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Antique Radio Technical Forum
Zenith 5S56 Voltage on Chassis

Posted by Will Hodges on 11/26/2005 23:47

:As far as I can see, I think that C1, next to the 6A8 tube (in the schematic) in the antenna circuit, is one of the two gangs of your tuning condenser, and C1, connected to the oscillator circuit under the 6A8 tube (in the schematic), are the two gangs of your tuning condenser. They are both connected to the chassis, which means that the frame of your tuning condenser is connected to the chassis. Tuning condensers, whether connected directly to the chassis or not, are commonly isolated on rubber bushings. This dampens out vibration that might otherwise cause frequency modulation feedback. This happens when the speaker plays a really loud passage and then vibrates the condenser plates. This changes the frequency that is tuned in, and causes a fluctuation in the radio circuits, which then passes on to the speaker again, and it howls like a microphone placed too close to the speaker. This problem isn't common, but manufacturers often isolated the condenser anyway. New rubber bushings can be found at your hardware store. Purchase many. This way some can be placed in the original holes. Then others can be cut in half and used as shims, if necessary, for putting the condenser back to its original height.
:
:Have fun with tubes. They are a lot of fun, and are easy to understand. I have heard, though, that people who start off with solid state technology, have trouble with tubes sometimes. Tubes are amazing devices, capable of far more than most people to-day realize. They are more sensitive than any other device of similar nature (transistor), and are faster responding than any other similar device. Unfortunately they aren't extremely stable (emission dies off with age), and they take up a lot of space. Though they could make computers faster than they are, the computers would take up huge buildings. Noone knows how to put a tube in a chip. They make radios sound really good, though, and will cook your food really fast. Your radio, though it will likely sound great, won't have the best sound, since it doesn't have push-pull output. Push-pull output is used on all fine radios, both modern and old. Most car stereos and high quality home stereos use push-pull output. Push-pull output, by nature, cancels a lot of distortion in audio. These distortions may either be in the form of clipped off audio waves or in the form of non-uniform frequency response. Push-pull is deep and rich, and of full range. A properly designed singe phase output can sound really nice, though.
:
:Thomas


Thomas,
Thanks for the help. As I mentioned, I have AC present on the chassis when the set is plugged in but not turned on. the amplitude depends on the orientation of the plug. 120 volts when the hot side is connected to the on/off/volume switch and millivolts when the neutral is connected. This afternoon I traced the 120 from the line input to the switch and then to the 6B6 2nd detector. I may have a leak in the switch (R7 on the map). I plan to remove the switch and all its' leads and see if it measures correctly. If it doesn't I'll take it apart and have a look see. this evening I put the speaker and chassis back in the cabinet and I'm listening to it as I type this message. One other thing that I failed to mention is that the 260 VDC on the chassis when the set is turned on is -260 and not B+. I guess you call that B-, right? This is one of those sets where the power supply reference floats and the first filter cap is not grounded to the chassis but uses the speaker field coil as part of the supply. By the way, I checked the speaker field and voice coils for shorts or longs and they seem to be perfect.
Thanks again.

Will



Zenith 5S56 Voltage on Chassis 
Will Hodges 11/24/2005 23:22 
TonyC 11/24/2005 23:58 
TonyC 11/25/2005 07:54 
TonyC 11/25/2005 08:05 
Will Hodges 11/25/2005 22:52 
Will Hodges 11/25/2005 22:53 
will Hodges 11/25/2005 23:00 
Will Hodges 11/25/2005 23:24 
Thomas Dermody 11/26/2005 00:15 
Thomas Dermody 11/26/2005 00:20 
TonyC 11/26/2005 13:23 
TonyC 11/26/2005 14:17 
Will Hodges 11/26/2005 15:30 
Thomas Dermody 11/26/2005 22:53 
Will Hodges 11/26/2005 23:47 
Billy Richardson 11/27/2005 09:37 
TonyC 11/27/2005 10:58 
Thomas Dermody 11/27/2005 14:35 
Will Hodges 11/27/2005 17:25 
TonyC 11/27/2005 18:17 
Will Hodges 11/27/2005 22:53 
Will Hodges 11/27/2005 23:04 
Thomas Dermody 11/28/2005 00:16 
Billy Richardson 11/28/2005 11:09 
Thomas Dermody 11/28/2005 12:06 
TonyC 11/28/2005 10:19 
Rick Skowronek 11/28/2005 20:07 
Thomas Dermody 11/28/2005 21:57 
Donnie Land 11/30/2005 21:39 

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