Will changing to 6L6's from El34's hurt my Rivera?

[Andrew]

This is what the Rivera web site states:

"6L6's require a different bias setting and require that the amp is re-biased when changing from EL-34 to 6L6. Ideally, 6L6's require a different B+ (High voltage) and Plate loading (Output Transformer Impedance). In our Quiana and Knucklehead Reverb 55 6L6, we use a different Output Transformer, designed to match the tubes better."

So, what does this mean in simple terms? Can I do this safely or not?

[Chiba]

You'll have to wait for John P to drop in :)

I thought about doing this same thing to my Fandango, and borrowed a pal's Quiana for a few days to see if I liked it enough to go forward. His Quiana was basically the same as my Fandango - 55w 1x12. The two amps sounded pretty much the same to me - the Quiana has a slightly better clean, the Fandango a slightly better crunch.

--chiba

[RandyO]

I found this on the Rivera website under Knucklehead Series:

Unlike other amp brands that claim to allow different types of output tubes (6L6 and EL-34) to be used in the power amp section, we optimize the 55 Watt with a different and special Reichenbach® designed Output Transformer for each version, specified on order. If in the case you want to try the other type (EL-34 in the 6L6 version or vice-versa), you can by using a match pair or quartet, and adjusting the internal bias control. However, the amp is optimized for the tubes it is ordered with. This means the best of tone and output power not to mention increased reliability and tube life.

[Dan Desy]

Even though Rivera "designs the amp for the tubes", I'm pretty sure that with a rebias, it'll take 6L6s without problems. Maybe not as well as a "6L6-designed" Rivera, but it would still sound different and be safe.

[Stratmeister]

<Disclaimer>First, don't dig into the amp unless you know how to safely drain the filter capacitors.</Disclaimer>

Yes, a rebias would be required, sounds like there is a trim pot on the board for adjustment.

One of the differences in the tubes is their impedance. That's the part about the transformer matching. I can't answer the question about your amp in particular, but the note from Rivera sounds like they discourage it. There are circuits that handle this automatically and have hefty transformers, like the Univalve, but they're kinda unique.

Unless you know how to rebias and have the meters (Weber Bias Rite or such) to safely read plate voltage and current and then do the math to find if you're in safe operating dissapation range (watts) I suggest taking it to a tech for this.

In case you just swap the tubes for a quick sound check watch the plates on the tubes. If they start to glow turn off the amp and take them out.

[Andrew]

Thanks all! I'm going to try JJ E34L's first and see what they sound like.

[Baba]

Two things, first, I wish I could understand this stuff. I read and read, but still don't know what the hell 'plate voltage' and all that crap is. Is there a tube book for dummies?

In the player vs. tech world, I'm WAY more on the player side. /rant

Second, Andrew, I've had a chance to crank the KHII a little, everyone was right, the JJ's DO darken the tone a bit, which is fine for me, because I don't like too much brittle highs in my tone. I still have my treble at about 6-6.5, so it's not a huge difference. I think we need to get together again so you can hear it, or just try them in yours. Your ears are alot better than mine, I can't really describe what they sound like, just that my head sounds better, more even harmonically, tighter, and I'm actually not minding the recto 2x12 cab so much now, it basically sounded pretty good this morning.

I'm still experimenting whether I like all the knobs pushed in, or the sweet (treble) and cut (mid) pulled out, that's a nice tone that sounds like it would cut with a band well.

I'll tell you, kind of reminds me of the tone Petrucci was getting on that EB video we saw a bit ago.

Sorry to hijack the thread, Andrew was waiting for that from me, but this has been a sick (literally) and crazy week.

[Stratmeister]

Hey Baba, don't try to understand it all at once, but the pieces will fall into place, don't worry. Anyway Gerald Weber and Aspen Pittman both have some good reference material. First you need to know how a tube works, then you can go on to how an amp works. Doug has great prices on this stuff at:
http://www.hoffmanamps.com/MyStore/perlshop.cgi?ACTION=thispage&thispage=parts13.htm&ORDER_ID=338655883

Oh yeah, plate voltage is the voltage that is applied to the "plate" component of a tube or valve. That's the receiving part of the tube. Electrons flow from the cathode to the anode (plate) and in between are screens or grids. They can effect the flow of electrons, and that is adjusted by biasing the amp (tube really). The heater element actually heats up the tube elements allowing electrons to flow. The idea is to set the operating current at the right level for best performance and tube life without getting into cross over distortion (in a 2 or more power tube arrangement called a push-pull design). Think of it as one tube being "on" during half of the sine wave, and the other power tube being "off" during that same time. Then they switch phases. So one is always passing signal while the other rests. Setting the tubes for the correct on/off is the object.

Hope that confused you some more, er, I mean help explain tube/amp logic...