200s RECTIFIER TUBE QUESTION

[LPB]

 My amp is '67 and had no tube chart when I got it. The rectifier tube that was in it is a Mullard which is labeled GZ34/5AR4. The replacement JJ tube is labeled GZ34 only.

 In a recent conversation with a friend who is seems knowledgeable, I was told that these two tubes don't necessarily "truly" interchange in both directions because voltage levels can vary. I have a feeling that my 200s if fine either way but she is old and I'm not trying to squeeze 110% out of her, if you know what I mean.

[EdBass]

I'm pretty sure that the reason you sometimes see both types on the same tube is because GZ34 is just the European designation for the 5AR4, and that they are identical. At very least identical enough to be completely interchangable.

[Isaac]

My 200S schematic calls for a GZ34, so don't sweat it.

[Soundmasterg]

I used to think they were identical, but after reading this >> http://music-electronics-forum.com/t26515/ I'm not so sure. I think everyone knows that the Mullard GZ34 is the best ever made of either type and that they last a long time, so unless the Mullard was bad, I'd say leave it in the amp. The JJ "should" be fine, but you never know. Modern GZ34/5AR4 production hasn't been all that good. If it was up to me, I'd be going with larger filtering in the first two sections in the amp and use a solid state rectifier or a Weber Copper Cap replacement....especially if I was going to use the amp for bass.

Greg

[EdBass]

I don't know if any of these are left, but I'll find out for you if you want.



They aren't cheap, but they are NOS early 60’s F31 code Mullards; the real deal. Arguably the best GZ34/5AR4. period.
I posted about them back in March when they got here;
http://sunn.ampage.org/sdp/index.php/topic,6049.0.html

[LPB]

 Gosh Gang!

 I really appreciate all the info, info and suggestions! I've thought about running a SS cap, and yes I do use this for bass(don't even own a guitar!). My feelings are; it sounds so damn good the way it is, that's important. Sure there may be times when a bit more headroom(or perceived volume) could be advantageous, but I think a lot of the magic lies in the cab and speakers. These original, untouched JBL's are still kicking and I want to keep it that way for as long as possible. I'm guessing that SS rectification, in my hands anyway, would result in more driver heat and stress.

 I gig 3-5 times weekly, but I don't get to use this amp too often. Next time I get some time off during the day I'm going to A/B the JJ and the British Mullard to see if I can hear a big difference.

 Does any of this sound reasonable?

[Isaac]

Quite reasonable. However, if you really want to know whether or not you can hear a difference, have someone else switch out the tubes so that you don't know which one is in the amp. Figure out whether or not you can hear a difference before you worry about whether or not you prefer one over the other.

[EdBass]

I'm thinking you won't hear an appreciable difference between rectifier tubes, which may be Isaac's point.
It's not like it's in the signal chain, it just affects the power supply. Which, as has been pointed here on a few occasions, can increase distortion in high demand situations over a SS rectifier; but while IMO there is a noticeable difference between SS and tube rectifiers I don't know that there would be between two tube rectifiers.

Only one way to find out, I suppose... 

[Soundmasterg]

If you are swapping around rectifier tubes and/or trying out a solid state rectifier, you should rebias in between as each may change the plate voltage which will change the bias point.

I swapped around GZ34's in my AC30 years ago and didn't notice a huge lot of difference. Even the Weber Copper Cap was close to the others. I ended up using a used Amperex (Mullard) GZ34 I had around as the amp sounded just a bit better with that. It was probably the case though because the voltages and bias level in the amp changed to where the power tubes were biased in a slightly sweeter spot. This works in an AC30 without rebiasing because the map is cathode biased, but a 200S is fixed bias and will not self-adjust. I wouldn't hesitate to use a Weber Copper Cap in the AC30, or any of the other GZ34 types I tried as they were all within 5% of each other for sound. A straight up solid state rectifier wouldn't be my first choice though as it will have a much less voltage drop across it and the result will be much higher voltages in the amp. The Weber Copper Cap emulates the voltage drop of a tube GZ34 and emulates some of the sag characteristics too. I used one in a 200S that I have since sold that had larger filter caps in the first two sections and it works great.

Greg

[LPB]

Well, what you guys are saying makes a lot of sense. I have to tell you, after playing the rig on a couple of gigs the last two weeks(one large outdoor stage w/ a quality mic on the cab and one medium indoor "club" venue) I'm going to sit where I'm at with it for a while. This rig with a Precision has the ideal combination of muscle, warmth and definition for what I've been doing. The Bass Boost engaged, Bass and Treble around "3" and Volume between "2" and "3" is pretty much heaven with the tone knob rolled-off 60%-90% depending on how "forward" I want to be in the mix.

Sorry for the gratuitous mush but I really love this rig. I've been making a living playing great basses through great amps and cabinets for almost 30 years now and it's invigorating to find a combination that to me, seems to be "made for each other". I gig 3-5 times weekly and will probably only get the opportunity to use the 200S once or twice a month based on the work I've been doing. The anticipation really does a lot for my general enthusiasm.