Recs for Tubes & tweaks for HH Scott separates

Have had LK 150 amp LC21 pre pair as 3rd system.  Love the midrange, dynamic range, and layering (front to back separation and instrument placement) of the sound stage that it does.

Disappointed in mushy base and rollEd off highs.  Was wondering if anyone had experience with these or similar amps and could recommend tubes or other tweaks to improve the sound.

Pre amp uses six 12A7X and one 6X4. Have 4 Sovtek and 1 telefunken + 1 Realistic holdover in now.

Amp uses two 7199 phase inverteters, four 6550  output,  and two 5AR4 rectifiers.  Have nos 7199 RCA and JJ 5AR4 in. Have new Russian Tung Sol 6550s in preferring them to SED 6550 and Sovtek KT 88s.

Have used primarily w budget Morrow MA1 interconnect and SP1 cables and budget bookshelf speakers like Athena BS1, Infinity Primus 143,  and Epos ELS8.

Thinking of trying new Russian mallard kt88 output tubes. Matched preamp tubes and upgraded cables also probably also help.

I'd appreciate any tube new or NOS or other recommendations that anyone out there might have.


Peplace the 12AX7s with Electro Harmonix or Gold Lion.

NOS 12AX7s are getting rare and expensive.  If you don't mind rubbed off labels and such, you might avail yourself to (no affiliation) . He calls them ugly but the prices are very fair.  If buying new consider the Gold lion or the more economical current production Tung Sols.

For the output tubes I love the  current Gold Lion KT-88s. 

Something else to be considered, given the advanced age of your components, if it hasn’t already been addressed. The higher the power supply impedance, the worse the peak compression and bass performance. The older/dryer the electrolytic caps, the lower their value/the higher their internal(and hence, your PS’s) impedance.   As far as the rest of the system’s performance, there are a lot of electrolytic caps, and carbon comp resistors in these older gems. Replacement with film caps and wire wounds, will generally offer a substantial improvement in overall presentation.

Thanks for the tube and other advice.  I think rodman had the best advice.  I have had it gone over by a tech previously and about 12 capacitors and 6 resistors were replaced In the amp.  There are still many original caps and parts that should be replaced.  It will be a while before I get the time and courage to dig into that myself or the money to have someone else tackle it since it mre than simple tubes and Tweaks. 

If anyone else out there has ideas, let me know. I'll update or aastart a new thread when i get back too it. 

Thanks again to all for your comments.