[Test-Equipment] Lafayette VTVM

[k4pf at juno.com]

> Ron Bussiere via Test-Equipment <test-equipment at mailman.qth.net> wrote

>Hi. I just purchased a Lafayette VTVM model 174. This is a pretty unusual VTVM. It is unclear if it was a kit or not.......
It is in mint condition but not quite working correctly. Although the case states just Model 174, it may indeed be a KT-174.
I have had this dilemma before. I purchased a KT-208, which is a signal generator/tracer, which may or not have been factory wired. 
The KT-208 is identical to the Accurate Instruments 154.

>The VTVM is 'unusual' in that it uses a 12AX7 (which is marked on the PC board), and a 6BL8 alongside. The 6BL8 nomenclature is NOT marked on the board, so, I'm not even sure if it's the correct tube.The usual other VTVM tube is a 6AL5, right? <snip>

Hi, Ron

The Sams publication "Know Your VOM-VTVM" by Joseph A. Risse, 1963,
has a description and a schematic for the KT-174.  It shows a 6BN8
and a 12AU7.  The 6BN8 triode section serves as an amplifier before the dual-diode section of the 6BN8 (peak to peak ac rectifier),  
allowing measurements of lower ac voltages.  

The 12AU7 acts as the standard dc bridge amplifier for the meter. 

73,
Ed Knobloch