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Old 8th November 2010, 07:12 PM   #1
chrisb is offline chrisb  Canada
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Default "favorite" outputs for Simple P/P?

George's last answer helped fit the final pieces of the puzzle on my Simple P/P EL84 project, but made me realize that I'll probably need to invest in new outputs.

All my previous EL84 builds have been triode mode, for which SV83 family devices were fine - actually these can sound rather more than just fine - but due to screen rating are limited in ultimate power in pentode mode - with full B+ voltage on the screens, I doubt they'd last very long.

So, the question is of current production EL84 / 6BQ5 types, any particular standouts or warnings?
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Old 8th November 2010, 08:40 PM   #2
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In my own SP-P, I first installed Electro-Harmonix EL84's. Immediately, I noticed a very slight redness of the plates (B+ around 300v). This phenomenon was also reported by Russ, here on the Forum. I had two quads of the E-H's to try, and all tubes acted the same way. However, the redness never went beyond very slight, even with the amp working hard for several hours. The sound was fine. Very detailed and clean. Will the EH's have a short life? I may find out as I'm still running with them most of the time.

Next I tried (on Russ' suggestion) some JJ EL84's. As Russ predicted, the plates did not glow on these. The sound was also very good. I couldn't really pick them over the EH's. According to guitar players, the JJ EL84's have a rep for toughness (unlike their KT88's which are garbage).

Finally, I bought some 6P14P-EV from a Russian guy I've dealt with before.
These tubes were NOS military issue by the Reflektor plant. They also ran for hours with the amp at high volume, and no distress from the plates. Again, after about 50 hrs break-in, I couldn't detect any substantial sonic differences.

Currently, I'm waiting for a quad of Gold Lion EL84's; another Russian tube that is supposed to have excellent sonics. It better offer something special as they are around $30 each!

I'm starting to think that the Tubelab SP-P design is not as fussy about tubes as some amps are.
I'd suggest you install some of the Russian 6P14P-EV. They can be found fairly cheaply, and appear to sound good and are ruggedly constructed.
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Last edited by neonthecat; 8th November 2010 at 08:49 PM.
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Old 8th November 2010, 08:51 PM   #3
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Quote:
Originally Posted by chrisb View Post
All my previous EL84 builds have been triode mode, for which SV83 family devices were fine - actually these can sound rather more than just fine - but due to screen rating are limited in ultimate power in pentode mode - with full B+ voltage on the screens, I doubt they'd last very long.
Why not regulate the screens at 250-300v? That way, if your B+ is a little high (Hammond PT), the tubes will last longer.

jeff
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Old 8th November 2010, 09:49 PM   #4
chrisb is offline chrisb  Canada
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Originally Posted by vinylkid58 View Post
Why not regulate the screens at 250-300v? That way, if your B+ is a little high (Hammond PT), the tubes will last longer.

jeff

well, the point of this particular build was to keep things simple - as far as I digressed from bone stock was to upgrade the cathode bypass and coupling caps, and add choke after first filter cap

regulated screen supply and other zoomy tricks will probably be reserved for the next rebuild of the current 'lil Scottie amp or the Jolida/Dynamutt also currently in parts on the workbench

neon: thanks for the tip on the 6P14P-EV, it occurs to me that I might already be using a set of those that I got from Dave in an existing amp.

BTW, just how "left" coast is your location? - so far this seems to be an all maple leaf thread
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Last edited by chrisb; 8th November 2010 at 09:52 PM.
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Old 8th November 2010, 11:16 PM   #5
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Quote:
Originally Posted by chrisb View Post
well, the point of this particular build was to keep things simple - as far as I digressed from bone stock was to upgrade the cathode bypass and coupling caps, and add choke after first filter cap
Sorry, I should have said "unregulated". Old school amps used a simple RC section after the B+ tap to drag down the voltage for the screens.

jeff
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Old 9th November 2010, 01:54 AM   #6
rmyauck is offline rmyauck  Canada
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Would a choke added lower the B+ maybe enough for those EH etc? It shouldn't cost much either and may help PS.

Be carefull with those Gold Lions as I'm sure I read somewhere they won't take high B+ too. I think Jim McShane as a warning on his site as he sells them.

I was using JJ EL84's in an old Heathkit AA-151 which is supposed to run B+ high and they worked great too. It needs recapping so I went back to an Eico HF-12 for now which I think runs the tubes at less B+.

Maybe that mentioned Edcor spec'd 280-0-280 or less PS trans. would solve the problem. A little loss of W/CH though!

Would the JJ's and Russian EV tubes last longer at the lower B+ too?

I bet the Simple PP amp would run 7591 types as the drive requirements are supposed to be similar to EL84? Lots of B+ would be great then for up to 30W/ CH! Maybe 35W if pushed.

Sockets would have to be external as they are Octal, but all the Dynaco ST-70 boards work that way.

Randy
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Old 9th November 2010, 03:08 PM   #7
rknize is offline rknize  United States
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I tried to lower the screen voltage on the EH tubes, due to the issues that neon mentioned. I did this with an external power supply. Indeed it brought plate dissipation down, but at the expense of additional harmonic distortion. This was with no feedback, though.
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Old 9th November 2010, 05:43 PM   #8
rmyauck is offline rmyauck  Canada
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Shuguang has a new series of high end 9 pin tubes to complement their Treasure series of Octal tubes. They are called Psvane series and they have an EL84 tube in it. I think they are $67-70 a pair and would be probably compared with the Gold Lions. It is unknown if they can take higher B+.

Randy

Last edited by rmyauck; 9th November 2010 at 05:47 PM.
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Old 9th November 2010, 10:20 PM   #9
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Default Hey Chris,

Quote:
Originally Posted by chrisb View Post
George's last answer helped fit the final pieces of the puzzle on my Simple P/P EL84 project, but made me realize that I'll probably need to invest in new outputs.
If it helps you decide, you may borrow my NIB Edcor 25W 8K OPT's. They're waiting patiently for me to finish the top plate for my amp. They are wired with 40% screen taps etc.

EDCOR Electronics Corporation. CXPP25-MS-8K

jeff
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Old 10th November 2010, 08:52 AM   #10
Ian444 is offline Ian444  Australia
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My favourites are the JJ EL84, they sound good, and they take higher voltages without complaint. The 6P14P-EV came a close second in my amp, I haven't tried anything else in there. My amp has no NGFB either so YMMV.
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