[captainclock1988]

Greetings everyone, I just acquired a 1961 vintage Zenith C845Y AM/FM tabletop radio that I had replaced almost all of the paper caps in it except 2 of them because they were in difficult to reach/access locations in the radio, and the radio tuner is extremely out of alignment, especially on the FM Band because stations that should be on the lower end of the tuning dial are showing up on the middle of the dial and stations that should be in the middle of the dial are showing up on the top of  the dial and the stations that should be on the top of the dial are non-existent, also the audio quality coming out of the speakers isn't quite up to snuff to where i would expect the audio quality to be on this radio. What could be causing these aforementioned issues with this radio? I was thinking possibly the IF Alignment is way out of adjustment but I'm not sure if that would cause the lackluster audio quality issue, and more the dial alignment issue.

Any help would be appreciated.

Thanks.

[David]

Please check the 19T8, 6BJ6, 6AB4 an 12AT7. Have a love hate for the 19T8. Posting some info. David

Zenith-Radio-Corp-C845Y.pdf Size: 162.71 KB  Downloads: 34

[Jayce]

First off, did you replace the selenium rectifier with the correct diode and resistor combination? (Can't think of them off the top of my head, so someone help me here.) The 19T8 is then the next candidate due to all the jobs it handles. If audio is bad on AM and FM, that could be at least part of the cause. Also, recheck your 35C5 while you are at it or even try another good 35C5 or even 50C5 as those can be swapped. The alignment issue with FM seems to be common. My Zeniths are not as bad as yours, but still a little off. All these old AM-FM radios need a proper FM alignment, but I don't have the equipment and have never known anyone with the equipment to do so. AM usually just needs a signal generator and the correct instructions and perhaps some special tools. FM also needs an oscilloscope.
I do agree with the attitude towards the 19T8. They can go bad without warning, even if NOS. I have had two do that to me. One was used, lasted a week, then went to a short on one section. A NOS Sylvania tested great, worked for three days and went to a dead short!
Of course, always check the 12AT7 and 6AB4 as those tubes can be weak due to not being used on FM much. The filaments stay on when switched to AM, but the plates get shut off, which is actually hard on any tube.

[captainclock1988]

I never touched the selenium rectifier, as I'm unaware of the correct replacement parts, although I have used a 1N4007 before and never had any issues (I never used a resistor with the 1N4007 Diode, just did a straight drop-in of the 1N4007 in the radio and it seemed to work fine.) as for the tubes, I did replace the 12AT7 because the original (and yes I do mean the original Zenith branded 12AT7 that was from when the radio was made) had gone to air at some point as the getter was non-existent and white colored, I tested all of the rest of the tubes and they tested like brand new yet including the 19T8 which was a GE branded replacement from 1963 as for the 6AB4 and the 6BJ6 they were the original Zenith branded tubes from 1960 and they tested like new yet according to my Sencore Mighty Mite VII tube Tester, and the 35C5 was an RCA replacement from the 1970s because it had the Block Lettered RCA emblem on it. As for the Alignment goes, I was attempting an Alignment job and I was working on the 3rd AM IF can and my diddle stick broke off on me inside the IF Adjustment slug and I have no way to get the broken diddle stick out of the IF can, does anyone here have any ideas of how to go about removing the broken diddle stick from the IF can adjustment slug?

[MrFixr55]

Hi Captain Clock,

Haven't seen you on the Phorum in a while, hope all is well!

If the diddle stick is a hex head and if it has not fallen through the slug, and if the slug is fully hollow, and if either there is no slug below or if that slug is hollow, and if there is an access hole at the bottom of IF transformer, then use a tool to push the broken tool from the bottom to the top.

Otherwise, you have to open the can of the transformer and remove the tool.

Sometimes these slugs start to swell and crumble, and can't be turned, hence the tool breaks. For the purpose of breaking the slug loose, one can use a metal hex wrench but note the use of the term to break the slug loose. You may successfully break the slug loose or you may break the slug (or the coil form), so the procedure has risk to it. Of course, once the slug can be turned, you must use the plastic tool to align.

[captainclock1988]

Yeah, the reason why I haven't been on in a while was because I had some stuff come up recently that made it hard for me to do anything repair wise recently, such as losing my job I had held for 8 years suddenly without any notice because the employers decided they wanted to do away with the custodial department at the place I was working at and instead hire an outside firm to do the cleaning, so I had to watch my spending for awhile. Thankfully I have another job and it pays a lot better than my old job did I have the ability to work the same amount of hours I did at my old job.

Unfortunately this radio is turning out to be more of a hassle than I had counted on to repair, because its turning out to have a lot more issues wrong with it than just replacing the old wax paper caps was able to fix.

[captainclock1988]

Here's a video of what the radio is doing currently, as I said the audio is very weak sounding (when the volume control is at 1/4 volume the audio is barely audible and when its at 1/2 volume, it's very distorted and there's a little bit of an audible hum in the background that is contributing to the distorted audio, and the hum is adjustable with the volume control so its not filter cap hum, because the hum actually goes away when its switched to the AM Band, but the badly distorted audio doesn't.

See video link below to see what I mean by the audio quality being absolutely horrendous on this thing.

https://youtube.com/shorts/dLE82kz68VM?s...aRJXNvTMJm

[MrFixr55]

Hi Captain Clock,

I have a similar Zenith AM / FM that does the same thing. Have had it for 50 years, but haven't got around to fixing it. Did get a schematic finally when I bought a similar set.

Try the ol' divide and conquer technique. This set has a Radio / Phono switch. Connect a signal from an external audio source such as an MP3 or CD Player to the Phono jack and put the Radio / Phono switch into Phono. If the sound is still garbled, then the audio section is at fault. This is a much easier section to troubleshoot than the RF section!

!!!!!!!!!!!!CAUTION!!!!!!!!!!!!
This is a HOT CHASSIS Set, not a warm chassis set, meaning that one side of the line is connected to the chassis. This is done through the power switch! Therefore, if the chassis is connected to neutral through the power switch, the chassis poses little danger when the switch is on but is extremely dangerous when the switch is off. This is because the chassis becomes hot through the unswitched side of the power line through the tube heaters which have very low resistance when cold. Use a battery powered input source!

See the following link:
https://antiqueradio.org/safety.htm

If the issue is in the audio section, review the schematic. There is a feedback system in this radio involving feedback from both the output tube plate and a transformer winding to the low end of the volume control. Test by shorting the 1K resistor and disconnecting the feedback circuit and tone control. If this solves the issue, then troubleshoot the feedback circuit. Replace the 1K resistor between the volume control low point and chassis ground.

Hope this helps!

[captainclock1988]

Mr. Fixer,
Thanks, I'll look into that. I do have an Isolation Transformer, so the Hot Chassis isn't an issue for me, I did get the Beitman's Service Data for this radio, which is pretty detailed for what it is. 
I do have an iPhone and a Bluetooth receiver that I can hook into the phono input to test the phono input stage with.

Thanks for your assistance.

[captainclock1988]

A little update, I figured out that the phono stage is unaffected by the garbled audio issue, the phono stage is working perfectly, I was running my Kindle Fire through the phono stage and it sounded great. So it looks like the issue is in the radio section somewhere unfortunately.

[radiorich]

Hello captainclock1988,
good news that you were able to narrow down the problem !
Sincerely Richard