Sound of EL34's

[deveng]

I need some information and advice. I've been playing guitar through vintage Fender amps (6v6 and 6L6) for many years. My 1955 Deluxe and 1962 Bandmaster sound very good and they have a signature sound. I designed and built a tube preamp stage with a Marshall tone stack and it does add some flexibility but they still sound Fenders (no surprise). I do both recording and performance and have been looking at some of the boutique amps to get an additional sound that I've not been able to get from the Fenders. Interestingly, I've found that amps with EL34 or EL84 output tubes are the ones I like.

I just happened to have an old Altec 345A amplifier my father gave me! It's a 60W stereo amp that uses EL34 output tubes, Peerless transformers and it works. One channel has a pair of old Amperex EL34's. As an experiment I ran my guitar through my tube preamp (which has both line level effects loop and a high impedance output to guitar amp) line output into the Altec. To my pleasant surprise the tone was there.

Has anyone here modified an old tube amplifier like this to use as a guitar amplifier? I'm thinking about keeping the Altec generally intact and adding additional preamp gain stages (externally) using one channel as a "clean" and the other with more gain to push the EL34's. I don't have a schematic yet. It uses a 6AU6 and a 6C4 with each pair of EL34's. It also has a 5U4GB rectifier. The amp is fairly quiet but suspect it could use new filter caps (Mallory FP 40uf 500V) and will likely need new coupling caps.

Before I take on this beast, do you think it's worth the effort? I figure for a couple hundred I may have the makings of a very good recording amp.
Any comments?

Regards,
Jeff

 

[JRE Productions]

When rack systems for guitar were all the rage, I did the same. I used a Camielion preamp and a simular altec tube power amp. Great sound! It became a hassle to lug around and I went back to a combo amp. If you like the sound of EL34 mod your guitar amps. I use a Rivera chubster that came stock with EL34 and converted it to 6L6 because to me...that is the sound.


JD

 

[Gus]

People have been modding older tube PAs mono hifis etc to guitar and bass amps for years.

One thing to think about the stock amp might have more $ value left as it is you might be able to sell it or part it out and make some good money or maybe not. Or maybe replace some old parts and use it as a monitor amp.

I have bought old SE pa amps for $5.00 to $10.00 dollars in the past. It is fun to build old champ/princeton style amps with them.

The "sound" of a guitar amp is not just the output tubes it can the operating points, ultra linear or screen supply at the output tubes. It also has a lot to do with how the gain comes up in all the stages. Some output tubes have more gain and if driven from the same PI will distort before another tube But then you have the pre tubes and there gain then you have the high and low pass filters between stages.

FWIW I tend to like the sound of a champ SE type amp with a 6v6 over an el84 the el84 has more gain and it changes the way the distortion happens in the amp. In this case the output will distort more at the same input than a 6v6.

Then there is feedback or no feedback, ultralinear triode mode...........

 

[deveng]

Thanks for the quick replies!

JD, I don't want to modifiy the Fenders since I still love the sound of these amps and want to keep them stock. Also, when I record I need these sound too! Since most of my work is recording, I'm not concerned about moving the amps (I have my own recording studio). Did you modify your Altec amp?

Gus, I thought about selling the amp (worth maybe $700-800). But, this won't buy the amps I've been looking at. They run close to $3k! I also like the idea of having a somewhat unique sound. I do realize the total sound comes from the entire chain (pramp, output, speaker and cab) but there is a specific tone that comes from these tubes that is one of the keys to the tone I'm looking for. I'll add the rest as needed.

Regards,
Jeff

 

[martthie_08]

if that amp is still worth more than $500 I wouldn't hack it up - that's my personal opinion, of course. With that kind of money you could DIY almost any amp out there (just the head).

If I were you I'd hunt around to find the basic, classic design that you find suitable and then copy that and adjust it to your specific needs. I too have been playing a lot of Fender amps, mostly 61' brown princeton (love it), but aquired an orange matamp about a year ago, which has been a really interesting alternative. Last time in the studio we hooked up an old AC-30 from a friend and, well, what should I say, I really need to have one right now, absolutely killer deep tone. As you can see by now, I am kind of addicted to this topic, but maybe you should look at some of the classic British amps available: Vox, Hiwatt, Orange, and well, Marshall of course. Also have a look at the 18 Watt project, while you are at it. Also write a little on your playing style, whether you crank it up, etc..

cheers, Marten

 

[pmroz]

.
think it was alk509 who put this link up before:
http://www.geofex.com/Article_Folders/old2new.htm
Dunno if it helps much.
paul

 

[CJ]

The best amp I have ever made uses a high fidelity output transformer from a Fischer stereo. Pair of Amperex EL 84's thru that trans is great. Guitar amp makers usually skimped on the output iron because
1) it was cheaper
2) the rolled off edges on the freq plot fit the electric guitar eq curve.

But, the stereo transformer really brings the guitar to life.

Peerless made the best iron back then, so steal that transformer and make yourself a killer amp.

 

[clintrubber]

I'm fairly sure about how this powertube would sound ! :wink:













sorry

 

[Flatpicker]

[quote author="martthie_08"]...I am kind of addicted to this topic...[/quote]As of lately, me too! Obsessed is more like it. I don't know what has come over me. I've been studying the 18 Watt site like I was preparing for my master?s degree.

Btw, I posted on another thread about converting a Bogen CHA10 to a guitar amp. I finally got around to modifying the PS with proper grounding and fuse, put in a new cap can, swapped that whacky mic jack for a ¼?, and started jamming away! After about an hour or so, it died. Killed the rectifier tube, me thinks? (Should have put a 20 ohm after it for short circuit protection, but hindsight is always 20/20.) Anyway, it sounded great cranked up, but had very little sustain at lower ?clean? volumes. I?ll eventually get back to it and resurrect the thread when time allows. Too many other irons in the fire right now?

 

[deveng]

Guitars, Tone and music. That's what brought me into the world of design and DIY! I've always sought after the sound that is best. Of course this is another topic on this board.

Marten, my plan is to keep the amp as intact as possible. Document all connections and save all original parts. Since it already sounds pretty good I don't expect I'll need to make any global changes. Maybe just some gain adjustments, cap value changes a bit of rewire. I'll build the preamp sections on a turret board and mount close to the original amp. Not much different than it was designed to do as a matter of fact. To collect or buy all the parts of quality in this amp would cost more than this amp is worth. Sockets, chassis, switches, pots would all add up to even more. As for a style and tone I really like, check out Buddy Whittington on the title track of "Blues for the Lost Days". I believe this is a Dr. Z, EL84 amp with a Stratocastor. Sounds fantastic.

Paul, thanks for the link. I found that one too!

CJ, The Peerless transformers (2 output and power) must weigh in at about 35lbs! I've priced the Amperex EL34's and they run anywhere from $40-125. So, I agree. I don't want to go out and try to buy transformers that will compete with these. I'd bet they would cost me a bundle. I think I actually prefer the EL84 low wattage amps and I may build one of those after this one..............Do you have details on your preamp mods and how you did this?

Flatpicker, I can vote for low wattage amps! For recording, they are the best. Also, when I go to play for fun, I plug into my Deluxe. Fantastic tone at low volume. My "new" amp is a power amp only so I'll need to set up at least 2 preamp gain stages possibly 4, to get the overdrive, effects loop and tone stacks.

Regards,
Jeff

 

[deveng]

I forgot to mention. I've ordered the schematics for the Altec 345A and I'll post as soon as I get them if anyone is interested. It's got an interesting speaker switching setup that I'll probably modify a bit and use for channel switching.

Regards,
Jeff

 

[CJ]

I wouldn't sweat canibalizing an Altec chassis unless it was something real cool.

Now an Ampex chassis...that might be tough to start ripping from.

 

[deveng]

I'm working on the preamp stages to feed the Altec amp and of course there's a 1000 different ways to do this. I've found in previous designs that placing a typical Marshal tone stack off the plate changes the contours due to the higher source resistance. So, I've looked into using 2 tube stages in parallel (1-12AX7 actually). Is the source resistance now the 2 rp's in parallel with the plate resistor? Other than a slight reduction in noise (a possibly unwanted increase in capacitance) and the reduction in output impedance at the plate, is there any other advantage to doing this? I could use a cathode follower but it appears the only advantage would be low output impedance. Comments?

Regards,
Jeff

Also: I'm trying to get access to a scanner to post the Altec 345A schematic and I'll add my preamp stages as well.


P.S>>> Sorry for asking this question too soon. I just found the link:
http://www.groupdiy.com/index.php?topic=52031&sid=d621c2cbdc43c87ae10a6d3f6cf297fc here that talks about this already!

 

[deveng]

With my studio projects I have unending patience.....but with guitars and amps I have no patience at all. I want tone and I want it now. So, I ditched the Altec amp idea, went and bought a Dr. Z MAZ 38. All I can say is WOW. This thing sounds really good. It doesn't have EL34's but it does have EL84's and mixed Celestions. The tone knocks my socks off with single coil pickups. Now I can concentrate on finishing DIY studio gear to record this thing.....now only if I can just put my guitar down long enough to grab a soldering iron.

Regards,
Jeff

 

[Flatpicker]

[quote author="deveng"]So, I ditched the Altec amp idea, went and bought a Dr. Z MAZ 38...[/quote]Cool! A friend has a MAZ 18 and I really liked it. I'd like to see a MAZ 18/38 schematic just for curiosity's sake. I read it is similar to some old Hammond el84 amp (forgot the #). Guess it could be reverse engineered from photo's off the web, but I haven?t gotten that desperate yet, haha. Anyway, they are nice sounding amps.

 

[deveng]

Flatpicker,

Yes it does sound awesome. It's the sound I've been looking for. Very versatile but not for everyone. Not for metal or fusion players. It's interesting since I think that both the EL34's and El84's have a certain sound that is "similiar" although I'd be hard pressed to describe exactly what that similarity is! I don't have schematics but I'd like to see them for both the MAZ 18, 38 and also the Carmen Ghia. That one sounds really good too. These amps are very reasonalbe so I don't think building one would be a good way to go (but I thought about it). Theres an interesting circuit Dr. Z used a version of out the Radiotron Handbook. It's called "cut" and is very effective. I want one on all my amps! He talks about it openly on his web site. Sounds like a great guy and he knows what he's doing that's for sure.

Regards,
Jeff

 

[CJ]

You can look at the tube specs and see why they sound different.

Do a chart for Rp Gm and bias on 6L6GC, 6BQ5, and 6CA7/EL34for a rough comparrison.

I think it goes somethin like this:

6L6GB 23,500...5700...-22.5
EL34 15,000...11,000...-13.5
EL84 38,000...11,000...Rk = 135, whatever that translates to.
Probably about -10 volts.

 

[mr coffee]

Saw\Heard a Dr. Z and was very impressed by the range of tones coming out of one amp.

Did it come with a schematic? I'd sure like to see what was going on in there.

 

[Flatpicker]

[quote author="deveng"]...Theres an interesting circuit Dr. Z used a version of out the Radiotron Handbook. It's called "cut" and is very effective...[/quote]I think the "Cut" control is just a 250KA pot in series with a .0022uF cap (or some similar values) across the phase-splitter outputs. VOX, Matchless and other amp mfgs use this method.

I would reverse engineer my friend's MAZ 18 if he'd let me take it apart. :razz: But like I said, there are many photos of the insides floating around and it could probably be done from those.

(Edited to correct cap value typo - thanks dabo!)

 

[dabo]

That should be .002 uF. At least that's the standard value in the V*x circuits.