Amp recommendations

"Just Listen"...to you! "Love the sound", "Don’t feel you have to turn it up much", "20+ years on the tubes"," Listen to jazz and some pop". First, it does not surprise me one bit that you need to replace the tubes....way late! But, since you never felt the need to turn it up much, maybe it wasn’t overdriven and therefore need to have (all/though probably some) of the caps and resistors replaced. Most of the time, problems with tube amps are the tubes. Try that first.-Your least expensive option.
Keep your speakers if you like them. Use 4 ohm taps on your amp (maybe, always listen), but tubes generally do like 8 ohms better. Have fun listening to more modern 8 ohm speakers at shows in the meantime or try buying used well-reviewed 8 ohm ,more efficient speakers here on Audiogon. Speaker design has improved in 20 years!
Moving up the power tube chain will likely lose some of the "aire" and Magic that I think you’ve become used to with the 300B’s. However.....
Parting thought: You might try a Croft Series 7RS Hybrid amplifier if you get a chance.

@z32kerber
Because you stated "I’ve always loved the sound", the following list starts with the highest priority:
1) Get your Cary Audio CAD 300B working again.  Finding a sound you love is the holy grail of audiophiles.  As amplifiers age, the sound quality gradually diminishes as the parts wear out.  You may not have noticed as this is a very gradual process.  Refurbishing/upgrading parts (tubes, capacitors, resistors) should at least bring the sonics back to the original level.
2) Get the designer's (Dennis Had?) opinion on what to do along with suggested other amps
3) Contact Cary Audio to get opinion on what to do along with suggested other amps

If you change your amps and/or speakers you will get a different sound, likely an upgrade but no guarantees that you'll like the change.  

With your budget, get a pair of VTA M125 mono block amps at 120 watts each. You can build them as a kit for all of $2300, or get them fully assembled and tested for about $3000 - less without tubes.

If you feel that you don’t need or want that kind of power, VTA has the ST-120, 60 wpc tube amp which is a Mac 275 killer. Full kit is $1200 and fully assembled/tested at about $1700. Without tubes fully assembled is $1455.

As usual folks negate to include the LxWxH of the room they're playing their system in but in this case it doesn't matter.

Man have you got the wrong amp for a 4Ω speaker, with a 88SPL that has a frequency response of 26Hz-20kHz. Once you get a demand for a note dipping under 60Hz you're pulling a freight train with a burro when you need a locomotive, (nice speaker by the way). Little wonder you fried your 30W amp. (nice pre-amp too).

You've got a tube pre-amp which will give you your classic tube sonic signature (before turfing that SPL 70 you may want to consider installing Mundorf Supreme Silver/Oil capcitors). Now you need a quality Amp with brains and brawn to man handle those speakers.

It's a wide variance but IMHO consider a used Bryston ST4B, a Krell KSA 200S, one of the Class A Thresholds, or if you're dead set on the headache of driver tubes, a new ANTIQUE SOUND LAB HURRICANE 200 DT, or a used RAY LUMLEY M-150 (if you can find one).


  I'm with Russ69 save the 300B if you can and use it for a second system.

1 z32kerber used the Cary amplifier driving the Chapman speakers for 23 years!!! I doubt that he "fried" the Cary amplifier.
2 Agree that the Bryston, Krell or Threshold amplifiers will provide a different sound presentation, better? Maybe or maybe not, but he loved the Cary-Chapman combination. This is a major positive point.
3 I like his idea of getting more sensitive and easier to drive speakers if he were to  make changes.
4 Of course the opportunity to hear different amplifiers is a good step if this is feasible to arrange.
5 On paper the recommended higher power /current solid state amplifiers will certainly drive the Chapmans but this doesn’t mean in actual listening sessions they would sound as good as the 300b push pull Cary. A direct comparison would be great to do. My money would be on the Cary for superior overall sound quality. 
Charles