• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

I would like to upgrade my power transformer

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#5
youngie said:
I just keep seeing people talking about a big sound approvment. I don’t really want to waste money. But I would like a little bit more advice. Before waste my time and money. Many thanks lee
Click to expand...

If your amp doesn't sound good, changing the power transformer won't bring the anticipated ecstasy...in fact if the present transformer is working properly, a replacement won't change anything for the better.

Mike
 
#6
I've had a wee look round the net, but have not come across any references to changing the power transformer. Most punters seem happy with the amp and even state that the transformers are worth the cost of the amplifier on their own. I trust you are not being unduly influenced by opinions on the likes of YouTube? If the mains transformer is providing the required currents at the required voltages then it is doing its job and I would leave well enough alone. Maybe some other owners of this amp will tell a different story so I'll continue to tune in with interest.
 
#8
I doubt replacing a power transformer will make much difference unless it is miserably under-specced. Replacing one, on the other hand, is a real pain in the neck.

The only time I'm aware of where replacing a power transformer has a "big sound improvement" is when the old one has failed, causing the amplifier to produce *no* sound
 
#10
H713 said:
I doubt replacing a power transformer will make much difference unless it is miserably under-specced. Replacing one, on the other hand, is a real pain in the neck.

The only time I'm aware of where replacing a power transformer has a "big sound improvement" is when the old one has failed, causing the amplifier to produce *no* sound
Click to expand...

Thank you all for your input. I will not be replacing the power transformer I wish there was a thanks button I could press. So I could thank you all. many thanks lee
 
#13
Thanks youngie! The following schematic for the Yaqin MS300B clearly shows a 220V mains transformer as mentioned in your link.

http://www.4tubes.com/SCHEMATICS/BY-BRAND/China-Brands/YAQIN/Yaqin-MS-300B.jpg

The problem seems to be that the use of a 220V power transformer on the UK mains may lead to overvoltage on the valve heaters which will shorten the lives of the valves.

An alternative to replacing the mains transformer is to add a 'bucking transformer'. Details are given in the link below.

Bucking Transformer DIY (Drop 240V to 220V) | Sound Kontrol (DASK)

Before worrying about overvoltage, you should first see if it exists by measuring the valve heater voltage.

(I presume you know all about the safety precautions to be followed when working around the dangerously high HT voltages inside a valve amplifier!).

The heater voltage should ideally be 6.3V, 6.6V is acceptable but 6.9V is pushing it!
 
#14
I see from the schematic that three of the transformer secondary windings should produce a heater voltage of 5V ac - these secondaries should not read higher that 5.5V ac.

This would be the best place to measure - directly at the 5V ac secondaries.

Note that this 5V ac is rectified and smoothed to produce a dc voltage for the left and right channel 300B valve heaters. The rectifier valve gets a straight 5V ac.
 
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