AW23 amp problem

[Y2K Bruce]

I recently acquired the amp for an AW23. It has been recapped etc per the seller. I plugged it into a known working chassis and speaker and powered it up on a variac. Tubes used were good ones.

 

The 2 voltage regulator tubes on the main chassis lit up but NOT the mazda dial bulb nor any other tubes that I could tell on the main chassis. I thought this seemed odd.

 

I was wondering if this could be a simple fuse problem? The 2 fuses look to be ok but I have not measured them yet. Any thoughts on this ?

 

Thanks all.

[Thomas Day]

Bruce:

Check the 6.3 volt filament voltage. You should have the B+ feed to the radio chassis if the voltage regulator tubes glow. 

There could simply be a broken wire in the chassis plug, or the cable or in the chassis itself. You can check the filament voltage at the amplifier socket for the radio chassis and check for continuity across the two large pins of the chassis plug. 

With all tubes and the pilot lamp in place there should be only a few ohms resistance across the pins. 

[Y2K Bruce]

The chassis works fine with another amp. That's why I am curious why the 2 VR tubes lit up but not anything else with the suspect amp plugged in.

Thomas Day said:

Bruce:

Check the 6.3 volt filament voltage. You should have the B+ feed to the radio chassis if the voltage regulator tubes glow. 

There could simply be a broken wire in the chassis plug, or the cable or in the chassis itself. You can check the filament voltage at the amplifier socket for the radio chassis and check for continuity across the two large pins of the chassis plug. 

With all tubes and the pilot lamp in place there should be only a few ohms resistance across the pins. 

[Thomas Day]

Bruce:

Since the radio is ok with another power supply, then there could be a problem with the 6.3 volt winding of the supply you trying to use. The 3 amp fuse is in the AC power feed to the amp chassis and the 3/4 amp fuse is in the bias supply for the output tubes. All the tubes on the amp chassis light up? Looks like you could have a bad or broken connection in the amplifier.

Y2K Bruce said:

The chassis works fine with another amp. That's why I am curious why the 2 VR tubes lit up but not anything else with the suspect amp plugged in.

Thomas Day said:

Bruce:

Check the 6.3 volt filament voltage. You should have the B+ feed to the radio chassis if the voltage regulator tubes glow. 

There could simply be a broken wire in the chassis plug, or the cable or in the chassis itself. You can check the filament voltage at the amplifier socket for the radio chassis and check for continuity across the two large pins of the chassis plug. 

With all tubes and the pilot lamp in place there should be only a few ohms resistance across the pins. 

[Norman S Braithwaite]

It is very unlikely that the 6.3-volt winding is burned out (but not impossible).  The first place that I would look is the filament connections on the "set" socket.  It is not unusual for the contacts in the socket to become spread out and not make good electrical contact if the set plug has been inserted and removed many times or if a former owner had a habit of jiggling the set plug in the socket.  The second place I would look is the set plug making sure that the filament wires are well soldered in the plug pins.  If the orientation of the plug and cable is different between the two power supplies, an intermittent bad connection may act differently.  Once in the tuner chassis, the filament wires connect to an IF amplifier tube and are divided several ways from there.  The fact that all filaments do not light implicates the set plug and socket.

Norman

[Y2K Bruce]

As Norm suggested, I now realize I did have a hard time plugging in the "set" plug into the amp.I believe this may be the major problem so I will dig into it and check.

I thought it strange the VR-150's both lit up but not the Mazda dial lamp.

 

I used the same tubes in the other 'good' amp and later blew a fuse which turned out to be due to a shorted 2A3 tube. Swapped in some replacements from my la France into the 'good' amp and have been listening all morning. Its fun to play with all the adjustment knobs to get the sound just right.