David,
Sonics - The KT88's will have a bit of mid bass bloom (sounds good!) a bit forward in the mid-range, and fairly extended highs. In comparison the 6550 is more linear from the bass through the mid-range and a bit soft in the highs. I use both of these tubes in amps.
Amps or speakers which are inherrently warm can sound a bit overblown with KT88's and the 6550's would help produce a more neutral tone. Conversely a KT88 would warm up a 'cooler' amp or set of speakers. Kind of a matching to taste issue. I'd recommend that you start with the tube type selected by the manufacturer, i.e. KT88's. SED's are a good rugged tube and worth buying. After you have spent a long time with this tube you can proceed with experimenting with other power tubes and small tubes to tune your system to taste. Those little tubes can make a huge difference, don't overlook them. Its really a combo of power tubes and small tubes that will get you were you may really want to be.
V1 & V2 go together as do V3 & V4. Matched tubes is good but since you have individual bias pots if you have to replace a single tube (again) you can just get a new one of the same brand with a similar bias point.
The bias range should be close with each tube type especially if its established for KT88's. IME 6550's are a bit more rugged and can take a higher bias point. For example I will bias my 6550s between 45 and 50 ma in my amps whereas with KT88 its more around 40 ma.
The biasing procedure. After installing the tubes, and before you turn on the amp, turn the bias pots counter clockwise to a zero setting. Turn on your amp with no sources operating and let the amp warm up for a few minutes. The set the bias as recommended, say 55 ma and let the amp run for a few hours, then go back and adjust bias again (it will probably have fallen off a few ma). I usually check it again in a few days and then I check it every couple of months thereafter.
Re - your 'cheap' multimeter. Probably good enuf, so long as it provides for reading DC in ma. Some use digital. I like analog. Mine cost about $15 to $20 at my local electronics store.
I don't know if operating you amp without all of the tubes in place would actually damage the amp. But, I would err on the cautious side and not recommend it. Besides biasing the new tubes really isn't, as you will discover, a big deal.
Have fun with your new toy. Oh, by the way, most tube amps like to be connected with speakers when you turn them on.
Sonics - The KT88's will have a bit of mid bass bloom (sounds good!) a bit forward in the mid-range, and fairly extended highs. In comparison the 6550 is more linear from the bass through the mid-range and a bit soft in the highs. I use both of these tubes in amps.
Amps or speakers which are inherrently warm can sound a bit overblown with KT88's and the 6550's would help produce a more neutral tone. Conversely a KT88 would warm up a 'cooler' amp or set of speakers. Kind of a matching to taste issue. I'd recommend that you start with the tube type selected by the manufacturer, i.e. KT88's. SED's are a good rugged tube and worth buying. After you have spent a long time with this tube you can proceed with experimenting with other power tubes and small tubes to tune your system to taste. Those little tubes can make a huge difference, don't overlook them. Its really a combo of power tubes and small tubes that will get you were you may really want to be.
V1 & V2 go together as do V3 & V4. Matched tubes is good but since you have individual bias pots if you have to replace a single tube (again) you can just get a new one of the same brand with a similar bias point.
The bias range should be close with each tube type especially if its established for KT88's. IME 6550's are a bit more rugged and can take a higher bias point. For example I will bias my 6550s between 45 and 50 ma in my amps whereas with KT88 its more around 40 ma.
The biasing procedure. After installing the tubes, and before you turn on the amp, turn the bias pots counter clockwise to a zero setting. Turn on your amp with no sources operating and let the amp warm up for a few minutes. The set the bias as recommended, say 55 ma and let the amp run for a few hours, then go back and adjust bias again (it will probably have fallen off a few ma). I usually check it again in a few days and then I check it every couple of months thereafter.
Re - your 'cheap' multimeter. Probably good enuf, so long as it provides for reading DC in ma. Some use digital. I like analog. Mine cost about $15 to $20 at my local electronics store.
I don't know if operating you amp without all of the tubes in place would actually damage the amp. But, I would err on the cautious side and not recommend it. Besides biasing the new tubes really isn't, as you will discover, a big deal.
Have fun with your new toy. Oh, by the way, most tube amps like to be connected with speakers when you turn them on.