Attn; Ken Fox, Tim Marcus, etc..Biasing tubes in HRDeville

Todd Brown · Post by **Todd Brown** » 31 Jul 2011 5:24 pm

Fender recommends biasing the dual 6l6's at 60. Apparently Fender sets them a little colder from the factory? What would be the most ideal for pedal steel? I think the higher you go numerically ,the hotter it will push the tubes, I know this decreases tube life , but what does it do for overall tone of the amp?

The factory tubes are still in . Would it be worth trying to re-bias these to get the best performance out of whats left in them? Or just replace ?

Factory power tubes are White label Groove Tubes GT6L6B's . What other power tubes would be recommended for pedal steel?

Factory preamp tubes are Red label GT12AX7's . What are some differences with these and the 12AU7 and 12AT7's , or the 12AY7's in relation to a pedal steel players needs,(more volume, less breakup).

If anybody has a HR Deville, and plays steel through it, what tubes are you running ?

I'm also gonna put the Eminence Steel King 15"speaker in this Deville.The won that looks like a JBL. I know of a couple forum members from North Carolina, Tony Prior and Chuck Snider , that have put a 15" in their Deville , anybody else?

Ken Fox · Post by **Ken Fox** » 31 Jul 2011 7:08 pm

This post might answer a few of your questions:

http://bb.steelguitarforum.com/viewtopic.php?t=209379

60ma per tube seems awfully hot for that amp!

Ken Fox · Post by **Ken Fox** » 31 Jul 2011 7:11 pm

this is fromthe HR Deville manual, I see no refernece to the bias level at 60ma.

NOTES REGARDING BIAS:
Your new Fender amplifier has an internally mounted
variable bias control. The bias control is used to set the
idle current in your amplifier's output tubes, properly
matching the amp's performance characteristics to the
types of tubes you intend to use. Each different tube
brand and manufacturer may require a slightly different
bias setting. If you replace your tubes with the Fender
types your amp was originally outfitted with, no bias
adjustment is necessary. Having said that, an amp's
bias can drift over time in much the same way the
intonation settings on your guitar can. Both need to be
looked at periodically. The bias setting of a tube-type
amplifier is analogous to the idle setting on a car. If it is
not set properly, every other aspect of the system
suffers. A properly biased amp will sound great and
will run reliably and safely.
Also, beware! Internal voltages of tube-type amplifiers
are lethal and capacitors are capable of storing these
lethal charges. To ensure tone and safety, biasing
this amp (and all other amps) should be carried out by
qualified personnel only.

Todd Brown · Post by **Todd Brown** » 31 Jul 2011 7:18 pm

thanks Ken, yeah ,I know the manual has no reference as to what level to bias the tubes.

To clarify, the 60ma bias level is total for the 2 6l6's. 30ma per tube. this is what is found on the web. Wondering what kinda thoughts and opinions some fellow steel players would have.

Check out this video I found
http://www.youtube.com/watch?v=19IUadZJ ... r_embedded

Ken Fox · Post by **Ken Fox** » 31 Jul 2011 7:36 pm

Nice video. Not a bad method for that amp. I use a bias meter and actually calcualte the bias current based on the plate voltage and actual power dissipation. You can follow that link above for more info.

Todd Brown · Post by **Todd Brown** » 31 Jul 2011 8:02 pm

So if I were to change the power tubes , and pre-amp tubes, do you have any recommendations on tubes with these amps for steel? Does the 30ma seem about right on the 6L6's, or is it just matter of taste and how fast I want to burn through tubes?

Ken ,I really appreciate you help and willingness to share your knowledge with everyone here. I feel like I've bothered before with questions and to get your opinion on things. You've always been there to answer my questions and give what you know.

I'm just one person ,but I know there's plenty more out there like me, that you've taken your valuable time to help, expecting nothing in return. For this, I and everyone else owe you!!

BTW , just scored a '73 Twin Reverb on ebay, very clean, pair of Celestion G12 vintage 30's, serial #A54162, I'll be contacting you about going over it for me..

Larry Robinson · Post by **Larry Robinson** » 1 Aug 2011 3:12 am

The HR Deville schematic shows the tube current to be 60ma for the pair of 6l6GC with Ep at 485VDC. There is a 1 ohm resistor in cathode circuit of 6l6GC tubes. The voltage drop accross this resistor in mv correlates to current thru the resistor in ma (ohms law). As tubes age, the ability of the cathode to emit electrons diminishes which reduces current flow through the tube. Bias voltages rarely change unless there is a power supply problem. reducing the bias voltage will increase the tube current. However, the dynamic characteristics of the tube will also change and it may operate in the non-linear portion and disortion will result. It is important to insure that 6l6GC tubes are used because of high plate voltages in this amp or distortion will likely occur.

Ken Fox · Post by **Ken Fox** » 1 Aug 2011 5:39 am

A handy web page:
http://www.webervst.com/tubes1/calcbias.htm

That page shows a max of 43.2a per tube at 485vdc. Fender is certainly running them in a safe range at 30 ma. Without your amp on my test set up I could not recommend a bias setting. Properly setting bias to a given value is not a generic answer that I know how to give. 30 ma per tube is certainly safe, but may not be the optimum tone for the amp. Remember that as that bias current is increased the plate voltage will in fact go down. The higher the bias current is means the harder the tubes are working and also more stress is put on the primary windings of the output transformer.

Tim Marcus · Post by **Tim Marcus** » 1 Aug 2011 7:27 am

Todd Brown wrote:So if I were to change the power tubes , and pre-amp tubes, do you have any recommendations on tubes with these amps for steel? Does the 30ma seem about right on the 6L6's, or is it just matter of taste and how fast I want to burn through tubes?

It depends on how rich you are feeling. A full set of new old stock tubes is always best, but could cost as much as the amp. You can try a NOS tube in the first stage and then a pair in the output.

I spent a lot of time going through new manufacture tubes in order to find the right ones to put in my amps. I don't want to bore you to death with all the details, but if you are going with new tubes I can tell you some of what I have found that work well in my experience:

Avoid the new production tung sol at all costs. Especially output tubes - those things pop right when you don't want them to.

Also, I've had a hard time finding JJ output tubes that don't rattle after only a few hours. JJ preamp tubes are awesome - I recommend getting them from Ruby Tubes because they come with a 6 month warranty. But the 6l6 and 6v6 are frustrating to use.

Any ruby branded tube comes with that warranty, so I use them exclusively now. And they test their tubes more than any other distributor. It's a good place to start.

Ken Fox · Post by **Ken Fox** » 1 Aug 2011 7:30 am

Having installed and used well over 100 JJ power tubes for over 6 years I have not found that to be true at all, Tim. I have amps all over the coutry using JJ power tubes as well as repaired amps, never heard of that as an issue.

Ken Fox · Post by **Ken Fox** » 1 Aug 2011 7:34 am

Ken Fox wrote:Having installed and used well over 1000 JJ power and preamp ntubes for over 6 years I have not found that to be true at all, Tim. I have amps all over the coutry using JJ power tubes as well as repaired amps, never heard of that as an issue.

Tim Marcus · Post by **Tim Marcus** » 1 Aug 2011 8:35 am

maybe you get the good ones over there in Georgia!!

Seriously - every amp I build with JJ output tubes rattles eventually. I do a lot of testing before I let something leave the bench, and even gig with the amps a little bit before they go to make sure this does not happen, but it always does so I eventually threw my hands in the air and stopped using JJ's on the output.

I have found a good alternative to JJ's now after some searching. I have only had them in my amp for a few weeks so I am still skeptical, but so far they appear to be free from rattle and they sound better too. Hard to believe - because JJ have such a great reputation, but I am telling you my recent experience has not been anything but frustrating.

At this price point, I can't sell an amp that is not 100% guaranteed therefore the JJ's are no longer invited to the dance.

Note: their preamp tubes are excellent and I will continue to use them with the Ruby brand

Todd Brown · Post by **Todd Brown** » 1 Aug 2011 9:50 am

Guys, what about the Groove Tube 6l6 GE's for the output? Supposedly made with majority USA made components, on old General Electric equipment that made tubes back in the day? It's easy to find a matched pair around $50 shipped.

The Sovteck 12AX7wc is stock for all three preamp tubes. These are reported to have very low microphonics and noise , while low gain as well.

Looking at the back of the amp , with the 2 6l6's on the left side,which preamp tube is position #1? Is it the one on the left or right

Rich Santucci · Post by **Rich Santucci** » 1 Aug 2011 10:54 am

[Looking at the back of the amp , with the 2 6l6's on the left side,which preamp tube is position #1? Is it the one on the left or right[/quote]

Looking atht the back of the amp with the o/p tubes on the left, it is the preamp tube furthest to the right.

Des Hetherington · Post by **Des Hetherington** » 8 Aug 2011 1:46 am

Ken, in my Fender 1992 Blues Deville, i am running two 1960 RCA 6L6GC output tubes, and new Tungsol preamp tubes, i notice when i plug my Steel guitar into it it makes a strange harmonic rumble,lower notes seem to trigger it more than top end notes.. Could this be that the tubes havnt been biased? its not so noticeable when i play my Telecaster through it, i love the warm sound of the amp but the harmonic rumble is ghastly. cheers Des

Ken Fox · Post by **Ken Fox** » 8 Aug 2011 8:52 am

Low bias will result in cross-over or notch distortion, very noticable on low notes and not a nice distrotion to the ear.

Tim Marcus · Post by **Tim Marcus** » 8 Aug 2011 4:39 pm

Des Hetherington wrote:Ken, in my Fender 1992 Blues Deville, i am running two 1960 RCA 6L6GC output tubes, and new Tungsol preamp tubes, i notice when i plug my Steel guitar into it it makes a strange harmonic rumble,lower notes seem to trigger it more than top end notes.. Could this be that the tubes havnt been biased? its not so noticeable when i play my Telecaster through it, i love the warm sound of the amp but the harmonic rumble is ghastly. cheers Des

If you are hearing a ghost note below or around the notes you are playing, it's not a tube issue (like transistors, tubes don't "do" frequency). You probably have to replace the filter caps in the power supply. A 1992 amp was probably built in 1991 which was *gulp* 20 years ago so it may be time to replace those electrolytic caps!

Des Hetherington · Post by **Des Hetherington** » 8 Aug 2011 11:27 pm

Hmmmmm ok so i need new caps in the output stage? and need to get the bias checked what would be a average setting for these old but new RCA 6L6's, my local electrical repairman is 70 years old and done his apprenticeship on valve amps, ie, Radio, TV. Ham Radio.etc, and as i live in the wop wops, he would be the only guy handy to check this for me, lol cheers Des

Ken Fox · Post by **Ken Fox** » 9 Aug 2011 4:34 am

I think it wise to have the caps checked for proper operation. I do not believe in the "shotgun" approach for repair of putting in parts until it fixed. The idea of this discussion is get ideas to investigate, as least from my perspective.
Without proper test equipment and knowledge of the amp's circuits you can't diagnose the amps problems properly here on the forum. One can only theorize as to what they have seen in the past that has created similar circumstances.

Rich Santucci · Post by **Rich Santucci** » 9 Aug 2011 6:02 am

Des Hetherington wrote:Ken, in my Fender 1992 Blues Deville, i am running two 1960 RCA 6L6GC output tubes, and new Tungsol preamp tubes, i notice when i plug my Steel guitar into it it makes a strange harmonic rumble,lower notes seem to trigger it more than top end notes.. Could this be that the tubes havnt been biased? its not so noticeable when i play my Telecaster through it, i love the warm sound of the amp but the harmonic rumble is ghastly. cheers Des

Des,

I don't believe you have a bias problem, but you could check that to make sure.

Sounds to me like you may have a microphonic output tube. Set the amp up as you would normally play it, plug in, but keep the guitar volume down all the way. Go to the back of the amp and lightly tap each output tube with your finger. If it starts to rumble, or make that low noise, you have a microphonic tube.

Ken Fox · Post by **Ken Fox** » 9 Aug 2011 6:14 am

Good idea, Rich. The more I read his problem above it does not sound like distortion, my error in interpreting what I read. I need to start using my "seeing eye dog" more often when reading these post!

As the problem seemed to follow the power tubes that seems very logical. However, it would not hurt to check the bias any time you change power tubes.

Des Hetherington · Post by **Des Hetherington** » 9 Aug 2011 11:16 am

Hey thanks guys, i do appreciate you tips my knowledge of electronics is one big fat zero, but i do know what sounds good, i will try tapping the preamp tubes, and if it still prevails , i will take to my my tech, thanks for your info and knowledge.. my Webb 614E still sounds great with the steel but cant find a Reverb tank for it, and its just a little to bright for my Telecaster.

Tim Marcus · Post by **Tim Marcus** » 9 Aug 2011 3:48 pm

Just put any old reverb tank in there! It should be fine.

Ken Fox · Post by **Ken Fox** » 9 Aug 2011 5:43 pm

Be aware there were two types of tanks used on Webbs, as the tank drive circuit on the early models was a class A transistor circuit and the later amps had the tanks driven by a push pull transistor arrangement.

From Tom Bradshaw's website:

Pre-1980 amps used at least three Accutronic 2-spring reverb tanks: the 4FB3A1B and the
4FB2A1B.

Later, the short, 3-spring, 4BB2A1B tank was used.
• Manufacturing of the first series was suspended in 1981.