EL84 discussion on the Dr. Z Forum

Over on the Dr. Z amp forum I have a column in their Ask the Experts area.  Yesterday I was in one of the other areas and came across a post on the Doc's new Z Wreck amp.  

For a year or more this amp was not a product offered in the Z lineup.  The amp was only in the hands of Brad Paisley.  The amp is now available to all. 

As a side note, there is info on the amp at http://www.drzamps.com/amp/z_wreck/ 

One of the owners of one of these amps had posted some comments on the EL84 output tubes he uses.  I jumped into the thread.

The amp owner's initial talk was about some NOS Bugle Boy tubes from Holland:

I have no problem taking these out but how about a matched quad of matched Amperex Bugle Boys from Harleen in the early 60's.......got two spares also. I also have some RCA Blackplates but I will probably never try them

My initial comment back:  I would save the NOS stuff for the studio. The JJ EL84S is a great sounding tube that has a long life and is reliable. Cathode biased EL84 amps go through tubes somewhat rapidly so I would save the NOS output tubes.

In many of Brad Paisley's amps the output sets are changed every 10 or so shows, about every 30 or so hours. I hand trace tubes about 20 quads at a time for Chad Weaver (Brad's tech). If anybody wants info on what I look for on Brad's tubes feel free to drop me a note.

In the case of Buddy Whittington; he and I share a common Z amp model where he always says mine sounds better than his when he borrows mine. Mine is dead stock as is Buddy's. The difference? Buddy changes his output tubes when there are months of hard use on them. When he borrows my amp I only have 5-10 hours on a new output set, enough time to assure reliability.

One of the other folks chimed in with:

Thanks for the great advice and info Myles!

Anyway you would want to post "what I look for on Brad's tubes " here? or is that super duper private info?

That brought on my reply that I was the basis for this particular post:

Not private at all.

First, I ask my vendor to only send me tubes in a plate current range of 39-44 milliamps from their test machine. My test equipment is calibrated to the same standard as theirs, RCA book standard spec for an EL84.

Industry spec for an EL84 is 48mA but if plate current is dropped a touch the amp is a bit cleaner at Brad's settings and fits his personal taste better.

If you go to http://www.guitaramplifierblueprinting.com/Tube/6BQ5-rca.pdf and look at page 4 of the data sheet you will get an idea.

I look at some of the specs such as plate current, transconductance and plate resistance as initial checks but then I curve trace all quads and match them into sets based on their curve traces. There is a reason for this.

Just about every tube vendor I know matches tubes at idle for plate current. In some ways this is good enough but it only tests the tubes at idle. This is sort of my setting my Scion Xb to idle at 750 rpm and having the Doc set his BMW idle to 750 rpm and then stating the cars are matched.

I match traces over the entire operating range of the tube because I am pretty sure that when I have heard and watched Brad he does not play with his volume controls on the guitar and amp turned all the way down. Most tubes which are matched at idle show many places where they are not matched when operating.

I also look for rise time on the tubes because Brad sometimes plays notes that follow each other as fast as a speed metal player. Can't have a laggy tube in the set or articulation is compromised. There is also more background hum if things are not closely balanced.

As a side note, if Brad wants to soften things up Chad Weaver has a selection of different phase inverters so those can be changed to drive the output tubes in a different way to change output, clean headroom or change rise time and some aspects of distortion to the output set.

The tubes come from http://www.arselectronics.com/ where I deal directly with Marty who I have known for years. As he goes through EL84 tubes for their business he puts aside tubes that he knows I will need so when there is a need they are there to be sent to me in bulk.

A few EL84 data sheet links to go along with some I have posted on my GAB website:

http://frank.pocnet.net/sheets/155/e/EL41.pdf
http://frank.pocnet.net/sheets/010/e/EL84.pdf
http://frank.pocnet.net/sheets/084/e/EL84.pdf
http://frank.pocnet.net/sheets/129/e/EL84.pdf
http://frank.pocnet.net/sheets/163/e/EL84.pdf
http://frank.pocnet.net/sheets/030/e/EL84.pdf 

I hope this answered some questions. If folks have others feel free to ask.

Myles Rose is the founder of Guitar Amplifier Blueprinting which provides support services and training for touring bands and individuals as well as blueprinting services.   You may contact me from the link.  My direct contact information is provided as well as links to two of the Internet forums where I answer technical questions.  You may also ask questions in any post in this blog by using the comment application on each post.

When I am not doing something related to music I do what I can to support the homeless of Los Angeles either directly on the streets at night or through my good friends at Union Rescue Mission.

www.urm.org