[Bradley Rush]

I have been working on this one for awhile. Just need tubes and a cal. I hope. I replaced the 3v batteries with a power supply. Pic to follow

[Bradley Rush]

I made a 3v power supply to take the place of batteries

[Bradley Rush]

Few var res and resistors replaced

[Bradley Rush]

New fuse and input jacks

[Bradley Rush]

T2 and 3v power supply

[Bradley Rush]

Connectors

[Bradley Rush]

I tried putting meter protection on. I t allowed only half scale on the meter. I used 1n4000 thru 1n4007 no luck. Any ideas as to why. The meter was slamming side to side until i put a 220uf 35v on. It slows on each side but does not slam.

[Bradley Rush]

I put the battery back same problem with diodes and slamming

[Bradley Rush]

The current on the power supply I built is not enough. Installing a 8amp old monitor power supply. The meter slams what I would call to hard. If i put in a 220 uf it does not hit. It slows down a just before the limits of the meter span. I will start again with the diodes attached to meter. I have been studying the difference between a 232 EICO VTVM. The 209A Hickok is not attached in the same way to the bridge circuit. Does either give better results?

[Bradley Rush]

I read on another forum about the importance of 6SN7 being matched. Is this set up impossible to protect the meter with the diodes?

[Mondial]

You might try connecting several diodes in series in two reverse parallel strings. A single diode will begin conducting at around 0.7 V so if the voltage across the meter coil the exceeds this level the diode will conduct and affect the meter reading. 

If you connect three diodes in series, conduction will not start until about 2 V which should not affect the indicated reading and still afford some protection.

[Bradley Rush]

Is this what you mean?

[Bradley Rush]

I found several mistakes I put in. They are fixed. During finding these I found at least four very leaky resistors. So im replacing all of the carbon resistors.  R57 300K  was very leaky. Read 330K then would drop to 280K.  R58 20K was very high read (39K) . I have only been testing the Ohms circuit. All others in the bridge circuit were dead on.

[Mondial]

Is this what you mean?

Yes, that is exactly what I mean. The meter is protected from both positive and negative excessive current and with three series diodes it should not affect the readings.

It is somewhat important that the two triode sections of the 6SN7 match. If one section has a cathode that heats faster, it will conduct first and could slam the meter. You can try some other 6SN7 tubes and see if it makes a difference.

[Bradley Rush]

Pic of most of the resistors replaced. Three more to go.