Fender bandmaster rectifire problem. - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th May 2011, 04:26 PM   #1
diyAudio Member
 
Join Date: Jul 2010
Default Fender bandmaster rectifire problem.

While changing the tubes in my Fender the other day I made a stupid mistake and put a preamp tube in the wrong way( i thought it was in but the legs bend and shorted but the heater worked) The short was from one anode of the 12at7 reverb tube to the heater. Needless to say it went up in smoke! After replacing a vapourized bypass cap and the anode load resistors I turned on the amp only to find that the rectifire tube's( a 5u4 ) heater was not glowing. Not completly off just a VERY faint pre red kinda glow. I had a gig so rather that fart around anymore I stuck a coulpe of 1N4007 diodes in its place and got on with it. Is it posible that I blew the 5v rectifire heater winding? Unloaded it measured 4.9v. I was in a rush and didnt measure the voltage with the tube in place. I find this od because the short was with the 6.3v winding for the rest of the tubes. Can anybody please diagnose the problem or point me in the right direction. I can live without the tube rectifire just want to know possible causes.
Thanx!
Mario.
  Reply With Quote
Old 10th May 2011, 08:36 PM   #2
diyAudio Member
 
Join Date: May 2011
I don't think you blew the rectifier secondary, there is no connection to the 12at7 preamp tubes. But maybe your transformer was damaged in that shorting event ... then it won't be only the 5V tap.
If your amp worked afterwards though I think the power transformer is good and you should repair the other damages asap.

(can't for the life of me think how to insert a 9-pin type the wrong way ...) Good luck!
  Reply With Quote
Old 10th May 2011, 11:10 PM   #3
diyAudio Member
 
Join Date: Jul 2010
Thanx for the input mate! I didnt think you could insert a 9 pin wrong either thats why I thougt it was in place!!!
  Reply With Quote
Old 10th May 2011, 11:40 PM   #4
tomchr is offline tomchr  United States
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Greater Seattle Area
Have you tried a different rectifier tube? I wonder if the heater got cranky by getting B+ on it. I'm kinda doubtful, as the current would be limited by the plate resistor for the 12AT7, but still...

It would also be interesting to know the heater voltage under load.

~Tom
  Reply With Quote
Old 11th May 2011, 09:42 PM   #5
diyAudio Member
 
Join Date: May 2010
Location: Ball Ground, GA
My bet is the rectifier tube is physically damaged, such that a small leak is now present. Over the years, I've ever seen a few tubes with a very small physical breach, and one of the characteristics I've seen happen before the inside finally turns chalky white, is that the heater starts to glow dimly for a period, before it finally burns out.

What I don't understand is how there was any damage to the reverb circuit in the first place. If a plate pin bends over and touches a bent over heater pin, so what? Assuming the heater pin was either pin #4 or #5 for the section that had the bent plate terminal, one section would still glow -- and drive the reverb springs -- while the other simply would not. Either that, or I'm not sure which circuit you are using, as the only position that Fender used a 12AT7 in in the reverb portion of a Bandmaster Reverb was the driver tube, right? Just trying to figure this out myself!

Dave
  Reply With Quote
Old 11th May 2011, 10:30 PM   #6
diyAudio Member
 
Join Date: Jul 2010
Thank you all for your usefull input on the matter. I finnaly found that the problem is the rectifire tube itself. I didnt have a spare so i connected the 5v fillament secondary to another tube a GZ33 to check and it lights up just fine. The secondary reads 4.8v under load. Does anybody know if I can use this tube in the bandmaster? The old bassman used a GZ34 so it seems to be an ok option...I would re wire the socket ofcourse since it has a diferent pinout.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
5e7 bandmaster build q's bakerlite Tubes / Valves 1 6th March 2011 02:15 AM
bandmaster ab763 fx loop hi_im_sean Tubes / Valves 2 17th November 2009 11:38 AM
1967 Fender Bandmaster for sale......... cadaverdog Swap Meet 4 12th October 2008 03:56 PM
Fender Roc Pro 1000 Feedback Problem transistance Solid State 0 9th September 2008 03:11 PM
Fender Twin Reverb VIBRATO PROBLEM - weak vibrato gibsonripper Tubes / Valves 2 19th January 2008 04:23 AM


New To Site? Need Help?

All times are GMT. The time now is 05:47 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2