Remove & Replace K1-SW 6A/B Assembly in 800B

[Joseph W Strickland]

I recently removed the K1 SW 6A/B assembly from the Late 800B radio tuner chassis that I have to use in repairing another 800B. Here is some information on that process.

Removing K1 SW 6 from 800B

The relay coils of K1 have delicate solder lugs. I had to remove wires from the relay coils as part of the process. I managed to break one off while trying to remove one wire that was wrapped really tight around the lug. So, in the case of removing wires from the relay coils I would strongly suggest that you simply clip them off and deal with reattachment later.

With the exception of the two buss wires to SW 6B, the stranded wires connected to SW 6A and SW 6B have short stripped-back exposed wire strands. These were simply inserted through the switch section contact lugs and soldered. They were not wrapped around the contact lugs before soldering. This is the best practice for connection and disconnection in this very congested area. DO NOT wrap these wires around the switch contact lugs when re-soldering after replacing the switch/relay assembly.

SW 6B Top Half Only:

There are two buss wires from SW 2B area RF compartment that connect to top contact lugs of SW 6B. These can be heated at the SW 6B solder lug and carefully removed while the solder is liquid. Then carefully bend them toward you and out of the way.

Only the top visible half of SW 6B has contact lugs. There are five. The two buss wires are to the contact lugs closest to the rear of the chassis.

First contact wire is bare tinned.

Second contact wire is a tinned with a black sleeve on it.

Third contact wire is cloth insulated White wire with Brown and Yellow dashes on it. It has a Red painted dot near the solder lug to distinguish it.

Fourth contact wire is cloth insulated White with a Brown and Yellow dashes on it.

Fifth contact wire is cloth insulated Brown with a Red painted dot near the solder lug to distinguish it.

SW 6A has contact lugs on both the top and bottom half of the switch. The wires to the top half (as viewed while looking down upon the bottom of the radio chassis with the bottom cover removed) are control circuitr wires. The wires to the bottom half are audio signal coaxial cable wires. Several of these audio cables have their shield braid soldered to a lug that is grounded to the side of the bracket holding the K1 relay coils.

SW 6A Top Half:

First contact lug wire to SW 6A closest to the rear of the chassis is Red plastic insulated.

Second contact lug has two wires; both Red plastic insulated with a green painted dot on them.

Third contact lug has two wires; one is cloth insulated White wire with Brown dashes, the second wire is a Red plastic insulated wire. Both wires have a Yellow painted dot on them.

Fourth contact lug has an Orange plastic insulated wire.

Fifth contact lug has a cloth insulated White wire with orange dashes on it.

Sixth contact lug has an Orange plastic insulated wire which goes through a rubber grommet near the SW 2C switch in the RF compartment.

SW 6A Bottom Half:

First contact lug wire closest to rear of the chassis is Brown cloth insulated.

Second contact lug wire is White cloth insulated.

Third contact lug wire is the long audio cable coming from the Power Supply chassis.

Fourth contact lug wire is Brown cloth insulated.

Fifth contact lug wire is Green cloth Insulated.

All of the SW 6A Bottom Half wires are audio coaxial cables with short ground leads that will readily stay in place after their signal leads have been unsoldered from the SW 6A switch contact lugs.

After all connections to SW 6A and SW 6B have been disconnected, rotate the chassis to the top side. Remove the chrome cover over the RF compartment. You will find two screws near the front section of the tuning capacitor, inboard a bit from the two 6J5 tubes. Remove those two screws and star-washers. Keep all hardware removed during work on the K1 relay and SW 6A and SW 6B assembly in a zip lock back with identifying label for use when replacement relay and switch assembly is installed.

Rotate the chassis so that you can see the bottom again. Now the entire K1 SW 6 assembly is loose and can be lifted somewhat away from the chassis. It will not move a great deal as there is a group of audio coaxial cable shields that are attached to a solder lug secured by a screw at the rear bottom of the K1 SW 6 assembly. You will need a ratcheting right angle common-tip screwdriver to loosen that retaining screw for the coax grounds. Once you get that loosened and removed, you should then be able to carefully lift the K1 SW 6 assembly out of the chassis for replacement.

When reconnecting the RF buss wires to SW 6B and securing it to the chassis, get the wires loosely placed back in the switch contact lugs such that there is no bending of the switch contact lugs. There should be no stress there – then solder the leads to the contact lugs and look for smooth solder flow and allow them to cool without disturbing them while they cool. The result should be smooth and shiny with no crustiness.

Reverse the sequence when installing the replacement K1 SW 6 assembly into the chassis. When soldering the wires, make sure that the wire strands are close enough together before any soldering to be inserted through the openings of the switch contact lugs without damaging the lugs. Then once a wire is in place, solder while making sure there is good liquid flow and allow the solder to cool until solid without moving the wire. This will ensure a good solder connection. If the soldered connection is crusty or not shiny, reheat the connection until you see the solder flow smoothly and then allow it to cool again.

Do not use excessive flux or excessive amounts of solder to avoid the solder wicking all the way into the moving contact pieces. You do not want to damage the moving parts by getting solder on them.

Recheck all wiring to be sure you have reconnected the wires correctly. Be sure to use the correct screws and star-washers to secure the various parts to the chassis.

[Joseph W Strickland]

I want to add a couple of comments about the above information.

1) The Early production 800B models may not necessarily use the same wire color codes. You will need to make your own mark-up where you encounter differences with your existing unit. (Mine does not match the Late version completely).

2) The contact lugs that have two or more wires soldered to them, I grouped together and put a small nylon cable tie around them to keep them together to make it easier to identify which wires went together when reinstalling the replacement relay/switch assembly.

3) After another look at the top side of the radio tuner chassis, I see that it is not necessary to remove the chrome cover over the RF compartment in order to remove or install the two screws that hold the relay/switch assembly to the chassis metal. The two screws are easily visible with the chrome cover in place.

4) Before installing a replacement relay/switch assembly in the chassis, check and re-lubricate the moving pivot points and shaft of the switch where it passes through the axle sleeve of the switch shaft. You want the part to move freely after installation. It is far easier to do this while the switch is outside the unit than after it is installed in the chassis.

I took another look at my Early version 800B wiring in that area and it has more plastic insulated wires to/from the relay/switch assembly than the Late version. More variations may well exist than what I have covered in regard to wire colors. Using some acrylic or vinyl paint to apply identifying color dots to aid in your particular situation and wire types/colors if such color dots do not already exist would be helpful during reassembly.

Be aware that the relay coils are different between the Early and Late versions of the 800B. In the case of the K1 relay SW 6A/B assembly the AC voltage rating of the coils is 24VAC in both cases, but the late version has a higher DC resistance and impedance, so it uses less AC current. Some of the other relays used in the two cases are different as to AC working voltage rating, so be careful about replacement and make other necessary wiring changes if using parts from dis-similar versions.

Joe

[Joseph W Strickland]

Here are some pictures of the K1 relay SW 6A/B assembly:

The first two pictures show swith 6A in each of its two positions. You can see which connections are made and broken between the two conditions. The last picture shows the relay/switch assembly top surface that mates with the chassis metal to secure it to the chassis. Those two screw holes are tapped so that extra hardware is not needed - just the two screws and star-washers applied from the top of the chassis.

Joe

[Joseph W Strickland]

In the third picture above you can see that the rear lug of the relay coil on the right side is broken off. This happened because I tried too hard to un-solder the large cloth covered wire from that lug. Unfortunately someone at the factory had wrapped the wire around the lug so tightly that trying to get it off required too much force. I should have just clipped the wire off.

Today I managed to make a new solder lug from some of the copper strap material I have. I used a 2-56 screw, nut and two star-washers to secure the new lug to the bakelite. The corner of the bakelite broke off as I was removing the remains of the original lug. I had a thin piece of Bakelite that I made a small back-up plate for the original bakelite and put it all back together using some 2-part epoxy to make the area sturdy again. The unit will sit undisturbed 24 hours for a full cure of the epoxy.

This relay will be used in a repair later.

Joe