Need 7 and 9 megaohm resistors, where to get?

Thread Starter

ScottCT

Joined Feb 17, 2009
3
For a Heathkit VTVM, need 1% resistors at least 1/2 watt, 7 and 9 megaohms.
Any idea where to get them, Mouser and Digikey no have.

TY
Scott
 

strantor

Joined Oct 3, 2010
5,033
For a Heathkit VTVM, need 1% resistors at least 1/2 watt, 7 and 9 megaohms.
Any idea where to get them, Mouser and Digikey no have.

TY
Scott
Why do you need at least half watt?
It would take at least 2,100V to dissipate 1/2W into a 9Mohm resistor.
 
strantor said:
Why do you need at least half watt?
It would take at least 2,100V to dissipate 1/2W into a 9Mohm resistor.{/quote]

With a 1000 V input (guessing) and a 2x safety factor, that isn't to bad.

I had to buy a 1 Meg 200 W resistor once and on the other side of the scale a 0.5 ohm adjustable resistor rated at 1000 W and I did buy a few 400 M resistor onec.
 

GopherT

Joined Nov 23, 2012
7,983
When I googled "Heathkit VTVM" I saw a bunch of VOMs that only measured up to 15VDC.
They are reference resistors for the vacuum tubes. I think 1/2 watt is recommended to limit heat extremes of "properly" sized resistors and limit heat effects on accuracy.
 

Thread Starter

ScottCT

Joined Feb 17, 2009
3
The 7 and 9 megaohm are part of the main voltage divider reference. The existing ones have drifted a little high, which throws off
voltage readings. Ohmcraft might be a possibility if they will sell one off. TY Keepitsimple
 

JohnInTX

Joined Jun 26, 2012
3,801
Here's a search at Mouser that gets pretty close. 9.09M 1/2 Watt, 6.81M .4W, in stock. Monkey around with the filters for other close ones. Lots more 1/8Watts. Maybe parallel a couple. Vishay is a good go-to for things like this.
 
Top