Mbira

Bugger -- time to take apart the Deluxe
« Reply #40 on: February 07, 2008, 12:59:41 AM »
Quote from: "Flatpicker"
Another trick is you can roll the tube pins between your fingers and thumb, lightly pressing them in closer to each other. This will create a tight fit even if the sockets are loose.


How do you get to the pin?
Joel Laviolette

Rattletree   |  https://www.rattletree.com
The Rattletree School of Marimba | https://www.learnmarimba.com


Flatpicker

Bugger -- time to take apart the Deluxe
« Reply #41 on: February 07, 2008, 06:32:16 PM »
I'm referring to the pins sticking out of the tube. Hold the tube by its pins between your thumb and finger, and roll it back and forth while applying just enough pressure to bend them all inward a little bit. Then when you insert the tube, the pins are all tightly pressing themselves against some portion of the individual sockets, regardless of the socket tension. Rules out a faulty tube socket pretty quick.

okgb

Bugger -- time to take apart the Deluxe
« Reply #42 on: February 09, 2008, 06:00:58 PM »
Paul , we await the end of the debate

True , if solid core a wire may be broken inside the insulation ,
part of the arguement is the amount of time taken to find the problem
and eliminate it , not to mention having the amp out of commision .
The heat build up and drying properties of time can have odd effects
a new socket won't hurt  , [ sell it on ebay , oughta fetch .50 ]
but if wiggling the wire inside while on doesn't do it , but touching
different tubes does , seems to narrow it , and maybe removing the
 socket will reveal something , and hopefully
at the very least that it wasn't the socket , but then you can look
 elsewhere .

 O.k. time to start a poll and taking bets . good luck & skill Paul
[ you're sure the backwards message didn't warn of this ?? ]
GKB Audio / Greg Boboski

pstamler

Bugger -- time to take apart the Deluxe
« Reply #43 on: April 14, 2008, 01:56:52 PM »
I finally got enough spare hours to do the repair.

First thing, I did replace the socket, and can testify that the "exact replacement for Blackface Deluxe" socket, isn't. There's a shield turret in the middle of the lugs on the bottom which makes it impossible to bend the two cathode lugs together the way Fender did (so I soldered in a jumper).

More important, the holes in the mounting ears are not the same size as the originals, which were attached with self-tapping (#6?) screws. Instead, they're tiny, requiring #2 screws, which I swiped from my collection of cartridge-mounting hardware. Exact replacement, my eye.

Anyway, once that was done I connected the socket up, using all new wires from the tag-board. While I was in there, I replaced the 1M resistors and the 22k resistor, both of which were looking pretty ratty.

Then I put the original tube back in, and got very different voltages on the plate, indicating severe unbalance. They were also on the high side, indicating that the tube's output was weak. I replaced it with the only other 12AT7 in the house, which at least had balanced voltages (well, roughly) on the plates. It still was weak, but at least I got results.

So I buttoned the amp up and played for an hour, and it didn't drop its gain once, that problem seems to be fixed. It didn't sound all that great, though; no real balls, a classic symptom of a weak driver tube in a Fender. I'll get a good 12AT7 next time I order something.

Thanks, all, for the ideas and support! I still don't know what the original problem was (my guess: wire with an internal break), but it's fixed.

Peace,
Paul

bcarso

Bugger -- time to take apart the Deluxe
« Reply #44 on: April 14, 2008, 03:09:19 PM »
Frustrating not to find the clear cause.  But I'm glad the story otherwise had a satisfactory ending.

Once around 1970 I think, I was asked to help the late George O. Abell, who was Chair of the department at that time, with a problem he and his sons were having with one of the top-of-the-line Heathkit home hifi receivers.  He was bafffled at some excessive noise on a line-level input channel, which he couldn't understand would be noisier than the phono preamp, given the latter's higher gain.

They had labored long to assemble the unit and were certain that they'd done everything per directions.  I asked to see the schematic.

I noted that the line-level stages had a fairly complex arrangement of bootstrapping of the bipolar input devices.  I conjectured that Heath might have engineered the circuit when transistors were typically a little slower, and not been aware of the potential for oscillation.  I picked a device from the lab that I was fairly sure was slow enough and gave it to him to substitute.

He came back a week later and went through a long and almost lugubrious account of all the work it had taken to take the unit apart and perform the change, and then reassemble (dial cord restringing, yada yada...), clearly building to his climax with the maximum drama he could bring to bear.

And...it worked.  He admitted to being astonished, having been frankly doubtful of my diagnosis.

Some years later I assisted him with a section of a new edition of his successful text The Exploration of the Universe (I used to quip it should have been titled the Exploitation of the Universe).  He gave me thanks in the preface, but as was common at UCLA, like the acknowledgments in research papers, there was a careful distinction between Dr. and Mr.  A sure sign of academic insecurity, which many more prestigious institutions do not observe.


 

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