question about power tubes

Dave Zirbel · From: Sebastopol, CA USA

I have 6L6s in my Fender Twin right now. What tubes will give me more power and headroom? I 've been gigging with it for the past two months and haven't had to turn it up past 4 yet, but I'm sure I will need to in the future.

Thanks-Dave Z

Jack Stoner · From: Kansas City, MO

If you want to modify it, do a search on fender here in the electronics forum. There were several threads about Fender amps including one long one that had a lot of info on modifying and also power tubes.

Len Amaral · From: Rehoboth,MA 02769

5881 is a direct replacement for a 6L6 power tube and will give you more head room. More importantly, you should replace the power tubes with a matched set. A Fender amp or any amp that has an adjustable bias should be adjusted with a new set of power tubes. Any amp technician can do this bias adjustment and it is well worth it as the tubes will last longer and the amp will operate at it's optimum. New Sensor Corp. has
Sovtek Russian made 6L6 or 5881 tubes and they are the best bang for the buck.

Michael Brebes · From: Northridge CA

As previously stated, a matched set of tubes with the correct bias adjustment will give you the max output before distortion. For best sound and volume out of your amp, I would recommend either Groove Tube or Svetlana 6L6/5881 tubes. They will be of the highest quality. I am partial to the Svetlana tubes because their various tubes do sound very musical.

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Bill Terry · From: Bastrop, TX

Check out some of the previous posts Jack mentioned. Somewhere in there somebody posted a whole lot of info about various pre-amp mods that give a little more headroom. Could have been Bob Metzger, but I'm not sure.

You might search on 12AT7, 12AU7, or 12AX7, the discussion involved the various gains available from different preamp drivers.

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bterry.home.netcom.com

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

Dave,

I'm going to take a different approach than the other respondents have. First, while you didn't elaborate as to what specific amp you have (Twin, Twin-Reverb, Blackface, Silverface, late Silverface, etc) I will assume it is a Silverface Twin-Reverb.

Now, if you're only running at 4 now, you have a lot of "headroom" left by simply turning up the volume, since you're probably only using 30%-40% of what the amp was designed to do. I don't think you'll run into clipping (distortion) until you get past 7 or 8 on the volume control, but a lot depends on what type of tone you're trying to project, and what kind of tuning you're using. The E9th is much less demanding in this respect than the the C6th. Some clipping will take place at the speakers themselves. Your amp will probably put out close to 100 clean watts, but those stock speakers in an open cabinet will have a hard time keeping up, especially with the intermodulation distortion caused by expanded chords. (To put this in layman's terms, when a speaker is asked to produce both high and low notes at a high volumes, the notes interfere with each other, and the speaker breaks down, causing distortion.)

Second, have you considered using an extension speaker?

When I played the big clubs, I made a simple box so that I could use an exension speaker cabinet with 2 more speakers. This box let me use 4 speakers, instead of just 2, and kept the impedance at 4 ohms. It's really simple to make, and it doubles your speaker radiating area. That makes QUITE a difference, believe me! Using an extension cabinet has a couple of good points. It lets you distribute (aim) your sound to a larger area, or just different directions. It maintains the value (originality) of the amp. It also maintains the reliability of the amp (an amp is like a car engine...the more it is hot-rodded, the more likely it will fail sooner).

The above thoughts are passed on because if you boost your amp output significantly, and use that all power with only the stock speakers, sooner or later...you'll be buying speakers...maybe not extension speakers, but replacements for the ones you've pushed too much...too often.

Been there...done that!

Bill Crook · From: Goodlettsville, TN , Spending my kid's inheritance

Dave...

After re-reading your post,I believe I would go with Donny's suggestions first before I started to tinker with the amp. He has definded what I think you are looking for here.

Headroom is a subjective matter, depending upon the size and shape of the room, if the floor is carpeted,even how many people is in there, and of course, if your playing outside, Headroom takes on a whole meaning ! Experienced players look at the site when they setup to help determine how much volumne they feel they should use in a situation.

Dave Zirbel · From: Sebastopol, CA USA

Thanks everyone! I wasn't really planning on hot rodding the amp. I was remembering a conversation I had with Dan Torres, the tube amp guru, and he had suggested some tubes that would increase power and headroom without having to modify the amp. I wanted to hear what the steelers choices were. I should probably try to dig up some old threads from the forum archives.
The amp is a 1971 Twin Reverb in a Vibrasonic cabinet with a JBL E-130. With the current set up it sounds real good. I'm playing a Sho-Bud Super Pro with George'l 10-1 pickups.
Donny Hinson: I like the extension speaker idea. How can I run another 4 ohm 15" speaker and keep a 4 ohm load with two speakers? Does plugging into the ext. speaker jack change the ohms or impedance?

Hooked on tubes! Dave Z

C Dixon · From: Duluth, GA USA

When referencing power capabilities of amps/tubes, remember that there are many ways to state the amount of power a given amp puts out.

Most responsible engineers say that continuous RMS Power using the amps own power supply is the only true power rating that is correct. I agree. Also it is a common mistake to confuse Power with Gain.

Thus wattages of over 55 amps for tube amps is usually a play on words.

As to the original thread's question; Unless you are driving your output stage to maximum power consistently, ya probably won't hear much difference between 6L6's and 5881's

And even here, we no longer have a number of manufacturers in this country making tubes that you can compare. We are probably limited to one or two foreign countries making tubes.

I would recommend you stay with the 6L6's.

Also, be very, very skeptical of "amplifier" technicians. I have found it extremely rare to find a tech who has a clue as to how to even set the bias on Fender Amps although NONE of them are hesitant at all about adjusting it.

Fender along with most other manufacturers was very inconsiderate about informing users/technicians on how to measure and adjust their amps. Sadly I must admit.

And most repair shops do not even have equipment for measuring power nor the technical "know-how" to do it if they did.

Not trying to be pessimistic folks, but I was in the business for over 34 years. Worked for RCA that entire time.

The above statements are true, albeit sad facts of life.

God bless you in what ever you do,

carl

Jay Ganz · From: Out Behind The Barn

Well, I've got NOS 7581A outputs in my old
'65 Twin Reverb. They're military versions
of the 6L6. They will increase your headroom for sure.
All you have to do is readjust your bias
to get the right current flow thru them.
If you adjust them a bit on the low side,
your amp will stay alot cleaner at higher
volume.

Jack Stoner · From: Kansas City, MO

One thing to consider on modifying "upgrading" "hot rodding" or whatever you want to call it to ANY amp.

Many responsible repair shops will not touch an amp that has been modified. Unless it is the shop that modified it, you have no idea what has been done to the amp and as a tech or shop owner you can't guarantee repairs. I used to turn away any known customized amp for repair.

I'm not saying customized amps are bad, just that getting them worked on after they have been modfied may be a little touchy.

Bob Metzger · From: Waltham (Boston), MA, USA

My three favorite tubes for loud and clean are: 1) Svetlana 6L6GC 2) Phillips JAN 7581A and 3) 6550. The 6L6GC and the 7581A are drop in replacements that only require re-biasing. The use of 6550's requires that you upgrade the filament supply of the amp and there's a few other minor considations, as well (this is a mod). Plan on having you bias looked at by an experienced tech when you change tubes and make sure he/she knows you play an instrument that appreciates clean sound, max headroom, ect. (that is, unless you're the King of the Fuzz Steel!) As most 6L6 type tubes are similar, don't expect alot more volume, as this is also a function of the transformers, gain structure and speaker efficiency. Instead focus on the tone and having the amp set up for clean sounds and not overdriven ones. Also, try not to be ruled by 'the numbers', instead use your ears to guide you; you'll be happier in the end.

No, plugging another speaker into the 'Ext. Spkr' does not change the ohms or impedance on a '71 Twin Reverb. It is still a 4 ohm output. What you can do: If you always use the two speakers, use 2 - 8 ohm JBL D-130's wired in parallel (which equals 4 ohms). Plugging into the ext. speaker jack with an extra speaker is the equivalent of speakers wired in parallel. This is the best possible 2 speaker solution; others involve compromise (to your sound and to the safety of the amp). If you have a 4 ohm JBL 15" speaker in the amp now and want to use another speaker, you could use an 8 ohm speaker. Wired in series, it'll be a little more than 4 ohms (but not 8 ohms, yet) and wired in parallel, it'll be a little less than 4 ohms (but not 2 ohms, yet). Trying to keep your combined speaker ohmage above 2 ohms or greater is a good idea for safety reasons and below 8 ohms for efficiency reasons. In this configuration, the 8 ohm speaker will not be as loud as the 4 ohm speaker, but that could be a blessing, especially if the ext cab's on the other side of the bandstand!

Bob

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

Dave, Bob is right. Since you already have replaced the two 12" speakers with a 15", you can simply plug another speaker into the extension speaker jack. Another 4-ohm speaker would give equal volume from both speakers, while an 8-ohm would be a little lower in volume than your existing speaker. One thing for sure, another 15" speaker added to the one you already have would give you a "really big" sound!

Dan Tyack · From: Olympia, WA USA

To go slightly afield of the original question, I have a VHT tube power amp with 4 tubes which they call KT-88s. I understand these are 6550 type tubes, but this amp is rated at 180 watts(stereo with 90 watts a side), but it is goes a lot louder and cleaner than a pair of twin reverbs.

I would imagine you would need to replace a whole lot of components (transformers, etc) to get this much power out of a single twin.

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www.tyacktunes.com

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

Dan,

A "Super-Twin", which is rated at 160 watts RMS would come pretty close, and would probably be a lot cheaper than paying someone to try and double a Twin's output...which, by the way, is well under 100 watts.

Bob Hoffnar · From: Austin, Tx

To get a tube amp up to Matchless or VHT type specs you must use a massive power transformer. They are real heavy and expensive.
Dave whatever you do, do NOT ever play through an amp that uses KT88's ! It messes up your mind and makes all those Fender amps look like Barney Fife compared to Mr. T.

6L6

KT88
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Franklin D-10

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Steve Feldman · From: Central MA USA

I just took delivery recently of a VHT 2/90/2 that I got on E-bay (the one Dan was talking about above) and boy, it's great. Real b@llsy low-end with a lot of punch, very warm and clean tone, sustain forever, and enough headroom to crank it. I admit that I don't know amps from a hole in the ground, but compared to what I've played previously (which has been some pretty nice stuff, if I say so myself) this thing seems to be on the next level.

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