Seeking advice on vintage audio gear I was recently given

I've recently acquired some vintage audio gear & am looking for some advice/insight on a sound issue that I'm experiencing.

Here's a list of the audio components I'm using.

-Altec Lansing 1567A Mixer Amplifier
-Altec Lansing 1568A Amplifier
-Altec Lansing Flamenco 848a Speaker

(currently I'm feeding the Mixer/Amp a signal from my laptop via a dragonfly USB DAC)

I know very little about vintage audio equipment & am trying to figure out why suddenly I'm not getting the great sound that I was getting the first couple of weeks.
Overnight it went from an extremely dynamic and life-like / bold sound to something that seemed like the speaker was suddenly underpowered & thin (and the speaker hummed). I figured the tubes needed to be replaced so I went out and bought all new tubes.

The original tubes were GE "Electronic Tube's" and then one Sylvania.
The replacement tubes are made by "ARS".

(I replaced all the tubes in both the 1567a Mixer Amp and the 1568a)

After the new tubes were installed the hum was gone, but the overall sound quality compared to before still feels underpowered and thin / distant (I have to turn the volume up a lot more).

Any advice or insight would be greatly appreciated... I want that great sound back (but with no hum).

Please excuse the very basic questions (I don't know up from with audio).

thank you,
Michael

Also (adding to my post below)... I'm looking for a capable tube amp technician who lives/works in or around Los Angeles that can update my 1568A & 1567A; anyone interested please feel free to contact me - I'd like to get this done asap.

I can't believe I was tinkering around with this equipment (even while it was plugged in) ... I had no idea it was so dangerous (I just happened to read an article outlining the dangers when I was trying to figure out the best replacement tubes for my amp.
Anyway - I'd like to get it sounding as good as possible & have the proper electrical modifications made to ensure I don't touch the chassis and die... Does anyone use GFCI's with they're vintage tube equipment?


Lastly: Anyone interested in selling their Altec Lansing 1568A Amplifier? If so, please contact me.

thank you,
Michael

I suggest ( if you can't find info here ) that you use the advanced search function for ( 1568a ) over at the Altec forum ( that's located at HostBoard ) .

( For instance ), I just read through quite a few posts/threads about your amp .

Search !

:)