Can we talk about tubes for a bit?

Gerald Menke · From: Stormville NY, USA

Hello,

I searched the archives but didn't see anything. The longer I play the greater my sensitivity to the kind of tube an amp has grown, since I have a few amps, all with 12" speakers, I do think the kind of tube compliment in them has a big effect on their tone.

I think as time has gone on I prefer the sound of an amp with 6L6s in it, and I have amps (or have had them) with EL 34s, 84s, KT88s, 6V6s. At first I loved the tone of the VHT 2/90/2 amp, but lately since I have been playing some amps with 6L6s off and on, the KT88s sound a bit cold and hard, could it be that the KT88s are such powerful tubes that they don't sag or compress the way lower output tubes do? Or maybe I don't ever use it up loud enough to really get them going.

A Deluxe sounds sweet, but 6V6s get dirty too fast for my taste for the steel, and EL84s, like in an AC-30 get too compressed. I think I just like the sound of an old Fender, but hell I have been playing through Twins since 1985, so big surprise there.
What do you guys think?

Gerald

Jon Light · From: Saugerties, NY

Hey Gerald. Cool that you are finding these things. I can't say that I have enough experience with enough tubes to feel confident that I know their characteristics. I do have 6L6's (properly biased) in my Deluxe Reverb and I like this amp better this way. I feel that the 6L6's have more roundness and punch than the 6V6's this amp came with. But the increase in wattage likely is a significant part of the difference too. I have a 4x6V6 amp I may bring to Hanks this Sunday to give it a workout. Your comment about 6V6 getting dirty too quick is tough to evaluate since 2x6V6 generates such low wattage that it is easily overwhelmed by steel. But this amp just doesn't have the puch that any 6L6 amps I use have and I'm starting to think that this is a characteristic of 6V6--softer attack.
As to the VHT, I think it is entirely possible that you just aren't able to drive it hard enough. Since you don't have enough gear,

, you could try a good speaker attenuator to allow you to run the amp in its sweet spot without blowing out the windows. It's a good way to find out what an amp really sounds like. Turning down an amp really can take it out of its best operating zone (you've probably often heard it said and heard for yourself that a Fender turned down to 3 just isn't going to sound like a Fender) and this probably applies to any other tube amps. Probably solid state amps, too, for that matter.

Donny Hinson · From: Glen Burnie, Md. U.S.A.

Gerald, I think you've figured out why American manufacturers were so fond of the 6L6GC...it worked, and very well, at that! Of course, the circuitry and speakers have a lot to do with sound, too, (that's why Brittish amps sound, well, "Brittish").

As an all-around beam power tube, the 6L6GC was sort of like the 327 Chevy, or the 289 Ford. It just worked very well, was cheap and reliable, and put out a lot of power for its size. Maybe it's the plate area, or maybe it's the inter-electrode spacing and capacitance. Whatever it is, few will argue that that venerable old design is a "tone king", and very, very hard to beat for use in instrument amplifiers.

As far as those "powerful" KT-88's, they really ain't so great! In fact, they kinda remind of Alka-Seltzer bottles!

They're tall and skinny, and have no "beef" They were designed for "Hi-Fi" use, and they sound a little "flat" and cold because that's what Hi-Fi nuts want..."colorless sound". We musicians like body, color, and "roundness" in a tone. And as far as "powerful" goes, I'll take 6550's (the 6L6's big brother), over KT-88's any day!

[This message was edited by Donny Hinson on 24 March 2006 at 05:24 PM.]

Bill Creller · From: Saginaw, Michigan, USA (deceased)

I have an old Gibson G8 with 6BQ5s that I always thought was a trebly sounding piece of junk, until one day I cranked it up on the volume, and it came ALIVE. Problem is, like mentioned above, too much volume. I never run my guitars with the volume knob backed off because it affects tone too much.
So the old Gibson needs an attenuator, whatever that is. Is it like an L-pad? and can I build one?
Regards BILL

Jon Light · From: Saugerties, NY

Yeah, Bill, you've got the right idea when you say L-pad although at the wattage we are talking about, we looking at some honkin' resistors. But for reasons that are far beyond me, attenuators based on simple resistance are sort of discredited in the amp/tone community now. (My minimal understanding is that amp/speaker impedance is not a fixed quantity across the spectrum and therefore an attenuator needs to be responsive to the variations of the amp output in order to not color the sound.) More sophisticated units cost a bunch. The Weber choices are your best bet for the money but I have no personal experience of any of these (although a guitarist friend uses and swears by the THD Hot Plate.
http://www.tedweber.com/atten.htm
http://www.thdelectronics.com/products/hotplate.htm
http://www.drzamps.com/airbrake.html

Delvin Morgan · From: Lindstrom, Minnesota, USA

Are attenuators only designed for tube amps, or do they have them for SS amps like the N112?

John Billings · From: Ohio, USA

I use a Z Air Brake. It is very good. Built by Dr. Z, designed by Ken Fischer of Trainwreck fame. It has 5 levels of attenuation, the last level has an adjustment pot on the outside, but you can open the box up to adjust the "click" settings 1 through 4. They're fairly expensive.
I always take everything Weber says with a grain (block) of salt.

James Quackenbush · From: Pomona, New York, USA

Gerald,
There is a "sweet spot " for just about any tube ......A lot of Fender players favor 6L6's as when running 4 of the them you have a good 100 watt's or more at your disposal ...You can crank up a Twin and get a good clean tone with the tubes in a good sweet spot ..Not only do you have power tubes, but you also have to remember your preamp tubes ....Preamp tubes play a HUGE part in whether your tone will be a clean tone or an overdriven tone ..... The various frequencies that are used in a preamp also play a HUGE part in the tone of the circuit .....Don't overlook the preamp and the preamp tubes ....A good example is 2 amps running 6L6's ......One amp would be a Fender Twin , and the other amp would be an Engl Powerball !!....Both run 4- 6L6' s..... One is for chicken pickin and good ol country, and the other is for some of the heaviest metal you will ever hear in your life .... If you're not pushing the amp hard enough to get the tubes working or getting into the "sweet spot" than you don't need that amp 's power ...
I'm not happy with my 2/90/2 at lower volumes , but crank that sucker up and it will give you enough clarity to fill a room, and a bottom end that does NOT turn to mush .... Playing at bedroom levels the 2/90/2 is somewhat boring to me , but then again, this is not the way I use the 2/90/2 !!....CRANK IT UP !!......Jim

PS.....Want HUGE BASS and good mids and high's at bedroom and higher levels ?.....Try some KT66's !!...

Jack Stoner · From: Kansas City, MO

Along with the Model of tube is the Brand of tube. Even in the "old days" (back in the 50's and 60's)RCA was considered by many as the best tubes. I only carried RCA 6L6's in my shop, and that was what most wanted anyway. GE and Sylvania didn't seem to cut it like an RCA 6L6.

But tubes are only part of it. Many consider the amps with a rectifier tube better than the ones that had a solid state rectifier. And the actual circuitry and particular components also has a major part. e.g if you built a new amp, using an old Fender schamatic and built it exactly like the old amp, with NOS RCA tubes, it would not sound the same because of the components that are available today.

There is also a parallel to the sound with solid state power amps. Amps that are designed for general purpose audio amplificaton (e.g. PA use) such as the Peavey DPC series of amps, the Carvin solid state power amps, ART power amps, etc sound very harsh and "sterile" amplifying musical instruments. On the other hand power amps designed for musical instrument amplificaton such as the MOS Valve amps, ADA power amps (which have a 12AX7 as the input amp) are totally different and have much warmer sound. I din't meant to hijack the tube post with the solid state issue, but mentioned it for comparison.

Gerald Menke · From: Stormville NY, USA

Very interesting you guys! Keep those replies coming. Not directly related to tubes, but when you switch an amp to Low Power, as you can do on the 2/90/2, what is happening there electronically? I am guessing the idea is to be able to get the sound of the tubes really working at a volume that won't take your hair off. I wonder how this is done. I also wonder if the the 2/90/2 has a solid state rectifier or not. I have generally preferred amps with tube rectifiers, myself.

Bob Hoffnar · From: Austin, Tx

Gerald,
A thing I used to do with my 2/90/2 is just use one side of it. Cranking up just 2 of the KT88's gets to the sweet spot a little faster.

When I was experimenting with the THD BiValve I tried every combination possible with tubes. To my ear the absolute best sound was with 2 KT88's in the power section. Also one of Greg Leisz's main amps is an old Fender showman that he had modded for KT88's. I used it out in LA for a couple gigs and it was just about perfect.

I have been happy with the stock Fender reissue twins and my old stock showman is all I will use for recording anymore so I'm happy with the 6L6 sound these days.

------------------
Bob
upcoming gigs
My Website

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

There have been a few recent discussions on tubes. For example:
http://steelguitarforum.com/Forum11/HTML/008531.html
http://steelguitarforum.com/Forum11/HTML/008442.html

As I said there, IMO, anybody interested in the current status of available tubes should read the Watford Valve reports:
http://www.watfordvalves.com/reports.asp

They talk a lot about the range of currently available tubes of many types, both from a hi-fi and guitar amp perspective, which is very useful for us steel players.

IMO, each tube type has a lot of range in it. Some 6L6s are almost 6V6s and some are almost 6550s, in terms of power, headroom, and plate voltage handling. 6V6 tubes range all over the place, as do all the others. Then there are the preamp and rectifier tubes - they are also not all created equal.

One needs to also consider the fact that amps are designed around a particular tube - not just the nominal designation like 6L6, but specs are often tweaked to suit a particular variety of tube - the ones readily available at the time in large quantities and at an appropriate price.

To give you an example - a typical Deluxe Reverb puts around 420-430 volts on the plates of 6V6 tubes. In the old days, this was no big deal since the good old American tubes were overdesigned. Now, only the hardiest tubes will survive, and I know lots of guys who have given up on 6V6 and moved to 6L6 - and hope they don't blow the filament winding on the power transformer. But I owned a real early Tone King Imperial (two-tone white/green naugahyde), which used the cheesiest Russian 6V6s imaginable - it actually sounded much better with the cheap tubes than with my usually-preferred NOS GE, Philips/Sylvania, or RCA 6V6 tubes. The designer built the amp around the lower-voltage design center tube, I assume because that is what is mostly available these days in quantity.

Of course, there are a lot of other differences between a Twin Reverb and a Deluxe Reverb - tone stack, transformers, plate voltages, and so on, not to mention tolerances in components, which can vary up to 10 or 20% even on exactly the same design.

Whatever one thinks of Groove Tubes - good or bad - I think Aspen Pittman made a big contribution by convincing guitar players to listen to amps with different tube types, and evaluate them using their own guitars and ears. I don't think there is any "algorithm" to determine which tube an amp should use - there's just tone and human ears. There are some general principles, but it isn't an exact science and personal preferences and psychoacoustics play a major role.

On the subject of power attenuators, I don't generally like them because I don't like to push amps to the point that they get "ratty" sounding. If I don't want to be loud, I prefer to use a smaller amp turned up to its sweet spot. But Jon is correct - the typical speaker load an amp sees has quite a bit of inductive reactance, due to the speaker coil and magnet. I have used things like the Scholz Power Soak and other purely resistive attenuators - they sound, to me, ratty and thin. I suppose if one just cuts 3dB or so, it isn't too bad. I have tried some of the reactive attenuators, and they were OK, but I usually prefer the non-attenuated sound.

One can make a cheap inductive power attenuator by cutting the cone out of a speaker, being very careful to stabilize and not otherwise mess up the voice coil. I tried it on a 70s Twin Reverb speaker whose cone was torn up about 10 years ago after reading a "how-to" article in Vintage Guitar Mag by Gerald Weber of Kendrick Amplifiers. I used it to replace one speaker in a Twin Reverb to "tame" it a bit. It worked pretty well. I believe the point of that article was to make a "silent speaker" for running a tube amp silently with a line out for recording, but it worked fine as an attenuator run in parallel with a regular speaker.

Hey, Bill - if you're talking about a GA-8 Gibson, now you're talking one seriously great amp for guitar, slide, or lap steel. I have owned several of the tremelo-model GA-8T amps over the last 20 years, and cranked, I don't think there is a better-sounding guitar amp on the planet. The GA-8 power tube is 6BQ5/EL-84, but the GA-8T uses the 6BM8, which is a dual pre/power tube with one-half of a 12AX7 and 6BQ5 in the same bottle. Both these amps are great. Right now, my main Gibson is a GA-20T Ranger with the original RCA 6V6 tubes. Sounds pretty similar to my GA-8T amps, but stays a bit cleaner with the 12" Jensen when I push it.

All IMO, of course.

Ken Fox · From: Nashville GA USA

http://www.vacuumtube.com/FAQ1.htm

Another superb article on current production tubes and the problems/improvements that exist.

Well worth the reading time!!

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

Yeah, another good article with lots of "insider" info. IMO, these articles should be required reading for anybody who depends on tube amps. The penalty for not keeping up is the potential to get tubes that literally destroy the critical components of an old amp.

Bill Creller · From: Saginaw, Michigan, USA (deceased)

Jon, thanks for the attenuator links. The Webber stuff looks like something I could try.
BILL

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