Traynor YBA-2B clone...advice needed

[mbailey]

I am planning to build a yba-2b (schematic here http://www.schematicheaven.com/barga...a2b_manual.pdf the last dwg.)
I am using my buddies as a guide but I have a couple of questions.
first my buddies amp has the plates running @440V!!! @ 23ma measured across a 1 ohm res. from the cathode to gnd (class A?). this amp has been played weekly without any problems for years and sounds awesome thru any cabinet I've put it thru.
I am trying to decide on an OT 5e3 maybe or a 18 watt replacement?
any suggestions, ideas or comments will be appreciated!

[Chuck H]

I don't suggest cloning in the overvoltage. It is part of the tone but it's just not a good idea. EL84's begin to change character above 340Vp. Morphing into a tighter, bigger sounding tube instead of thier signature creamy, Voxy tone. IME they should do what you want at 390 to 400Vp. That's still high, and also IME (contrary to your friends) tube life will be shortened somewhat. But you will get that really tight sound from them.

That said...

Why not just use Hammond transformers? That's what Traynor did. A 270EX PT will put you right at 400Vp. A 1608 OT is a nice big one for the job (more bottom end) and has exactly the right primary impedance. The combo should sound very much like what Traynor used. Pay no attention to the 1608's 10 watt rating. I can tell you from personal experience that it will live forever and sound great in a 20 watt amp.

Affordable, great sounding, easy to source and it's the same brand as the amp your cloning.

My personal amp uses this tranny set and FWIW I couldn't be happier.

Chuck

[mbailey]

Thanks Chuck...I appreciate your advice. I was planning on trying to keep the voltages closer to the schematic (395 @ the plate 390 @ the screen grids) as I thought they seemed pretty high in my buddies amp. So you don't think I'll hear a big difference in tone? Also am I figuring the class of operation correctly? I don't really care if it is class A or AB just want it to work and sound like the yba-2b. You said you have the Hammond xformers in your amp. what circuit are you using? once again thanx!

[Chuck H]

Thanks Chuck...I appreciate your advice. I was planning on trying to keep the voltages closer to the schematic (395 @ the plate 390 @ the screen grids) as I thought they seemed pretty high in my buddies amp. So you don't think I'll hear a big difference in tone?

All other things being equal (and they never are) it should be real close. The higher you go with plate volts the more things tighten up. I've heard the same brand and lot EL84's at 398Vp and 355Vp in the same amp and the difference was truely small. I think 395 to 440 the difference would be smaller since the tubes are already well past that 340ishVp where they morph in character. But I've never heard EL84's at 440Vp so I'm just speculating. Perhaps they change character again above some 420Vp or something. I don't know. Also, we've all heard it said how amps seem to sound good right before they smoke and die. At 440Vp with EL84's that's the game you're playing.

Also am I figuring the class of operation correctly? I don't really care if it is class A or AB just want it to work and sound like the yba-2b.

It's AB. At 23mA your friends amp is under the max plate dissapation and we haven't figured for the screen current or the voltage differential at the cathode resistor yet. I estimate your friends amp at 8 to 9 watts of plate dissapation. You do need to be at or a little over the 11 watts max plate dissapation to get class A *Correction: This is untrue but is typically how it's done. You can run run any tube at some lower plate voltage that limits it's potential dissapation and bias accordingly to achieve any class of operation at a lower output* and you just couldn't do that at 400Vp without a melt down. The screen grid current and cathode voltage differential are one of the reasons you read occasional posts about EL84 amps running the tubes at 14 watts dissapation. It's a bit of a misnomer really. Not to mention the fact that EL84's seem especially prone to grid loading. Trying to draw grid current even at nominal drive levels. This causes a positive charge to form on the grids which drives the bias cooler and sort of nudges most class A EL84 amps into class AB as quick as they start to break up. So, almost without exception, if your running any EL84 amp overdriven it's running in class AB.

You said you have the Hammond xformers in your amp. what circuit are you using? once again thanx!

It's my own design. And I've built a few for friends and one for a customer too. I also built a couple for a big name amp MFG but those used custom Heyboer OT's. They decided to steer away from the "boutique" market when the economy crashed but I did get to present at the 2009 winter NAMM show. The amp was well recieved but in the end it was decided that we would be chasing a shrinking market. My 15 miutes was too short.

Like the YBA-2 (a/b) my design get's the power tubes into overdrive ahead of the PI and the PI into overdrive ahead of the preamp. So in that respect they're not dissimilar. I run my amp dimed A LOT and the trannies don't even get hot (though sometimes my attenuator does). I'm running a Vp of 355 via a 150 ohm resistor following the diodes in the power supply. I wanted a pinch of that signature chime and a little rectifier type sag while retaining the bigger bottom that EL84's get at higher voltages. I think I hit a real good compromise for what I wanted. I did add the 150 ohm resistor as an after thought to the circuit and my original Vp was 400. That's how I know what your loaded voltage will be. When I was at 400Vp I used a 180 ohm cathode resistor for a plate dissapation of roughly 9.5 watts and the tubes did fine. I only changed it to accomodate my own tastes.

FWIW another Ampager we don't see here anymore (unless he's operating under a new screen name) used the Hammond 1608 OT in his Marshall 18 watt clones and won a fairly high profile sponsored amp shootout. Sorry I can't remember the details now.

If you find your amp isn't as big, loud, tight sounding as your friends there are some design changes that can get you there without outlandish plate volts. You can up the cathode cap value, increase plate supply filtering and even use a diode circuit across the cathode circuit to "fix" the bias as the amp nears overdrive. All worthy mods IME.

Happy building.

Chuck

[tedmich]

Chuck's got good advice. IME the ultra high voltages in the Traynor are required to get its sound, as is everything else in its design! The Hifi guys are pretty much dumbfounded when they hear of running an EL84 that hot, a 7189A is designed to go that high but most decent EL84s can handle it AOK (JJs are good IME, there are some russian versions available on the Ebay that take HV too). Early EL84 designs use <330v!, 10-16w max in PP!

Easy to wire it up for a high/low voltage switch too, maybe with a "Maida" regulator. You want a Traynor; clone it!

[BiBi]

"The Hifi guys are pretty much dumbfounded when they hear of running an EL84 that hot"
Check out the Dynaco Stereo 35 schematic-- they run EL84s at around 380 volts on the plates in ultralinear. Both pairs share a 95 ohm resistor.

[tedmich]

Its not too bad if they are cathode biased, guitar amps are routinely used above 400v B+ with a fixed bias, like the PV Classic 50 at 410v with 10w dissipation on each tube. The Sovtek/EH EL84(L) are actually Russian 6P14P, and can dissipate ~14w at 450v! For a vanilla EL84 the Traynors are on the ragged edge, with a reported 25 watts RMS out of 2 EL84s in the Guitarmate all from EL84s with a "max" voltage rating of 300v....

see this thread:
http://music-electronics-forum.com/t10833/