UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Attenuators

Argus25 · 12th Dec 2017, 10:46 pm

Nice work on the attenuator, it will be a useful device to have on hand.

I have used the Teledyne relays mainly as band change switches for my home brew MW-SW radios that go to 18MHz, so any lead inductance or capacitance issues were not a problem. I did this because I could use a miniature robust high capacitance industrial grade motor switch on the front panel. In my Fetron radio I used latching versions to save power and pulsed them via capacitors.

I found something here: there is significant cross coupling between the leads (in high impedance circuits), this caused feedback and oscillations in my high gain RF amp circuits, unless the body of the relay is grounded. So , not wanting to solder to it I made a spring 1 turn brass wire clip to earth the body. Also found the same issue with Fetrons,with a similar base, the body must be grounded.

I really like the Teledyne relay designs but obviously they start to have some limitations above 200MHz.

It always amazed me how they compressed the design of some into a TO-5 sized metal housing, and they always make plastic relays look cheap and nasty by comparison. I was surprised by the heat dissipation of a TO-5 type that I used to replace a faulty relay in a PM5519 pattern generator, so to be kind to it I put a TO-5 transistor heat sink on it, but it probably didn't need it.

12th Dec 2017, 10:46 pm	#46
Argus25 No Longer a Member Join Date: Oct 2016 Location: Maroochydore, Queensland, Australia. Posts: 2,679	Re: Attenuators - theory and the design of. Nice work on the attenuator, it will be a useful device to have on hand. I have used the Teledyne relays mainly as band change switches for my home brew MW-SW radios that go to 18MHz, so any lead inductance or capacitance issues were not a problem. I did this because I could use a miniature robust high capacitance industrial grade motor switch on the front panel. In my Fetron radio I used latching versions to save power and pulsed them via capacitors. I found something here: there is significant cross coupling between the leads (in high impedance circuits), this caused feedback and oscillations in my high gain RF amp circuits, unless the body of the relay is grounded. So , not wanting to solder to it I made a spring 1 turn brass wire clip to earth the body. Also found the same issue with Fetrons,with a similar base, the body must be grounded. I really like the Teledyne relay designs but obviously they start to have some limitations above 200MHz. It always amazed me how they compressed the design of some into a TO-5 sized metal housing, and they always make plastic relays look cheap and nasty by comparison. I was surprised by the heat dissipation of a TO-5 type that I used to replace a faulty relay in a PM5519 pattern generator, so to be kind to it I put a TO-5 transistor heat sink on it, but it probably didn't need it.