We visit the Heathkit IM11 VTVM Vacuum Tube Volt Meter again and fix all of the precision resistors out of specification and replace them and do another recalibration.
I am working on fixing a Heathkit IM-18 at the moment, and I am having to change all of the resistors (including the precision resistors)! Its actually fun working on these older equipment, especially the challenge of finding the resistors and making sure that the higher value resistors such as the 7M and the 900K can handle the higher voltage drop. I am just really surprised that all of the precision ones were so far out of tolerance!
note that 12AT7/12AV7/12AZ7 are adequate, verified substitutes for the 12AU7 . 12AU7s are getting expensive and 12AV7 or 12AZ7 can still be found NOS at low cost.
My VTVM is very unstable...even new. I have check everything, the tolerance of components is NOT the problem but the bridge that Heathkit use is flaw. Anything leaking will unbalance it. So this is a piece of s****.
![มองหน้ากันไม่ติด (Awkward) - โอ๊ต ปราโมทย์ FEAT. MAIYARAP [Official MV]](http://i.ytimg.com/vi/4b02SY_r6Gw/mqdefault.jpg)
I am working on fixing a Heathkit IM-18 at the moment, and I am having to change all of the resistors (including the precision resistors)! Its actually fun working on these older equipment, especially the challenge of finding the resistors and making sure that the higher value resistors such as the 7M and the 900K can handle the higher voltage drop. I am just really surprised that all of the precision ones were so far out of tolerance!
note that 12AT7/12AV7/12AZ7 are adequate, verified substitutes for the 12AU7 . 12AU7s are getting expensive and 12AV7 or 12AZ7 can still be found NOS at low cost.
Good meter, good video!
@Retro Tech & Electronics
How do you now the resistors are out of spec. Unless you measure them.
At
The cal pots are compensation for the precision resistors.
What probe type VTVM i have missing test probe
Hmm not another parts changer, shot gun technique. The recap crew?
All the pots are fudge " factors" for ok op.
Good video. Just a small beef.....you keep saying "collaborated" when you actually mean "corroborated".
EICO 232 layout is better, cal pots are accessible.
My VTVM is very unstable...even new. I have check everything, the tolerance of components is NOT the problem but the bridge that Heathkit use is flaw. Anything leaking will unbalance it. So this is a piece of s****.