Admiral Combo Chassis - Dead LV Rectifier?
 

Greetings -

Have an Admiral combo where I changed out the electrolytics in the power supply, yet the rectifier does not light up. Tube tests good. Ther is no hum or sound coming from the speaker. Any suggestions as to where to dig first?
20B1 chassis.

If the rectifier doesn't light, it's either bad or not getting proper voltage. Measure across filament pins to see how many volts. Test the tube or substitute a good one.

Is it the 5U4 or the 6X5 that isn't lighting? Do the rest of the tubes light?

If the tube tests OK, then you either have a bad tube socket, or an open rectifier filament winding on the power transformer (very unusual). If none of the other tubes are lighting, check the power cord, power switch, line fuse, and power transformer primary.

I think it is the socket. Tube feels loose in there but I would think if I wiggled it it would make some sort of contact. I will try to shim it somehow.

:confused:Actually now I am not sure this is a socket. Some other tubes don't look like they are lighting. I'm wondering if I have a bad resistor somewhere in the circuit?:scratch2:

The tube filaments are wired in parallel so it's odd that some would not be lighting. What AC voltage do you get on the rectifier tube filament pins when it's out of the socket ?

Are you sure of the chassis number?
All the chassis have to be plugged in to get everything to work. That includes the radio. They had a crazy switching arrangement in those sets.

The LV rectifier filaments are usually on a separate winding.
Mainly because if it shorts H-K having 150V on the other
filaments is not a good day.
For the socket you can carefully remove pins from another
socket & replace a pin or drill out & replace the old one.
On some sockets you can also use a jewelers screwdriver
from the top & squeeze it tighter. Used that on tuners a lot
to save a rebuild.
For some filaments not lighting some sets use both a series &
parallel string or 2 series strings. Having more than one open
fil. tubes would be near imposable.

73 Zeno:smoke:

I guess the question is I should see some glow in the tube, correct?

never mind.

I just realized you've got a combo set. That means some tubes will not light depending on the mode (TV, Radio or Phono) including the 6X5 rectifier tube.

Both the Sams and Riders service info are available here: http://www.earlytelevision.org/tv_sc...s_postwar.html

You got it - just figured that out myself in the garage. The 6x5 lights in TV mode. OK - so I know I have to figure out why no audio or hum. Guess I will start with the audio transformer. Also crossed speaker wires etc. BTW - I am doing this with a 300 watt dim bulb and variac. That will restrict alot of voltage.

I can see why people avoid combo models - many points of failure and huge schematics. But what a challenge. This is no AA5! But my approach will be to work on things obviously not functioning to see how much life is actually left in this set. So far it looks like the transformer is good and the CRT lights. If either or both were bad - the set would be trash.

For sure! Just curious; what do you need the bulb for if you have a Variac?

The bulb will give you a quicker indication of a short or excessive current.

If you have a fully metered variac with an output ammeter, you don't need it.

often if a rectifier tube is burned out... its because it was overloaded from a shorted filter capacitor, so check that before you try putting a new rectifier in.