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Rectifier Tube Rolling in a Modwight LS 36.5DM

I was hoping to get advice, I have been rolling Rectifier tubes in my two box preamp I am blown away how different tubes change the sound ,I own two sets of Mullard GZ37/CV378 a set of GE 5U4GB both vintage early 1960's and a set of stock Sovtek 5AR4 also have a NOS set of 6H30 DR I am trying in the clean  box , both the Mullard's and Dr tubes only have about  five hours of run in time but the sound seems defused on the top end ok on the bass the GE Tubes are good in the mids but soft on the highs and bass so far the stock Sovtek seems to sound best ,Dan says try 5R4-GY Tubes, any one tell me about  the Mullard's in this preamp I am getting frustrated,  thanks 
goofy
roberjerman
4,319 posts
 
I have found more data: same pin-outs and construction, equivalent electrical characteristics. So the Russians just copied the 6CG7 (including its internal shield). Shame on ARC and others for calling it a "super" tube - and boosting the prices! Another audio "myth" revealed as just clever marketing!
facten
2,947 posts
 
Haven't been able to find any online source that states that the 6CG7 is a drop in replacement for 6H30 ; what did Roger have to say?
goofy's avatar
goofy OP
33 posts
 
Thanks for all your Advice,  I wouldn't have tried using GZ37 MULLARD'S if Dan Wright didn't ok this move  I am still using the Mullard's in both the PS 36.5 and the PS 9.0 with great success, I will watch out for glowing red tubes, thanks again all of you fantastic Audiogon posters 
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mars2k
12 posts
 

Yes don't go all crazy with tube swapping but...well researched substitutions can make a world of difference.  I have a Modwright PS 9.0 that came with Sovtek 5ar4 tube. That one blew after a week.  I replace it with the same tube...6 months and another blow.  I put one last Sovtek in it and worked but sounded like crap. Edgy grainy unlistenable. I'm new to tubes so I started asking Mr. GoogleI settled on NOS Tung Sol 5R4GY which sound so much better. This was not an expensive tube and I learned what rolling could do.  Next I popped for more expensive NOS Phillips 5R4GYS and bang Jackpot!  Now lets see how long this one lasts

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