I don’t have experience with the Rhea but with the Calypso the 12AX7 probably has the most effect on sound. Adding warmth in the midrange while keeping the highs airy and the bass tight is not easy to do. I’m not familiar with a killer tube that works magic in the Calypso so I’m going to suggest a couple of tubes that are considered among the best.
Amperex Holland. They come with various brands; Amperex, Phillips, etc. They are identified by a left facing right triangle etched into the glass at the beginning of the tube code. If you want to learn about tube codes, check out Brent Jessee’s website. In the yellow boxes on his home page in the middle of the second row there is a "Euro Tube Codes" box and a "Telefunken Tube Codes" box.
I think the Amperex 12AX7 might be what you’re looking for. Get them from the early to mid 60s. They would have white printing on them. I65 would be the tube type, also etched into the glass. Some people feel the later tubes with orange or green printing are not as good.
Many people believe that Telefunkens are the best tube ever. They would not add any midrange warmth, but are considered among the best overall, the result of the fabled German engineering and manufacturing. Many have date codes painted on them but often they don’t. I don’t think there’s any time period that is considered better or worse for these tubes. They come in two varieties, smooth plates and ribbed or laddered plates. There is no significant sound difference between them, but the smooth plates are usually more expensive.
If you want to try a tube that is known for being warm, check out Mullard. You may lose a little in the highs and bass though. If you’re using the stock tubes any of these and more would probably be an improvement.
If you want to get into really expensive tubes, we could talk about the Mullard 10M or the Telefunken ECC803S.
If you want advice on where to buy or get a professional opinion on these, especially about a mix of tubes to get your Rhea and Calypso working together really well, let me know.
Amperex Holland. They come with various brands; Amperex, Phillips, etc. They are identified by a left facing right triangle etched into the glass at the beginning of the tube code. If you want to learn about tube codes, check out Brent Jessee’s website. In the yellow boxes on his home page in the middle of the second row there is a "Euro Tube Codes" box and a "Telefunken Tube Codes" box.
I think the Amperex 12AX7 might be what you’re looking for. Get them from the early to mid 60s. They would have white printing on them. I65 would be the tube type, also etched into the glass. Some people feel the later tubes with orange or green printing are not as good.
Many people believe that Telefunkens are the best tube ever. They would not add any midrange warmth, but are considered among the best overall, the result of the fabled German engineering and manufacturing. Many have date codes painted on them but often they don’t. I don’t think there’s any time period that is considered better or worse for these tubes. They come in two varieties, smooth plates and ribbed or laddered plates. There is no significant sound difference between them, but the smooth plates are usually more expensive.
If you want to try a tube that is known for being warm, check out Mullard. You may lose a little in the highs and bass though. If you’re using the stock tubes any of these and more would probably be an improvement.
If you want to get into really expensive tubes, we could talk about the Mullard 10M or the Telefunken ECC803S.
If you want advice on where to buy or get a professional opinion on these, especially about a mix of tubes to get your Rhea and Calypso working together really well, let me know.