need help with simple pp
First Happy new year everyone :)
After long hard year I finally have time to get back on fixing this amp.
My tubes are jj el84,jjGz34s and jj eec81
My power trans is Edcor Xpwr008-120
600v, 200mA center tapped 6.3v 4A,5v 3A
output trans are Edcor Cxpp30-ms-6.6k
30w primary 6600 ohms 40% screen
secondary 4,8,16 ohms
connected in UL configuration
my speaker sensitivity is 86db
when I turn it on all the tube light up but music sound weak no bass when I turn the volume up it start to distorted
These are the voltage I measured
R106 320/114 R206 320/107
R107 115/0 R207 108/0
R108 319/201 R208 318/205
R109 330/319 R209 331/319
C103 203/0 C203 211/0
C105 115/0 C205 108/0
T1RED 300 both
I have no idea what is going wrong please help.
Why do you have a brown wire connected next to the white/blue on the left channel connectors? It should be blue with the Edcor transformer. Also, double check that you have about 6.3 volts AC at the connector that has the 2 red wires connected. They should be brown wires using the Edcor power transformer. I realize that you may have spliced these wires & used different colors but check anyway.
I have three Simple PP amps & they all work flawlessly. One has the same power transformer as yours & Edcor output transformers (although 8,000 ohm). I'll check voltages this afternoon and see if yours are proper.
Your voltages look fine. I'm working on a spreadsheet that displays the voltages found on mine. I'll email it to you soon.
Could it be my speaker not efficiency enough? If you ever use your pp amp to drive any 86db speaker?
And the two brown wires are too short so extended with red wire I have.
Some speakers that sound OK with a transistor amp will sound absolutely awful on a vacuum tube amp. This is due to the speakers not having a consistent impedance throughout it's frequency range.
Long story short, trying different speakers may help quite a bit.
Try cleaning up your wiring layout as much as you can. Long leads can cause crosstalk and oscillation, which can cause sound quality issues.
Try installing a 680pf capacitors in C101 and C201. Those are the feedback compensation capacitors. 680pf may not be the optimal value (optimal will likely be between 500pf-800pf), but it will close enough to help. Not having these capacitors installed will cause the treble to be slightly louder and distorted.
Disconnecting the feedback loop all together may help if you are having oscillation problems. You can do that by removing the wires from L_FB-1 & R_ FB-2, then connecting the output transformer wire directly to the corresponding speaker out wire.
Make sure unused output transformer taps are isolated and not connected to anything or each other.
Make sure the input and output connectors are not accidentally shorted to ground.
Even with 86dB speakers, you should get reasonable amounts of volume with this amp. If it sounds weak and distorted, something isn't right.
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