V72 canonical voltages

[jeffbro]

I am trying to sort out a V72 that has DC voltages all over the map. When I searched to find what they should really be I found a surprising and frustrating variety of values. I've collected some of them on the attached schematic.

Is there an official V72 voltage chart I have failed to find? Or does the GDIY group mind have a consensus set of values?

 

[CJ]

I bet that when someone does a rebuild that they replace the toxic and failure probe selenium rectifiers with 1N4007's that the lessened fwd voltage drop across the rectifiers is causing a plethora of readings. (awkward sentence , minus 5 pts)

And if operating the V72 in the US, some provisions have to be made to adapt the 220 mains circuit to 120, which means a step up transformer might be used which could address to the variance depending on the XFMR used.

Then there are the diy versions that could be thrown into the mix.

Original drawings just have a few voltage listed so I feel your pain.

 

[jeffbro]

Original drawings just have a few voltage listed so I feel your pain.

As my friend says..."and that's where the troubles began"

It's frustrating those 1940-50's engineers didn't leave us more information.

 

[CJ]

You can get a pretty good idea by looking at the first half of the v76 schemo which has voltages

First tube 67 plate 97 screen

Second tube 175 plate (because choke loaded)
165 screen 2.3 cathode

 

[Michael Tibes]

I found a surprising and frustrating variety of values.

So did I in real-life measurements on many originals. The dc voltages seem to be more like ballpark numbers than exact science, I atributed that to the many possible tolerances in tubes, transformers, coils and selen rectifiers. Audio measurements seem more useful to me in order to determin if the unit is ok, but dc checks will show if something is obviously totally off or needs to be investigated.