Re: [Harp-L] Continuing trouble with '59 Bassman LTD:blows fuses, substitute rectifier tube?

["Bob Maglinte" <bbqbob917@xxxxxxxxxxx>]

----- Original Message ----- 
From: "Veli-Pekka Haanmäki" <vphaanmaki@xxxxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Monday, July 04, 2005 4:29 PM
Subject: [Harp-L] Continuing trouble with '59 Bassman LTD:blows 
fuses,substitute rectifier tube?


Hi all!

I have a new Fender '59 Bassman LTD amp and I'm having continuing trouble 
with it.This is actually third Bassman LTD I have here now,the other two I 
sent back because of the same fault in them: all of them blow fuse around 
every 5th time I turn them on.

I replace the fuse with correct one (F1.6A250V,this is EU export model) and 
it works another 5 times turning ON and OFF and then it blows the fuse 
again.
Fuse doesn't blow during the amp is ON (while playing) or when the Standby 
is switched ON,just when the amp is TURNED ON,usually after 15min-1 hour 
break.May have something to do with tubes since the rectifier and power 
tubes are warmed up when the fuse blows,in most cases anyway.

I don't switch the power ON and OFF all the time,I use Standby for shorter 
breaks.Standby is OFF when I turn the power ON,I use correct,correct quality 
fuses.Power source is not the problem since this has happened in several 
different locations.I've swapped all pre-amp tubes,no effect.

Any idea what could be wrong? Where to look for the fault? I will take it to 
repairtech,yes but we need to find the REAL cause of this trouble before he 
can fix it.Like I said,this is third '59 Bassman LTD with same fault in 
it,does anyone else have similar experiences and what was done?

I also changed the 5AR4 rectifier tube to 5U4G rectifier tube.Most of the 
information I've searched say that this is OK to do,in most cases anyway 
since 5U4G is weaker that 5AR4.I'm not sure about this though,is it safe to 
use 5U4G as a substitute for 5AR4 on Bassman LTD?
This doesn't have anything to do with blowing fuses since it happens with 
both rectifiers.But I've changed back to original 5AR4,I'm not taking any 
chances now.By the way,5U4G does have better sound,gives the amp a bit more 
sag than 5AR4 and allows me to turn the volume to 5-6 (pre-amp tubes are 
ay7-ax7-au7,right to left from the back of the amp,good combination for this 
amp,sound is great but that is the only good point of this amp for now)

Any information on these problems will be appreciated,thanks.

(all this makes me wish I had money for Victoria 45410-T though : - (

Hi,
But when you replaced the rectifier tube, did you make sure the amp was 
rebiased FIRST before swapping the rectifier tubes?? Why?? It is is 
EXTREMELY important because the voltages are very different and you risk 
frying the amp like a piece of chicken if you don't get that done PRIOR to 
swapping the rectifier tube, and it can be one of the causes of your 
problems. Also there could be really terrible wiring in the socket your 
plugging the amp into.

Sincerely,
Barbeque Bob Maglinte
Boston, MA
http://www.barbequebob.com
MP3's: http://music.mp3lizard.com/barbequebob/