Dating fender tube amps by serial number
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.
Reliability It's a risky proposition for repairs Old and still going strong Price I bought my YBA-1A [used] about 15 years ago for USD.
[...] The 2nd [used] one I bought off ebay [for] 5 USD was totally moded for guitar with extra pots on the back [...].
If you are looking for something original sounding and with a good bit of style, this is it (if you can find one)!
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.
A YBA-1 has a nominal 8 ohm output, and the two speaker jacks are wired in parallel.
Runs on less than 440 volts, weighs 39 pounds Dimensions: 8"x18"x10" (HWD); weight: 40 lbs. (source: Catalog) Silvery grey grille cloth; Original layout was very close to the tweed Bassman and the Marshall JTM-45 50-watt models; noticably huge big heavy transformers are a Traynor hallmark in these units up till the approximately 1972 models; Early models were tube rectified (5AR4) and used two 7027A power tubes.
[...] When [the YBA-1] ran on 7027s, it was a rock machine (think Black Crows, Zep, etc.).