Upgrade capacitors in tube amplifier?

Thank you all for your input. 

I will do as recommended by many of you: roll tubes first and then consider the caps.  I took the bottom off the amp and found that the caps mentioned by most are two large 0.33UFD 5% 630VDC and four 0.022UF 5% 630VDC.  I realize you can't tell much by looks but they did look pretty good.  They are oval.

I have some ECC82 (Tung-Sol black glass) and 5751 (GE black plate) on the way and now I'm trying to decide on the EL34/6CA7.

Thanks again.

For your coupling capacitors (particularly the 0.33mfd), and importantly, if you physically have the room, consider either Jupiter Copper Foil Paper & Wax or Miflex KPCU-01. The Jupiters are a bit more expensive but you won’t go wrong with either.

I’ll second (or third) the suggestion for Takman REX Carbon Film resistors. Very musical.

While you’re at it, consider the output transformers. Look into Lundahl.

And look at the power supply rectifiers. I don’t see a tube, so it must be silicon. If it has Schottky rectifiers, you could consider replacing with (third generation) silicon carbide (SiC) rectifiers.

And has been pointed out above, once you start down this road, you’ll probably end up spending as much on component upgrades as the initial cost of the amplifier. Be sure your comfortable with that.

RAM tubes, best computer matching on planet

thanks to the genius of Roger Modjeski ( RIP )

Tung Sol EL34B.

I agree - don't mess with the circuit if it sounds good.  Their branded tubes are decent and I did not hear any significant difference with other tubes but the tube construction is a little better with Tung Sol or some others. 

The biggest upgrade you can do is buy the R-300B model. It is amazing! I also have the R8 with KT88 tubes and the R-300B is significantly more organic sounding. I have not owned the model you have but likely is similar in tone to the R8. I am running the R-300B thru Klipsch Forte III....simply amazing match.