Fuse blowing-Twin Reverb problem

Problems with equipment? Problem fitting them into the above forums? Post 'em here.

Fuse blowing-Twin Reverb problem

Postby pi-man314 » Fri Feb 20, 2009 10:18 pm

hey all,
here's my situation it breif. I have a '73 silverface twin reverb that's keeps blowing fuses. The first time I changed the power tubes out myself, biased it, and watched fuse blow....only after 5 or 10 minutes of playing. Confused, I brought it to my amp tech who blamed tubes, changed tubes, collected his pay and called me to pick it up. It worked for a good four hours and then the fuse blew again. What???

My amp tech does not play guitar and the amp will not blow fuses unless it is being played...usually at about volume 5 or 6...after about 10 minutes. it can sit on a bench forever and glow a lovely red and orange but will not blow unless it is being played. depending on the volume it will blow sooner at higher volumes than lower.

any help would be appreciated
pi-man314
Regular
 
Posts: 5
Joined: Fri Feb 20, 2009 10:06 pm

Re: Fuse blowing-Twin Reverb problem

Postby ricochet » Fri Feb 20, 2009 10:38 pm

Don't know, but a couple of possibilities would be too-hot biasing and power tubes that are slightly gassy. The latter's a very common problem. As the tubes get hot, adsorbed gas on the plate gets cooked off into the "vacuum," gets ionized by flying electrons, the positive ions are attracted to the negative control grids, shift the bias more positive, more current flows, the tubes get hotter and cook out more gas... The problem escalates exponentially till the fuse blows or the amp burns up, whichever comes first. Everything's fine when the tubes are cool.
User avatar
ricochet
Regular
 
Posts: 10256
Joined: Thu Jan 01, 1970 12:00 am
Location: Bristol, Tennessee, USA

Re: Fuse blowing-Twin Reverb problem

Postby pi-man314 » Fri Feb 20, 2009 10:46 pm

would a fan help with this problem. also, i did go some time without playing the amp at all...maybe 3-4 months. could this mean the filter caps are bad? could this be part of the problem or should i find less "gassy" tubes?

thanks
pi-man314
Regular
 
Posts: 5
Joined: Fri Feb 20, 2009 10:06 pm

Re: Fuse blowing-Twin Reverb problem

Postby ricochet » Fri Feb 20, 2009 11:33 pm

A fan might help, but shouldn't be needed. However, anything that blocks natural airflow, like tipping an amp back or putting it too close against a wall, is asking for trouble. Gassy tubes may "clean up" by the "getter" coating in the tube absorbing the gas after using a while, but they're likely to keep being troublesome. Lots of present day tubes aren't purged thoroughly enough during manufacture. I'm a fan of setting bias about as "cold" as you can go. Reduces problems a lot.
User avatar
ricochet
Regular
 
Posts: 10256
Joined: Thu Jan 01, 1970 12:00 am
Location: Bristol, Tennessee, USA

Re: Fuse blowing-Twin Reverb problem

Postby pi-man314 » Sat Feb 21, 2009 11:27 pm

maybe this is a stupid question but are there any tubes manufactored that would be less gassy. right now i have sovtek tubes in the amp (for the last three sets actually) never been to thrilled with the way they perform but i don't really want to invest in a really good set until i can work out the bugs.

any ideas/suggestions?
pi-man314
Regular
 
Posts: 5
Joined: Fri Feb 20, 2009 10:06 pm

Re: Fuse blowing-Twin Reverb problem

Postby texas blues » Sun Feb 22, 2009 12:23 am

Tung Sol, EH, Tesla, Svetlana...I have a combo of these split between my 5F1 and 5E3 Clarks. No worries. As far as your '73 SFTR, I personally wouldn't have anything but the best tubes I could possibly afford. I have JJ's and Ruby's in my Marshall 2204. With the aforementioned tubes in my amps they all sound like death rays!

Cheers, TB.
User avatar
texas blues
Regular
 
Posts: 1580
Joined: Thu Oct 19, 2006 12:13 am
Location: Wrong side of the tracks

Re: Fuse blowing-Twin Reverb problem

Postby ricochet » Sun Feb 22, 2009 12:56 am

None of the currently manufactured tubes are reliably free of this problem.

But I've had good luck with even the cheapest of the cheap Russian tubes. you get bad ones sometimes, sometimes you get good ones.
User avatar
ricochet
Regular
 
Posts: 10256
Joined: Thu Jan 01, 1970 12:00 am
Location: Bristol, Tennessee, USA

Re: Fuse blowing-Twin Reverb problem

Postby pi-man314 » Sun Feb 22, 2009 6:10 am

I actually bought this particular amp (while shopping for a pig nose amp...man was my wife happy) with Tung-sol tubes in it and it sounded like a dream. Hasn't sounded that good since.
pi-man314
Regular
 
Posts: 5
Joined: Fri Feb 20, 2009 10:06 pm

Re: Fuse blowing-Twin Reverb UPDATE

Postby pi-man314 » Sun Mar 15, 2009 5:38 am

hey all, just an update on my amp. I dug into it and took a close inspection of all connections and voltages on amp...one of my filter caps was bulging slightly, and discolored. Changed it...correction, carefully changed all filter caps and have had great success with it.

Could use a litte more headroom, but overall the tone is fantastic.

My amp tech has grown complacent and will be getting a bulging filter cap in the mail in the next few days!!!

Thanks for the advice
pi-man314
Regular
 
Posts: 5
Joined: Fri Feb 20, 2009 10:06 pm

Re: Fuse blowing-Twin Reverb problem

Postby ricochet » Mon Mar 16, 2009 10:39 am

All right! Glad you got that fixed. Filter caps can blow up quite violently and messily.
User avatar
ricochet
Regular
 
Posts: 10256
Joined: Thu Jan 01, 1970 12:00 am
Location: Bristol, Tennessee, USA


Return to Equipment Blues

Who is online

Users browsing this forum: Bing [Bot] and 3 guests

cron