Hi,
Please tell me where I go wrong.
I have a el95 PP integrated amp in parts. The el95 are in triode mode.
Now it has output PP opt's with windings 38:1 anode to anode.
It says on the back the amp is for 5 ohm speakers.
I'm rebuilding it and when I do the math, these opt's seem totally wrong:
el95 PP expect 10k ohm in PP. But (38/2)^2 * 5 = 1k8 !
Am i missing something?
Thanks,
Daniel.
Please tell me where I go wrong.
I have a el95 PP integrated amp in parts. The el95 are in triode mode.
Now it has output PP opt's with windings 38:1 anode to anode.
It says on the back the amp is for 5 ohm speakers.
I'm rebuilding it and when I do the math, these opt's seem totally wrong:
el95 PP expect 10k ohm in PP. But (38/2)^2 * 5 = 1k8 !
Am i missing something?
Thanks,
Daniel.
Hi Daniel,
the output impedance reflects to the primary according to Zprim = Zout * 38^2. Thus, a Raa of 10k were achieved by a loudspeaker impedance of about 7 ohms.
Best regards!
the output impedance reflects to the primary according to Zprim = Zout * 38^2. Thus, a Raa of 10k were achieved by a loudspeaker impedance of about 7 ohms.
Best regards!
EL95 expect 10k ohms anode-to anode, so try 38*38*5 which gives 7220 ohms on 5 ohm load.
Likely, the transformer made for 8 ohm load (result 11k).
A little low on 5 ohms, but useable with a small increase in distortion.
Likely, the transformer made for 8 ohm load (result 11k).
A little low on 5 ohms, but useable with a small increase in distortion.
Thanks guys. I mixed up the anode to anode impedance and another calculation from the valvewizard.
You will get less power with the tubes in triode mode.
With the impedance resulting from your 5 Ohm speakers, and the output transformers you have, you will likely get low distortion, and good damping factor, without resorting to using negative feedback.
Pentode mode has more power, but to get low distortion and good damping factor, you would have to use negative feedback.
The transformer may not be optimum for triode wired-mode,
But try it with triode-wired, and no negative feedback, you may be surprised.
Let us know how it sounds (I bet you like it).
With the impedance resulting from your 5 Ohm speakers, and the output transformers you have, you will likely get low distortion, and good damping factor, without resorting to using negative feedback.
Pentode mode has more power, but to get low distortion and good damping factor, you would have to use negative feedback.
The transformer may not be optimum for triode wired-mode,
But try it with triode-wired, and no negative feedback, you may be surprised.
Let us know how it sounds (I bet you like it).
I have it working, triode PP. It sounds very nice, really!
I have a very loud noise/hum though, which seems to decrease when i turn up the volume. It gets louder when i measure grid voltages, which are correct.
Gotta find out where this comes from.. any ideas?
I have a very loud noise/hum though, which seems to decrease when i turn up the volume. It gets louder when i measure grid voltages, which are correct.
Gotta find out where this comes from.. any ideas?
Maybe a ground loop of the input circuit, maybe other causes.
Is it hum 50/60/100/120Hz, motor-boating, noise, high frequency oscillation, etc.
Is there a signal source connected to the input, turn it off, turn it on, disconnect it; is there a change in the hum or noise?
A complete and accurate schematic will be helpful to get ideas of what to check, and how to do the troubleshooting.
Is it hum 50/60/100/120Hz, motor-boating, noise, high frequency oscillation, etc.
Is there a signal source connected to the input, turn it off, turn it on, disconnect it; is there a change in the hum or noise?
A complete and accurate schematic will be helpful to get ideas of what to check, and how to do the troubleshooting.
I think it is 50Hz but i'll check when I get home today.
I have breadboarded the classic Williamson amplifier.
If I touch my iphone which is the input the sound changes. The noise gets dramantically louder when I check grid voltages.
I think it's got to do something with grounding.
Breadboard wires everywhere. Could that be a problem with interference?
I have breadboarded the classic Williamson amplifier.
If I touch my iphone which is the input the sound changes. The noise gets dramantically louder when I check grid voltages.
I think it's got to do something with grounding.
Breadboard wires everywhere. Could that be a problem with interference?
el95 mu is 17......like el84 ...19.in my experience power tube with mu more than 10 ... Hume of power supply com to speakers .el95 or pl95 are nice small power tubes i have more than 200 of pl95.
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What does it do if you 'touch' the iphone as you said, with the iPhone connected as the signal source, but with the iPhone turned off?
It should be silent.
Many digital devices, including a cell phone create multiple interference signals.
Check your input cable, and the grounding of it, the mini phone plug ground, and the ground of the RCA Phono input jack.
Is the iPhone on the charger? That will also create interference.
Touching a Grid with a multimeter lead, etc. is like connecting an antenna that picks up all kinds of noise, including power line hum.
Your hand around the multimeter lead is also an antenna.
Is the amplifier common lead (the "- return lead" of the B+ supply) grounded to the power line safety ground?
Is one lead of the output transformer secondary connected to ground?
There are multiple schematics of Williamson designs, they are not all the same.
How about a schematic of your exact setup?
Include power and ground connections, iPhone and cable, loudspeaker connections, etc.
It should be silent.
Many digital devices, including a cell phone create multiple interference signals.
Check your input cable, and the grounding of it, the mini phone plug ground, and the ground of the RCA Phono input jack.
Is the iPhone on the charger? That will also create interference.
Touching a Grid with a multimeter lead, etc. is like connecting an antenna that picks up all kinds of noise, including power line hum.
Your hand around the multimeter lead is also an antenna.
Is the amplifier common lead (the "- return lead" of the B+ supply) grounded to the power line safety ground?
Is one lead of the output transformer secondary connected to ground?
There are multiple schematics of Williamson designs, they are not all the same.
How about a schematic of your exact setup?
Include power and ground connections, iPhone and cable, loudspeaker connections, etc.
> Breadboard wires everywhere. Could that be a problem with interference?
The world is full of e-crap. Lightning. Inside rooms, AC power lines and devices. Today, Ipods and sellfones and magic devices to order more laundry soap.
Hay-wired breadboards are an open invitation for all this junk.
The world is full of e-crap. Lightning. Inside rooms, AC power lines and devices. Today, Ipods and sellfones and magic devices to order more laundry soap.
Hay-wired breadboards are an open invitation for all this junk.
okay, i found the culprit. First I tried grounding everything together, thinking my ground wires weren't sufficient. Didn't help. Then I tried holding the 300V b+ with my fingers, though not voluntarily. That helped for a short while, until I came by. Then I noticed that when i plugged in my drill, which is grounded, in the same outlet the hum (which was very loud!) got a little less. Then i grounded my power supply, didn't help, then i also grounded the proto board, and voila! crystal clear sound.
In short, i had to ground everything to earth.
Next problem is my phase inverter. The cathode part is much louder then the anode part. Is this normal? Shouldn't they be exactly the same?
This is the schematic: http://www.oestex.com/tubes/WW12-1943-BPT.jpg
Although i use a 12ax7 as preamp and inverter and a 12au7 as the driver stage.
In short, i had to ground everything to earth.
Next problem is my phase inverter. The cathode part is much louder then the anode part. Is this normal? Shouldn't they be exactly the same?
This is the schematic: http://www.oestex.com/tubes/WW12-1943-BPT.jpg
Although i use a 12ax7 as preamp and inverter and a 12au7 as the driver stage.
Yes, V1 that is shown in your schematic should have the same amplitudes on the cathode and plate, just opposite phase.
But you have to use a measurement device that will not significantly load the tube.
A pair of 10x 10Meg Ohm scope probes are a light load for the cathode, plate, and the 25k Ohm resistors.
But what do you mean by "12AX7 as preamp and inverter"?
The schematic only shows a single triode as a split load inverter.
And the 25k Ohm load resistors are not right for a 12AX7.
And you said your circuit is in triode mode.
Is your circuit different than the schematic link you gave in post # 15?
A full schematic is needed to properly troubleshoot any problems.
But you have to use a measurement device that will not significantly load the tube.
A pair of 10x 10Meg Ohm scope probes are a light load for the cathode, plate, and the 25k Ohm resistors.
But what do you mean by "12AX7 as preamp and inverter"?
The schematic only shows a single triode as a split load inverter.
And the 25k Ohm load resistors are not right for a 12AX7.
And you said your circuit is in triode mode.
Is your circuit different than the schematic link you gave in post # 15?
A full schematic is needed to properly troubleshoot any problems.
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