EL84 bass/treble - help me understand!

[Gainzilla]

El84s are often referred to as chimey. My limited experience with them confirms that assessment as long as you don't venture into high gain territory or push them too hard. I've found them to get harsh and unpleasant. I bought a Jet City 20watt head (basically a jcm800 into a pair of fixed bias el84s) as an experimentation platform and home practice/recording rig.

I've changed out some of the component values, mostly to bring it closer to a stock jcm800, and make the el84s a little happier (PI to AC15 values). At practice volumes the amp sounds fantastic. If I turn it up to anywhere approaching gigging volumes it gets harsh and the bottom end drops out (either causing or exacerbating the badness), and the tone becomes thinner, less full. What gives? I've pulled together a lineup of suspects and would really appreciate any help identifying the culprit!

* El84s with plexi values in the PI don't sound good when driven hard. They're loud though. Is this a function of too much grid current causing early breakup and/or crossover distortion?
* El84s with AC15 PI values (lower grid leak especially) sound better but aren't as loud.
* El84s don't have enough oomph to reproduce lows as well as other tubes. Thus, they sound full at low volume, but not too skinny when cranked.
* El84s are just fine. It's probably your speaker (WGS reaper 30 loaded sealed 1x12), or the circuit.
* This speaker sounds good when not pushed, but harsh when it really gets moving.
* It's biased such that it sounds best at lower volumes.
* I'm nuts and should just go buy a pod, realize that these aren't the droids I'm looking for, and I should go home and rethink my life.
* Something else I haven't considered.

I get that I haven't posted a schematic which makes all this more theoretical/speculatory. I'm at work right now and wanted to understand this a little better.

Thanks in advance!

[JazzGuitarGimp]

The first thing I would suspect is ultrasonic oscillation. Did you change any of the lead-dress? Did you give the amp more gain?

Do you have an oscilloscope you can use to look for oscillation?

[RockinRocket]

I had a jca 20 not to long ago and had the same problems as you for the mot part. I even have a thread on here about it. I think the problem was the PI values drive the el84s to hard and sounds awful when driven. Also 360-370 plate Volts are way to much for el84s the amp is just so crisp from the volts the amp didn't have a good feel to it.

The solutions that were mentiond that I ended up not doing was doing a split load PI to reduce the output from the PI.

A even better solution that I came up with after I sold the amp was to get 6v6 converter sockets. The PI would drive the 6v6s properly and the lower volts on the power tubes would hopefully reduce the stiffness lack of feel in the amp.

[Reeltarded]

AC30 doesn't even have enough headroom to chime barely louder than bedroom levels...

I think you are looking for another droid and it might simply be twice the output section but the chimey sounds you hear recorded are not loud at all. Very low volumes.

[Colossal]

Output transformers make a HUGE difference with EL84s. Get something oversized with wide bandwidth, not a paper wound A-frame vintage clone. Voice a high gain preamp to cut excess low end early and let more through later on. I built a high gain preamp with a 4xEL84 power section and it had massive, tight, low end. It is absolutely not true that an EL84 cannot handle a high gain format. I will take that Pepsi challenge with any naysayer. For an immediate answer, check out the demo with John Petrucci playing a Boogie 5:25 (2xEL84) through a 1x12 Vin 30 loaded Rectifier cube cab.

I agree with the aforementioned comments about driving EL84s to excess. They only need about 12V to get there. Keep the power amp cleanish. Just get them shimmering. It's all in the voicing. My amp was putting out something like 44W.

[RJ Guitars]

Hmmm... if i understand correctly, you have a loss of low end as you add gain... and or sounds ratty? EL84's are generally famous for sounding great when pushed hard.

I do agree with Colossal that the OT is key and that might be the whole story here.... also the speaker choice is very significant.

But if not... In this case i am more inclined to wonder whether the power supply is maybe not up to the task.

If the PS is adequate then as mentioned b4 I'd start to look for something going on that is robbing either signal or power... oscillation or interference somewhere.

The Trainwreck Rocket (refined AC30) is occasionally and fondly referred to as the "fat bottom girl" for a couple reasons. Brian May for sure owns part of that but those amps can really move some low frequency air and the Songwriter 30 has even more of the same. Hit either of those amps with a high gain input and they respond well.

[rp]

I think you are looking for another droid and it might simply be twice the output section but the chimey sounds you hear recorded are not loud at all. Very low volumes.

Exactly, or big amp up and guitar down. But, I've seen live vids of early Brit bands sound chimey as all heck through hard charging AC30s and Selmers, though when I've seen bands using loud AC30s I've never really heard that 60s AC30 sound, so I'm not sure how it all comes together. Hiwatts have their own form of chime, a huge CLANG. Anyway, it's more than an EL84 thing.

These are high powered 4XEL34 amps, Klemt Echolettes PA amps IIRC, and are very chimey here. Lots of headroom, I'm guessing amps up till some good bite, guitar down, and whack the strings with Marriott's cosmic mojo. And maybe it helps to have a drummer w/ a 1966 drum kit to you don't have to turn it up past hopes of chime.

https://www.youtube.com/watch?v=5oaw7evBdrE

Convert it to cathode bias might help. Someone else can explain why but it adds a bounciness that is one component to the sound, as is the not mediocre OT suggested - try an Edcor for cheap. Maybe lift the NFB if it has it. If the thing is running silly high voltages, above 340V I'd leave the fixed bias. You could try to lower the gain some, maybe just stick one or two 12AY7 in there and see what happens. Honestly, I'd probably leave it alone, just cause an amp has EL84 doesn't mean it was meant to or has to "chime" even at low volumes. I'm guessing the Jet City was made to raawk modern, hard, and cheap, but I've never even seen one so can't say.

[Malcolm Irving]

.... But, I've seen live vids of early Brit bands sound chimey as all heck through hard charging AC30s and Selmers, though when I've seen bands using loud AC30s I've never really heard that 60s AC30 sound, so I'm not sure how it all comes together. Hiwatts have their own form of chime, a huge CLANG. Anyway, it's more than an EL84 thing.

Yes, I've noticed that too. In those days players used much heavier string gauges. The light gauge strings came in when Jeff, Eric et al. started to emulate Albert, BB and Freddie. Also, with heavy gauge strings you usually got a wound third string rather than a plain. Not sure but I wonder if heavy strings give more chime and clang? I think they also really used to hit those strings hard with heavy picks to get as much as possible from relatively low gain amps.

[RJ Guitars]

The claim is that Stevie Ray could play the meanest strings and hit them harder than anybody... I'm not sure he ever got chime but he sure got tone! On the other hand the early Beatles stuff was definitely Voxy and those guys were using Gretsch guitars and heavy flatwound strings. Could it be that we have let that little piece of mojo untapped for the last 40+ years? I can still recall going to the local music store and buying a set of Sound City "Slinkys" with a picture of Eric Clapton on the package... I'm not sure I could go back??

[Gainzilla]

Hi all,

Thanks so much for the great replies! There is a lot of great info here.

Just to clarify, I'm not looking for chime. I just mentioned that EL84s have a reputation of being chimey. I'm more wondering why when I turn the master down to bedroom levels (regardless of gain level), the tone sounds great but thins out when cranked. It sounds like the answer lies in a combination of carefully tuning the PI/PA to run as clean for as long as possible, possibly reduce voltage, and consider swapping out to a higher quality OT.

Before I consider also adding a new OT, I think I'll simulate this supply in Duncan's power supply simulator. I do think it's possible that there just isn't enough juice to support the low end at louder volumes. From the info Colossal presented, it sounds like I can definitively rule out the tubes (Great to know, btw!! Thanks for confirming, and with such whole-hearted conviction! I'm sold!).

Any suggestions on PT? I heard one vote for Edcor. I was also looking at Hammond, and possibly Classictone, but the latter look like they're built more to vintage spec. I found this little baby at Edcor. Thoughts? I'm not looking to metal out with Drop C tunings. I just want to get a more full tone at louder volumes.

Spec: 21W, push-pull tube output transformer for 8.6K Ohms to 4, 8 and 16 Ohms.
https://www.edcorusa.com/cxpp21-ms-8_6k

[rp]

That edcor is 20~20K Hz which for guitar is more like a 40 Watter. Their 15W should be plenty adequate, though you only get one output tap. They make a 10W w/ 4/8ohms it's also 20~20K Hz which is pretty cool for a 10W - I guess maybe into a big horn you might move a tiny bit of air at 20Hz with 10W

http://www.allenamps.com/parts.php#transformers
TO20, TO22, T026 - IIRC the AC15 was ~6K so these are not out of spec.

speaking of which:
http://www.mojotone.com/transformers/Vo ... C15-OT.pdf
there's also the classictone AC15.

$34 for the GXPP15-8-8K seems about right for the Jet City. Edocr has nice documentation so you can see if it fits. Report back if you try it.

[RockinRocket]

The stock transformers were quite big from what I remember. The power tubes made a lot of mechanical noise when I attenuated a maxed master vol down to wisper volume. A lot more noise than any other el84 amp ive owned and I don't think any of my other amps had this amount of excess voltage. I had a laney cub 12 at one point and that had 290 volts on the tubes and is probably the best sounding amp for price ive owned and the power valves made no mechanical noise at its 290 volts. My 18 watter makes a little bit at 330volts. The el84s go off like fire works when you apply signal to them in the JCA.

You should spend the 20 bucks for the 6v6 socket converters. Im convinced I would have liked the amp had I done this. If this did solve the problem I would probably pick up another Jca 20 to tinker with

[Gainzilla]

What do you guys think of these? Nice of them to put the specs right on the trannies!

[Gainzilla]

And this.

[Gainzilla]

The stock transformers were quite big from what I remember. The power tubes made a lot of mechanical noise when I attenuated a maxed master vol down to wisper volume. A lot more noise than any other el84 amp ive owned and I don't think any of my other amps had this amount of excess voltage. I had a laney cub 12 at one point and that had 290 volts on the tubes and is probably the best sounding amp for price ive owned and the power valves made no mechanical noise at its 290 volts. My 18 watter makes a little bit at 330volts. The el84s go off like fire works when you apply signal to them in the JCA.

You should spend the 20 bucks for the 6v6 socket converters. Im convinced I would have liked the amp had I done this. If this did solve the problem I would probably pick up another Jca 20 to tinker with

Absolutely, dropping the voltage is probably the first thing I'll try. Might pick up a pair of the adapters just for fun in any event. Cheers!