I’ve got C-5034-L Pittbull 50/12 2x12 combo with EF86 reverb driver tube, untouched inside the chassis so these are my observations;
1.) there are no simple mods that can be made to change character of the amp so don’t try to do it. The amp already have options (rectifier tube, cathode bias for output tubes etc). Every, even minimal change will make it sound less good. Try only different preamp tubes. My final combination is; V1(guitar input and reverb recovery) - chinese high grade, V2 (drive and clean final preamp tube) - NOS EI ECC83 (selected), V3 (drive channel tube) - NOS RFT ECC83.
2.) reverb sound is thin. It sounds better only when there is compression/overdrive in the output stage (which is by the way hiwatt inspired, not in schematic but in the spirit).
If You want the amp to have clean and drive channels and “fenderish” reverb You must make changes in the reverb recovery circuit.
You’ll need only 56kOhm resistor and 4,7nF or 6,8nF condenser (read the text, my advice is 4,7nF - You don’t have to disassemble preamp PCB). Optional; one resistor in the range between 220kOhm and 1MOhm and 470pF or 500pF ceramic condenser (read the text and check the amp).
First; C18 (orange condenser near pin 1 of V1, value - 2,2nF) should be in the range of 6,8nF. Simple solution is to add 4,7nF (or 3,9nF) from pin 1 of V1 to central conductor of grey coaxial cable which is near C18 and goes to 100kOhm reverb pot (if You change C18 for 6,8nF cap You risk damaging printed board trace - usual problem with Sprague caps due to their bended wires - learned from servicing Mesa Boogie amps). VOLTAGE value of condenser must be MINIMUM 400V
Second; 100kOhm reverb pot (which is not soldered on pcb - reverb was optional). My amp had grey coaxial cable center wire soldered on the wiper tap of the pot (center tap of the pot), shields of the both grey coaxial cables soldered as usual on the ground tap of reverb volume pot and output of the reverb signal is on the 3rd tap of the pot (central conductor of the second grey coaxial cable - that one goes to reverb mix point of the preamp, between V2 and V3 near C31 - follow the coaxial cable). Between input and output tap of the reverb pot is soldered 2,2nF ceramic condenser. Mod; unsolder central conductors of both grey coaxial cables and 2,2nF condenser from the pot. Solder 56kOhm resistor to the wiper tap (center tap) of the pot. To the other side of the resistor solder central conductor of the grey coaxial cable that goes to C31 (to the reverb mix point of the preamp). Central conductor of the grey coaxial cable that goes from the C18 solder on the input tap of reverb pot (the grey cables are now practicaly reverse soldered with 56k resistor added to mimic original circuit when the wiper is at around middle position of the pot).
Remaining 2,2nF condenser that we removed from the pot should be soldered on C17 position near pin2 of the V1 (like in Fender silverface reverb circuit). My amp didn’t have any condenser instaled in that position so it’s easy to do that.
As the preamp PCB is the same for Pittbull 45 and C-5034-L check C31 condenser. For C-5034-L it should be 1nF (on my amp it was 470pF so I added another 470pF in parallel).
Check position of R7 near the gain pot of the drive channel. On my amp no resistor is soldered there. It doesn’t have any function when the gain is on max but 1MOhm resistor soldered in R7 position made a difference in lower position of the gain pot. I don’t know original value of R7 so feel free to experiment with any value up from 220kOhm. I found that 1MOhm suits me the best. It was easy to solder it in place.
BE CAREFUL, HIGH VOLTAGES INSIDE. DON’T DO IT IF YOU DON’T HAVE ENOUGH EXPIRIENCE.
By the way You can install wheels on 212 combo. Holes are already made on the bottom of the cabinet. Check around reverb pan for them.