Dead Transformer of a Guitar Amplifier

Thread Starter

aq_rules

Joined Oct 28, 2009
168
Yep.
That's why I suggested the photos. Voltage and current requirements would depend most on what appears to be a 5-pin amplifier chip mounted on the heat sink. (Maybe a TDA-type) And, the photo in post 14 shows a 13W input power.
So what do you guys suggest a 100v-16v transformer with 0.81 A current from secondar? Am i right....but i guess the speaker needs 20w input...it wont work..
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
To get an idea of the correct VA size, match up the physical size on the Hammon web site, they should also have a suitable replacement.
Max.
 

tubeguy

Joined Nov 3, 2012
1,157
One more helpful bit of info would be the part number of the amplifier chip.
It appears that the transformer is center-tapped and the supply is a +/- DC power supply.

The speaker is rated 20 watts. That doesn't mean it needs that much power. The amp power may be less based on the 13 watt input rating.
 

sheldons

Joined Oct 26, 2011
613
if this is the transformer in question it will be a simple fix to locate the thermal fuse and either replace it or just remove it etc and quickley test the transformer on its own with your meter to see if its working or not
 

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Thread Starter

aq_rules

Joined Oct 28, 2009
168
I reached the thermal fuse it is bad...but the primary winding is broken by my mistake while i was unwinding...now what to do?


And there is no continuity in the primary winding wires end to end without the fuse...thats why i was unwinding the whole primary to see if wire is damaged...
 

sheldons

Joined Oct 26, 2011
613
noooooooo all you needed to do was temporarily sc the fuse and then check the transformer worked not unravel the primary winding-now you need a replacement transformer............the fuse was in series on the live side of the ac supply to the primary-the other side of the primary going to the neutral-you've probably wrecked a working transformer now
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Usually the primary is the first wound on, so you would have to take the secondary off first.
It is what you call brilliant design, the fuse opens for what ever reason and saves the transformer, but makes it unusable in the future, this is why I always shorted them out, to make them virtually the same as any other off the shelf transformer.
Max.
 

Thread Starter

aq_rules

Joined Oct 28, 2009
168
Primary and secondary were wounded separately on two different divisions of formwork...but i ruined it...thinking of getting it wounded by some professional as someone told me that in my city there are many places where they give services of winding...

The primary was wounded for 110V...the core area was 4 cm(sq) so by constant 42/4 we get 10.5 turns per volt....so for 110 VOLT no of turns were 1155 turns..

I am thinking of getting it wounded for 220volt that means 220×10.5 ...which is 2310 turns in primary...i will leave the secondary in its original condition..


Am i right??
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
I would have though an off the shelf replacement via Hammond etc would be the most economical?
Or Buy a toroidal version which is far easier to modify the secondary if needed.
Max.
 

Thread Starter

aq_rules

Joined Oct 28, 2009
168
Some how i made that transformer usable...it is performing as it was earlier....but the circuit is not working....the power led is very dim..

And the bridge diodes are overheating along with the transformer....
I guess the thermal fuse was gone for protecting the circuit due to only this problem with the circuit
Please help me trace out whats wrong...

I even tried changing all the bridge diodes with the new one but still heating both...transformer and bridge
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
Disconnect the capacitors and load first, if still heating then disconnect all and if still heats, the transformer is shorted.
Max.
 

#12

Joined Nov 30, 2010
18,224
Likely suspect is filter capacitors shorted. The fuse died for a good reason. Wrong to put a fuse inside a transformer.:mad:

Add a fuse holder somewhere to provide proper protection.
 

sheldons

Joined Oct 26, 2011
613
ok first off if you have replaced all diodes in your bridge are they connnected the same way round as the originals-are the same or similar type to the originals...if so disconnect the power supply side from the rest of the amp,if you have an audio ic fitted desolder it completely and power up again...you are checking the supply comes up with no heated stressed components.
Also,did you check the transformer on its own connected to your mains supply and is it running cool and producing a steady ac voltage on the secondary....
 

sheldons

Joined Oct 26, 2011
613
if you have removed the filter caps,desolder the TDA2030 and remove it from your circuit,replace the capacitors and try again.....you are sure the diodes in your bridge are of the correct type and the right way round in circuit....
 

Thread Starter

aq_rules

Joined Oct 28, 2009
168
My amp is now in working condition i just changed the TDA2030A

But its humming...when i pluck bass strings...

Whats the reason?
 
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