Rickresource Rickenbacker Forum

Tube amps are a pain, but I've only found the kind of sound I like with a tube amp.

As I'm fairly clueless when it comes to such things, a few of questions....

I hear that tubes should be "matched".... that when replacing one you should replace all of them (kinda like a guitar string set I guess). Is that so? If so, why?

Is anyone familiar with the VOX AC-15 (baby brother to the VOX AC-30 of Beatles fame)? WHat tubes would be good for that amp?

Tube amps have a "standby" setting. How important is to use? How long should this be on before fully powering up? ... before turning power off?

When replacing the power tubes in an amp that uses fixed bias and only has 1 coarse bias adjustment pot, its a good idea to use matched tubes. Also, a cathode biased amp such as the AC30 or AC15 should have matched power tubes too. Having said that, back in the day, Fender never matched their tubes and they made amps of both types. It can sound better and give slightly better power, and hum less with matched tubes, but it isn't as if the amp will die if you don't use matched tubes.

For preamp tubes, just replace them with new ones when they go bad and don't worry about matching there. Generally, preamp tubes will outlast power tubes by quite a bit, so if you have to replace the power tubes, just do those.

For the AC15, a good choice for the power tubes if you want good sound and longevity would be most of the NOS EL84's, but of course they cost a lot more. They do last longer however due to better constructino. For modern manufacture, go with EI for great tone, and/or JJ or EH EL84's for reliability and decent tone. Some people have trouble with the EI's and microphonics, although I've only noticed that with EI's 12ax7's and not their EL84's. I use an AC30 and use EI's in it myself. The JJ's or EH's will sound ok, and work fine, but the EI's sound better. For preamp tubes, I also use EI ECC83's and haven't had any problems. Other good choices would be the Sovtek 12AX7LPS, the new JJ ECC803, or the EH 12ax7.

For the standby, use it between sets or while taking a break, or when you first turn the amp on, but otherwise its not necessary. Leave it on standby for 30 sec to 1 min or so when you first turn it on. Any more than that is crazy.

You can get all the tubes I mentioned at www.tubesandmore.com.

ok... thanks so much... at Tubesandmore.com I see the "EL84/6BQ5 - EI ELITE GOLD PINS" for $10.95 and the "EL84/6BQ5 - EI BRAND" for $7.95 plus an additional $1.25 per tube to get them matched. I dont mind spending the extra $$ on the gold pins and the matching if that is what it will take to get my beloved AC15 back to its normal good sound.

.... and here comes the REALLY dumb question... for the AC15 I need 4 power tubes, right?

So if I get a set of matched EL84/6BQ5 - EI ELITE GOLD PINS and just pop them in I should be ok? .... anything else I need to do (other than make sure all the preamp tubes are lighting up)?

I'm trying to get this done by a week from tomorrow. We have a gig that Friday so I'd like to place the order asap. Hopefully they can ship it out quickly.

Gold pins are a waste of $$$, Kent. The gold plating is at most a micron or two thick, and the simple act of inserting them into a soket will scrape off the plating.

However, the gold does a good job of preventing tarnish on the part of the pin that DOESN'T make contact.

ok... good info. I spent some time on the phone with the sales guy at www.tubesandmore.com.

He said that the sound from the NOS EL84's is much superior than the EI's. The NOS is about $21 a tube whereas the regular EI are about $8 each. But he said that he didn't have enough NOS tubes on hand to find a matching set of 4.

I'll probably go with the EI's. I need to doublecheck tonight that 4 is the correct number to order for the VOX AC15. This was something that (surprisingly) the sales guy was not able to confirm.

Anyways, I'm all ears if anyone has any recommendations for VOX tube selection. I did find out (from another web site http://kcanostubes.com/content/newsletter_details.asp?ArticleID=2) that the AC15 is "self biasing" so at least it appears that even an electronics dummy like me can do the tube swap.

Its a pain.... but when it's healthy the AC15 is one beautiful sounding amp.

Kent, you might consider purchasing a used but working tube tester. I got one at a flea market for $45, and it's worth every penny.

BTW, don't throw out all your old tubes, there may be one or two still good (it only takes one bad one to mess the works up) and if so, you can sell them to make some money back (or hang on to them for back ups! - that's where the tube tester comes in handy).

good idea! (I'll get the hang of this tube amp stuff one of these years)

Does anyone know of another amp that cam compete with the VOX AC15 (or its big brother the AC30) in terms of sound type / quality?

What about the newer VOX amps? I see one that is a "modeling" amp and that sends chills down my spine.... I once went a few rounds with a LINE-6 Spyder 212 modeling amp. It was gawd-awful and luckily I killed it before it killed me.

Kent, I personally prefer the early Fender silverface amps that have the Middle tone control and no Master Volume. For speakers, nothing can beat the JBL D-series; when used with the Fender amps, my Rics absolutely chime.

Now, here's a recommendation you won't expect: my older (c. 1998 vintage) Crate GX40C+ solid state (heresy!) is exceptionally good at matching the sound of my 1968 Fender Twin Reverb except for the very low end (8" speakers don't have quite the push of 12" ones). In another thread I detailed how I used my 370/12v64's dual mono outputs to tweak the controls on the Crate to match what I was hearing out of the Fender at the same time. This just goes to show that there are some good solid state amps out there, just as there are some stinker tube amps (the later silverface Fenders with the Master Volume circuit do not have the same quality of tonal output of the earlier, non-master-volume ones).

Of course, "hearing is in the ear of the beholder", and it's all very subjective!

I started out on "new" amps (after 24 years with my '60 Fender Pro 15) with an all solid-state Line 6 Spider 112.

Kent, I'm curious to know why you think it's so awful, but I have my own observations.

It's primarily a kid's shredder amp, but I didn't know when I bought mine (sorta on impulse). I found it to be OK on clean, with a very similar sound to my old '67 Thomas Vox Berkeley III, which was one of the first solid state Voxes and not the best for power or flexibility. Too clean and down on power.

Next, I picked up a new AD30VT Vox Valvetronix, to keep around my office. Really good value, and a big step above the Spider, despite the lower price. Sweet li'l practice amp with a lot of flexibility. Tube preamp and solid state power stage.

Then an ART 825 (first-gen modelling amp) joined the fold. This is an amazing piece of equipment, with a tube preamp stage, 130 watts of solid state power, and 75 "saves". I'm still crazy about it. Classic styling, too. I've always preferred the Fender sound and the Marshall look. This looks like a classic '60s Marshall, sort of. This thing is another entire topic by itself.

My good experiences with the AD30VT, along with a Forum member's comments about how much he loved the Tonelab SE, prompted me to try one out and I ended up buying one.

This, as you may know, is a Vox Valvetronix modeling console built into a floorboard, with amp, cabinet, stompbox, and room dynamics settings and two assignable and programmable expression pedals. It also features a tube preamp section. The amp simulator on this one is the best I'd heard, with the AC30TB program especially being very, very "real" sounding.

The new Valvetronix AC30s are Orient-made, but are getting good reviews. Seems the place of manufacture is the biggest gripe, and at $1000.00 with the classic VOX cabinet and lots of power, it is on the right track to be a big hit.

I tried one out just before I bought the Tonelab. Not having a handwired UK version to do an A>B, I can't speak to the differences, but on its own it performed really, really well. Also couldn't really crank it (store policy) but lots of power in reserve.

Things have come a long way since the Spider 112. Let the shredders and squidleys play their VH after school. They're a market segment, too. But there's still lots of meaty stuff for the grownups.

Here's a shot of the 825. Ain't it a beaut? Eight years old, too, although I've only had it about 6 weeks. $280.00 on flea-Bay.

I use the Tonelab mostly for headphone practice with my guitars and my vintage keyboards, right now.

Kent, your AC15 only has 2 power tubes. Also, because it is cathode biased, and doesn't have a global negative feedback loop in the amp, the tubes will sound like they are worn out in this amp and in an AC30 before they would in a comparable Fender since a Fender usually has negative feedback. So when your EL84's are worn out in your AC15, you can save them for use in another amp that uses EL84's if you have one, or sell them on ebay as good used tubes. Or just save them for spares.

The NOS tubes WILL sound better than the EI's, but the cost a lot more too. I prefer GE EL84's in my AC30, but they cost too much, and using the EI's gives me most of the sound for a better price. I have a quad of GE EL84's that I put in for studio use.

The AC30 is double the amp of the AC15, so yours has two power tubes and an AC30 has 4. As far as comparable amps...thats hard to say. Nothing quite sounds like a Vox except a Vox. Matchless or Tophat or others copied the AC30 circuit and then made some changes, so they sound similar. The older Fenders sound good too, but because of the 6L6 or 6V6 tubes they use, I think they usually have a better bottom end response and the mids aren't quite as sweet as on the Voxes. I prefer the all tube Vox amps to the newer modelling ones myself. They sound richer to my ears. Kind of like the difference between a great singer and a good singer. A pair of regular EI EL84's would be fine for your AC15. I usually get matched ones because they do sound a little better since both tubes share the cathode resistor, it will sound better if the tubes are matched.

If you decide eventually to get a tube tester, then make sure to look for one that tests for mutual conductance. I have a B and K model 747, which is a solid state mutual conductance tester, and is one of the nicest ones they made in years past. It was about $150 at the time, and goes for more on ebay nowadays. The problem with tube testers is that they test at a lower voltage than what your circuit sees, so the true test of the tube is always in your amp. The tube tester does weed out non functioning or weak tubes pretty well however, as long as it is the mutual conductance type and not just an emission tester. For more info on tubes and amps, visit the boards at http://www.webervst.com/vstbbs/bbs.html, and at http://www.firebottle.com/ampage/. For ampage, click on the "more" button at the bottom right to get more amp forums.

Another board to read regarding tube amps is the Plexi Palace Vintage Amps BBS. Even though it's called the "Vintage Amps" board, they discuss and love all sorts of tube amps. There's even a special section just for discussing Vox amps.

wow... all great feedback!

Paul: I found the Spyder 212 to be a shreader amp also, but I couldn't get a decent clean sound and that was my frustration. But my amp experience is one billionth of yours and was even less at the time of the line-6 experience (2 years ago). It seemed like it did EVERYTHING but none of it very well. From there I went to a Fender Deluxe which was a major step in the right direction. Then I got the VOX and I REALLY love the sound (when its healthy).

Ok, HERE's MY VOX AC-15 SITUATION---------- this morning I took apart the amp to get at the tubes... and I do mean "took apart"... for some reason VOX requires you to disassemble the back and completely remove the chassis just to get at the tubes. If there was some other way to get at the tubes I didn't see it (but hey it was pre-coffee 7am!). A previous amp tech had also remarked on the awkward cabinet design. Anyways......

The VOX AC-15 contains:

2 power tubes: both were Groove Tube EL84S

5 preamp tubes: I found three Groove Tube 12AX7M, one Groove Tube 12AT7 and one Groove Tube 12AU7.

1 rectifier: Sovtek 5AR4

My first question is why were 2 of the preamp tubes different? Did the amp tech who put these Groove Tubes in just not bother to use all the same.... or is there a specific reason? Unfortunately I didn't pay attention which preamp tube came from which hole, although the preamp slots are marked (in pen) with different labels. Is it ok order 5 similar preamp tubes?

Secondly, what do you all think about Groove Tubes in a VOX? Could it be that I have yet to get the most-est best-est sound out of this amp?

Thirdly, I'm thinking I might as well spend a few more bucks and completely replace them all. I dont see any EI rectifiers of that type on
http://www.tubesandmore.com/ but I do see a FENDER and a RUBY. Any thoughts? Stay with the SOVTEK?

Thanks again for the help and advice.... I'm trying to pull this all together by a week from today.

oh yea... ONE MORE THING.... when I had the chassis out I powered up the unit and observed all the tubes to be lighting up. The two power tubes seemed to look the same, but a couple of the preamp tubes definitely glowed less bright than the others... possibly the two mismatched ones? I dunno.

Okay, where to start...? First off, preamp tubes don't need to be matched. But you do need to make sure the right ones are in the right place. That said, I was under the impression that the modern AC15 did not make use of a 12AU7 or 12AT7 and had AX7s all around in the preamp section. I'll check on that, especially as if those tubes are in the wrong positions you'll lose a lot of gain.

Second, the reason it's so hard to get into the amps to replace the tubes is due to CE regulations. Without that metal shield in place, the amp could not have been sold in Europe.

Finally, as long as they've been properly screened and tested for microphonics, most people I know seem to prefer the Yugoslavian EI tubes in the AC15. Ruby Tubes are much like Groove Tubes -- they do not manufacture tubes. They buy them, test them, and re-sell them. A couple of the EI's I have are re-branded as Ruby.

Thanks Kevin .... yea, if you could let me know about the preamp tubes that would be great.

>>>>tested for microphonics

Can you tell me what that means? Is that something I should specifically mention when I order or should I assume that the EI tubes will be ok?

As for the rectifier, it sounds like I could either order the Ruby or another Sovtek? How much does the rectifier come into play? Is it as important to the sound as the tubes themselves?

haaaa... I feel like a first grader on the first day of school.... this is great.

This kind of stuff I just soak up! Kevin is a priceless source. There are others in this band of miscreants who are also quite knowledgeable.

I'd like to recommend that you pick up "The Tube Amp Book" (don't remember the author, but he was the founder of Groove tubes.) Loaded with this sort of info, and also has classic amp reviews and schematics galore. Interesting ring binding so it'll lay flat, too. $50.00 at Borders...