Heathkit Tube Tester

[Mike Jobe]

I am replacing the meter rectifier in a TC-2....The schematic shows a reversed polarity,..Is this right??

 

[N11778]

I looked at the manual, at first glance it looks backwards but......
Heath Did not make many mistakes in their manuals.
Did you get it to work?

 

[Mike Jobe]

NO

 

[Nigel Goodwin]

Have you tried a diode, and if it didn't work turn it round

 

[cowboybob]

This site has a pretty good discussion about your issue with the TC-2.


In essence, CR-1 (not ID'ed above) can be replaced with a 1N4007 without any issues, except that the 1.2k resistor (shown as "1200Ω" in the schematic) may have to be adjusted so the meter can be accurately zeroed.

 

[N11778]

Looks like the diode is only used for setting the line voltage.
Is this the diagram you have.

 

[Mike Jobe]

yes, but the diode polarity is reversed with respect to meter polarity

 

[cowboybob]

Yes, it is.

Have you tried putting the new (or old, for that matter) diode into the circuit in reverse of the schematic (as Nigel offered in post#4)? That action certainly won't hurt the diode.

The site I referenced had a post stating that HK screwed this one up (hard as that may be to believe ). Even suggested that the Knight(Kit) 600 schematic had it right... (and you'll note that it is, indeed, reversed from the HK schematic).

 

[JonSea]

Is the diode there to clamp the max voltage the meter will see?

 

[cowboybob]

Is the diode there to clamp the max voltage the meter will see?

Only to the extent that it's internal resistance influences the circuit (which isn't much).

Its primary purpose is to rectify the AC to provide a "rough" DC (no filtering) for the DC mA meter,

 

[Mike Jobe]

Yes, I also have a KK 600 schematic that is nearly identical, showing diode installed the opposite of the Heathkit....I will try reversing the polarity, should fix the problem.