transformer getting warm

karachay

Member
2018-02-16 4:37 pm
hifriends i have one transformer from an old pa amp. it was 3 channel 300w. i take out seconder wires and rewind again for my new amp b500 apex.

last 1 month it was ok but ampp always get different problemd 4 5 times. i was make a gift for my friend bar. and now it come back again i make 2 channels new pcb and testing but with one channel transformer getting warm a little bit. its not doing that before . amp working now but that warming making me feel bad. not hot but warm

my seconder voltages are 2x42vac and 2x17vac.

any advice?
 

karachay

Member
2018-02-16 4:37 pm
Checked the bias? High bias in one amp will pull more current from the secondaries.
thank you for answer mark,
this is the schematic abouth amp. i write some mesurements but no one answer abouth bias. i have 0,47vdc on 5200 transistor base and 0,33vdc on 1943 transistor base i think it show the bias is not right isnt it?
 

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karachay

Member
2018-02-16 4:37 pm
You measure the voltage across the 0.33 ohm resistors to determine the bias current - here you have 4 measurements to make and sum top and bottom.


I'd check that output offset at the same time (no load connected), it sounds off.

0.33R are have 0V :))))

can you please write me which resistors i need to mesure? and what should they need to be?

ty for your time and helping.
 

karachay

Member
2018-02-16 4:37 pm
What's the resolution of your multimeter? You would be expecting maybe 10-15 mV per resistor.

Does the transformer still get warm if you pull the two 10 A fuses for that side?

when it stay no input, its not getting warm but when i test with half volume with input on 8ohm dummy load then it getting hot :(( i just dont know how to check bias everyone saying check it but no one let me know how it can be.

i am testing now withouth fuses.

thankyou.
 

karachay

Member
2018-02-16 4:37 pm
What's the resolution of your multimeter? You would be expecting maybe 10-15 mV per resistor.

Does the transformer still get warm if you pull the two 10 A fuses for that side?

not warming witouth fuse.

i put back fuse and try with 4ohm dummy load again and now i just see my main power is 60vdc going down to 20 and moving to 60 not stable positive side.
 

Vovk Z

Member
2011-10-30 10:32 pm
Kyiv
Always use fuses. Fire isn't a joke.
Measure bias current with usual multimeter, at 2 V (first), than 200 mV range., on that low-ohm emitter resistors, as you was told earlier.
Use Ohm law to calculate the bias current.
Bias measures at warm amp, without sound, but you have to know how it changes with time too.
 

Ian Finch

Member
Paid Member
2010-04-11 4:22 am
Coffs Harbour, NSW
Mark described in brief, how to check bias at post #3. Did you not understand what he was saying?

You measure the voltage across (that is, from one lead to the other) of the emitter resistors and calculate current by I=E/R which you now know by measurement. As you have 2 pairs of output transistors, you must measure the current in both parallel pairs and add them together for the total bias current. Do this for the upper pair (+ rail), then compare with the lower pair (- rail) of output transistors. They should all share roughly equal DC current.

Note that the amplifier must be powered on to make any current or voltage measurement and your meter should be capable of reading down to 0.5 mV DC reliably.
 

karachay

Member
2018-02-16 4:37 pm
Mark described in brief, how to check bias at post #3. Did you not understand what he was saying?

You measure the voltage across (that is, from one lead to the other) of the emitter resistors and calculate current by I=E/R which you now know by measurement. As you have 2 pairs of output transistors, you must measure the current in both parallel pairs and add them together for the total bias current. Do this for the upper pair (+ rail), then compare with the lower pair (- rail) of output transistors. They should all share roughly equal DC current.

Note that the amplifier must be powered on to make any current or voltage measurement and your meter should be capable of reading down to 0.5 mV DC reliably.

ty for this i understand now how to calculate bias ty soo much. but i think that is not my amp problem.

for the 5200 and 1943 i need get at the base min 1vdc yes? i cannot get dc1 v there. well some times it coming 1v and then drop the 0.97vdc.

15033 and 15032 are geting their base 1v.

bias mesurement on 0.33r i take multimeter on 200mv and still showing 0v cause of power transistors not open. this can be the problem? still dont explane why transformer getting warm.
 
not warming witouth fuse.

i put back fuse and try with 4ohm dummy load again and now i just see my main power is 60vdc going down to 20 and moving to 60 not stable positive side.
????
Are you saying that the voltage with "no load" is 60 VDC, and WITH load falls down to 20V DC ?
Do I understand correctly?
Maybe one of the output transistors is shorted, faulty?
Try disconnecting the amplifier from power. Wait till all capacitors discharge.
Then take the multimeter and set it to 200 ohms or "Diode check".
Test if the output transistors are not shorted between collector and emitter.
If you see "zero ohms" - that might suggest a problem.
 
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karachay

Member
2018-02-16 4:37 pm
????
Are you saying that the voltage with "no load" is 60 VDC, and WITH load falls down to 20V DC ?
Do I understand correctly?
Maybe one of the output transistors is shorted, faulty?
Try disconnecting the amplifier from power. Wait till all capacitors discharge.
Then take the multimeter and set it to 200 ohms or "Diode check".
Test if the output transistors are not shorted between collector and emitter.
If you see "zero ohms" - that might suggest a problem.

yes its correct. i check it they are ok now i checking maybe psu have problem.

this is how i make the gnd connect. i just see when i put cooler on chasis that problem coming out so i think some where i have short on cooler but all insulators good i will post again if i find some thing.

thank you for helping.
 
yes its correct. i check it they are ok now i checking maybe psu have problem.

this is how i make the gnd connect. i just see when i put cooler on chasis that problem coming out so i think some where i have short on cooler but all insulators good i will post again if i find some thing.

thank you for helping.
Test the PSU separately. Connect a dummy load (high power resistors on heat sink) so that comparable Ampers will flow as in normal amplifier working conditions. Test if voltage sags or is it steady close to 60V ... maybe 57V, but not less.
And NOT 20V.

First, you NEED to be sure that the PSU is working correctly, before you do anything else, in my opinion.
 

karachay

Member
2018-02-16 4:37 pm
Test the PSU separately. Connect a dummy load (high power resistors on heat sink) so that comparable Ampers will flow as in normal amplifier working conditions. Test if voltage sags or is it steady close to 60V ... maybe 57V, but not less.
And NOT 20V.

First, you NEED to be sure that the PSU is working correctly, before you do anything else, in my opinion.

ty. i check psu nothing wrong. this amp kill all my life time i dont know what is wrong with it.

i disconnect chase gnd from psu if some thing going on cooler i think problem will be stop so i will start check with MICROSCUPE tomorrow :p

every things is ok but nothing workign good :mad::(:confused: