Chat about Equipment Info
 #117399  by mgbills
 Wed Aug 15, 2012 7:51 am
Good Morning All,

I acknowledge this is not strickly an amp forum. But...there is some real sharp Cats about, who may be able to lend a brain-wave or two for lend.

I have a '68 Deluxe Reverb which has a Jerry modded tone stack & a D120. Love it. Here is what I know.

The only non-original part is the Power Transformer.
It is loaded with NOS tubes. Mostly RCA. The original rectifer was a Chinese Ruby.

I have read 3 Weber books, and wasted a fair amount of time checking the interwebs.

About 3 weeks ago I flipped it on. Nothing. No jewel light & no sound. As I waited I realized the Preamp tubes were glowing. Hmmm. Also, the Power tubes are not glowing. Jan RCA. They don't seem to ever glow, with one exception...see below.

Assessment Phase #1. I have AC power to the heaters, and that is what is glowing. From my studies I conclude that it's most likely a tube, and all signs point to the rectifier. I find myself a nice NOS Sylvania 5U4GB, and pop it in. Sound & jewel lamp are back! Now, I've read enough to know I need to bias this thing. So I ordered up a cool-guy bias probe. Read more stuff, and set the bias slighly to the warm side for a Deluxe. 22mA IK 428 Plate Voltage.

Oh Boy! My Deluxe is back. Wrong! Blew another Rectifier! Phuck!

Assessment Phase #2. A systems approach methodology leads me to the following points.
A) Tubes are tubes, and this old tube could've just failed. Buy new tube. Solve problem. Maybe
B) I haven't assessed the upstream & downstream systems, so I'm just as likely to blow another tube.
C) Something in the past caused the PT to fail. Could all this be related?
D) I'd also add that in the weeks that led up to the rectifier failure, I had an intermittant noise which sounded vaguely like a moth fluttering through one of the tubes. "Wha wha Wha wha"

My next thought was to dig into the filter caps. I also think it prudent to perform resistance tests on the PT. The amp appears to be recently recapped, but apparently even new caps fail. In multiple we searches, I really didn't find much on what stresses rectifier tubes. I would like to note that the Power tubes do not glow, with the exception of a faint glow on a horizontal plate near the top of one power tube. This glow seems unresponsive to changes in bias.


Thanks to All.
 #117404  by strumminsix
 Wed Aug 15, 2012 8:32 am
#1 cause I've seen for Rect tubes blowing are the poweramp tubes
#2 is that the caps are shot and sufficient power isn't there

Of course I'm not a tech so there will likely be other people with better answers.
 #117425  by mgbills
 Wed Aug 15, 2012 3:36 pm
Thanks Strum. Waiting for more Rectifier tubes. I'll give it a shot.
 #117439  by Bear62
 Wed Aug 15, 2012 7:29 pm
I have a a boutique Holland Gibb Droll. Bassman type circuit. 3x12ax7 2 x 6l6 power tubes and 5U4GB Rectifier. It started to make lots of noise. Then it blew fuses and rectifier.

Upon tech inspection, it was the CAPS! Save your tubes and check the caps!

I also changed the power tubes to Sovtek 6l6 wxt+ for extra power and headroom. Love it! It is a 3x10 and a 1x10 reverb amp w/ it's own single 12ax7 and 6l6!

 #118348  by 1dallek1
 Thu Sep 06, 2012 12:03 pm
it’s strange you would blow a tube without burning a fuse? you should go over the rectifier tube socket first in fact clean and tighten all your power sockets, and while you are at it I find most people like the solid state rectifier replacement, they are easy to make. it would help you in trouble shooting. by the way you need a tube tester, for simple go no go testing?

you are saying the pre tubes are glowing and the power isn't ? check your filament voltage first, on all tubes 6.3v ac, if that’s there they are glowing

by the way the jewel lamp is part of the heater circuit . The heater circuit has nothing to do with the rectifier?

the way it is right now do you have a proper B+? and i suggest doing a serious chopstick test, bang it!
 #118458  by gpilcher2001
 Sun Sep 09, 2012 9:36 am
Did you do the resistance test on the pt? It could be the high voltage ac winding is bad. Try amp debugging. Best thing to start with is read all your voltages against the schematic. Keep in mind the to be in spec, your reading should be +/- 20% of the votages on the schematic. Greg....