Help! Fenders blowing up right and left...

Bob Carlucci · From: Candor, New York, USA

HELP!!!.. My Bassman 70 has now gone south to join the Vibrosonic thats also cooked!... Also had two Bassman, a 68 and a 65 both self destruct all within about 8 months.. 4 Fenders fried since Jan.. this is all with about 2-3 hours of EASY use a week. Sold BOTH of the BasSman amps, but I can't keep dumping these things every time they break..... The Bassman 70 problem is my fault I guess.. My son plugged the speaker wire from the speaker out female to the ext speaker out female.. He always does this when we pack up and leave church after I perform in the praise team.

I ALWAYS catch it when I am setting up, but THIS time, I did NOT use the amp on SUN at church.. I just set my Willy up to practice tonight, tune her up etc. .. I plugged the amp in, FORGOT the speaker wire was in both jacks, and it was on for several minutes... Finally, I saw the wire[when the amp made no sound]... grrr..

Now I have a fairly loud hum, 1 output tube glowing bright red/orange... I put two different 6L6 tubes in and now the OTHER tube glowed red.. THE PROBLEM MOVED..... I am about to swear off Fenders forever.

I have been having REAL bad luck with all my old Fenders the last 2 or 3 years... I get them all set up,[for BIG bucks] and within a few months they're distorting, noisy and carrying on...... Anyway.. Any ideas what to look for with the scenario I just described with this Bassman 70?... bob

[This message was edited by Bob Carlucci on 03 August 2005 at 09:20 AM.]

Ken Fox · From: Nashville GA USA

What you have done is blown the output transformer! The amp had no load on it! The jacks are in parallel, so nothing was shorted. The main jack has a shorting jack to ground when unplugged. This protects the primary windings, as there is a load on the secondaries to transfer the energy across to. With no load on the secondary winding, you blew the primary windings out.

Bob, if you want, send both amps (chassis only) down and I can get them both back and running good for you.

[This message was edited by Ken Fox on 03 August 2005 at 12:32 PM.]

Bob Carlucci · From: Candor, New York, USA

Thanks Ken.. I was afraid of that... bob

Jody Carver · From: KNIGHT OF FENDER TWEED

My 2 cents Ken is right on.That problem is very well know among those Fender reps of a time back then. "Ouch"

Ken has it down to a "T".

Thank you Ken. edited

Ken we sure could have used someone like you at FENDER. Great diagnosing.

[This message was edited by Jody Carver on 03 August 2005 at 12:59 PM.]

Mark Herrick · From: Bakersfield, CA

Bob Carlucci · From: Candor, New York, USA

Mark..After the amp is off ,, just to carry the wire. From now on, [IF I get the amp fixed] the wire gets taken OUT of the amp.... bob

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

Bob Carlucci · From: Candor, New York, USA

Donnie.. Well I would say I'm really the one who screwed up. I know better.. He doesn't... I KNOW that cable should have been in the gear bag,.. LAZINESS!..

I dunno, Im starting to sour a bit on these old Fenders.. Last 3 years I've just had a ton of problems.. I think I really need a TOP tech to go through them and make them RIGHT. This amp only cost me $145 shipped, but was a good runner.. No headroom to speak of for steel however.

By the way, I got an email from a forumite who took great pleasure in my amp implosion. Rubbing my face in it, calling me an idiot etc... I truly hope his miserable email made him feel better,perhaps a bit more manly. Sure,maybe I AM an idiot, but the LAST thing that would give me ANY pleasure is the misfortune of a forum brother. bob

[This message was edited by Bob Carlucci on 03 August 2005 at 07:23 PM.]

Andy Zynda · From: Wisconsin

Just thinking...
Loud hum, and glowing plates usually doesn't equal a blown OT. That sounds like the screen grid resistors may have shorted, or some of the tubes internals, or both.

Every blown OT that I've rewound barely made any sound, and the sound was nothing but distortion. Hum and glowing plates were not evident.
2 cents.
-andy-

Bob Carlucci · From: Candor, New York, USA

Andy.. I have replaced grid resistors, on several Fender amps and you are correct about the symptoms.. The amp still has some volume too... The only thing that weirded me out was the fact that, the glowing tube MOVED.. Looking at the back of the amp, standing behind it, the left 6L6 tube was glowing bright. I shut her down, took TWO 6L6 tubes from another Fender head, fired her up,.. now the tube to the RIGHT was glowing orange/red.. If it was a grid resistor, shouldn't the problem have stayed put??.. Or am I thinking of Twin/Showman heads with $ output tubes.. In any case, I will check the resistors and sockets.

The amp was really distorting lately, I just thought maybe I was pushing it too hard... perhaps this problem was starting and I never noticed it.. However the HUM did NOT happen untiul AFTER the "wire in the holes" fiasco... thanks for your very helpful thoughts... bob

[This message was edited by Bob Carlucci on 04 August 2005 at 02:45 PM.]

Ken Fox · From: Nashville GA USA

I would test the grid resistors for sure. However the function of the screen grid is to assist the electrons on across to the plates! An open 470 ohm screen would not red-plate the tube.

An open 1500 ohm control grid resistor would do the number on the tubes! With no bias voltage the tube will saturate, thermal runaway! You would need two open resistors for a pair of tubes to be red-plating.

Typically if you play a chord on the guitar, with no load on the amp, it damages the primary windings. The way I test it is with an impedance meter. I unplug the tunes and leave the speaker connected. I check from center tap (where the B+ is applied) on the primary to each primay leg. The speaker will oscillate and a reading for each half of the primary can be obtained. If you have shorted windings on 1/2 of the transformer's primary side, two of the tubes will red-plate.

That is not an expensive transformer, Bob. you can get one from Sovtek, if that is what it needs.

I had a blown OT on a 135 watt Twin a while back and it acted as you described! Still, that may not be the problem! Just food for thought.

[This message was edited by Ken Fox on 04 August 2005 at 05:56 AM.]

[This message was edited by Ken Fox on 04 August 2005 at 05:58 AM.]

John Tipka · From: Reynoldsburg,OH

Antique Electronic Supply Tempe AZ
Stock Number P-TF22871 - less than $64

Scott Appleton · From: Ashland, Oregon

I have had blackface, silveface and brown Fender amps. Yes they have thier problems but I must say
once I got one running top notch they stayed running for years and years. i allways replaced the
tubes once a year, the big caps when they looked leakey and replaced the input resistors with shielded
ones. All Fender amps are subject to heat damage
but if you love the tone the maintainence just goes with the territory.

------------------
Mullen S12 Almost Mooney
71 Tele, Regal 45
Sho Bud S10 NP
Line 6 Flextone 3 + JBL D130, Acoustic 100 W all tube, Nash 112
digitech 2101 FX

George Redmon · From: Muskegon & Detroit Michigan.

wow Bob...are you talking about that great sounding amp i heard you play through the other night? or was that your Randall? it sure sounded good to me...hope you get it straighten out and everything is ok.. Bob as far as the dude with the smart mouth...just consider the source..if it were not for other peoples problems..some people just wouldn't have any excitement in their lonely lives...and as far as your son bob....DON'T HURT THE BOY!!!...lol don't worry..i fried my little Fender many times...they can take a lick'in and keep on tick'in..good luck

Bob Carlucci · From: Candor, New York, USA

George.. No that was my Showman ... Its been pretty good so far... I guess I'll get these amps fixed... It'll cost me, but I'm tired of selling the damn things. I'd LOVE to send them to our friend Ken F, but the shipping both ways on two amps would be murder!...

As far as the nasty email, I'm not worried about it. I just would not think that way about ANYONE with a problem... Most folks, even when they dislike someone, do not revel in thier misfortune. I am thankful MOST folks are not of that persuation...

anyway,, I think If I just EAT IT and take these amps to someone GOOD and say .. MAKE THEM RIGHT!, I'll get the dependability in Fender amps that I've come to expect.. They DO sound beautiful.... bob

David Ip · From: Canada

I don't think it's a Fender specific issue either. If you abuse any amp (running a tube amp without a load is abuse) it's bound to get messed up. A little bit of care & common sense goes a long way.

In any case, I would get the amps serviced & up and running properly (from a reputable tech) first. I have an old 1970s Twin Reverb that I fixed up 10 years ago, besides replacing the tubes now and then, I've never had any trouble with it and haven't had to perform any maintenance since!

Bob Carlucci · From: Candor, New York, USA

a little update..[in case anyone really cares

]

pulled the chassis, nothing looked amiss,.. took an ohm meter to a few resistors [in circuit, mostly just comparison checks].. looked ok.. turned amp on.. quiet for a second and then a pop.. one tube flashed blue, and the amp started to hum and the tube that flashed got RED BLISTERING hot in seconds.. shut her down.... Found a couple of other "unknown" 6L6 tubes in another amp.. plugged them in.. fired up... amp is now quiet, no hot tubes and sounds wonderful.... Now ,, that was TWO different sets of tubes I had the SAME problems with.. this 3rd creepy looking set is in and the amp is FINE!!. ... I guess I'll keep my fingers crossed and monitor the amp closely.

Could I have just cooked an output tube by running the amp without a speaker load??

I am REALLY beginning to wonder if the main reason I am having so much trouble with Fender the last few years,is because today's tubes STINK... They seem to last two months and then crap out in one way or another..
I have used Fender amps since the 60's and its only the last few years I'm having reliability problems.... Years ago tubes lasted years and years,.. maybe thats the problem . I'm expecting 60's tube reliability from 2005 tubes...... bob

[This message was edited by Bob Carlucci on 04 August 2005 at 02:48 PM.]

Ken Fox · From: Nashville GA USA

You could have damaged the tube for sure with a no load condition. I strongly suggest you get the bias checked on this amp before it goes south again! If it is a Silverface it is not adjustable, unless it was modified. it will likely have a bias balance adjustment.

Sovtek 6L6WXT+ is worst tube I have ever dealt with for failures! I have had no problems with JJ tubes. The production runs in the last year seem to run a bit cold side! i have had to change the bias resistor to get enough adjustment. They are rugged tubes and have been virtually trouble free in my experience.
I have now been trying some TAD (Tube Amp Doctor) tubes from Mojotone. So far they seem very good and great tone. Svetlana is also touted as a great 6L6GC tube.

[This message was edited by Ken Fox on 04 August 2005 at 03:13 PM.]

Jerry Erickson · From: Atlanta,IL 61723

I bought some Shuguang(sp?) 6L6's from Lord Valve (he'll always be Fat Willir to me.) They were the closest matched tubes I've ever put in an amp and they sound great. At the time they were $38 a quad.

Andy Zynda · From: Wisconsin

A Tube short makes sense. No load causes arcing inside tube due to the reflected impedance being much higher than the tube's plate resistance.
Another (BIG) vote for the JJ's. It's the best current production tube that I've laid ears on, and they're built like a tank.
I have them in my Twin, Super, Super Reverb, Vibrolux, Vibroclone, Silvertone 1484, Bassman, PV Rockmaster, and DumbleClone.
I've not lost a single tube in way over a year, when I switched to them.
Only had one that was bad, and it was dead out of the box.
-andy-

[This message was edited by Andy Zynda on 05 August 2005 at 09:48 AM.]

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

As others have said, you could have cooked a tube. I also strongly suggest you get the amp carefully checked out before you start using it again. It may be fine - those old Fenders do 'take a licking, and keep on ticking' - but I wouldn't assume that.

I still use NOS 6L6s - what's mostly available these days are pretty much Phillips/Sylvania production from the 80s and they're not exactly for the faint-of-pocketbook. But I agree that the JJs tubes are quite good. Saved my butt on my MusicMan HD 130 210 - 6CA7 amp.

Joseph De Feo · From: Narberth, Pennsylvania, USA

Hi Bob...
I have to second what Dave said. NOS is the
way to go. A bit pricy? yeah, but I have
many vintage amps and I find they sound
better and last longer than newer production
tubes. With all those Fender amps, I know
you care about tone

The internal construction of the NOS tubes is far superior to the new suff and the stability
is worth the extra $,IMHO. After all, those
amps were designed around the older tubes and give you the sound Leo intended

David Ip · From: Canada

I've used the "Winged C" (formerly Svetlana, NOT the same as the currently branded Svetlana) 6L6GC for years and years, sound great and never had any problems with it. I'd love to use NOS, but the 7581As that I like are now $250 a quad (used to be $100 10 years ago) and the Winged Cs are $65 a quad, so you do the math

7581As are supposed to last twice as long, but even then it's still not practical, and I'd rather re-tube with fresh tubes more often.

I hear good things about JJs too, I have a JJ 6V6 in a Champ that just COOKS and eats bad tubes, the JJ runs great.

Bob Carlucci · From: Candor, New York, USA

I think I'm done with Sovtek tubes,AND Groove tubes.. I use to like Groove Tubes years back....no longer.. I do believe I'll stick with JJ's but I haven't had great luck with them either.

I refuse to pay $200 for a set of "NOS" tubes.. I have a feeling a lot of them are bogus... Flash back to the mid 80's.. It was HARD to find NOS tubes.. REAL hard.. I know, as I have been playing Fender amps almost exclusively since the 60's... Fast forward to 2005.. NO longer a problem buying NOS 6LS tubes,, as long as you are willing to pay $50 a tube or better. I'm REAL suspicious...bob

[This message was edited by Bob Carlucci on 06 August 2005 at 08:40 AM.]

Ken Fox · From: Nashville GA USA

I will no longer use NOS tubes, had too many microphoice preamp tubes!! I have no trouble with JJ tubes, they are as rugged as any RCA, etc I have ever used!!

Forum Index > Electronics		Next oldest topic :: Next newest topic