Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ALBATROS1234 on June 01, 2019, 10:43:57 am
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i bid on an old phillips el-3514 r2r (made in holland) which looked to be in decent shape physically, untested no cord. i won and it arrived last night. i purchased it because in was circa 1961 and i found a schematic online which showed it had and actual transformer, a 12ax7, el95. i figured it would be worth the $10 plus shipping if there was a juicy holland made 12ax7 but figured i could use other spare parts including the tranny for a preamp or whatnot. well i get it and it looks to be in great condition externally. i have had great luck buying stuff like this and have "knock on wood" never gotten a bad tube in any old gear i bought, some were worn and not as strong as could be, once i got a chassis that had a bad power transformer. anyway enuff rambling, i just wanted to set the stage. anyway the el35 was busted with a chunk of glass "blown out?" of the top portion and the 12ax7 ( a 61 or 62 phillips holland miniwatt) which looked ok physically but was dead/not output although filaments lit.upon closer examination the top around the tip look a bit odd, possibly cracked so i lightly pinched the tip between my forefinger and thumb and the tip came off with very little pressure , i gasped as i watched the perfect silver getter fade away to milky before my eyes withing 30 seconds. i know many will say you rolled the dice and lost, which is fine and i did take that risk but testing the tranny showed it to be fine and i just wonder what would cause tubes to just crack and or blow a chunk off the top of the power tube when externally the case is undamaged even ggod looking, even the clear plastic top was perfect shape. just odd to me.
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i just wonder
some greats from the way-back-days walked around all day doing the same, in the mean time the Ox cart still had a busted wheel :icon_biggrin:
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lol, i just wouldnt have expected physical damage to the glass on both tubes that were in the unit when the outside shell of the tape recorder wasnt cracked, or even remotely beat up(actually there is a submini dm71 also but its fine) . was thinking maybe something in the circuit could have caused really high current. or maybe if the tubes had been really hot then the thing got dropped causing a shock. i guess i over think everything. was really disgusted when i saw the phillips miniwatt and when i put it in an amp it did not work, my wee heart sure did sink because i have been really lucky with that kinda of stuff in the past.and i know that very tube type in that time frame is one of the holy grail 12ax7s, at least thats what i have read and the prices for those in good shape are crazy.
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that damage appears to be impact related and not electrical. something inside chassis came loose and struck those tubes. in those pictures there is no evidence of overheating/arcing, etc.
--pete
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I wonder if it could have been some sort of thermal shock? Especially with both affected? Any evidence of water intrusion? Beer intrusion from a wild 60’s hootenanny in the tiki themed basement?
There was a band back in the day who opened for us. They had CO2 fire extinguishers that I’m sure they ripped off from the previous bar they played at. Anyway they used them for great effect on their last song blowing them from behind the amps. One their drunk “roadies” blew one directly into the back of of the guitar players Hiwatt which quickly became silent. Kind of silly having them jump around all over the stage with just the bass and drums and the guitar player doing windmills in silence. Actually pretty hilarious! When they were tearing down I walked over and asked what happened. Both power tubes were cracked, not sure about any of the preamp tubes.
Jim
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I have an old Serviscope S51 that has a half dozen small tubes inside.
I was servicing it as some of the controls needed cleaning.
I pulled the tubes (don't remember offhand what they are, small 9 pin types, all Mullard)
and one of them (glass) came apart in my hand.
Note that the 'scope was working, it just needed some controls cleaned.
Close examination of the tube revealed almost paper thin and very "crumbly" feeling glass.
Of course I treated the rest with kid gloves and found an NOS replacement for the broken one.
Other than treating them gently and not throwing them down concrete stairs... I got nuthin... :laugh:
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Best practice for shipping is for the seller to pull the tubes and safely pack them. Reputable eBay sellers state that they will do this.
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Thanks guys, and thermal shock had crossed my mind.no evidence of liquid intrusion but I was Speculating a bit thinking perhaps the thing was run for a long time then shut off and packed it up and brought it outside to the car trunk on a winter day so that it got really cold after being really hot. Or some scenario where it was hot then became cold fast. I still got a twitch from the loss of that miniwatt lol. I basically use all old tubes either lightly used or nos. The new ones I got don't impress me