Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: tubenit on November 28, 2010, 09:04:50 am
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Guys,
I installed a brand new Hammond 269EX PT in my outboard FX-Reverb unit. I wired it like in the schematic and photo.
I used the 269EX because it was a standup PT and I had little room and it was reasonably priced.
Flipped the switch on & it got hot and started smelling in a matter of a couple of minutes. The thing stayed hot for maybe 10 minutes after being turned off. This was abnormally hot. The amp doesn't even have power tubes & the PT was hotter than on any amp I've built.
The filter caps and the 1N4007 are oriented correctly.
I then checked the PT secondary and there is NO voltage! However the PT secondary wiring shows continuity & with the CT wire also.
The heater is only showing about 4.2 volts. There is not a heater center tap wire, so I am presuming that the CT is inside the power trannie.
Can you see anything that I have wired wrong from the schematic and photo?
I am trying to determine if I messed something up ........... OR actually got a bad brand new PT???
My starting place is that I goofed somehow. I've never had a brand new PT be bad before.
IF I smoked the PT, I am hesitant to buy and install another one until I can figure out what in the world I did wrong?
With respect, Tubenit
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Your wiring looks fine. Disconnect both red wires from the diodes, plug it into the wall and recheck the secondary voltages. If still bad, the PT is bad. If you now have proper voltage, look for a short (to ground) on the B+ rail. Use an ohm meter. Could be a wiring error or shorted filter cap.
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I then checked the PT secondary and there is NO voltage! However the PT secondary wiring shows continuity & with the CT wire also.
A short will show continuity. What is the windings resistance?
The heater is only showing about 4.2 volts. There is not a heater center tap wire, so I am presuming that the CT is inside the power trannie.
The 269EX has a heater CT, with GRN / GRN/YEL / GRN leads.
Can you see anything that I have wired wrong from the schematic and photo?
Nope.
I am trying to determine if I messed something up ........... OR actually got a bad brand new PT???
I'd say defective PT. What are the markings on the Hammond sticker?
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Could be a wiring error or shorted filter cap.
I am applying for goof ball mistake of the day award here ........................
I toasted the PT and wired it mistakenly on the wrong terminal and sent it to ground. UGH !!!!!!!!!!!!!!!
That was a rather expensive OUCH!!!! :cry: :cry:
Besides buying a new PT, ......... any thoughts about what else might be bad??? Do I need to order new filter caps also? They look just fine and I don't see any bulges and none of them exploded and they are oriented correctly.
FYL, There is no heater center tap wire of yellow/green. Just two green wires. I think Hammond changed it. And that is how it also reads on the PT box that it was shipped in.
With respect, Tubenit
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Are you sure you toasted the PT? After rewiring it may just work. It's a Hammond.
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Filter caps should be OK. Those 3 dropping resistors on the B+ rail have been stressed though. Did you measure any AC secondary voltage after disconnecting the red leads from the diodes?
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Oh, the PT is definitely toasted .................. :laugh: :cry:
I unsoldered the secondaries and tested it. 4 volts on the 2ndry.
Then I removed it from the amp and hooked up the primaries to a typical cord to AC outlet. Same thing.
Amazing how bad they smell and how quickly it was done in.
It's gone, gone, gone ........................
I'll get another one .......... oh well!
Thanks guys, Tubenit
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Yeah, Oh well. Done stuff too.
Let's see if we can learn something to pass on to our children...
Why didn't the fuse blow? Was it too big?
Did you use a Light Bulb Limiter gadget on power up?
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Yes, the fuse was possibly too big? All I had was a two amp fuse in that short size.
No, I disassembled my light bulb limiter a few months ago when I needed the cord for something else. In the past, I typically do use the light buld limiter.
My kids are waaaayy smarter than I am, so they'd probably never do such a silly thing. :laugh:
Took a chance and lost on this one.
:wink:
Tubenit
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No, I disassembled my light bulb limiter a few months ago when I needed the cord for something else. In the past, I typically do use the light buld limiter.
I can't help but to laugh... I would do something like that in a heartbeat.
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No, I disassembled my light bulb limiter a few months ago when I needed the cord for something else. In the past, I typically do use the light buld limiter.
:laugh: :laugh:
oh no...wait a sec...
:cry: :cry:
but...still...
:laugh: :laugh:
sorry you fried the PT jeff, we all have up and down days. yesterday i got zapped by 300V+ on a pre-amp i was building - first time in over 3 years.
PT is likely fried - it gave it's life to save a fifty-cent fuse... :lipsrsealed:
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No, I disassembled my light bulb limiter a few months ago when I needed the cord for something else.
:huh:
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No, I disassembled my light bulb limiter a few months ago when I needed the cord for something else.
:huh:
How coincidental... I was tempted recently to use the cord and outlet box on my bulb limiter, but resisted and went to the hardware store for the stuff I needed. Sorry to hear about the PT tubenit.
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I have to admit that I've never used a lamp type limiter. :angel The PT in my really old National amp started making gurgling sounds, along with a really loud speaker hum. Two things to fix. One filter cap and one coupling cap. The PT was really HOT! But amazingly it survived and still works. Maybe those Hammonds aren't as tough as we think they are ! :smiley:
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Maybe those Hammonds aren't as tough as we think they are ! :smiley:
Recent production seems to be irregular.
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Quote:The heater is only showing about 4.2 volts. There is not a heater center tap wire, so I am presuming that the CT is inside the power trannie."
You need a virtual center tap.There is no 'center tap inside the PT".