on the tuning capacitor the local oscillator kicks back in. This is another 6BE6 symptom. The I.F. transformer casings are notorious for shorting to the I.F. cores and adjusting sections. You may find that just be rocking the case slightly, the FM will instantaneously come to life; check that the I.F. transformer innards and adjustment is not touching chassis ground underneath where they protrude. I've been through all of this on the CR-216. It's amazing how these parts expand as the chassis warms up. Again, changing the 6BE6 may be your best bet.

Thanks all, still no FM

I have 2 6BE6's. The one that came with the radio does not work AM or FM. The other one works AM. I tried a 6CS6 and a couple of 5750's all supposed to be valid subs. Still only AM...the 6SC6 provides the best sound.

I used contact cleaner on the socket (and went a little heavy on the switch waffers but they have dried out) but no change.

I took the FM osc coil out and have continuity in each of the sections, and no shorts. Seems like the 6BE6, coil, C33/C21/R94/R80...the variable cap and the trimmer are the only components in that osc circuit. I replaced R80, R94, and C21(with NOS ceramic)...and all of those are common to the AM osc circuit wich works. C33 measures .004 and it is ceramic so it should be OK. I did not like the look of the trimmer cap a 3-12pf (adjustable metal fin on top looks like some kind of coating(just a sliver of it) on the bottom. I tried to take a picture but a cell phone picture is unusable. I layed it on the scanner but it is not much better.

I read in another topic about using a siggen to replace the oscillator function to confirm that the converter will do its job is that possible with FM? How would that connection be made?

Yes, that is also possible on FM. You can inject a signal from your signal generator (probably turned up pretty far) via a 50 pF cap (value not critical) to pin 1 on the 6BE6 converter. You might have to temporarily disconnect the exisiting cap at that pin for this to work. The ground lead of your signal generator would be connected to the chassis of the radio.

You would set your "unmodulated" signal generator for a frequency 10.7 MHz above or below the frequency of a known FM station in your area. For example if you had a known station on 99.9 the generator would be set to either 110.6 MHz or 89.2 MHz. Make sure the dial of the radio is set to approximatly the right place to receive the station (99.9 in this case). Then depending on the accuracy of your generator you might have to it tune back and forth a little to "tune in" the station. Once you get the generator tuned to the right spot you might be able to "peak up" the signal a little by adjusting the dial of the radio itself slightly (this just gets the antenna section tuned to match the incoming station).

Make sure you have an antenna connected to the FM antenna terminals for FM reception of the station.

Curtis Eickerman

Update: Working!

Thanks Curtis. I connected up two siggens (one modulated 100.7MHz to the antenna, and the other unmodulated 90.0MHz thru a 50pf to pin1 of the 6BE6) The radio worked I poked around a bit more, tweaked the IF's and found I could disconnect the 90MHz oscillator replacement and it still worked. I backed out the FM OSC trimmer cap replacement and was able to back the siggen output down to the level of the local FM station. I have it up on an antenna and am receiving a few stations...it is a little distorted. Following the alignment proceedures I am not able to get the discriminator transformer peaked up at 10.775 and then set to 0v at 10.7 and see the opposite votage at 10.625.

Also when I am peaking the FM IF's it is a negative DC voltage that I see on the limiter grid resistor R110, is that right?

Actually maybe the noise is because C38 and 39 are missing (I ran out of .01's) they are there to short RF to gound (RF filter)?

Thanks All
R/Doug

Good progress. That alignment problem is probably the cause of the distortion. This part of the alignment is what allows the FM signal to be converted to audio. I don't have any suggestions there at the moment.

I would expect that to be slightly negative.

I think I found the 38 blob on the schematic. Is that the one on the supply side of the Discriminator (12)? If so, it might be a factor in the discriminator alignment problem. What I think might be the 39 blob appears to be on the 6H6 filament. I doubt that is a big factor, but might help with noise reduction.

Edited to add: Just so you know, there is nothing magic about 10.7 MHz. If you can get that discriminator to do it's Plus-and-Minus thing centered at 10.6 or 10.8 that is just as usable. All you have to do is go back and re-peak the IFs to match your revised center frequency.

Curtis Eickerman

Here's another variable I've learned from: these Magnavox FM tuners do not do well at all with reduced B+. There is usually a candohm resister mounted on the inside of the chassis. You may want to ohm it out to make sure it is within spec. I've replaced a few with wire-wounds.