Zenith H845 - help needed

[DavGoodlin]

This unit is a testament to Zenith's pulling out all the stops to make a better radio than even Nordmende and other makers of early 60's table treasures.

I had one for years, then I found another one on the "free table" at a swap meet. All original tubes tested strong and free of shorts. well...it sort of played but crackles, so it was there for a good reason (if there is such a thing) and here it is...H845a.JPGH845b.JPGH845c.JPG

I cannot believe Zenith would use these damn things in those big, impressive IF cans, but they do. This radio has no less than seven of these, so how do you know which one is the bad guy?

The problem was isolated to one can, the first AM IF can affected both bands;
#1- Grounded the grid of the second IF tube, silence, then grounded the grid of the first IF tube, silence again. This placed the trouble in the cans BEFORE even the 1st IF stage. Next, I used a modified chopstick to prod the terminals on the bottom of the suspect cans and the crackles stopped, so I powered down, loosened the big nut in the bottom of the can, plugged in and VOILA...clear AM signal came through! and FM came back also

As can be seen of the L8 A4-A5 can in the schemo, the caps are not labeled as to the value.

I can't replace them all, so I will do this one and see how it goes.

Does anyone know the value of these capacitors?

[Reece]

I don't have the exact schematic of your radio but this should be close. If the same tubes are used then the transformers are probably the same. Zenith made several AM/FM's in those days that were similar.

PM me your email: I have a PDF of the schematic and can't figure out how to insert it here.

[DaveWM]

pretty sure am caps will be around 130-150pf

[Reece]

Right. The schematic I have shows:

AM input IF xfrmer: 150/150 pf
AM output IF xfrmer: 125/125

FM input IF xfrmer: 40/40
FM output IF xfrmer: 24/24

[wa2ise]

In a Zenith like this, I had the silver migration problem. Migration that causes leakage paths from primary circuits to secondary circuits. I just took a sharp tool and scribed the mica between cap sections to server the migration paths (after I removed the mica wafer), then put it back in and no more problem. Didn't have to even realigh the transformers after doing this.

[tlavergne]

Don't mean to steal thread but I have the same radio. Does anyone have a suggestion for a shop to send it to to have the radio gone over? Everything looks original and not pulling in stations like it used to. After 50+ years it could probably use some TLC from a tech.
Thanks.
Tom