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Thread: Deliverance 120 story and questions

  1. #1
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    Default Deliverance 120 story and questions

    Hello fryette forum users! I am new here and have a quick story and some questions of concern about something that happened with my beloved Deliverance 120 head.

    I had ALL the tubes (all JJ's from Eurotubes) replaced by a local technician about a week ago, and when I got it back it worked and sounded great. And then the second day I turned it on and waited for the tubes to heat up; when I turned the standby switch to operate, I heard a little noise from the guitar and then sound went away. At that point there was absolutely no sound coming from the amp but the power was on and power button was lit up green. I called up my technician and explained the issue and I brought it back down to him.

    Right infront of me he examined the fuses, which were all fine. So he went to the preamp tubes next. They were all fine except for one. When you are looking at the rear panel, the 12ax7 all the way to the right in the row with 3 tubes (I think spot V1) was clouded white on the top and he said that was the problem. So i bought another one off him and he replaced it right then and there. He suspected it failed due to the spring on top inside of the shield being too tight and putting to much pressure on the tube. I then noticed the failed tube was actually a 12at7 that was put in spot V1 accidentally by him during the original tube replacement.

    So i happily brought it home and plugged it in to play, and the same thing happened again, I turned it on and no sound was coming out. I called the technician back up and he told me to remove the 12ax7 (V1) that was the problem the first time myself and see if it failed again, and it did.

    I then noticed that there was a 12ax7 in the spot where the phase inverter buffer tube was (V5 i believe) which in the manual states there needs to be a 12at7 in that spot. And then I remembered there was a 12at7 in the V1 spot the first time this issue happened. So my technician essentially accidentally switched the V1 and V5 tubes it seems to me.

    I took an extra 12ax7 I had and replaced the blown clouded tube in V1. After that I put an extra 12at7 tube I had on hand in V5. I tested out the amp and it finally was producing sound, and sounded very good.

    The questions I have are:
    - Could any serious damage have been done from playing the amp for about an hour with a 12ax7 tube in the phase inverter buffer spot in V5? And a 12at7 tube in V1?
    - Would that have something to do with the 12ax7 tube failing in V1 the second time the issue happened? What do you guys think could have originally caused the problem?
    - I took the springs out of all the preamp tube shields, and left the shields on because the technician originally suspected the spring putting too much pressure on the tube could of been the reason why it failed. Should I put the springs back?
    - From this story, do you think any of the power tubes could have suffered any damage in the process? Or any other part of the amplifier like the circuit board or transformers? Are there any other concerns or things that could of been effected from all of this?

  2. #2
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    welcome. the bbcode functions on the board are currently broked for some reason so I'm just pasting your questions and my answers below them.

    Q: Could any serious damage have been done from playing the amp for about an hour with a 12ax7 tube in the phase inverter buffer spot in V5? And a 12at7 tube in V1?

    no. the ax7 and at7 have relatively similar characteristics (from an engineering standpont), with the at7 having higher transconductance and the ax7 a higher gain factor, but the differences are not enough to cause any permanent damage, though the sound will not be optimal.


    Q: Would that have something to do with the 12ax7 tube failing in V1 the second time the issue happened? What do you guys think could have originally caused the problem?

    I don't think that's likely. cloudy whiteness inside the tube means the getter (normally a shiny silver coating on the top end of the tube) has reacted with oxygen, which is indicative of a vacuum failure. this is a mechanical failure of the tube to maintain a vacuum seal. the most common causes of this vacuum failure are leaky construction or physical shock causing the glass to crack. my first guess would be the former; try a different brand or supplier of tube.


    Q: I took the springs out of all the preamp tube shields, and left the shields on because the technician originally suspected the spring putting too much pressure on the tube could of been the reason why it failed. Should I put the springs back?

    the springs are there to retain the tubes so they aren't dislodged accidentally. if you're not worried about the tubes becoming dislodged there's no harm in leaving the springs off. at the same time, it seems unlikely to me that the spring pressure would cause mechanical failure of a good quality tube.


    Q: From this story, do you think any of the power tubes could have suffered any damage in the process? Or any other part of the amplifier like the circuit board or transformers? Are there any other concerns or things that could of been effected from all of this?

    unlikely that anything else was harmed by the preamp tube failure specifically. in the vacuum failure mode (unlike some other failure modes) the tube draws less current, not more. I'd chalk up the two consecutive failures to bad luck, and try replacing V1 and the phase inverter tube with good quality tubes from a different supplier. Fryette does not suggest JJ tubes.

    edit: I would guess if you were to ask Fryette support, one of the first things they'd say would be to ditch any JJ tubes in your amp and replace with better tubes...
    Last edited by metalhobo; 1 Week Ago at 11:43 AM.

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