Originally posted by dreamconduit
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B-52 AT-100, won't power on... please help!
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If it still won't get loud enough, it's probably broken. - Steve Conner
If the thing works, stop fixing it. - Enzo
We need more chaos in music, in art... I'm here to make it. - Justin Thomas
MANY things in human experience can be easily differentiated, yet *impossible* to express as a measurement. - Juan Fahey
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When you powered up the amp, was the standby switch on or off? Were the tubes in or out?
If the light bulb lights up brightly and stays lit up, the next step is to test the power supply diodes, the power transformer and the related circuits. If you remove the two high tension fuses F2 and F3 and power up does the light still stay bright?
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ok, so i tried both 30, 40w bulbs- same result. bulb glows bright as soon as power switch is turned ON. Standby switch was in Standby, but remains unchanged if switched on, as well. i've pulled out all 12 tubes (4 power, recto, 7 preamp) and it is still making all lightbulbs glow bright/steady once power switch is ON with NO tubes installed to Short the amp. obviously, they could all be bad, too. but that is a different issue. If i remove the 2 HT fuses (F2,F3)- i get the same result, bulb glows bright & steady once Power Switch is turned ON. the amps jewel light never lights during any of these powerings, just to be clear (i've never gotten any flickers or flashes).
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Next step would be to remove the secondary connections to the power transformer and see if the light still stays bright.
Disconnect the filament windings 5 volt and 6 volt, and disconnect the windings for the high tension and the low voltage supplies. If the bulb stays bright then you'll have to test the transformer and the wiring. If it goes dim, then there is a circuit problem.
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on this amp, the 6.3 v windings are soldered directly to the recto tube socket. so i've disconnected all the rest of the wires from the transformer ( 2 green 5v, 2 red HT, and the 2 white/1 black ctr tap low voltage connector on PS board ), and the bulb doesn't dim at all. it still stays bright. HOWEVER, let me repeat- the 2 yellow 6.3v lines are soldered to the recto tube socket, so i have not removed those windings, yet. they will have to be de-soldered 1st. i'm unsure of the impact of this difference.
i really appreciate everyone's help with this so far. thanx again.Last edited by dreamconduit; 07-16-2015, 06:17 AM.
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Well if you disconnected those wires first and the light bulb is now dimming, well then that is good news. Instead of worrying about disconnecting the rectifier heaters... Try to attach one section back on at a time. Start with just the low voltage ones and reattach then test with bulb limiter. If no short then disconnect and try again with the HV connection reattached. At some point you will reattach a section of the secondary and the bulb will light back up with a short. Basically, just have to narrow it down to which section is the fault located.
Also, note that if the tube rectifier is removed from circuit that should isolate those heaters wires. Not sure that is true completely but if the HV secondary taps are removed too then yes.
Edit: Just wanted to point out that the green wires are 6.3v to the heaters on all the tubes. Yellow wires to the rectifier tube socket are your 5v taps.When the going gets weird... The weird turn pro!
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The wires to the rectifier tube pins 2 and 8 are 5v, not 6v. The greens are 6v, yellow is usually 5v. Pulling the rectifier tube should open their circuit anyway.Education is what you're left with after you have forgotten what you have learned.
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thanks DrGonz78, but the bulb is NOT dimming. i've yet to see any dimming. as i last posted- it stays bright. no change. that is why i was inquiring as to whether the 5v (yellows) still being connected to the recto socket had any impact.? i didn't think so, w/ no recto tube installed... but just in case, i had to ask. i'm not going to just assume it is fine. anyways, no luck so far. so, what should be next?Last edited by dreamconduit; 07-16-2015, 08:26 AM.
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thnx again DrGonz78 (btw- i love your avatar! i've been a lifelong fan of hunter's work), i had a feeling it was gonna go this way. what a bummer. that being said, i've been really happy about the tone i've gotten from this model. it is still totally worth it for me to fix, IMO. could someone tell me a method to check to ensure the tranny is indeed defective? i'm guessing it involves fully removing all PT connections, then checking it's winding values in some technique. i'm sure this is described in detail here already somewhere, i just can't seem to find it. so, even just a link would be great, save yourself some typing. i hate my limited knowledge here, so, again sorry the remedial questions...but any tips on the specs i'm looking for in this specific transformer replacement? ideas / sources for a $ budget $ version (that is compatible with the b-52 at-100) would be very helpful. at least this PT appears to be a straightforward swap-out. it looks easier than working on some of the many relays in this amp, for example. we shall see.
thank you everyone for all of the help. super cool of yaz!
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It is simpler than that. Since it likely has to come out anyway, just unsolder those last two wires from the socket and see if the transformer alone still lights your bulb bright. if it does, that pretty much says the end for the transformer.
You can also go over to RG's Geofex web site and look up his very simple transformer tester, which you can make in minutes and use.Education is what you're left with after you have forgotten what you have learned.
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Also, before you buy a replacement PT, consider that the OT may also be bad. It should be tested before investing money into this unit of unknown origin.Originally posted by EnzoI have a sign in my shop that says, "Never think up reasons not to check something."
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