SUT With a Manley Steelhead RC?

I've been demo'd through Tube Rolling the 50's CCa and the 60's Holy Grail, along side same Brand and other Brands Tubes through to the 80's Production.

All Tubes were above Factory Spec, with each Pair being almost identical in their Test Readings. 

There are a few Brands from the 60's that have equal impression with a slight difference to the end sonic.

The CCa and Holy Grails are very Similar, extended periods of time used for comparison might reveal a little more than I detected. 

As a result of the cost required to purchase at the time of my acquiring Vintage Valves, I got a very respectable matched pair of Holy Grails, via two different suppliers at a steal.

I also to date, have acquired a non Siemens Brand from early 60's Production as well, both flavours were seen as equal in value. 

rdk, where did you get the 50mV spec for phono overload? Since the Steelhead has both MC and MM inputs, and since MM inputs generally tolerate much higher signal voltages than MC inputs, there ought to be two different specs for phono overload, one for MC inputs and one for MM. The output from any SUT ought to be connected to MM inputs, and the gain set for the minimum 50db.

By the way , using a 0.5mV cartridge with a SUT that has a 1:20 gain factor into an MM stage that provides 50db gain is way overkill so far as total phono gain. Most MM stages proved 38 to 45db gain, typically 40db. 1:10 ought to be more than sufficient, with that cartridge into the Steelhead’s MM stage.

@lewm - specs at https://www.manley.com/hifi/mshlr  However, there are two numbers listed 50 mV and 93 mV at various dB levels - the 50 mV likely at the lower 50 dB gain.

Usually the overload margin is inversely related to phono gain. I read the spec sheet too and it’s ambiguous Anyway the real problem is using a 1:20 SUT. in the first place.