Newbie: KT88 amp info needed

[alexg]

Just bought an Audio Space 8i MkIII, with the following tubes:

4 pcs KT88
1 pc 12ax7
4 pcs 12au7

I know that the KT88 are the driver tubes and the rest for the pre-amp.

Based on this configuration, what is the one piece 12ax7 for? How about the 4 pcs of 12au7?

If I wanted to try new tubes, should I start with the pre-amp?

[richwalters]

Youv'e gotten things the wrong way round...the KT88's are the outputs in octal sockets ! The rest B9A sockets are the driver and preamp tubes.

Don't go haphazard with the KT88's....only change them when you suspect they aren't behaving right or the sound is bad. Experience will tell.
The 12Ax7 is probably the driver for the output stage. The output stage tubes are usually the first to be replaced.
If you haven't experience with the output stage when changing to different versions of KT88, find someone who knows about
setting stages up especially when used with fixed bias. Or see instructions. For example, a Tesla JJ KT88 will require different bias setting to others in same family.
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Tampering with tube amps isn't to be taken lightly and can be dangerous. Change components only when necessary.

richj

[alexg]

Thanks for your very informative answer.

The audio dealer I got the amp from suggested to me that replacing the preamp tubes (12au7 and 12ax7) would create the best impact since "those Chinese tubes really does not sound that good." So am thinking of getting some RCA 12au7 clear tops and a GE 5751 gold to play with.

Thanks.