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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
pindac's avatar
pindac
3,829 posts
 

My most recent experience if Tube Rolling 6SN7 using the KR VT231 Black Glass, as the tube to be compared to as the Base Tube, ended with a unexpected outcome.

In my circuit, two Valves from different Brands, but similar production era's to the KR, showed the KR's as having a artificial bloated bass and not competitive in any way the Bass that was on offer from the other two Valves. The KR fell way short in being able to create the impression the other two Valves were capable of in the Mid's and Highs.

A stated in my circuit on my Power Amp's.    

medium_grade
134 posts
 

@drekow 15v

drekow
4 posts
 

@medium_grade, Thanks.

lewm
14,650 posts
 

Pindac, surely you can reveal what two tubes you preferred over the KR. And if possible, can you say what function in the amp? (Gain, phase splitter, driver?) Thanks.

pindac's avatar
pindac
3,829 posts
 

At this stage, I will say the KR Blacks took quite a period of time to receive Valves which were achieving the measurements my Valve Friend advises to work with for Valves intended to be used as a long-term circuit component.

At this stage, I will also say the KR VT 231 Blacks, were a Valve I was Wed to, and was liking their noticeable capability to add  a tight controlled clout to the lower registers.

It does seem throughout 2024, I was exposed to experiences within audio that were to have a profound effect. During the past year this profound effect has evolved to the place there is an upheaval to what was an unequivocal position on owned audio equipment. This is now quite developed in making changes within the owned audio system. There is a new premise as good as put in place, which will be quite different to what I am very familiar with in my home system when experiencing an End Sound.     

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