The 2nd one I bought [...] was totally moded for guitar with extra pots on the back and stock EL34s. I [...] have [an YBA-1A Mark II amp] that goes with [the YT-15 cabinet] and it's all sounds great. i believe, though i am not sure, that these 1a's operate in class "a". Other than the old no ground power cord and serious shocks and buzz it sounded better than what i was using.i stuck a master volume on the back, jumped the channels, and cranked both channels to 7-8, plugged in my custom shop '61 reissue sg, and it kicks so much ass [through 4x12 25w greenbacks] its indescribable i bought both a 1971 yba-1 and a 1972(? [...] the yba-1a is currently beating the snot out of an old mesa 4x12 with 90 watters in it. this would make sense to me considering how very crushing it is and yet chimey. The only real problem was it seemed to be blowing fuses.typically playing a new gibson les paul "faded" through them. Even after a friend helped me switch the power supply to todays standards and no buzz and shocks occured. I am told it may need some work on the tubes (cost about same as amp itself). 1971 YBA-1A Bass-Master Mark II (top not removable despite later style case), front view, angle 1971 YBA-1A Bass-Master Mark II (top not removable despite later style case), front view 1971 YBA-1A Bass-Master Mark II (top not removable despite later style case), back view YBA-1A Bass-Master Mark II, catalog page YBA-1A Bass-Master Mark II, schematic 1/1969-12/1970 YBA-1A Bass-Master Mark II, schematic 1/1969-12/1970 YBA-1A Bass-Master Mark II, catalog pages, manual, fan conversion, schematic 1/1966, schematic 1/1969-1/1972, schematic 1972-2/1973 YBA-1A Bass-Master Mark II: Looks to be the same as the other one with a choke except it shows 6CA7 as the power tube instead of 7027 (Larry).(Aaron, Craig, Dan Kukkonen, Dan Lear, Eric Knudsen, Greg, Jay Rogers, John, Jon Aley, Kraig Olmstead, Laws from Lawsstudio Canada, Moon Keith, Tim Baier, viva Analog at bc.ca/~jc, Features volume and tone controls only; it has two inputs, seems to be high and low, no major difference Two 6V6 power tubes This one is a '67 [amp] and is in amazing shape. ) speaker that looks identical to the 15" Jenson in my '64 Fender Vibroverb.437 volts); this may have gotten higher after 1971, but into the summer of 1971 I'd expect the plate voltages on 6CA7s to be down substantially from the YBA-1A; have the chassis sliding-in ala Fender.Last versions have that easily identified rubber and 'chrome' molding running around each end of the head cabinet; mine is from 1971 and is this last version; 1972 models have no choke; [a 1978 is] black with the black plastic fabric and [has] the baby bumper trim, [it has] two 6CA7 and three 12AX7A tubes in it [and] no fuse holder, just a red reset button I put Mullard EL34s in my YBA-1.I caraked open the top on my 1975 YBA-1 just to look, and sure enough it's a 68K.(Dave, Nov 11, 2014) - corrected version (Brian, Craig, Dan Lear, Dave Rutherford, DCloud1050, Eric Knudsen, Glen H., Greg, Jay Rogers, Jonathan Krogh, joth, Kraig Olmstead, Moon Keith, Ron Waters, Tim Casey, Tony Flagg, Vernon Fitch, viva Analog at bc.ca/~jc) Features Two channels (bass and guitar), two inputs for each channel, upper inputs are slightly attenuated; Treble and bass controls, a "tone expander" section with low and high knobs (according to Dan Torres, these are actually midrange and presence controls); there are two volume knobs that can be blended to get different sounds.
Better sound as a Fender Bassman; lower powered, would work just fine in a blues or lower volume setting (when used for bass or guitar). ] 0 [used], a 1978 YBA-1 together with a 1977 YT-15, both mint [US?
I've used it regularily throughout the years, gigging throughout the Detroit area, and later in the E. A plate load of 6K8 would have essentially zero gain and probably lots of other problems.
That part of the hand-drawn schematic from 6/1971-1974 is smudged and hard to read, but it's definitely 68K.
[...] When [the YBA-1] ran on 7027s, it was a rock machine (think Black Crows, Zep, etc.).
It probably has a bit less bottom end and more mids and highs now. It must have been one of the last YBA-1 Traynors made.
These mods are worth doing to any Signature/Bass-Master, IMO.