Test Equipment Anonymous

Here's a thread for us to talk about Simpson meters.

Let's start with that Canadian Made Bach-Simpson 260 Series 5P with the 661 DC current adapter that was in the lot of apparently very questionable equipment I picked up yesterday.





That's the whole unit together. I was ohming out the current shunts on each range to make sure they weren't open and they checked out for continuity. I don't know what values they should be and if they've drifted but low resistances like current shunts should really be checked with a four wire setup if not a milliohm meter.





Quick and dirty test jig looping a power supply through an 8 ohm dummy load so as to not generate into a near-short and then through the 1 A range terminal on the 661. A quick check with the 3478A confirms continuity and a combined total resistance that looks plausible given how loosely I was one handed holding the minigrabber clips onto the banana plugs.



I set the 260 to 50 VDC and got no deflection so I pulled the 661 off and went direct from the power supply in and ran it up to near the top of its 20 V range and the 260's 50 volt range looks good at first glance so I'm going to have to pull the instructions for the 661 adapter later and see what I'm doing wrong and maybe test it independently and see what voltages are present on its back panel banana plugs that seat into the meter.

A friend want's to go for dinner so I'm going to take a break for now. More later.

It looks as if that poor meter has been in the wars. At least at first glance, the movement is OK.

I have a couple of AVO meters, which both work. I rarely use them. It's a strange thing to explain, but I'm glad I've got them, because when I'm out and about and see them for sale, it's fairly easy to resist buying another.

Zenith wrote: ↑Fri Mar 10, 2023 2:49 pm It looks as if that poor meter has been in the wars. At least at first glance, the movement is OK.

I have a couple of AVO meters, which both work. I rarely use them. It's a strange thing to explain, but I'm glad I've got them, because when I'm out and about and see them for sale, it's fairly easy to resist buying another.

Smirk

While picking something else up, I might be able to pick up some of these if you (or anyone else nearby) are interested...

Tek 2445, 2445A, 2445B, 2465, 2465B, and a couple of spare CRTs and other salvaged parts/boards.
Tek TDS-210 Fluke PM3084 Iwatsu SS-7840H Kenwood CS-6040 Topward 4303D
Thurlby PL320 with K2 Module

Assume they all need work; the Thurlby is old brown variant, and various spoke generators have kicked into action.

I'll send you a PM.

Zenith wrote: ↑Fri Mar 10, 2023 2:49 pm It looks as if that poor meter has been in the wars. At least at first glance, the movement is OK.

I have a couple of AVO meters, which both work. I rarely use them. It's a strange thing to explain, but I'm glad I've got them, because when I'm out and about and see them for sale, it's fairly easy to resist buying another.

As much as I love these analogue meters, I don't use them as often as I should. The go-to for me on the bench are the HP 3457A and two 3478A beneath it unless I need more voltage range or functions present on the two 34401A. It isn't like I'm lacking for DMMs on the bench and it definitely isn't as though I'm lacking for handheld DMMs in any way either. You're right about the condition though, everything in this lot is dirty.

First project was to change out the speakers in the workshop stereo system for a pair of floor standing B & Ws I picked up cheap from a pawn shop during the pandemic so I can free up the shelf space being occupied by the bookshelf speakers I had been using and get better bass response. The bass situation has been resolved if not over corrected. Then I decided to take another crack at the Simpson 260 + 661 DC ammeter combo this evening starting with taking the 661 apart to reverse engineer it and see how it should work since I couldn't find any manuals online.



This is what I'd expect with the string of current shunts but the pigtail with the banana plug was a surprise.



Looking at how the switch is wired and tracing it out, the + and - banana plugs that seat into the jacks on the meter are only in circuit if the switch is in the 260 Direct position. Only the - plug is when the switch is thrown to 661 but the pigtail is brought into circuit. Considering the brief instruction on the front of the adapter to "Set 260 to +50 VDC / Use DCV ranges", the only way this makes sense on the meter with the exposed sockets to plug the pigtail into is the 50 uA socket which also agrees with the 50 V DC range also having a 50 uA subscript. I should've clued in the other night that the voltage rise across the shunts even at 25 A isn't going to be enough to produce any meaningful deflection on the 50 V scale. What Simpson clearly intends to do is have a 50 uA full scale current output siphoned off the shunts directly on to the meter movement in the 260 which is also 50 uA full scale via the 50 VDC range switch position and the corresponding current input on the front panel via the pigtail.



I reassembled the 661 and put it back on the 260, reconnected the test setup and ohmed the current loop out then plug into the power supply and test.



We have an amp going out.



We have an amp going through.



And we're registering an amp going through on the Simpson 661 + 260 combo. This is fantastic - it's taking a bit of work but some of the duds in that lot of equipment are starting to come together. I'll see if I can dig into that 372 ohmmeter tomorrow.

The thing about old analogue meters is that they are very handy when working on very old equipment when voltages written down on the service charts would have been more than likely taken using a meter with 20,000opv impedance and anything else would provide you with misleading results. Also of course they are very handy when aligning a radio IF section as it is far easier and quicker than trying to tune for max output using a DMM with the digits jumping all over the place. I have plenty of AVO's and other analogue meters at my disposal, but have not used then in earnest for some time now, I might consider flipping some soon.