[morzh]

A former co-worker from over 20 years ago gave me this radio.
It was fully disassembled and came withthe cabinet and the chassis separate in a box.
No tubes, and the dial string was ripped.

I started on this radio 2 weeks ago.

The cabinet
   

The chassis
   
   
   


So, I found good SAMS book on dialcord stringing (the diagram in Riders was not very good) and re-strung the set.
Then 12/7 I ordered all the tubes from Bob Dobush.
Tube came today, 12/17. Fast enough.
I have just given them a quick check - all is good.

Probably this weekend I will start on the recap. The radio has never been restored: all caps are original Zenith. WIll make for good restuffing.
Also, the Selenum Rectifier will have to be taken care of. I guess, I will check it first. I kept one in my Grundig - it works marvellously. But maybe I will replace it. Depends.

The radio has the FM band, so will make for interesting alignment. They say one needs not to touch it at all. Maybe.

[MrFixr55]

Hi Morzh,

I have 4 AM / FM Zeniths. 2 of these are the 7H920 (like yours) and 7G820 (AM and both old and new FM bands). I can't remember the model numbers of the other 2 but they are late 1950s or early 1960s and are not in Rider's. All 4 of them have working FM which is great because I do not have the equipment need to align them.

The 8" speaker goes a long way in giving this set really good sound. The Selenium rectifier allows greater plate voltage than a tube rectifier which also helps to pump up the output pf the 50C5 (or 50B5 if your set is unfortunate enough to use that tube).

[radiorich]

Hello morzh,
I also have one but mine is the 3 band 7G820 I think .
mine too is all original and is complete and same darn broken dial string !!
I have not decided if I want to restore this one first or a am/fm bakelite I bought from Ron .

Sincerely Richard

[Arran]

I think that I may have seen an export model of one of these in an antique mall a few years ago, it had AM broadcast, and two shortwave bands, I should have made an offer on it like I did with the Mystery Control box. Interesting that Mike's example only has one Bumble Bee cap, I seem to remember that my T.Os from this ear were full of B.Bs, or at least the G-500 is.
Regards
Arran

[462ron]

Mike I have that very same radio and it sounds great and is a good performer. I tried doing FM alignment that worked out fine except for the detector. I bought an Eico 368 TV/FM sweep generator just for FM alignment but never got the results I expected. Don’t know if I’m missing something or did it wrong. I had a thread up about it that you commented on. Anyway, I was able to get the detector aligned without sweep generator. Have fun with yours!

Ron

[RodB]

MrFixr - I have used my AM signal generator to align an FM set and it's pretty accurate. You can set the sig generator to the FM IF without modulation and monitor the negative voltage of the AGC then tune the IF stages as normal in the instructions.

[morzh]

Thanks for insights guys!


Mr. Fixr: it is 35B5 in my case. Not 50B5 or the other one. Got it from Bob.
The 50 wouldn't work, as with 35V tube the sum of the voltages is 114V. The 50-volter would lack another 15V to warm up properly.

[rfeenstra]

I have that same radio in an earlier version. Model 7H820.  Mine has the AM band, the normal FM band, and the old FM band from 42 - 50 mc.  I'm not sure why in 1948 they included the old FM band, but it's there!  Perhaps there were a few stations still boradcasting on the old FM band. I use it almost every night.  I broadcast "sleep sounds" from Spotify and use this radio in my bedroom.  I improved the dial lighting with LED's.  The radio works well.

[MrFixr55]

Haven't had the back off it for a few years, yes, 35B5 (I think). 35B5s and 50B5s were short lived. The pinouts somehow violated some UL directive, hence the 35C5 and 50C5. The newer ones I have definitely have 35C5s. I can't remember if I had the 820 apart; the dial cords are good, and it played without recapping. If my memory serves me right, most of the caps in the 920 are ceramic disks. The later Zeniths definitely have ceramic disks for all but the power supply. Fortunately, none have SMD.

Yes, the 7H820 had 2 FM bands. I have to assume that there was a period of time allowed for FM stations in the original band to migrate to the new 88-108 MHz band. This was one of the wars between Sarnoff and Armstrong that drove him to suicide. Per Wikipedia, RCA suggested to move the original FM band to make room for Experimental TV stations and TV Channel 1 (Which no longer exists) and because the existing FM Band was prone to "tropospheric and Sporadic E propagation" (skip zones). The FCC did so, relegating the existing band to "non-governmental fixed and mobile" radio, ignoring the propagation issue. All commercial FM stations had to stop transmitting on the original band by 01/08/1949. This may be the reason why Zenith (who, along with GE advertised their radios as "FM- The Armstrong System") had both bands on this radio which, I believe was marketed in the 1948 model year, meaning that it may have been introduced earlier, or at least designed earlier.

Close to 400,000 radios that covered only the original band were rendered obsolete for FM by this change.

[Arran]

Found this page again, this guy's site is fun it has an example of the dual FM band version just mentioned. https://www.wa2ise.com/radios/fm45.html
I will have to keep my eyes open for another one of these brand Z models, I rather like the styling with the dial/speaker grille combo. There was an HMV radio from Britain that was designed in a similar fashion, with the dial made up of glass louvers, which had the speaker behind it, I don't know how much the louvers vibrated though, glass tends to resonate somewhat at certain frequencies, which could be annoying.
Regards
Arran

[Arran]

Yes, there was some U.L recommended change made with regard to 50B5 tubes, it had something to do with the pinout that if it were plugged into another socket by mistake something else would become live. I don't think that I have encountered a set with a 35B5 though, but the 50B5s stopped being used in new equipment after 1950-51 or so. https://antiqueradios.com/forums/viewtop...=50b5+50c5
Regards
Arran

[David]

If the set had a 35W4 and  50B5 or 35B5 and if reversed you would let out the magic smoke. David

[morzh]

https://www.ebay.com/itm/306656576761?_s...R5rr5MznZg


Methinks this is the one with the two FM bands.

[morzh]

I thought of not posting today.
Because of Gary.
But then I thought, Gary loved this place and I think he'd want us to keep posting.
So I've decided, I will post today's progress.


I started recapping the radio. The first surprise was this capacitor.
   

I quickly understood what it was. Then looked at the sch, and, yes - it was a shielded cap.
So, I figured, it probably a cartridge with some metal foil and a contact, and it is put over a regular cap.
I warmed it up, pulled ona lead, and the cap came out of the shield very easily.

   

So, I simply restuffed the cap, then put it back in the sleeve and warmed it up, so the remainder of the wax inside would melt and grabbed the cap again.

   

Never saw this type of cap before.

[David]

That cap goes between the volume control and the 19T8? Have installed the replacement without the shield and also made a shield by wrapping wire around the new cap. Nice work.