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Tube rolling in Hagerman Trumpet MC

I have been doing some tube rolling in the Trumpet MC and am trying to be a sure as I can that I don't substitute a tube that could cause a problem.

It looks like from my very poor reading of the schematics that the V1 12ax7's are for initial gain pre RIAA, the second pair V2 are phase splitter post RIAA, and the 12au7's V3 are driver/output/cathode follower (not sure about that last one as the circuit doe not look like a typical cathode follower circuit and even looks like anode follower?).  Any enlightenment here would be helpful.  This is because even tubes that are considered "drop in" substitutes are not actually identical on the manufacturer spec sheets.  For instance the 5418 has a slightly higher heater current than and au7 and there might be another parameter that is different (Vhk?).  Even the 7316 is slightly different.  And of course the 5751 has lower gain than a ax7 as well as other differences.  Many of the differences are still within spec, and given what I can see from the online schematic of the Trumpet MC, look like no problem, but I just want to make sure.  I have emailed Jim Hagerman and he has been helpful when I have, but I hate to keep bugging him with my questions, so I will bug you guys instead.

Thanks for you help and the bandwidth.

oceanica
oceanica OP
83 posts
 

I would like to know as well...

billpete
396 posts
 

So would I 

jimbennet
193 posts
 

First poster is asking about 12AX7s not 6SN7. The JJ E83CC is the most clear 12AX7  you can buy. Outperforms $200 Mullard 12AX7 long plate.

oceanica OP
83 posts
 

I am the OP, I have an amp that uses the 6SN7 tube that is why I was interested in @pindac opinion.  Have tried JJ in my equipment, not impressed.  I like the Siemens and Telefunken much better.  

lewm
14,650 posts
 

Oceanica, As you may know, within a given brand name one probably ought not to generalize, or to put it more clearly, if you like the TFK ECC83/12AX7 best of all 12AX7s, it does not necessarily follow that a TFK ECC82 will be similarly ranked if you heard a variety of different brands.  Then too, there were cases where a tube bearing one brand name may not have been manufactured in a factory owned by that brand. (An RCA branded tube might actually have been manufactured by Sylvania in a Sylvania factory, for one hypothetical example.) This even applies to venerated NOS tubes and is an accepted situation.  The real tube gurus know enough to spot these anomalies.  I am not one of them.

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