Rivera 55 tube selection

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Tubetec

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Nov 18, 2015
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Arrived to me with a fairly nasty set of EL34 (PM Brand) , known for 40% less power and being mechanically unstable .
He's complaining of low power /crappy sound ,
I see this unit can handle anything from an EL34 to a 6L6 to a 6550 ,
He tells me he wants all the clean he can get out of it , Its possible to crank the bias down to -52 and slot a set of 6550's in ,
Compared to whats in the amp now that would be a jaw dropping  jump in headroom ,a good set of 5881's would be almost as good but still a massive boost from where he is now ,

He's given me the go ahead ,so I think I'll send him back an amp that produces more like 150% of the specified power compared to about 50% at the moment , I'll give those tubes 24 hours to burn in and make sure chassis/mains tx temperatures stay reasonable .  Its often metal players who opt for the 6550 tube , just wondered if anyone chooses to run it just for the extra clean headroom alone .
 
I’ve had 6550s in my 50 w Marshall but went back to el34 for the grind.  It puts out around 40w clean.  I had kt66s In it .  They were clean and kind of Glassy sounding.  Still went back to 34s.  I had new old stock Vavos’s that were that old Marshall 60’s sound and were glorious in the amp.  I’ve never had new brands sound like those Valvos.    It’s like modern gas and the old tetra ethylene.  Your engine runs like you added 2 extra cylinders with a supercharger,  while you destroy the air around you.  Same air is destroyed with a crank Marshall.  Those days are long gone.    Try the 6550s.  I have 2 sets of original GE.  I might try them as well.  They are for some Dyna mark 3 poweramps that never get turned on these days.  Makes a good sounding space heater though . :D
 
Tubetec said:
He's given me the go ahead ,so I think I'll send him back an amp that produces more like 150% of the specified power compared to about 50% at the moment
I would not expect any serious increase in output power between a fresh set of EL34's and another equally fresh set of 6550's, because the EL34's already extract the last drop of juice from the psu and OT. Different break-up, yes, but not necessarily more pleasant.
 
In the end I settled for a pair of Sovtek 5881's over the 6550's ,better for reasons of effeciency like Abbey mentioned .

Its  sounds a bit lean and runs a bit cool at  the -47 volts prescribed by the schematic , I think I prefer the break up at -44 ,and those Russian 5881 can well handle the extra current without the anodes blushing . 

The owner may well have a  gig  in the local jazz festival coming up here alright ,
some of the jazz guys like it transistor clean all the way , others tube guys like it to start cooking off  a bit on the solo's ,more smouldering  low note distortions than any kind of shrill high harmonics of course .
For jazz sounds I like the way single ended amps round out the ocassional peak but seem to instantly recover to sweet sounding as soon as you lighten your touch .






 
For jazz sounds I like the way single ended amps round out the ocassional peak but seem to instantly recover to sweet sounding as soon as you lighten your touch .
.

One of the old valvos rolled off the bench to the floor and broke.  The other one survived and will be used someday for making a single ended amp like super champ or something.    I’m still gonna try a pair of 6550s in the 1970 Marshall.  I do like clean these days.  I’ll see what that sounds like again.  Jeff Beck used A 50w mK II and preferred 6550s. With a Klon Centaur OD or a Rat.  If you could play like beck, it doesn’t matter what amp your playing through.
 
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