30VA sounds slightly marginal. Most transformers are not rated at constant draw such as present in a Valve preamp so they will be operating fairly at the edge and the heating is a strong indication.
Is the heater supply off a separate transformer ?
Shoog
To shield a transformer you must fight mostly with the field B, so you need a ferromagnetic material, such as mu-metal, or at least iron.
A good conductor only can cope with the field E, which also helps, but less.
Hint: Put a copper belt that surrounds the winding outside the core grounded, and the set inside an iron box.
A good conductor only can cope with the field E, which also helps, but less.
Hint: Put a copper belt that surrounds the winding outside the core grounded, and the set inside an iron box.
You could try a separate heater transformer - it probably wont help a lot - but it might.
Can we get a photo of the whole box to get some ideas.
Shoog
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My case is pretty good then cos there is ventilation both in top/bottom lid at the back. My case have twice as many ventilation holes as seen in this pics so call it MKII 😀 I mean if i keep xformer in the case.
No, if i would use a xformer cover i would place it in the back over ventialtion holes and then drill some holes on the back in that cover i was thinking
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A salvaged wallwart transformer can generally be pressed into service as a heater transformer. 6V is good as underheating extends tube life. I run most of my valves underheated at 6V.
Shoog
Shoog
A Mu-Metal wall around your transformer and power inlet should help a lot. The power transformer doesn't look that undersized. When you do your final build out you can move the circuit boards right up to the front of the case which should help a lot as well. Your heater twisting isn't really adequate - they need to be tightly twisted right up to the circuit boards. Needs a general bit of a tidy up before you can tell where you stand.
Big cases are something you learn to always use when building, the frustrations of getting everything right in a pokey case are educational to say the least. Nice case though.
Shoog
Big cases are something you learn to always use when building, the frustrations of getting everything right in a pokey case are educational to say the least. Nice case though.
Shoog
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I think not necessarily, max heating in transformers core is at no load, max heating in the wire is at full load, so if there is heating problems, change the transformer.
Signal inputs seems very close to PT, try to put it near the on/off switch side, and PCBs in the other side, I mean PT at the left and PCBs at the right.
A mu-metal wall in between, as Shoog said, is a good idea.
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when the preamp is only powered on (no music) it get's hotter then when i play music. I've noticed this several times. I usually put my fingers on different parts to see if they are warm. I'm a touch-er 😀😛😉
Mu-metal?
Inlet: yes i can understand that. I put a BULGIN fused filter there too. I like it. Seem to have cleaned up the signal little and even made the amp little quiter.
Everytime i turn off/on there is a slight "pop/click" sound. IS it possible to remove this by adding a cap between the two solder-ears on the powerswitch (see pic above, in the front, orange/black cable) I have some WIMA mkp X2 10nF would that be ok?
Then, as un update, you must change the transformer, core is crap, meanwhile, try to put it in the correct place.
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