Rocket and Rectifiers

[rawnster]

Yesterday, I had the opportunity to try 1967 Mullard 5AR4/GZ34 rectifier in my recent rocket build. OMG. What a difference. I know there are those who think that rectifier tubes do not affect tone. I'm here to say that this is not true. The amp sounded more open and loose. There was a lower-mid shift in the tone stack. As my friend mentioned, it sounded a little more brown. It took some of the chime away; but a simple turn of the cut knob brought it back. I'm trying to decide if the low-mids are too muddy now, or if this is just something that I have to re-adjust in my ears. Even so, it's a fantastic tube, and should last forever!

Anyway, thought I'd share.

Anyone else play around with different rectifier tubes?

[Structo]

I thought the GZ34 was the spec'd tube for the Rocket?

Or are you saying because it is a 67 tube, that made a difference?

[Zippy]

Yesterday, I had the opportunity to try 1967 5AR4/GZ34 rectifier in my recent rocket build. OMG. What a difference. I know there are those who think that rectifier tubes do not affect tone. I'm here to say that this is not true. The amp sounded more open and loose. There was a lower-mid shift in the tone stack. As my friend mentioned, it sounded a little more brown.

Forgive me if I don't keep up with everyone, Rawnster, but compared to what? Did you measure the difference in voltages between the two rectifiers? Difference in voltage drop (hence internal resistance)?

I'm among the crowd, or maybe it's just a small gathering, that believes that everything can be measured, explained, and duplicated, if desired.

[rawnster]

Sorry, but didn't take any measurements. I just listened. Yeah the Rocket it spec'd for a GZ34. But there are many different brands of them. I was using a JJ before swapping it out for the Mullard. Yes, I neglected to mention that the tube is NOS Mullard. I'll attempt to do some measurement comparisons between the NOS tube and a JJ.

[M Fowler]

Rawnster,

I wouldn't bother to do any testing unless you feel you need to.

I'm sure zippy was just saying there is probably a heck of a good reason electronically why you prefer the sound of the older NOS rectifier tube.

Instead of buying expensive NOS tubes you maybe able to find out what the voltage differences were between the two tubes and duplicate that with the current variant tubes availabe, incase another rectifer tube is needed down the road.

Or maybe that isn't what zippy was getting at.

Mark

[dehughes]

I was there as well with Ron...they were my Mullards, both 1967, NOS. No question there was a noticeable difference in tone and feel with the Mullard. The other recto was a newer JJ GZ34, and it didn't sound bad at all, just really different. The JJ made the amp thinner and brighter and more chimey, whereas the Mulllard darkened and thickened it up noticeably. I know people by and large say rectifiers don't affect tone, but in my experience that's just patently false. Of course one could reduce everything to mathematics for an explanation of this universe....or one could just find the tube that gives them what they like in the amp they dig. I do think that really testing out a Mullard and finding what is different vs. a JJ would allow one to pick a new stock recto that would produce similar results...which would then lead to the ultimate shootout: Electrically identical NOS vs. New Stock recto in the same amp. That'd be tough to pull off though, for us non-EE types....but very interesting nonetheless.

[dartanion]

42 years of aging on the JJ may make it sound just like the NOS Mullards. Then again, maybe not. Same can be said for signal caps, speakers, transformers, etc.

Tone is subjective, so use what sounds good to you.

[rawnster]

Tone is subjective, so use what sounds good to you.

Of course.

[Zippy]

I'm sure zippy was just saying there is probably a heck of a good reason electronically why you prefer the sound of the older NOS rectifier tube.

Instead of buying expensive NOS tubes you maybe able to find out what the voltage differences were between the two tubes and duplicate that with the current variant tubes availabe, incase another rectifer tube is needed down the road.

Or maybe that isn't what zippy was getting at.

Mark

Hey! What I was alluding to is the difference between these various rectifier tubes. There isn't a whole lot going on there - what we get from the rectifier is a voltage and a dynamic resistance that varies with current draw. It's not frequency sensitive - it's not in the signal chain so even if it was, it isn't seeing a spectrum. So all we are left with is the variation of output as a function of current demand. You can measure the idle voltage and say that everything is the same but what of the dynamic response? That's what you hear and that's what matters.

Given that the lion's share of the amps built 'round here use a series dropping string (vs a parallel power supply as seen in Matchless amps and others), what ever voltage drop occurs due to power stage loading effects the preamp as well. So, yes, the rectifier has an influence on tone, dynamic response, et al., ad nauseum.

I'm with you, Rawnster. But I'll bet there is a reason why beyond the label and the vintage.

[M Fowler]

Zipply, speaking of Matchless I really like my little spitfire and want to try build a higher wattage matchless some time.

Rawnster, I really need to go tube hunting area my town this spring I want to see what I can come up with NOS wise. I just happen to know an old retired tech that used to build his own amps, including winding his own trannies and pickups. Steel guitar player. He has some tubes and test equipment I need to see if he will part with.

Good info guys we are all after that tone in our heads. How many amps are all of us going to build?

Mark

[skeezbo]

Dave Funk weighs in on this in his book. He wrote that KF wouldn't build a Rocket unless he had a Mullard 5AR4 to put in it.

I guess Ken would know if it sounded better.

Skeezbo

[rawnster]

Good info guys we are all after that tone in our heads. How many amps are all of us going to build? Mark

Yeah, good question. I've got a hanking to build something with a reverb circuit. Normster's Rocket with reverb looks intriguing. Perhaps a princeton reverb with kt-66s in the power section. Yeah! That'd be like back in the when some of my friends dropped in a 327 chey engine into their little Pinto wagons. Nothing but a rubber burning machine.

[Allynmey]

All the Rockets I've built for people left with a Mullard 5AR4/GZ34. I've tried JJ, Valve Art, etc. The Mullard did make a noticable difference. Unfortunately my stash is dwindling down

[Allynmey]

Here's one on TGP thats for sale...

http://www.thegearpage.net/board/showth ... p?t=522913

Worth checking out if you want one for a comparison

[M Fowler]

Is that the going rate for a well used GZ34 Blackburn Mullard?

Mark