Dumont RA-103...yep...Delay Relay Open

[Chris K]

I've searched through the forum and found several threads with solutions but I'm wondering if there's a consensus on the best setup to replace this failure prone unit. I'm installing a 12QP4 with an ion trap so the delay warmup really isn't necessary??? I don't know if that's the only reason for it. Can I just close it and not worry about it?

[Yamamaya42]

Originally Posted by Chris K

I've searched through the forum and found several threads with solutions but I'm wondering if there's a consensus on the best setup to replace this failure prone unit. I'm installing a 12QP4 with an ion trap so the delay warmup really isn't necessary??? I don't know if that's the only reason for it. Can I just close it and not worry about it?

The relay is there to protect the caps from the classic inrush at power up.

given that C6 is rated at 4uf at 150v, a good guess is that coil voltage was around 100v
so something like this may work.

https://www.mouser.com/ProductDetail...0X22clig%3D%3D
never hurts to try!

[Tim]

It is a 5000 ohm coil Potter & Brumfield plate relay designed for this application, to delay B+. I have several NOS original manufacturer replacements available. PM if interested.

[Chris K]

PM sent!!

[Electronic M]

Originally Posted by Tim

It is a 5000 ohm coil Potter & Brumfield plate relay designed for this application, to delay B+. I have several NOS original manufacturer replacements available. PM if interested.

If you have another you can spare after Chris gets his, I'd be interested in buying it from you at the ETF.

[Tim]

I have several. See you at ETF.

[Chris K]

Originally Posted by Tim

I have several. See you at ETF.

Hi Tim...sent you a PM. Let me know how you would like to proceed. I got your message as to price and all sounds good.

[Chris K]

Looks like the 25W 6K power resistor is gone on this as well. Ohmite to the rescue. I just hope it fits in the HV cage!

[Chris K]

The Culprit

[Chris K]

I’m a bit confused about wiring this new relay. It’s a little different from the original and there’s something of a mess in here anyway. Looks like the socket for V218, the 5U4, was replaced and instead of desoldering wires from the unused pin sockets used as tie points, someone cut the soldering tabs for socket pins 7 and 3. I’m looking at the schematic (Riders) where the relay is and the way the old one is wired is strange. Isn’t the pivoting foil that is pulled down by the electromagnet supposed to connect a coil from the transformer secondary to the rest of the set wiring? I know I’m being vague here so I’ll post some pictures tomorrow. The switch works…it closes after about 8 seconds but I don’t think I have it wired correctly. The coil is wired right but I don’t think I have the circuit wired to the switch terminals correctly.

[Tim]

Yes, the red-yel wire from the center tap of the transformer connects to the stationary contact and the other components shown on the schematic connect to the movable contact and feed the rest of the set.

[Chris K]

Ok let me see if I have this correct because, as I said, there was a socket replacement for V218 and the tech just clipped off pins 1 and 7 that were being used as tie points on the old socket so it's a bit of a mess in here.
I have the first terminal on the coil, the one on the right if you are looking at it from the front coil terminal side, connected to pin 5 of V224. I have a 4.7uF electrolytic connected between the two coil terminals, positive on the right coil terminal along with the V224 pin 5 connection and negative on the left coil terminal. I have the red-yel from the transformer connected to the the left, stationary terminal on the coil.

So, if that is correct, my first question is are either of the stationary coil terminals internally connected to the moving arm that is pivoted when the coil activates or the stationary contact it joins with when it moves? If not, do I need to connect the left coil terminal to the contact stationary terminal and the leads from the rectifier tubes, 80uF capacitors/100k resistors network to the moving arm part of the relay? That's what the schematic is suggesting to me but if the coil is attached to either of the contact terminals internally in a way I can't see, that will change everything. Anyway, if that made any sense... Let me know your thoughts!!!

[Tim]

You have the coil connected right. It is not in any way internally connected to the contacts. so yes, you need to connect the left coil to the stationary contact and the capacitors/resistor networks to the moving contact along with the wire(s) that connect to other parts of the chassis. Also, pin 5 of V224 should connect to pin 1 and pins 2 and 7 should be joined with the red-black wire from the transformer.