Hey dudes,
I've discovered that the volume pot on an old Philips tube amp doesn't work that well. On low listening levels, one channel is almost completely off. I want to replace the potentiometer but it is 500k. I only have a 100k pot. Can I use that instead?
My source is a regular computer if that matters.
Here's the schematic of the amp if it is needed.
Please note! I've cut off the loudness circuit as shown, and also bypassed the early stages of the amp, so the signal goes directly from volume pot to the 1K resistor on the second part of the ECC83.
I've discovered that the volume pot on an old Philips tube amp doesn't work that well. On low listening levels, one channel is almost completely off. I want to replace the potentiometer but it is 500k. I only have a 100k pot. Can I use that instead?
My source is a regular computer if that matters.
Here's the schematic of the amp if it is needed.
Please note! I've cut off the loudness circuit as shown, and also bypassed the early stages of the amp, so the signal goes directly from volume pot to the 1K resistor on the second part of the ECC83.
No problem, in this case it's the source that is loaded with 100k instead of 500k.
Save the old pot, it might be salvageable.
Save the old pot, it might be salvageable.
You'll get only the volume that the old pot provided at 100K as your new max volume. Set the old pots at 100K and see if that is acceptable. It may not get as loud as you're used to.
How do You come to this conclusion ?
What happens is that the source is loaded with 100k, but as stated
the source has low impedance and will not be loaded down.
When the pot is is "max" the signal goes from source to grid, just like before.
Not true, look at the schematic carefully. The input voltage will have exactly the same range referred to the grid,
as long as the audio source has a low enough output impedance. The DIN socket does have attenuation before the pot,
which will change from 1/3 to 1/11, because of the series 1M resistors.
If you leave the 15k resistors on the volume control tap, just shorting the series capacitors,
the tracking may improve on the old control.
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Look again. If the wiper is grounded (0) the volume is 0. If the wiper is at 100K on the 500K pot it is still at 100K to ground which is only 20% volume. The 500K to ground pot with the wiper at 500K is max. volume. He said, "so the signal goes directly from volume pot to the 1K resistor on the second part of the ECC83." Read his entire post.
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Ok, if the circuit topology has been altered, probably it's best to post the revised schematic to be sure.
Do you use the DIN socket or not for the audio inputs?
It's the difference between a 500K input impedance and 100K. The 100K to ground still attenuates the signal by passing more of it to ground.
100 kohm is not problem for comp. output. 50 kohm will be better. I use about 2-10 kohm that is better for small HF signals. Everyone can try to listen that amp sounds better. 2 kohm can not block outputs of new audio devices.
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If you are talking about R14 and R44 500K pots then changing that to 100K is going to alter the tone controls preceding it. I assume the two 500K pots are bass and treble.
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