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

pmmunro · 5th Jul 2005, 1:03 pm

John,

"Official" Avometer test leads are available from both RS (203-5632, £45-00) and Farnell (sorry, I don't have the catalogue to hand). They can also be bought from Avo (Megger) at Dover. If you contact Avo, you might like to buy some spare/replacement terminal caps at the same time.

You may want to pay this price for assured safety but most users are content with less expensive leads.

Gavin,

Thanks for the tip about the article. I would agree that front panel switches need to be treated with great care but not that it is impossible to work on them. In fact, it is a matter of necessity in some cases if a meter has to be repaired. The service manuals give several cautions about working on parts of these meters but the switches don't rate a special mention.

On the earlier post-war models the switches are in two parts; a rotary range switch with a two-part wiper which sandwiches the contacts moulded into the contact ring (rivetted in very early versions) and a function switch with telephone relay type contacts which are operated by face type moulded cams.

The range switch is carried on a die-cast aluminium centre which is pinned to the switch spindle. The two parts of the wiper are separated by nearly square spacers - but not exactly square. If wrongly assembled, the spacer can foul the switch bush making the knob stiff to turn. The exact angle of the wiper tips is also critical to smooth switch operation and should not be disturbed if possible. The tips and contacts do get burnt and sometimes need to be changed.

The function switches can need adjustment and cleaning or replacement. They are just as difficult, or easy, to work on as a Type 3000 relay - except that the adjustment has to be done in situ and the situation is very confined. These contacts have ceramic or plastic lifting pins which are easy to lose. Careful notes and/or photographs taken before dismantling are helpful. Considerable dismantling of the shunt/multiplier boards may be necessary to get access to the switches.

There is no doubt that jigs would be a very useful aid but if they are not available you have to decide whether to devote your time to devising and making jigs to save the, very considerable, time which you will otherwise spend working without them.

PMM

5th Jul 2005, 1:03 pm	#65
pmmunro Octode Join Date: Jul 2004 Location: Dundee, UK. Posts: 1,813	Re: AVO Multimeter survey John, "Official" Avometer test leads are available from both RS (203-5632, £45-00) and Farnell (sorry, I don't have the catalogue to hand). They can also be bought from Avo (Megger) at Dover. If you contact Avo, you might like to buy some spare/replacement terminal caps at the same time. You may want to pay this price for assured safety but most users are content with less expensive leads. Gavin, Thanks for the tip about the article. I would agree that front panel switches need to be treated with great care but not that it is impossible to work on them. In fact, it is a matter of necessity in some cases if a meter has to be repaired. The service manuals give several cautions about working on parts of these meters but the switches don't rate a special mention. On the earlier post-war models the switches are in two parts; a rotary range switch with a two-part wiper which sandwiches the contacts moulded into the contact ring (rivetted in very early versions) and a function switch with telephone relay type contacts which are operated by face type moulded cams. The range switch is carried on a die-cast aluminium centre which is pinned to the switch spindle. The two parts of the wiper are separated by nearly square spacers - but not exactly square. If wrongly assembled, the spacer can foul the switch bush making the knob stiff to turn. The exact angle of the wiper tips is also critical to smooth switch operation and should not be disturbed if possible. The tips and contacts do get burnt and sometimes need to be changed. The function switches can need adjustment and cleaning or replacement. They are just as difficult, or easy, to work on as a Type 3000 relay - except that the adjustment has to be done in situ and the situation is very confined. These contacts have ceramic or plastic lifting pins which are easy to lose. Careful notes and/or photographs taken before dismantling are helpful. Considerable dismantling of the shunt/multiplier boards may be necessary to get access to the switches. There is no doubt that jigs would be a very useful aid but if they are not available you have to decide whether to devote your time to devising and making jigs to save the, very considerable, time which you will otherwise spend working without them. PMM