Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Skip Hagey on October 29, 2015, 04:00:12 pm
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AAArrgghh! After my first power up of my first scratch 5E3 build, Dougs version, I have a dead short that I simply cannot find. I've checked and rechecked found some errors and corrected them, I think, but still have the short. Hooked up to a spkr, I get an initial hum immediately and then as the caps start to charge, the light comes on on my circuit protection. Then she really starts to hum! Could someone give me some ideas where to look, I've run out of my own?! I'm sure it's probably something staring me in the face but I can't see it! I do find I have trouble with the orientation of the input jack and vol/tone control wiring diagrams, but i've tried them in more than one configuration w no luck. Thanx, Skip :BangHead:
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Did you read ALL the pages Doug wrote/drew out on his 5E3? Link below;
http://el34world.com/schematics.htm#Hoffman_5E3_Tweed_Deluxe_ (http://el34world.com/schematics.htm#Hoffman_5E3_Tweed_Deluxe_)
I don't know how your double checking your build, but this is a great way to double check it;
http://el34world.com/Forum/index.php?topic=17701.0 (http://el34world.com/Forum/index.php?topic=17701.0)
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Go over your diagram with a bright light on the build and a yellow-marker to keep track. (This is probably Willabe's link.)
But first: it is OK until the tubes warm up. Pull the tubes. Actually, the small tubes are almost never able to suck enuff to light a light, pull your rectifier and power bottle(s). Does it still short? Put them back one at a time (rect first).
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As the others have requested
Do this first and then let us know
http://el34world.com/Forum/index.php?topic=17701.0 (http://el34world.com/Forum/index.php?topic=17701.0)
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I had this happen on a Bassman I rebuilt and it was a bad bias pot. I basically did'nt have any bias so as the tubes warmed up the amps started climbing rather fast...
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:icon_biggrin: I'd like to thank all you who took the time to respond and let you know that all this time it was a bad output tube! Go figure. I don't have a tube tester so assuming all tubes are good doesn't really pay off! I still have issues like the normal channel works but the bright one doesn't. I think i'll be able to figure that out though. this thing is quiet as a mouse and does sound good, but a little bass heavy. I'm running into a 2 by 12 running 4 ohms. my wife is sleeping right now so I haven't opened it up yet...can't wait. thanks again guys, i'll post some pics soon....
{EDIT- fixed munged icon -- PRR}
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.... this thing ... does sound good, but a little bass heavy.
That's normal unless you're plugged into the Bright channel and turn the Tone control up.
Some players reduce the value of the coupling below 0.1uF (to 0.047uF or 0.022uF) to reduce bass.
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Thanks, that's my next task, trying different coupling values. So many variables...!
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So I've had two Tung sol 6v6 tubes short out with this new 5E3 build...are these tubes just inferior or as it possible I have another problem. I have some NOS 6
v6's that seem to work fine..at least for now. Maybe the plate voltage is to high for these tubes and if so what would you suggest? Thanks...
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What is your plate dcv? What is the PT your using?
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5.8 and 6.1 @ pin 3, PT is the one Doug provides for his circuit. Ahhh...DC voltages are 322.2 and 321.8
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What is the DC voltage on pin 4, 5, and 8 of each 6V6?
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1st. pin 4=286.9, pin 5=4.0, pin 8=17.9. 2nd, pin 4 287.8, pin 5=4.6, pin 8=17.9
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Pin 5 should be zero volts. Recheck those pins again please.
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yeah, the meter was all over the place so I took an average of the readings...and the readings were in mv's so .004
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None of those voltage readings would put any stress on a good 6V6. Maybe you've just been unlucky? Try some JJs if you have them.
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Thanks, i've since read that the tung-sols don't tolerate higher voltages and that hte JJ's or the EH new releases are more tolerant... I'll have to order some!
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I wouldn't consider 325V as high for any 6V6.