Best Tubed Preamp For A Warm, Rich Sound, Yet Still Detailed and Agile

If you have not had a Direct Heated Triode preamplifier,, it is thr purest sound you 
Will find . After having  every type. This is the most direct type without question ,
Single ended. I am using a custom Lundahl based 4P1L Vacuum tube 
Preamp.  For 1/2 your  $6'k budget  you can best preamps are 3-4 that in resolution and refinement, Radu Tarta is one of the best engineers 
I have ever met .p.s just look up this tube it is probably the most linear Vacuum tube for  music ,just research  the 4P1L  Vacuum Tube.

As far as detail like a SET amplifier a Direct Heated Triode Preamplifier 
Has only 1 stage ,most preamplifiers gave 2-3:stages.
My preamp,,and latest being built use for one parts quality night and day better then 90% of Any commercial units which only 20- 25 % of the cost actually  go 
To the parts . With custom  builds 60% and fir less money's. 
My new preamp has 4 Lundahl  chokes for ultimate filtering and 3 Transformers also Lundahl and Heybourer which are all custom built.all transformer coupled 
Is much more Accurate then any Capacitor coupled. The key for a Exceptional
DHT preamp is the experience.  I compared mine to Coincident loaded with 
Inexpensive capacitors for coupling.  It s 101 tube is good but not as linear
As the 4P1L tube just do a search. It can be a bit microphonic if not isolated properly with mine not an issue,  and power supply only 4pole capacitors
All bypassed by Munforf Silver oil caps. For around  $4k with the excellent 
Khozmo remote control.  Research where uour money is going. I have had  no less then 10 conventional preamps . The only down side is speaker efficiency under 95db, and amplifier again  Radu Tarta  is the well known DHT builder who also 
Built me a a Class A Dual monoblock Pass labs clone with reference grade parts.