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Best Tube for SPUD Amp

juanitox

Member
2006-12-04 12:44 pm
hi , i 'm using a E55L in triode mode for my spud amp and i would like to build another one with a better tube if i could ..
WE437A and EC8020 are out unobtainable and too pricey .

so what are you'r best finding including pentode and triode . television tube etc..
low RP are preferred and not to high plate voltage for my safety .:)
 
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Russian 6E5P (pentode in triode mode), 6C45P
 

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juanitox

Member
2006-12-04 12:44 pm
the E55L is now an expensive tube and rare to find a good Nos pair , on the last pair i 'v bought on eBay one was oscillating and the others ones died in few hours.. the 6EP5 is perhaps not as good as the E55L but it is given as sweet sounding and you van find it for 5$ that's a reason to try it ( ok i'm also getting a little upset about the legend of pricey unobtainable tubes WE437 , EC8020, etc.. )
 
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Shoog

Member
2002-08-15 10:16 pm
Eire
Thats a good enough reason in of itself, but I managed to get 4 E55L (in two lots) for less than €50.00 a pair just over a year ago. There were lots of people asking silly money - but patience paid dividends in the end.

ECL82 makes a very nice, and relatively cheap SPUD. A bit of plate to driver cathode feedback really helps it sing.

Shoog
 
I've tried both the 6E5P and 6P15P. I couldn't get along with the 6E5P so I settled on the 6P15P and in the end I sacrificed gain for 'sound' (my version is switchable between pure pentode mode for high gain and a different mode with frequency dependent feedback which is something you might want). You might want to take a different path altogether of course.

There was a popular spud amp based on the EL84 (similar to 6P15P) on the Hawthorne forum that derives from an original design by a chap called Jef Larson. I've posted the schematic here: http://www.diyaudio.com/forums/tubes-valves/280167-yukon-gold-spud-amp.html
 
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juanitox

Member
2006-12-04 12:44 pm
thanks biggun but i have made few tiny 2 stage to one stage amplifier with 6P15P (EL84) and just don't like the sound with a magnequest 5K output transformer. same with the WE417A so i came to the conclusion that i prefer the sounds ( or distorsions) of low RP tubes and prefer to stay with 2.5 / 3.5K output transfo . even with the E55L i have made some test with a james transformer between 2.5 3.5 and 5K and prefer the 3.5K load by a large margin . that 's why i'm now using a Lundhal 1664 50ma
and sooner a Monolith magnetics Summit 3.3K .
past years i have build dozen of 2 stage SET : 26 / AD1 26/RS241
WE717A / WE421A and multiple driver too ..
all if theses sounds very nice but the " ultimate spud amp " i 'm trying to build sounds more "direct" to me . it's just a feeling not a fact :)
this is my way to build it: fullwave Rectifier 5R4GY LCLC with MKP and PIO cap , Ac heater , fixed bias with nothing on the cathode ( very important for me) , nickel choke on the grid with lithium coin battery for the bias. less parts means more time to fine tune them

in this config the E55L is extremely fast ( too fast ?) transparent and vivid with extended highs and lows . i only need a little more mellow or sugar on the cake.
thats 's why i want to try other Low RP tubes to see if it is this design who have this sound signature or if it is the E55L.
 
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juanitox

Member
2006-12-04 12:44 pm
thanks shoog
ferite beads are everywhere 1K grid stopper and 100R between plate and screen , i don't suspect oscillation symptom just a damn fast tube:)
lundahl AM transfo didn't help rounding the edges.. i will see how it goes with the Monolith Magnetic iron
 
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