Frender Tremolux - newby tube bias ?

fraser · From: seattle wa

Hi,

I would like to replace the tubes on my Fender Tremolux ( tweed, serial #01244 - controls on top, not in front ).

Can I just go buy the tubes and put them in or do I need a tech to bias adjust them? I've gotten two different answers so I would super appreciate any response here. One tech said that Fender amps that old do not need to be bias adjusted ( if that's the right term).

The original schematic from Fender calls for a 5U4GA, 2 6V6GT's, 2 12AX7's and a 12AY7.

Thanks in advance.

Fraser

Jay Ganz · From: Out Behind The Barn

The tweed Tremolux amps with a 5Y3GT rectifer tubes were cathode biased they're "self adjusting". No need to reset the bias on the 6V6's. If the 5U4 on yours is original and it's a slightly later model 5G9 (listed on the tube chart inside the amp), it is a fixed bias but there's no adjustment pot to easily set the bias anyhow. It wasn't until the early 60's amps that an adjustable pot was used.

[This message was edited by Jay Ganz on 08 January 2006 at 11:47 AM.]

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

My 2cents...

Fraser, despite what many techs will tell you, this "biasing thing" is really over-rated. I've been playing music over 40 years, and quite frankly, no one, and I repeat no one, even worried about it 30 years ago. It was only the demise of tube amps (and the resultant loss in all that repair work, solid-state stuff is very reliable) that made most techs say "You really need to have that thing re-biased when you change tubes."

It's kinda like precision-balancing the engine in the car that you drive daily. Yes, it makes a difference, but will the difference make any real difference?

Frankly, no.

Bill Hatcher · From: Atlanta Ga. USA

My 2 cents.

If Leo Fender had not thought it worthwhile, he would not have put a bias control in many of the amps.

A Fender amp will still work under the worst conditions--out of spec parts, sorry tubes, dirty, out of spec everything etc.

Nothing like hearing one that is set up with good in spec caps and resistors and good matched tubes and biased. I wish I knew how to do it 30 years ago.

[This message was edited by Bill Hatcher on 08 January 2006 at 12:29 PM.]

J Fletcher · From: London,Ont,Canada

An amp that old and valuable should be looked at by a good tech when new tubes are installed, if it hasn't been in the last few years or so. Just as a precaution in case anything else needs to be replaced. Capacitors, etc....Jerry

Ken Fox · From: Nashville GA USA

I have converted a lot of amps back to adjustable bias (Silverface amps). I am finding my favorite tube (JJ Telsa) can run cold in Silverface amps, as low as 12ma! That causes a terrible crossover distortion. I just did a Vibrasonic and it came alive after getting the bias up to 39-40 range!!!

Still, your amp is cathode biased, self regulating, so this does not apply. However, caps and resistors should be checked. Filter caps drift and change values and also become resistive (passing DC thru them). This is often evident when you see resistors in the bias network that have been overheated, a dead giveaway that there is a cap issue!

Jon Light · From: Saugerties, NY

I've got a blackface Showman just waiting for me to get around to rehabbing it--I have other good amps so there's no urgent need. I used it for a couple of gigs and wasn't thrilled. After I got some experience under my belt with a couple of my other Fenders I went iside this one to check some components. I found resistors that weren't within 200% of their specs (I'm talking about proper schemo values but totally degraded, drifted parts). Some of these readings are so out of whack that A) I'm lucky I didn't do serious harm and B) I am really looking forward to what I may have here when I finally fix this up.
But yes, unless you know that you have had some tech care on this amp within the last number of years, it really ought to get looked at.

Larry Robbins · From: Fort Edward, New York

Do any of you "Tech" type guys know anything about the newer reissue's from Fender? They claim that if you buy thier colour coded sets of tubes that there is no need for re-biasing. Anyone have any experince with this?

Ken Fox · From: Nashville GA USA

Sound like Groove tubes. They sell power tubes that are in a similar power range (similar mutual transconductance) and usually are rated from 1-10. Not a bad idea for someone that has no other means of setting tube bias.

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

Joseph Meditz · From: Sierra Vista, AZ

Why ya wanna change ya tubes for?

If it ain't broke don't fix it. Furthermore, if the tubes are old and made in the good ole US of A, there is a fair chance that they are better than most of the ones made today.

And as has been said, I would be more concerned with the capacitors. A 120 Hz loud buzzing is an indication of tired filter caps. And you might want to replace the bias supply caps just for fun. Lastly, if the amp has a two wire power cord you should have that replaced with a modern three wire cord and get rid of the so-called "death cap."

My dos centavos.

Joe

fraser · From: seattle wa

I really appreciate all your responses. Sounds like the general advice is to take it to a tech and let them decide what needs doing most. I did take it in a year or two ago and had the ? replaced. The tech said it was original....a largish rectanglar thingy. I can't quite remember today what it was...the filter caps?
It's been cleaned and looked at in prior years although not real often.
I thought I would replace the tubes because in old days they had those tube testing kits in the drug stores and you could watch the needle swing into the red when they were bad. I didn't think tubes lasted forever...don't they deteriorate? I can't remember the last time I changed mine.

Anyways, thanks for humoring somebody (me) who knows nothing about the topic.

Thanks
Fraser

Jon Light · From: Saugerties, NY

Fraser--the filter caps have a rectangular metal cover over them. So that's a possibility. Or your transformers, both power and output, are large rectanglular objects. Very very heavy iron. Replacement of one of them would be a significant and fairly costly thing, definitely not a routine maintenance thing--replacing a transformer would happen only if was blown---not an everyday occurance (not that it's super rare, either, but we are talking about a real injury to the amp, not routine age).
Yes, power tubes need replacement. Usually you replace them when the amp starts sounding bad, distorts too easily, lacks sparkle....it is hard to name the exact time when you need new tubes but often when you get them you realize how overdue the change was. OTOH, unlike the caps which should be changed on general principle after x amount of time, tubes don't really need changing if they still sound good to you.

Jim Sliff · From: Lawndale California, USA

"Fraser, despite what many techs will tell you, this "biasing thing" is really over-rated."

That WAS true - 40 years ago. tube quality cotrol was very consistent, and we would just go to the drugstore and buy one tube.

But nowdays the QC is awful, tube companies make varying versions of the same thing, some tubes called one thing are really another (Sovtek 5881's aren't 5881's...or 6L6's either. And their 6V6's are 6L6's that failed some tests).

So nowdays biasing is CRITICAL. Period.

I've put in sets of tubes in a Pro Reverb and had the bias range from 25ma to almost 40ma with no adjustment.

Forget 40 years ago. The same rules DO NOT APPLY.

Bias your amp unless it's cathode biased - and then have it biased by a tech, because even those should be checked.

Last - in a tweed, make SURE if you are going to play it that you have replaced the electrolytic capacitors and the two-prong plug with a properly grounded 3-prong plug.

PS - Biasing "by the book" is for propellor-heads. You use the book guidelines for safety reasons - but you play an amp for tone! Set the bias in a midpoint of the "safe" range, then tweal it for the best sound. Check it to make sure it's still safe, and you're good to go.

If you play a place with lousy line voltage, true, you may either suffer or have to adjust it. Instead, I carry a line conditioner that gives me constant 117 volts. It's worth the expense, especially if you do "generator powered" gigs....

Player's toolkit items (if you don't have a line conditioner) - small multimeter, Weber Bias Rite or a Bias King from Allesandro, Power plug checker (verifies ground and tells you if things are wired backwards), cable tester, soldering iron, solder, screwdrivers, needlenose pliers with wire cutter, krazy glue...and duct tape

[This message was edited by Jim Sliff on 13 January 2006 at 04:23 PM.]

Jim Sliff · From: Lawndale California, USA

"Fraser--the filter caps have a rectangular metal cover over them. So that's a possibility"

Not on his amp. On the tweed Tremoluxes the filter caps are on the circuit board.

You're thinking of the blackface and silverface amps.

Oh - and in regards to the " color coded tubes" question...bah! You still need to check the bias. Mesa has tried to pull the wool over everyone's eyes with that marketing ploy for years. It's BS.

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

J Fletcher · From: London,Ont,Canada

Late 50's Tweed Tremoluxes, 5G9 models, did have the filter caps in a "condensor box on back of chassis", to quote the schematic. I've owned two that had this feature, and worked on one of those last week....Jerry

Jim Sliff · From: Lawndale California, USA

My bad - I assumed the Tremolux had the same "filters on the board" as most of the other tweeds.

Donny - regarding old tubes, you and me both! I have a large hoard of NOS tubes - I give away Sovteks, EH's and Groove Tubes when I blunder upon them. The only current-manufactured tubes I've had nice results with have been JJ's, both in tone and consistency in manufacturing.

The biggest joke tube is Boob Tube's "6L6 GE", supposedly "Made in USA". Some parts are made here, but the actual tube is assembled (and the rest of the parts made in) China. I've burned up a box full of those that were given to me, plus the pair in the Vibroverb Artist Relations sent me were mismatched 7ma out of the box. Plus they sounded terrrible. That amp has a complete JJ set that I'm testing right now. It'll go back to Mullards, Amperex and Tung-Sols once I finish running the JJ's through their paces.

Ken Fox · From: Nashville GA USA

You can say what you want about biasing, but I deal with it on my bench almost every week. If bias is too low you will get crossover/notch distortion (typically not a problem in cathode biased amps). It is a nasty sound and low power, period! I can easily see it with a sine wave generator and scope. The bias has to be pretty cold for this to occur. There is rather wide range after the distortion disappears where you can set the bias. Too hot and the tubes will not last as long, too cold and the amp sounds cold and sterile.

I use a formula by Bias King that yields a high and low value for the bias current, based on the plate voltage and plate power dissaption (typical 25 watts for the 6L6GC and 5 watts of screen grid dissipation).

Still over time this will drift, but not enough to usually affect the tone a whole lot. A set of matched power tubes will not be so closely matched after hours of use! All things chnage as heat and time take their toll.

Leave them in till they die?? Not me! I do not like to see what power tubes can do to my amp when they fail. I have seen burned out screen grid resistors, burned out filament voltage balancing resistors and ever output transformers that have caught fire!

Just my thoughts and observations that I wanted to share from experience at my workbench!

J Fletcher · From: London,Ont,Canada

There's a late 50's Tremolux on ebay, with pictures showing the cap "doghouse" on the back of the chassis, for any one interested in looking. Some discussion of this amp on the Weber VST amp board. It's been refurbished, but there are some good pics of the transformers, and the interior of the chassis. FYI.....Jerry

Victor Denance · From: Rennes, France

I would worry about the 5U4 rectifier tube. This guy yields a significant higher B+ voltage, and draws more current out of the power transformer than the regular stock 5Y3.

J Fletcher · From: London,Ont,Canada

5U4 was the stock rectifier in late 5E9 and 5G9 Tremoluxes. Also they are fixed bias, not cathode biased, using a selenium diode to develop the negative bias voltage. A pretty sophisticated circuit, utilizing the long tail phase inverter, and a choke between the plate and screen supplies. Had a lot of the latest features that appeared in the top of the line Fender amps of the day, like the Twin and Bassman.

fraser · From: seattle wa

Sorry it's taken me so long to respond. A real wealth of info here. I believe it was the filter caps I had replaced.

Thanks again , friends

Fraser

Andy Zynda · From: Wisconsin

Thank you Mr. Sliff, for hitting the nail on the head. Saved me some typing, and you said it better.
-andy-

Dave Zielinski · From: Pennsylvania, USA

Electrical Engineer here, so excuse me is i get long winded and way out of hand!

Biasing makes a difference. I maintain a few of my friends amps and all my amps. when I bias a fender blackface amp for example, I take out one of the voltage divider resistors for the BIAS SUPPLY and replace it with a 25K pot. In a 6L6 style amp, you can adjust this to get about 10Ma- 60mA of current at idle (no input)I usually bias the tubes cold- and let the player play through it. unimpressive tone when biased cold. Then ill crank up the current by adjusting the pot. the amp comes to life and has headroom, sustain and more punch. Usually for guitar we end up around 35mA per tube and for steel more like 40mA. It is a simple procedure best performed by someone who knows a little bit about electronics. There are plenty of techs across the country, you should have no problem finding one. I DO recommend that you request to hear the amp during the process. I like mine nice and tight, while others may like a little more breakup (colder bias).

By simply installing new tubes and "not worrying about it" you are doing nothing more than compromising your tone!

however, certain amps- (small fender tweeds, champs, (temolux included) etc NOT 5F6-A bassmans) are "cathode biased" as someone above mentioned. If you look at pin 8 on your output tubes you will see a large resistor and capacitor form this pin to ground. These amps DO NOT need to be adjusted for bias, as they are self biasing circuits. These amps typically have great dynamics (tweed champ ring a bell?) but lack headroom and volume. Usually these are low wattage amps, and make great tone for their size and use.

Hope this helps.

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