Best Tube for SPUD Amp

[juanitox]

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 .🙂

 

[matejsirk]

Russian 6E5P (pentode in triode mode), 6C45P

 

[rock4016]

12GN7 pentode
6CL6 pentode
6p15p pentode

All work as Spud amps. Then you have the triode + pentode in one bottle tubes like the 6LR8, 6LU8 and also dual triode (dissimilar) 6EM7 and many others.

 

[juanitox]

thanks , i think 6P15P ( el84) have not enough gain for a spud amp .
6EM7 or 6E5P will like 5K loading.

i would like to stay with my 3.3K output transformer.

 

[smoking-amp]

Some TV triode+pentode types: 6LU8, 6AG9, 6AH9, 8AL9, 6LR8

 

[euro21]

6HV5A...7W... but with 10k OPT and over 1kV B+ it's presumably out of your range of interest. 🙂

 

[juanitox]

OK OK! a lot of candidates here but let me change my question:

TUBE for SPud Amp if you have too keep only ONE

 

[mwiebe]

The E55L spud has been my favorite. A 6S45 or 6E5P/6E6P (trioded) work fine with 3K load for me.
Matt

 

[rock4016]

thanks , i think 6P15P ( el84) have not enough gain for a spud amp .
6EM7 or 6E5P will like 5K loading.

i would like to stay with my 3.3K output transformer.

It does have enough gain when fed a 2v source. I know because I built 2 and still use one. Unless your speakers are 87db or lower.

 

[rock4016]

With 3.3k I'd lean towards 12gn7.

 

[juanitox]

thanks rock , so it seems that the 6E5P and the 12GN7
are the most close to the E55L . and they are many on eBay 🙂

 

[juanitox]

6E5P are ordered what is the optimal operation point in triode mode with 3K load ? i used my E55L at 160V 40ma ( 4V bias)

 

[Shoog]

I find it difficult to believe that you will get any better valve for a SPUD than a E55L.
That is what I am running and it is based upon those fantastic curves and a more than adequate mu for the job.

Shoog

 

[juanitox]

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.. )

 

[tomchr]

If you're willing to extend "spud" to include circuits that use one bulb, regardless of how many active structures/tubes are present in the envelope, the list grows to include various TV sweep tubes. 6LR8, 6GF7A, 6KY8, and 6LU8 spring to mind. There are also some that include three tubes within the same bulb.

Tom

 

[Shoog]

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

 

[Bigun]

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

 

[juanitox]

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.

 

[Shoog]

When I built my E55L spud I made sure to put ferrite beads on the g1,g2 and anode to prevent oscillation. Sounds as if these might help your build.

Shoog

 

[juanitox]

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