Cheap scope: worth installing bnc jacks?

[Luthier Vandros]

Hi, all. I have a few nice scopes and a cute little BK 1403a (5mhz) followed me home. What a fun little guy!  It’s got banana jacks across the inputs and I was wondering if installing bnc’s would be worth it. The vertical input sits at 1mΩ and I’m only using it to monitor waveforms for audio work. I have more sophisticated scopes for more detailed work. Unsure of the implications. TIA!

[ledtester]

Having a BNC connector would make it possible to use a standard scope probe.

The input impedance of the 1403A is 1 Mohm (+/- 20%) shunted by 30pf (max.).

Attached is some advice from another forum:

https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/equipment-usage-soldering-techniques-and-reviews/3157108-vintage-bk-precision-1403-oscilloscope

[Luthier Vandros]

Very helpful, thank you. Would I go for the standard 50Ω ?

[ledtester]

Very helpful, thank you. Would I go for the standard 50Ω ?

50 ohms doesn't really come into play when talking about oscilloscope probes.

At 8:30 in this video Dave shows the schematic of a switchable 1X/10X probe:

https://youtu.be/OiAmER1OJh4?t=8m30s

The main point is that having a BNC connector would make it easier to connect things to the scope and the 1403A has the standard input impedance that a scope probe expects.

[Luthier Vandros]

Understood. Thank you

[BillyO]

I don't know if you have the room, but if you go with the BNC connectors you might also want to add a switchable 50 ohm load.  Sometimes you might want to drive the scope directly from a 50 ohm source though a 50 ohm coax.  Not really important but nice bling if you can do it.

[bdunham7]

Hi, all. I have a few nice scopes and a cute little BK 1403a (5mhz) followed me home. What a fun little guy!  It’s got banana jacks across the inputs and I was wondering if installing bnc’s would be worth it. The vertical input sits at 1mΩ and I’m only using it to monitor waveforms for audio work. I have more sophisticated scopes for more detailed work. Unsure of the implications. TIA!

If the inputs are 3/4" apart you can use a simple BNC-to-dual banana adapter (e.g. Pomona 1269) if you want to use a standard scope probe.  I would personally not want to hack up the scope to put a BNC connector on it and there isn't going to be any performance improvement from doing so.

[BillyO]

If the inputs are 3/4" apart you can use a simple BNC-to-dual banana adapter (e.g. Pomona 1269) if you want to use a standard scope probe.

This is a great option too if you can manage it.  You can always wrap a 50 ohm resistor around the base of the adapter prongs.  Been done before.

[tooki]

Very helpful, thank you. Would I go for the standard 50Ω ?

50 ohms doesn't really come into play when talking about oscilloscope probes.

Yes it does, insofar as you don’t want to use 75 ohm BNC jacks.

[radiolistener]

Oh, these days this is more a museum exhibit than oscilloscope.
It would be blasphemy to deface museum exhibits 

[pcprogrammer]

Hi, all. I have a few nice scopes and a cute little BK 1403a (5mhz) followed me home. What a fun little guy!  It’s got banana jacks across the inputs and I was wondering if installing bnc’s would be worth it. The vertical input sits at 1mΩ and I’m only using it to monitor waveforms for audio work. I have more sophisticated scopes for more detailed work. Unsure of the implications. TIA!

If the inputs are 3/4" apart you can use a simple BNC-to-dual banana adapter (e.g. Pomona 1269) if you want to use a standard scope probe.  I would personally not want to hack up the scope to put a BNC connector on it and there isn't going to be any performance improvement from doing so.

That would be my choice to. Cheap ones on Aliexpress: https://nl.aliexpress.com/item/1005006137934895.html

[Gyro]

If you do use a BNC to dual 4mm plug adapter, which sounds like an excellent solution, be very careful with the orientation of the adapter. If you accidentally get the adapter the wrong way round, you will have the probe tip going to the (probably earthed) 4mm ground socket. This could give you a nasty surprise if you happen to be using a X1 probe. I recommend extra marking, a blob of Red paint for instance.