Rickresource Rickenbacker Forum

This may be a really stupid question but here it is anyway - what is a rectifier on an amp?

In simple terms a rectifier is the device that converts AC to DC voltage.

Dont worry Bill... I only just found that out myself.

Kent, I like the EI's in my AC30 over the JJ's because they have more everything...more lows, mids and highs, and they are sweeter too. The JJ EL84's sound bland to me. The JJ 12ax7's/ECC83's are very hot but sound clean and unrefined to me. The new JJ ECC803's sound VERY nice however. These are a higher quality ECC83/12ax7 type. The EI ECC83's tend to be microphonic, but when you get good ones they sound fabulous. The EI EL84's are great sounding tubes that give the grind and chime you should have in your Vox. I believe all the AC15's and AC30's from around '93 on have come with EI's preamp tubes stock. Mine did anyway and mine is a 1993 Korg reissue model. Mine came with GE NOS EL84's when new, and these sound better than the EI's, as will most NOS stuff, and they lasted longer too..but they cost a lot more and are getting hard to find nowadays.

Other good 12ax7 types to try would be the Sovtek 12ax7LPS, the EH12ax7, the GT 12ax7M that you took out, the Shugang Chinese made ones, and any NOS stuff like a Telefunken, Mullard, GE, etc. You'll notice the most difference when you sub the 1st tube stage, so it would be helpful to find out which one that is on your amp so you can concentrate on that one. JJ ECC83's make a good phase inverter tube because they are so strong then can drive the power tubes well. Sometimes if you use the JJ's in a tremelo tube slot, they can be too strong and cause the trem to malfunction.

Bill, as far as rectifiers, Jeffrey said it well. To elaborate a little further...different types of rectifiers work more efficiently than others due to various reasons. A solid state rectifier works the most efficiently, so it will give you a higher DC voltage out for a given AC voltage in. They also have more switching noise than a tube one, which can cause hum.

A GZ34 has a little less efficiency than a solid state rectifier, so the DC voltage on the plates of the power tubes will be a little lower than with the solid state, and the tube may get overloaded when what you're playing in the amp requires lots of current. When this happens, the GZ34 can't give you any more current, so it sags, and your notes compress a little. A 5Y3, 5U4GB, and other types are less efficient than the GZ34, so your plate voltage will be even lower, and they will also sag more.

Different rectifier tubes have different current requirements too, so you can't necessarily plug in one type in place of another without checking first to make sure the amp can handle it. You can emulate the effects of a tube rectifier sagging with solid state components and resistors, which is what Ted Weber at webervst has done with his Copper Caps. These are neat because you can just plug them into the socket in place of a tube, and they don't use the 5v filament so your power transformer will run cooler, and you can change the character of your amp depending on which one you plug in. You do have to rebias when changing these, and also when changing rectifier tubes also. If you have a cathode bias amp like an AC30 or AC15, the voltages and bias will self adjust, but you should still check to make sure it is self adjusting into the correct area. If you want to learn more about it, get some books and read, read, read!

Thanks greg..... I'll do EI's next time - or even sooner if I see that the amp is basically running well with the JJ's.

The JJ's should arrive tomorrow. I'll let y'all know how it goes.

Great to hear Kent! You'll find that changing tube brands can have a HUGE effect on your tone. Someday you may get to the same point I'm at where I use different brands for different amps because of how they sound. If you get the money, (EXPENSIVE!!) try some NOS Telefunken 12ax7's in the firs tposition in your amps. Some of the smoothest, most articulate sound you'll ever hear.

I only see them for sale at the Telefunken site and they wont even print the price!

http://www.telefunkenusa.com/products/show_product.php?item=11&cat=tubes

so how much are they?.... We're talking about the power tubes, right?... I only need 2.

So Here's what happened.....

Last night I popped in the complete set of new JJ tubes. I crossed my fingers and fired up the amp and ... IT WORKED! It sounded pretty good except that there was a quiet buzz (more a buzz than a hum) that wasn't there before. But it was pretty lowgrade and nothing that will prevent me from using the amp tonight. (no, there were no flourscent lights on in the house)

THEN.... I put the metal cover over the tube section. This inner cover has a padded strip that contacts the preamp tubes. As I screwed it down I heard... CRACK! When I got it off I realized what had happened... the JJ rectifier is significantly taller than the Groove Tube rectifier I'd taken out and it got squashed and imploded.



After a few well placed words (similar to "aw shucks" and "goll-darnit"), I put the original Groove Tube rectifier back in and the amp seemed to sound the same.... good but with that small buzz.

I wont be able to try out the footswitch until tonight so I dont know yet whether the older low-power preamp tubes were the cause of the reverb problem.

So I'm good to go for tonight at least. I'm still interested in trying out the EI's and possibly even the NOS Telefunken's. I'm also interested in getting rid of that little buzz. This whole thing has gotten my brain tube-oriented and I gotta say thanks again for all the advice and hand-holding.

Stay tuned.....

Polarity buzz, possibly?

hmmm ... polarity of what?

The wall plug. If it's a two-prong plug, flip it and plug it back in. If it's a 3 pronger, then it won't be polarity hummmmmmmm.

3-prong.

Hmmmm is right. I'll see how it goes tonight. But it's clear that my AC-15 still needs some more pampering.

You don't need to change rectifier tubes anyway, they don't really affect the tone. A SS rectifier will raise the voltages a little and is not recommended for old amps if it had a tube to begin with. Try touching the preamp tubes with your finger one by one, see if the buzz gets louder if so put it closet to the power tubes, also try changing them around, possibly you have a noisy one in the number one tube in the chain, also put that closet to your power tubes.

The JJ ECC83's are very powerful for a 12ax7 type, and because of this they tend to buzz a little more than a different type of 12ax7. Try putting one of the Groove Tubes 12ax7M's in place of the JJ's one at a time and see if the hum lessons. It would probably make most of the difference if you put it in the first position in the amp, but I'm not sure which one that is on the chassis, so just try subbing it in one socket at a time to see if the hum is less. You would want to do this with the amp on. Just carefully grab the 12ax7 close to the base and rock it out. Do it with the volume down a bit or you will get popping out of the speaker when you remove and put in the tubes. DON'T try this with the power tubes! They get very hot...but it is ok with the preamp tubes. They'll be warm but not too hot to touch.

Your old rectifier tube will work just fine in there. Too bad about the JJ breaking, but its not a big worry. The JJ GZ34 has been spotty so far, and the new chinese one may be a better choice. I believe that is the one that Groove Tubes uses.

For the Telefunkens, you could get the EL84 power tubes if you want, but they will be very expensive! I was actually talking about a Telefunken 12ax7/ECC83, as these are the ones that have the stellar reputation more so than their EL84's. The Telefunken 12ax7 is going to be noticeably more detailed and smooth sounding than any other 12ax7 type, but the EI comes pretty close since it is made on mostly the same production machines. The EI 12ax7 just tends to be microphonic sometimes. EI's EL84's are very nice and not microphonic for the most part. I believe they sound a lot better than the JJ's, especially in Vox applications.

If you were looking for a couple NOS EL84's to try if you have the cash, the types you should get for those would be Mullards, Amperex, or Valvo. Another good choice would be GE, but as with all NOS, they are getting hard to find and are expensive when you do find them. Another good NOS 12ax7 type is the Mullard or GE. I personally don't like the Mullard 12ax7's in my Vox all that much and prefer Telefunkens or GE's or newer stuff like the Sovtek 12ax7LPS, the new JJ ECC803, or the EI which are in there right now. The common theme here with the exception of the GE is that all the 12ax7 types that I like in my Vox have long plates inside them, rather than the shorter plates like the Sovtek 12ax7WA/WB and the JJ ECC83 use. They just sound more detailed and have richer harmonics, but because of the longer plate tend to be more microphonic.

There are lots of places that sell NOS tubes on the web, but you may check out Jim McShane and Triode Electronics among others for good quality NOS stuff. Jim McShane posts on the webervst board often and is a good guy.

http://store.triodestore.com/index.html
http://pages.prodigy.net/jimmcshane/tubes.htm

Wow...you guys sure know yer stuff! Greg, it is a pleasure and an education to read posts like this one.