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Zenith 7H920 Restoration
#16

Yep that's the one.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#17

@Morzh, yes, that is the dual band. I have the same radio; the cabinet on mine is painted red.

"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis

Best Regards, 

MrFixr55
#18

And it sold for a reasonable price and the shipping was not overboard.
Of course it still has to arrive in one piece, but the feedback on the seller was superb, specifically about the shipping.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#19

Another thing I have noticed: this radio is a bit different from the schematic.
For instance, 1st and 2nd IFs have some large resistors to GND from their pins 6 (SG) whereas they are only supposed to have 680 Ohms pullups to the Plates' Positive bus. They seem to be in 22K or so range.

   

(all points of interest are marked with red arrows)

You can seer that the pin 6 of this 12BA6 (left arrow) connects with the orange wire to the 680 Ohm small resistor (right arrow). As it should.
But also that same pin is connected to what seems to be 22K large resistor (middle arrow) the other lead of which goes to GND. 
You could also see another resistor like this one to the right (for the other 12BA6 tube).
The resistors are a large ceramic kind; I suspect at least 1W rated.

I wonder if the SG voltage on these was a bit high and they used these to lower it just a bit.

The soldering seemed factory professional, so I do not doubt this is not a mod/repair.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#20

Finished the tubular recap today. Took longer trhan usual: Zenith cap's wax is hard to melt and quickly solidifying.
Also the way the wires are secured made it harder to free the stubs. In sensitive places like chokes I just clipped them close.

The bumblebee, as expected, is solid inside and is not really restuffable, unless I could drill the axial hole (doubt it).

The last thing I did today was freeing the twistlock cap. Not only it was soldered by one tab to the chassis, but these tabs have those small burrs, and it took me over 30 minutes to free it. I have a huge old style wood handle flat screwdriver, probably 0.4" wide and as thick. It eventually persuaded that cap to come out.
The caps are mostly 3 times the value, so they do need to be replaced.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#21

Your set should play well and sound good the Foster Seely FM circuit was superior to the RCA circuit of that era. Odd the selenium rectifier gets stuffed in right near speaker but really maybe only place for it. I hope you have a nice Classical FM station to listen to in your area, enjoy. Paul

Tubetalk1
#22

Paul

There are at least a couple of Classical FM, from Phili.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#23

Mike;
I haven't tried drilling out one of those tan coloured plastic molded caps, but I have drilled out the Sangamo "Little Chief" ones, which are the same material as the Black Beauties and Bumble Bees. I was using a Unimat lathe, which is like a small machine lathe, started small, and worked my way up in the sizes of bits until the hole bored was large enough to fit one of those yellow poly film caps. It can be done, it was Russ that gave me the inspiration in that he did something similar with the Bumble Bees in a T.O.
Regards
Arran
#24

They may be either a factory mod or a documented post manufacture mod.  Often, this info does not make it into third party service info such as Breitman's, Riders or even Sams, whether or not the documents were published in cooperation with the manufacturer. 

In older radios, the use of "voltage dividers" to supply a predictable screen voltage that does not vary based on varying current was common.  I looked at the 920, 921 and 922 and can't find the resistors.  My guess is to measure the voltage for the screens.  If accurate and non-variable, then you are good to go.  if the resistors are out of spec based on their markings, replace them.  I used a 100V drop across the resistor, instead of the approximately 80V in calculating power dissipation which works out to be about 1/2 Watts.  1 watt resistors should be OK, 2W better.  Use carbon or metal film.  Since these are DC voltages that are likely bypassed by a cap, RF should not be an issue but do pay close attention to replacement.  Hopefully, you don't have to change them, as they look quite buried.

"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis

Best Regards, 

MrFixr55
#25

Mr. Fixr,

They are not badly buried and all is fairly easily accessed. But they seem to be close to their intended values (as are, in fact, all resistors I've checked so far). Hopefully, I won't have to do any resistor changing.


Arran,

I might try.
Or, I might find a Zenith shell and use it.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#26

I have had good luck with Zenith sets with regards to resistors.
#27

I have a TO 8G005 with the original caps, including the electrolytics, that still plays well. I will get around to recapping though. In fact, the 2 other Zenith Battery / Line portables, a 4G800 Zenette (recapped) and a 6G001 (not recapped) and a DuMont RA354 (not recapped) played well on the original electrolytic.

Sorry, I'm somewhat lazy but the only caps I restuffed was an electrolytic in the Zenette 4G800 and all the caps in an RCA 5BT and 6BT. The caps in the RCA were the amorphous gumdrops with a loose fitting cardboard tube and cardboard end caps.

"Do Justly, love Mercy and walk humbly with your God"- Micah 6:8
"Let us begin to do good"- St. Francis

Best Regards, 

MrFixr55
#28

Like I said many times before, it is not a requirement.
In fact, were I not too fond of doing this thing, my restorations would take from2-3 days to a week less.
But then, I have time. Or at least I think so.

And, sometime, when it is too onerous, I do exactly that. In fact, recently I did it. Forgot what it was...but the chassis was full of them yellow bright film caps.

Oh, and when I have to replace those small German caps....no way to restuff at all. But then, I do not treat 1950-1960 radios the same. They a modern, so could use modern caps.

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#29

Finished the tubular recap.

Now I have rebuilt the 4-way cap, just have to glue the cap back on.
Will do that tomorrow when it is dried up inside.

   
   
   

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.
#30

Glueing the cap together. Hopefully if the epoxy behaves the way I want it to (run down while it is still gooeym bonding tthe cap to the base, and then setting), I could set the cap in place tonight. Usually it behaves (JBWeld).

People who do not drink, do not smoke, do not eat red meat will one day feel really stupid lying there and dying from nothing.




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