collapse

Author Topic: sound city clean-up  (Read 17013 times)

ilyaa

  • Elite
  • ****
  • Posts: 296
  • Chip Points: 7
    • View Profile
Re: sound city clean-up
« Reply #60 on: July 03, 2014, 04:49:28 PM »
v4 turned ghostly white!

since there is no reverb tank to speak of, if i just pull v4 out and play without a tube in that socket, will the amp be mad?

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: sound city clean-up
« Reply #61 on: July 04, 2014, 06:38:40 AM »
Quote from: v4 turned ghostly white!
v4 turned ghostly white!

A sure sign of an air leak.

When valves are manufactured they are first pumped down with a vacuume pump connected to the seal off point (the top tip in 12AX7's and the like, inside the base with octal types).

They are then sealed off and an induction heater used to "fire" a gas "getter", generally barium, inside the envelope which leaves a silver deposit on the inside of the glass somewhere.  This patch continues to mop up any residual gas that escapes from the assembly during its life.  If the valve gets a gross leak, say around one of the leadouts, or simply by being broken, the remaining barium reacts with the oxygen in the air to form barium oxide which happens to be white.



A pair of 6L6's, a good one in front, a duff one behind.

Note: broken valves should be treated as toxic waste because they contain materials such as barium getters and thorated (radioactive) cathodes.
If you say theory and practice don't agree you haven't applied enough theory.

g1

  • Legendary
  • ******
  • Posts: 607
  • Chip Points: 71
    • View Profile
Re: sound city clean-up
« Reply #62 on: July 04, 2014, 12:27:22 PM »
if i just pull v4 out and play without a tube in that socket, will the amp be mad?
Should be fine, preamp supply voltage will probably come up a little.

ilyaa

  • Elite
  • ****
  • Posts: 296
  • Chip Points: 7
    • View Profile
Re: sound city clean-up
« Reply #63 on: July 04, 2014, 01:04:17 PM »
roly,

are you saying its a physical issue with the valve itself? another valve in that same socket has done the same thing - what non-physical/mechanical things could cause it?

nashvillebill

  • Regular
  • **
  • Posts: 40
  • Chip Points: 5
    • View Profile
Re: sound city clean-up
« Reply #64 on: July 04, 2014, 05:08:02 PM »
Yes, the tube (valve) has lost its integrity physically.  A tiny crack in the glass-- at the base, or around a pin perhaps.

If this is the second one to experience the exact same failure, then I'd look very carefully at the entire mechanical area around the tube.  How is it being inserted, how is it being clamped, is something hitting it or pressing on it.

Roly

  • Legendary
  • ******
  • Posts: 2184
  • Chip Points: 288
    • View Profile
    • Australian Valve Amps
Re: sound city clean-up
« Reply #65 on: July 05, 2014, 05:12:07 AM »
are you saying its a physical issue with the valve itself? another valve in that same socket has done the same thing - what non-physical/mechanical things could cause it?

Well it is possible to break a bottle with thermal shock, sudden gross red-plating causing the glass to crack;


(note the white getter in the top)

... but as Bill says, this is basically a mechnical problem (or perhaps a very unlikely co-incidence, they do happen), but I'd be giving the whole area of the valve socket/can/retainer a really good scrute, nothing caught down one of the socket contacts, pins actually going into and not alongside a contact (bent pins), something stressing one of the contacts underneath, ...too much force...?

Nothing, particularly metal, should be tight on the glass (shields excepted of course).
If you say theory and practice don't agree you haven't applied enough theory.

ilyaa

  • Elite
  • ****
  • Posts: 296
  • Chip Points: 7
    • View Profile
Re: sound city clean-up
« Reply #66 on: July 05, 2014, 03:40:54 PM »
ah yeah i see both tubes that have turned white have a crack in a similar place alongside some of the pins - ill check the socket closely - might be bent in one side putting too much pressure on the glass

 

* User Controls

 
 
Welcome, Guest. Please login or register.
Did you miss your activation email?

* Recent Posts

Laney VC30 Output Transformer by phatt
[Today at 12:03:26 AM]


signal tracing by g1
[December 10, 2019, 02:26:30 PM]


Eight Audio Kit TDA7294 and TDA2050 from India by laikairawk
[December 10, 2019, 01:57:45 AM]


The Dangers of Speaker Impedance Mismatching by Enzo
[December 10, 2019, 01:15:39 AM]


Fender Mustang II v.2 by Enzo
[December 08, 2019, 04:46:37 PM]

* Sponsors