January 4th, 2008, 08:50 PM
As I've posted about in the last few days, I've got a '70 Super. Its tag says AB763 but I'm led to believe this is inaccurate and that it is probably a 568. This is supposedly less desirable, but I think it sounds really good. So I'm wondering how people who have played the two would describe the difference. Obviously subjective, but I'd be curious. Also, is it expensive or complicated or even possible to change it to 763 specs? It sounds good as is to me, so I'm probably not going to fuss with it, but I'd definitely entertain the idea.
January 4th, 2008, 09:04 PM
Do you have any background working on amps?
It is unsafe to open them up and poke around (even unplugged, since caps hold high voltage)... but if you can take a look at the bias board and bias trim pot values, that can help identify the circuit. They both have different bias setups.
Regardless, the tube chart may be incorrect (they often had leftovers). One will be a blackface, the other silverface... but faceplates may have been swapped too :)
January 4th, 2008, 09:17 PM
So I would call myself an amp novice. I'm not very comfortable opening it up. I enjoy living! :-)
This is a silverface amp and as I understand they changed the circuit in the late 60's. Like you say, i've read that the tube charts are often wrong in this era.
Anyway, I'm taking it to get caps redone tomorrow, so I'll ask the tech which circuit it is, but I am interested to hear how people would describe the sonic difference between the circuits.
January 4th, 2008, 10:49 PM
I've got a '69 silverface and a '66 blackface.. the silverface tubechart says ab763 but I'm pretty sure it's 568, but I love the tone and I'm not getting it changed if it is.
January 5th, 2008, 01:40 PM
i own both, in my opinion the 66 blackface is warmer. the 68 is brighter, but not in a bad way. really, i think they are very similar. i wouldnt bother to have yours blackfaced if you like the tone. btw alot of people beleive that there are two distinct versions but the curcuit from 67-69 comes in various configs as far as the feedback loop. my 68 has been gone over a few times at this point... because it was very unstable and blew alot of rectofiers,after someone blackfaced it. thats another thing..do you have a gz34 or 5U4 recto?