Hagerman trumpet mc or Ear 834 classic phono pre amplifier.

I have heard changes generated in a Phonostage as a result of the design put in place for the Phonostage >  Power Amp Interface.

I have referenced this experience within other Threads on the Gon.

In a nut shell the Wire used as the Signal Path in the umbilical is PC Triple C.

The Cable Terminations were exchanged from the Manufacturers to Low Eddy RCA Connectors. The Phonostage Chassis Input / Output RCA's were exchanges from a Solid Copper RCA Connector to a Solid Copper Low Eddy RCA Connector being the dame brand as used on Cables.

There are other control measures in use that can be read about within other Threads.

The outcome being the Low Eddy Interfaces, where the assessment has been of the End Sound being produced, has substantially surpassed the Pure Copper Chassis RCA and Manufacturers RCA option.

I have now learnt that investing in this area, is as important as investing in the Circuit.

In the case of the H'man, the circuit already in use may be discovered to be more that adequate when an Interface between downstream devices is addressed.

Swapping out Valves can be costly, I know the types which are needed and have been demo'd a large selection of iptions from the 50' - 70's.

I know the cost of the 60's Vintage ECC 83 Valves and getting the selection correct for a Phonostage can for the unsupported be extremely costly.

I have bought Vintage Valves for owned Phonostages of which one design has a circuit that used the ECC 83 Valve Type.

Each Valve when received to be used in a Phonostage has been checked for being near prime as an example. Valves selected for committing to a purchase are almost identical in their measurements taken on each Valve Half and across each Valve selected to be used. 

A Quad set of perfectly matched Vintage Valves or more recent production Valves, expected to be supplied is a Fantasy. As a buyer it is not even a guarantee to get the correct circuit match of Valves if substantial monies are parted with to a very very trust worthy seller.

When without a support to be able to investigate what is purchased, the buying comes with an extremely high risk for the not achieving a matched circuit. 

I own Valve Hybrid - Valve Input / Out and SS Phon's, I take the first amplification, adding gain, to the Cartridges sent signal in a way that is very very focused on what is the best basics that I can put in place for the circuit.

I now have a new objective, which is what is the very best basics I can put in place for the interface between required umbilical's and other devices.            

fastricky, I have never seen a schematic of the Trumpet, but chances are the 12AU7s are not doing any "heavy lifting".  Chances are they are used as cathode followers in that circuit.  A CF does not add gain; its job is to convert voltage to current or in other words to provide a low output impedance so as to drive downstream components (a linestage most likely).  Because the CF does not add gain, it is less likely to color the sound. Now to repeat what I have said here many times before: 12AU7 is not a great sounding tube, no matter how much you pay for them or how exotic the brand. You can usually replace them with 6FQ7 or 12FQ7 (depending upon the filament voltage in the component), which are relatively cheap and to my ears audibly better sounding even as a CF in an output circuit of a phono stage or linestage. That is my opinion based on trials and errors in more than one instance.

After swapping out the first row of 12ax7s yesterday I can confirm that made a big impact.