test for output transformer
Moderators: pompeiisneaks, Colossal
test for output transformer
Just built a deluxe reverb, voltages look fine but absolutely dead quiet, I think I might have bad output transformer. Its an ultra linear type but I'm just using the brown and blue on the primary reading (40 ohms , 20 ohms to center tap). On the secondary I'm reading 1.5 Ohms (8 ohm tap).these values are measured in circuit. I've never had a dead duck like this one. Any advise would be welcome. Are these good values ??
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Stevem
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Re: test for output transformer
Your primary resistance readings are low to me, and your 8 ohm secondary tap is about a .5 ohm too high!
Be sure that when you hook up your meter that you make only one connection point with your hand, if you use both hands to hold the wire connection points your DDM will read wrong to some degree!
If you hook your meter up set for ac volts across a output tubes pin 5 to ground and play thru the amp you should see at least 8 volts if the amp is cranked!
I along with this test if you read over 300 vdc on a outputs pin 4 and at least the same on pin 3, along with at least a -14 vdc on pin 5 than the amp should have output to the speaker if the OT is grounded on its secondary and is good!
If your resistance readings are right on the primary I you have a shorted primary in that OT.
another way to prove out if the OT is good is to install a 2 watt 1 ohm or 10 ohm resistor in series from pin 8 on each output tube to ground.
If you than hook up a voltmeter across pin 8 to ground and play thru the amp then if all is well but for the OT you will read a voltage in MV go up from idle and down and you play the amp.
This test proves that the amps PI section is working to drive the output tubes, but the shorted primary of the OT is loading down the drive.
Be sure that when you hook up your meter that you make only one connection point with your hand, if you use both hands to hold the wire connection points your DDM will read wrong to some degree!
If you hook your meter up set for ac volts across a output tubes pin 5 to ground and play thru the amp you should see at least 8 volts if the amp is cranked!
I along with this test if you read over 300 vdc on a outputs pin 4 and at least the same on pin 3, along with at least a -14 vdc on pin 5 than the amp should have output to the speaker if the OT is grounded on its secondary and is good!
If your resistance readings are right on the primary I you have a shorted primary in that OT.
another way to prove out if the OT is good is to install a 2 watt 1 ohm or 10 ohm resistor in series from pin 8 on each output tube to ground.
If you than hook up a voltmeter across pin 8 to ground and play thru the amp then if all is well but for the OT you will read a voltage in MV go up from idle and down and you play the amp.
This test proves that the amps PI section is working to drive the output tubes, but the shorted primary of the OT is loading down the drive.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: test for output transformer
tried what you suggested to test the pi output, nothing. I wish my scope still worked so I could signal trace. I never had an amp that made zero noise. I think I better start looking for a scope. The output transformer should still work without the ultra linear leads attached (blu/wht, brn/wht)? thanks for the advise.
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martin manning
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Re: test for output transformer
No issue leaving the UL taps unconnected. You could always whip up a signal tracer probe, basically a cap-on-a-stick, and trace the signal path that way.
Re: test for output transformer
Thanks I'll give it go, good idea. Thanks
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dorrisant
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Re: test for output transformer
"Education is what you're left with after you have forgotten what you have learned" - Enzo
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Stevem
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- Joined: Fri Jan 24, 2014 3:01 pm
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Re: test for output transformer
I have built keens transformer tester and it works far far better on Pts, as it failed to confirm a OT for ne that I already knew was bad!!
Just sayin!
ALSO note that you can test out part of the preamp signal chain very easy this way.
The send to the reverb pan is the 8 ohm output from the reverb drive transformer, so if you hook up a speaker to that send and the circuit is working up to that point ( 3 gain stages on the tremolo / vibrato channel) you will have a 1 watt amp in effect, no pun intended!
Just sayin!
ALSO note that you can test out part of the preamp signal chain very easy this way.
The send to the reverb pan is the 8 ohm output from the reverb drive transformer, so if you hook up a speaker to that send and the circuit is working up to that point ( 3 gain stages on the tremolo / vibrato channel) you will have a 1 watt amp in effect, no pun intended!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: test for output transformer
Thanks for all the help everyone, I'm kind of embarrassed to say I found the problem. Instead of using the usual 12A switchcraft phone jacks I used the RadioShack closed circuit ones I already had in my drawer, I forgot why they were still there, the pinout is different and I remembered having this problem before!!! Duuuh! Hence the totally silent amp, once corrected I have a lush sounding reverb vibrato amp, beyond my expectations. Many thanks to Tag members as always, I learned more about the fine art of amp building. I will post a final when I get the combo cabinet built. Thanks again!
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Stevem
- Posts: 4576
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: test for output transformer
We all do dumb shit!
Two weeks ago I went crazy looking for a screw driver that Put in my back pocket a half hour before! Lol!
Two weeks ago I went crazy looking for a screw driver that Put in my back pocket a half hour before! Lol!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: test for output transformer
I spend half my time looking for something I set down 30 seconds earlier...
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Reeltarded
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- Location: GA USA
Re: test for output transformer
I walk around on the phone looking for the damned phone. I have said in conversation, "where is my phone".
Signatures have a 255 character limit that I could abuse, but I am not Cecil B. DeMille.
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dorrisant
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Re: test for output transformer
Fluorescent tool handles work really well... Except when the tool is in your back pocket. Don't ask me how I know this!
Tony
Tony
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: test for output transformer
It's hopeless. At this point I'm hoping for the point when I'm so senile I won't know I'm senile.
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Stevem
- Posts: 4576
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: test for output transformer
I have read lately that in test when older people with menory loss have show some great improvements within 45 minutes by just having a smokers nicotine patch appled to them.
The nicotine may be addictive, but it is not what causes Cancer in smoking so this my be a simple fix for your stated senility!
The nicotine may be addictive, but it is not what causes Cancer in smoking so this my be a simple fix for your stated senility!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: test for output transformer
What if I forget I just put one on and keep piling on the patches? 
Or I can start Vaping, all the kids are doing it! Nothing cooler than a plastic prosthetic cigarette in your mouth.
Or I can start Vaping, all the kids are doing it! Nothing cooler than a plastic prosthetic cigarette in your mouth.