Bugera V5 Infinium Low Wattage

[tdlunsfo]

On no that is full clip. If I drop to the onset of clipping the output is even lower at 0.6v. Sorry I have had a few others on the bench today so my test setup may not be exactly the same as this morning. B+ at idle is around 320v and at full tilt it is around 300v. Output transformer is kind of where I'm at as well. The amp doesn't sound bad.. just not loud.

[tdlunsfo]

I put the OT on the Variac. Looks like 24 to 1 turns ratio.

[Helmholtz]

I put the OT on the Variac. Looks like 24 to 1 turns ratio.

That would correspond to a primary impedance of 2.3k with 4R load. Definitely low. Typical is 5k to 7k with EL84. Try the neon flash test.
https://music-electronics-forum.com/...7&d=1590953469

[J M Fahey]

Transformer ratio is fine, DC voltages are fine, idle current times plate voltage amounts to 11W, enough for 5W RMS or so accounting for losses, drive signal is fine, plate voltage is TOO low so I strongly suspect shorted OT.

Load impedance is reasonable, notice it says *minimum* 4 ohm, I guess optimum is 8 ohm and 16 ohm is acceptable, so EL84 would see around 5k, not bad in my book.

And speakers, specially Guitar ones, tend to have higher impedance on most of the curve, except a dip to almost DCR typically between 250 and 400Hz, so that´s fine too..

[tdlunsfo]

Thank you all for staying with me on this one. I am pretty sure I don't have a neon bulb so I'll order one and report back on the transformer test.

[Helmholtz]

If the OT has shorted turns - what I've been suspecting for a while - the voltage ratio and apparent primary impedance may be off. So if primary turns are shorted they won't contribute to ratio and primary impedance would appear too low. Of course this would require a short between layers and not only between 2 adjacent turns.
May be wrong but I doubt that the amp was designed for only 2.3k impedance with 4R.

[tdlunsfo]

It has a 4 ohm speaker from the factory and this is where I get confused as most SE EL84 transformers appear to have 5000 ohm primary impedance for a 8 ohm secondary. This 24:1 ratio with 4 ohms reflects back a 2300 primary impedance. So begs the question, what would you replace it with? I tried to look up the OT but didn't find much. Here is a pic of it. In the end, the customer will likely not fork over this kind of money for an amp this cheap. Best bet may be to send it in as a warranty if one still exists. Regardless, I still want to know if it is indeed an OT issue just for the learning experience.

[J M Fahey]

Testing will answer your doubts , anything else is just guessing.

[tdlunsfo]

Got my neons in today and no light on both primary and secondary. Confirmed my setup works on some spare transformers I had lying around. Looks like this output transformer is FUBAR.

[Baronkarza]

Calculation is correct. 5W would correspond to 4.5Vrms into 8R. Did you try a new EL84?

BTW, what is EL84 cathode voltage?

Hi everyone.
Did you means 4.5 Vrms into 4R ? Or i miss something.

[Helmholtz]

Hi everyone.
Did you means 4.5 Vrms into 4R ? Or i miss something.

You're absolutely right. Typo, my bad.