[rtate]

I have had a Dodd Audio buffer sitting for a while and want to put it back in the rotation.
So I opened it up to check everything before powering up and noticed a switch inside that is labeled 6 and 12.
I'm assuming that it has something to do with "plate voltage" ?
Mine has always been set to 6.
When would I ever select the 12 ?

Currently have the 6h30-DP reflector tube in it

[S Clark]

Yes, 6v and 12V.  I also have mine set to six, but there are fans of the 12BH7 tubes ( and probably many others).   I've tried them, and I didn't find them special.  I do however, really like some of the 7dj8 tubes in my Dodds.   

[rtate]

So how do I know which tubes use the 12 volt setting ?
does the first number tell me ?
Could I use 12v on the 6h30 or would that damage it ?

[FullRangeMan]

So how do I know which tubes use the 12 volt setting ?
does the first number tell me ?
Could I use 12v on the 6h30 or would that damage it ?

So how do I know which tubes use the 12 volt setting ?
Usually tube numbers starting with 6 are 6Volts.
Tubes starting with 12 as 12AX7 are 12V tubes.

Could I use 12v on the 6h30 or would that damage it ?
6H30 is a 6V tube, 12V will damage the tube.

[FullRangeMan]

I have had a Dodd Audio buffer sitting for a while and want to put it back in the rotation.
So I opened it up to check everything before powering up and noticed a switch inside that is labeled 6 and 12.
I'm assuming that it has something to do with "plate voltage" ?
Mine has always been set to 6.
When would I ever select the 12 ?

Currently have the 6h30-DP reflector tube in it

I'm assuming that it has something to do with "plate voltage" ?
6V and 12V are the tension on the filament that heat the Cathode.

When would I ever select the 12 ?
Only when you are using a 12V tube.

[FullRangeMan]

For more info check this topic:
https://www.audiocircle.com/index.php?topic=144200.0

[rtate]

So I  also have a ECC803 S tube which I think came stock in the Dodd Buffer.
The data sheet says it can run on 6 or 12 volts. What would the difference in sound be with the 6 versus 12 volt plate voltage ?
How would it compare with the 6H30 tube sound wise?

[FullRangeMan]

So I  also have a ECC803 S tube which I think came stock in the Dodd Buffer.
The data sheet says it can run on 6 or 12 volts. What would the difference in sound be with the 6 versus 12 volt plate voltage ?
How would it compare with the 6H30 tube sound wise?

ECC803 is a 12AX7 version.
I never heard ECC803 or 6H30 so I cant comment.

As a side note the 6SN7 12V version named 12SN7 has a stronger electric emission than the regular 6SN7.

[FullRangeMan]

The Google AI says:
The ECC803 is a premium, long-plate variant designed to replace standard 12AX7/ECC83 tubes.

The long plates contribute to a fuller, more detailed sound, particularly in the bass frequencies.

Some high-end versions feature spiral filaments to reduce noise and hum.

It is generally recommended for hi-fi and line-stage preamplifiers, but high-gain applications may require a more robust tube like the JJ ECC83-S to avoid microphonics.

[rtate]

So research says that the 6h30dp isn't a direct replacement for the ECC803S  as the bias is different.
 I think the Dodd Buffer came with the ECC 803 installed and at some point, I heard or read that the 6H30 was a suitable upgrade for the Buffer.
Did I make a mistake swapping tubes ?
I know that it does work, but if it's not biased properly what am I doing to the sound quality ?

[FullRangeMan]

So research says that the 6h30dp isn't a direct replacement for the ECC803S  as the bias is different.
 I think the Dodd Buffer came with the ECC 803 installed and at some point, I heard or read that the 6H30 was a suitable upgrade for the Buffer.
Did I make a mistake swapping tubes ?
I know that it does work, but if it's not biased properly what am I doing to the sound quality ?

Did I make a mistake swapping tubes ?
Have no idea, there is various AC members that own this pre-amp, maybe they could help you.

I know that it does work, but if it's not biased properly what am I doing to the sound quality ?
This is a very specific question. There was audible distortion?

Tubes operating outside Bias range show undesirable sonic characteristics, which vary depending on whether they are operating cold bias or hot bias.

Cold Bias (Under-biased, low current)
Tubes operate close to the cut-off point resulting in:

Thin and Sterile Sound
Loses the saturation and warmth characteristic of tubes, sounding lifeless or without body.

Crossover Distortion
In push-pull amplifiers an audible crossover distortion can occur, one valve turns off before the other fully turns on, creating a dead zone in the signal waveform. This can sound like a weak and fuzzy sound.

Loss of Power and Volume
The amplifier does not reach its full power, and the overall volume is reduced.

Limited Frequency Response
Tone controls may seem to have little effect, with noticeable reduction in bass and treble.

Over-biased Bias
When Bias is set too high, the tubes work excessively, generating more heat and operating closer to saturation or clipping at the positive peak of the wave. This leads to:

Muddy and Distorted Sound
The sound may become too compressed and saturate earlier, resulting in a muddy or excessively distorted audio, even at low volumes.

Harsh or Excessively Bright Tone
The audio may sound harsh or have excessively bright highs, depending on the circuit design.

High Hum
A very hot bias can cause a loud and undesirable hum in the audio.

Risk of Damage
Physically, the valve plates may glow red (red-plating), indicating severe overheating, which can damage the tubes and other amplifier components, such as the output transformer.