the modder's diary part 17:
first of all i removed everything from the tu-05 where i was not sure of the pure improvement:
- the added coupling capacitors (wrong type not for audio)
- thicker twisted power cable between amp and internal psu
- the added voltage regulator board and capacitors (work in progress)
at the moment i am using the second psu board (anode voltage not changed) to run the tu-05 as original as possible
reading the posts and questions about the standard and enhanced output transformers i thought it's time to do something for all of us so here is the
TU-05 OUTPUT TRANSFORMER MOD:
Often SE output transformers are made using EI cores. the name is the result of the two parts looking like an "E" and an "I":
The small distance between "E" and "I" is called "GAP" and needed for the core not to get into saturation, getting magnetized because of the (low) DC current constantly floating in the case of and Single Ended (SE) tube amp.
This is a TU-05 output transformer:
and here one of my tu-05 output transformers after beeing opened:
as can be seen it uses a EI core:
The important point is the gap:
- the wider the gap, the lower is the risk to run into saturation,
- BUT the wider the gap, the lower the inductance and so the bass response
- the smaller the gap, the higher the risk to get the core saturated
- BUT the smaller the gap, the higher the inductance and so the low frequency and bass response
So to possibly improve the bass of the tu-05 by modifying the installed transformers it is nessesary
- to open them
- reduce the gap between "E" and "I"
- close them again
overall there should be room for improvements as the original output transformers are
- specified for an output power of 3 watt
- specified for a DC current of 20mA
- the tu-05 is far below this specifications, so a smaller gap should not result in a saturation of the transformer cores
Read more: (Click to show)
first step is to remove the frame around:
bending and opening the 4 metal tonques holding the core in the frame:
lots of glue used to hold everything together so now using a very thin and sharp knife to more or less carefully bend and widen the metal frame:
the slit between core and metal frame is glued (above the knife) and has to be widened:
after that you can bend the left and right side of the frame to the left and right side:
to remove the frame completely the easiest way is to use a pliers and some force:
this is the output transformer without frame:
unfortunately the "I" is glued to the "E" (glue between the first metal layer and the "I") so again use a sharp and thin knife to get the "I" removed:
here is the output transformer without the "I", the "I" on the right:
the correct width of the gap is usually provived by putting something in between "E" and "I", usually paper. in the case of the tu-05 transformer it is a small piece of plastic, obviously and no need to mention glued, so let's remove it using the same technique:
(on one transformer it was glued on the "I", but on the "E" in the case of the second transformer)
to know the size of the gap provided (this is important) i measured the thickness of the plastic foil (several times):
to provide a smaller gap i used paper cut into stripes:
to finally apply them you need just 2cm pieces of the stripes:
the paper above has a thickness of 0.08mm so i tried a different one with only 0.025 mm (two put together = 0.05):
if you don't know the thickness of your paper you can often just calculate the thickness (if you have a scale and enough paper or a milligram scale as i have) because usually paper has a weight per square meter value when buying it (letter paper for example 80 grams per square meter).
here the paper is put on the transformers before re-inserting the "I"s:
here the transformers with paper and the "I"s inserted (NO glue needed!):
and here the transformers closed with frame around (bend with a bench wise):
The SE Output Transformers now have a gap of (2x 0.05) = 0.1mm instead of 2x 0.12)=0.24mm.
finally to avoid soldering the wires each time some connectors added, so you can just use a screwdriver to connect wires to the transformers:
and here connected to the tu-05:
i haven't listended to the original tu-05 output transformers for a long time but as far as i remember bass response is improved (gap is smaller, so it must be improved, the question is if the improvement is big enough to be heard).
For example listening to J.S.Bach, Toccata und Fuge d-moll, the rumble and noise from the traffic outside is better to hear than before.
don't expect wonders as the output transformers and so the cores are really small, but nevertheless overall the sound has a little bit more body and "ground" so beeing sligtly more "complete" and as this mod is very easy to perform and gives you maybe just this small extra bit of bass you may want, .....
Edited by GermanGuy - 1/1/14 at 3:36am