looser feel

andrew · Post by **andrew** » Sat Apr 11, 2009 5:59 pm

Hi,What ways could I go about getting a looser feel out of my Rocket. I get the same voltages as contained in the Rocket docs and I used the recommended components,PT, OT, ect. Although it sounds very good it feels a little tight.Thank you for any advice.

funkmeblue · Post by **funkmeblue** » Sat Apr 11, 2009 10:36 pm

maybe try a 5v4 in place of the 5ar4.

andrew · Post by **andrew** » Sat Apr 11, 2009 11:49 pm

I have read that lowering the B+ would loosen things up too but I also have a 2-EL84 Rocket based build with 350v on the plates using a 100uf/100ohm on the cathode and it has the looseness I'm going for. Would lowering the cathode bypass cap help? The tight Rocket has a 220uf cap. I'd like opionions before I order. Thanks.

rooster · Post by **rooster** » Mon Apr 13, 2009 1:09 am

andrew - OK, this is a hard thing to get to if you don't have it. Since lately I am focusing on the ma draw of the power tubes in a Rocket, what is the ma current draw per power tube on you quad EL84 amp? And then what is this number on the dual EL84 amp? How different are the two numbers for either amp? See where I am going?

Maybe the little amp is biased way hot and it saturates very easily, feeling looser. And then maybe the bigger amp is not as hot and it feels tighter. Or maybe the opposite is happening with the tubes with the same loose /tight results, you know?

Really, you could do some crazy swapping of parts and your problem could be in the biasing of the power tubes. If you can't check this value, how would you know?

OK, just asking.

andrew · Post by **andrew** » Tue Apr 14, 2009 3:22 am

My big amp is at 37ma. and the two hole is at 27.5ma. If I raise the cathode resistor to a 62ohm I should get 28ma. Thanks for the insight Rooster! This saved me from a big parts swap.

andrew · Post by **andrew** » Tue Apr 14, 2009 3:47 am

Woah. I miscalculated the 2 holer. Is is at 55ma. Is that too hot? Sounds good.

rooster · Post by **rooster** » Tue Apr 14, 2009 6:57 am

Yeah, this is probably something to think about. 37 is very good actually, and 55 is too high - and you like the one that is melting down! Funny how that goes, isn't it?

So Class A is all about compression, the tubes are loaded from the gate. When you bias them too hot, the notes don't breath at all, they are just squashed so that everything sounds and feels smooth. Frankly , this is a sound that is supposed to happen in a well designed amp at higher gain levels. You are probably playing this at lower volumes and thinking this is pretty cool?

Well, I don't know how to advise you at this point. The tubes aren't 'cherry' at 55 ma I suppose? Old schoolers might tell you this is OK then, but eh, I think its like trying to reinvent the circuit, you know? You can always buy more tubes, yes, but the question is: Do you like the amp operating as it was designed to operate - or do you just like the amp because it is overbiased and squashing the notes?

It looks like you have some thinking to do.

I would probably change the cathod resistor on the small one or find some tubes that are more in the park. Then I would play it and see if you still like it. ???

andrew · Post by **andrew** » Wed Apr 15, 2009 1:46 am

I liked the sound on the two hole when the guitar volume was rolled way down. It wasn't distorted or overdriven and it had a clear acoustic guitar sound with a smooth feel. Less abrupt than the full sized Rocket build. I like it but not enough to keep buying tubes. I changed the cathode resistor to 162ohm and and got 40mas. I'll crank it up tomorrow. I've been paying income and quartarly taxes tonight - not in the mood. Maybe it will sound the same?

andrew · Post by **andrew** » Thu Apr 16, 2009 1:07 am

This is interesting but way over my head ---- http://music-electronics-forum.com/show ... 162&page=2

rooster · Post by **rooster** » Thu Apr 16, 2009 7:01 am

andrew - That link was interesting. I see that Clyde checked in there too? Oh well, sorry but when people start talking about crossover distortion while running the tubes into the ozone I just smile. EL84s are very cool tubes, good for hi-fi audio reproduction, too. But here they typically run at 3 watts, maybe 7 tops. Crossover distortion? No, not at that wattage rating. So, like I said, that was interesting. I see where the primary poster was from the Pac NW? I don't know him, maybe Seattle.

Any, by all means try the amp with the different cathode resistor. Pay your taxes, yes, but try it and get back here. I am recording some sound bites tomorrow on my Rocket and my AC30 for another post. Funny thing about EL84s in Class A PP, the ear 'gets used to' the sound/volume and you find yourself turning things up. The 'tone' of a Rocket or an AC30 is not about volume, per se, its all about the sweet spot. Find it and try to hang with it. Avoid the urge to turn it up, that's the ticket. Put a great mic on it and make a record, don't try to show the neighbors how loud the thing is. Take care.

Zippy · Post by **Zippy** » Thu Apr 16, 2009 3:04 pm

rooster wrote:Funny thing about EL84s in Class A PP, the ear 'gets used to' the sound/volume and you find yourself turning things up. The 'tone' of a Rocket or an AC30 is not about volume, per se, its all about the sweet spot. Find it and try to hang with it. Avoid the urge to turn it up, that's the ticket. Put a great mic on it and make a record, don't try to show the neighbors how loud the thing is. Take care.

Funny thing about EL84s... When you run them at voltages greater than about 300V, they are no longer in Class A. Hence my push to keep the voltages down on the Rocket. They are too high in the AC30.

Don't believe me, Randall Aiken spent considerable time making the case here:

http://aikenamps.com/

Go to: TECH INFO - Advanced (Aiken) - "Is the Vox AC-30 really class A?"

andrew · Post by **andrew** » Fri Apr 17, 2009 2:59 am

I put in an old Lowery organ 5U4GB and got the voltage down to 328v on the plates, 12v across the cathode resistor (162ohm). I figure 18.25ma per tube(2). TOMORROW I'll play it.

rooster · Post by **rooster** » Sat Apr 18, 2009 7:11 pm

That's pretty good right there actually. Let me know

rooster · Post by **rooster** » Sat Apr 18, 2009 8:45 pm

Er... I assume you are talking about your quad EL84 amp now?

andrew · Post by **andrew** » Sat Apr 18, 2009 11:26 pm

On the 4 El84 I lowered the first tube cathode cap to 4.7uf and I raised the 500uf going to the volume pot to 1uf. The 4 EL84 voltages are right in line with those in the Rocket Documents. This seems to work better with my guitar. On the 2 El84 ( 150ohm cathode resistor) I installed a VVR2 and put the GZ34 back in. It is dialed in around 300vts on the plates. I will eventually change the caps like I did in the 4 EL84. These 70's Bill Lawrence L-550 mini humbuckers are hot 11k pups. I wired each pickup in parallel and used the Lawerece Q-Filter that changes the impedence and gives a more acoustic guitar sound. Not quite single coil- not quite humbucker. It is hard to get used to having to roll the guitar volume to 3 to get a full clean sound without it getting too loud and rough (amp volume with 500k pot not past 9:00). However I did just order a set of NOS Bill Lawrence 560s with 6k output. Maybe that will help things a little. Other factors are my 56 year old ears. Keep up with a drummer? I can't go NEAR a drummer! I haven't played at that volume for 20 years. I wish I could afford a nice speaker Isolation Cab.

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