Finally starting 800B restoration

[Keith Lowe]

All, I'm finally ready to start on my 800B and I've got the power supply on my bench.  My plan  is to replace all the electrolytics and re-stuff the bathtub caps.  The power  supply has been worked on before and the bakelite canned caps have been relocated to a terminal strip below the chassis.  I'm thinking it would be nice to relocate these back to the cans provided they can be re-stuffed.  Can these be opened without having them shatter?  I'm hoping I don't need to replace the molded mica caps.  I'd love some advice on what to replace or modify in this power supply.  If I need to solder any connections to the chassis I'll need higher wattage soldering iron for sure.

Thanks in advance,

Keith

[Keith Lowe]

Thanks Norman, these are next to the tuning gang and I can replace them with difficulty.  If I have to change the molded mica's in the same vicinity I'm in trouble.  I was hoping you would say they go bad on their own.  Any chance it was something I did in the power supply that made them burn out?

Keith

[Norman S Braithwaite]

Keith:

It is not likely that anything you did caused those resistors to go bad.

Norman

[Keith Lowe]

I replaced all of the open and out of spec resistors that I could find but still no FM.  I failed to mention that the previous owner had disconnected the tuning motor.  This wouldn't effect manual tuning would it?  I'll get voltage checks on all the tube pins this weekend.

Keith

[Norman S Braithwaite]

Keith:

Does the FM tuning eye react to stations?  If not, the problem is before or at the discriminator.  If so, then the problem is after.

Norman

[Keith Lowe]

Norman, I've got no movement of the eye tube.  What I like about the Riders manuals is that they show the wiring schematic with the band switch in different positions.  Unfortunately they don't have a diagram showing the band switch in the FM position.  So with the problem before or after the discriminator then it must be something wrong in the powersupply module?

Thanks,

Keith 

[Norman S Braithwaite]

Keith:

Thanks for the report.  If AM is operational and you have filaments and B+ in the FM section of the tuner, it is very unlikely that the problem is powerT supply related.  If you do not have B+ in the FM section of the tuner, it is possible that the AM-FM relay contacts are dirty.  If the relay contacts are clean and working, the problem is almost certainly located between the FM antenna and the discriminator.  FYI, the plate voltages on the limiter tubes should be lower than the IF tubes and may vary greatly from the values identified in service data with no problem for operation.

Norman

[Keith Lowe]

Norman, as you can tell I have zero understanding of FM.  My approach that has worked before is to test each and every component and replace anything out of spec.  This is much more of a challenge.  I'll try to get back to you with the tube voltages tonight.

Keith

[Keith Lowe]

Norman, I've  got B+ in the tuner but surprisingly nothing on the tube plates in the FM section of the power supply.  It took me a couple of hours to fabricate a test socket extension so I won't be able to do any more trouble shooting tonight but at least it's clear why I don't have any FM.  My next project will be to modify my power supply stand so I can have access to the connections while it's upside down.  Then I can have everything plugged in so I can trace the B+ power.  Either I have a bad connection somewhere or I messed up when I recapped the power supply.  This is where the schematics that have the different band switch diagrams come in handy.  Too bad they don't have one for the FM section.  I tend to get lost when tracing connections that go through rotary switches.  Can you think of anything simple that would shut off the B+?

Thanks,

Keith

[Norman S Braithwaite]

Yes.  A bad AM-FM relay or bad contacts on this relay.  Also, make sure that the selectivity switch is not in the narrow position as this may disable the pushbuttons.

Norman

[Keith Lowe]

Norman, I'm getting closer to solving this problem.  The relay is fine but the power wire on the Jones plug leading to the relay was not attached to the plug (could it be that simple?).  I fixed this and the radio is now completely silent even on AM (which was previously working) This leads me to believe I still have a connection problem.  I'll keep at it and report back soon.

Thanks,

Keith

[Keith Lowe]

Norman, I spent a large portion of the  weekend carefully going over every connection in my power supply.  Everything was fine so I hooked it up to the speaker and tuner and this time everything is working.  This leads me to believe I still have a Jones plug issue.  The AM comes in loud and clear but the FM is relatively quite but I least I have FM.  With the volume at max, FM is about as loud as the AM with the volume switch about 1/8th on.  I will carefully go through the tuner to make sure I didn't  overlook anything.  The FM tuning eye isn't opening but the 1meg resistor in the eye socket is open (I'll swap that out  once I work out the other issues).  The last two radios I restored wouldn't work at all without having the antenna's hooked up correctly so I want to make sure this isn't the problem.  I'm using the internal loop antenna that plugs into the back of the tuner for AM (this has a rectangular metal rod for an antenna) along with a separate FM dipole antenna and a ground wire.  AM works great but I see no difference when I switch positions on the antenna switch.  In addition I've got two antennas that are built into the cabinet that I'm not using at the moment.  One looks like an FM dipole that wraps around the tuner portion of the cabinet and the other looks like a ribbon a bit over an inch wide and this one is wrapped around the lower portion of the cabinet that houses the powersupply and speaker.  I'm assuming the wide ribbon like antenna is for AM?  Once I'm confident that the radio is working  properly I'll do the tone modifications and swap out the burned out  tuner motor (fortunately, I've got a spare  tuner with a functional  motor).  Progress is slow but I'm getting closer.

Thanks,

Keith

[Norman S Braithwaite]

Keith:

The plugs and switches in an 800B that has been sitting can be a real pain.  Is the FM tuning eye not opening or not closing?  Usually the eye is open except when on a strong station.  The 800B requires an FM antenna for decent FM reception.  The rectangular tubular aluminum antenna is for AM shortwave.  The "ribbon" is for AM broadcast band.  The Scott service data in Sams and Riders show how to hook up the loop antennas.

Norman