UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Heathkit IM-28 VTVM

WaveyDipole · 11th Oct 2019, 5:59 pm

Colin, that sounds like a sound plan. I will try 120v first, but unfortunately I don't have a variac, but I can certainly use a 40w bulb to drop the current. There is a back round cable retainer of the very common type, but this flat rigid 3-core cable looks rather awkward in it. I will be replacing this with a piece of round flex. If it runs off the UK mains then I will use a UK standard plug. If not, then I have a step down transformer that I can use with it.

What you say about C1 makes sense, but can I clarify. You say that V-7A VTVM uses a 0.01 uF, 1600 V capacitor? This IM-28 uses a 0.047uF (47nF), my proposed replacement is 0.1uF (100nF). Can I just confirm that you did mean 0.01uF and not 0.1uF? If its 0.1uF, then it seems worth a try, but if its 0.01uF then I'm not so sure?

11th Oct 2019, 5:59 pm	#7
WaveyDipole Nonode Join Date: Mar 2013 Location: Leicester, UK Posts: 2,535	Re: Heathkit IM-28 VTVM Colin, that sounds like a sound plan. I will try 120v first, but unfortunately I don't have a variac, but I can certainly use a 40w bulb to drop the current. There is a back round cable retainer of the very common type, but this flat rigid 3-core cable looks rather awkward in it. I will be replacing this with a piece of round flex. If it runs off the UK mains then I will use a UK standard plug. If not, then I have a step down transformer that I can use with it. What you say about C1 makes sense, but can I clarify. You say that V-7A VTVM uses a 0.01 uF, 1600 V capacitor? This IM-28 uses a 0.047uF (47nF), my proposed replacement is 0.1uF (100nF). Can I just confirm that you did mean 0.01uF and not 0.1uF? If its 0.1uF, then it seems worth a try, but if its 0.01uF then I'm not so sure?