Belles 21A upgrade

I had a 21A on loan for an audition and it was the stock unit. I don't remember what the stock output coupling caps were. But definitely remember seeing several Orange drops. I advice replacing those caps as well. They tend to blunt the transients, especially the trailing end. Also, I'm sure you have rolled the tubes?

My preferred variant is the GE 5814A BLACK PLATE from the mid 1950's. IME though with your pre-amp, you will only get so far rolling the tubes. In order to make it sing, parts need to be upgraded.

Wig,

No one can answer your question as tubes are opinion orientated and specific to ones gear/taste.

There is no reason at all to spend more than $60.00 for a pair of 12AU7/5814A tubes for your particular unit. It would be a waste of money.

The GE BP 5814A is dead neutral in sound. That means wide bandwith. No rolled of highs, no rolled of bass, no excessive brightness, very dynamic etc.

E-mail me, I've got lots of tubes. I'm not out to make any $$$. I do not need the money, but also am not a library. Be specific as to what type of sound you like.

B