Tube Life ---------- [Everyone] should be aware of the importance of screen protection through the use of high value screen resistors. No Traynor amp goes through [Kevin O' Connor's] shop without the replacement of the common 470R unit with individual 1k-5W units. There are usually extra eyelets along the edge of the card so these resistors can be mounted securely between the card and socket. Individual bias controls are also installed and current sense resistors are added between pins 1+8 and ground. This also requires separate grid leaks and coupling caps for each output tube in 100W+ amps. Any carbon 1W/2W resistors are replaced with flameproof metal-films. These mods greatly extend tube life; allow the use of various grades of tubes; and even allow the use of dissimilar tubes. 6550s will give a full-bodied tone compared to EL34s, which can be brittle for guitar but okay for bass. The true 6CA7 and 6L6GC-family, including the 5881, have a tone similar to the 6550, wityh the lower powered units offering "slightly less of everything". (Kevin O' Connor (amps@londonpower.com)) YBA-1 Bass-Master mod Transient fidelity ---------------------------------------- This mod consists of an attempt to extract the most in terms of transient fidelity from the YBA-1 signal path without altering the gain structure or intended dynamics beyond, let's say what one might want to establish as a typically objectionable point in some kingdom somewhere... [1a] decoupling input bias circuits, i.e., replace the 820 Ohm/250 uF bias circuit of the input gain stages by separate 1k5/125 uF and 1k5/0.68uF cicuits. Cap value varies according to taste, the larger cap will give you deeper bass response - Traynors seem to sound woofy if a too large cap is used here... Some people like to keep the original functionality of the amp intact but then, in the separated cathode circuit version maybe have a large value on one side and a lean on the other as in Marshall 1986s and 1959s. I prefer [1b] disabling the second channel altogether and having a non-electrolytic 0.68uF cap as the only cathode bypass cap in the whole signal chain - the amp then becomes a pure single channel, high transient fidelity signal path ...this is especially noticeable during periodes of sharp transient attacks... even at low level it'll knock you out... [2] change 4Meg volume pot(s) to 1MegA for a less "spongy" attack ... [3] change tone stack to 5F8/6-A values, i.e., 47k to 56k and 0.1uF to 0.02uF. This network impedance matches well with the spectral nature of many typical guitar pickups... amongst other things it brings in the midrange dip and narrows the treble and bass peaks closer together... [4] I like the old presence control, i.e. the old "scratchy" style circuit with only the 4.7k Pot and cap on the wiper. Sometimes, as an add-on I like to use a [5] dual 4.7k pot wired to a DPDT switch (to yield a 2.5k equivalent pot) in the presence circuit in order to alter loop gain of output stage feedback mixing at the flick of a switch... this tends to favorise pentode distortion in the amp and also loosens the output stage a bit - at lower volume settings this gives a normaly stiff class-AB amp a slightly livelier feel... I learnt a simpler version of this this from Dave Vidal in Vancouver who worked for Red Rhoads in LA during the seventies - the version I explain here is my own... [6] I like reducing the 100k feedback return resistor to 47k, this tightens the output stage and balances things out with mod [5]... set to taste. [7] The power supply B+ filters caps could use a few more Farads, 80/450 caps can become 100/450 and 40/450 caps become 50/450; as long as these values are not exceeded this won't harm the PT... on the other hand the preamp filter caps I leave as they are value wise. You can experiment with the triode/pentode ratio when the amp is overdriving by altering the preamp voltage headroom. The values R21=4k7 and R32=10k can be changed to 1k, 2k2 repectively... I use 2Watt resistors for this... you will notice a cleaner and slightly brighter response from the amp... when cranked the pentodes will fire up earlier and give the amp a truely warm and sexy feel once [8] a careful biasing and funetuning of the output tubes has been done. I hope this encourages other YBA-1 owners to explore the hidden tone available in this underated beast... especially those who seek enhancements that don't alter the original set of dominant expressive characteristics surrounding the amp... these are my ideas and opinions only, feel free to add or change things to suit your own taste and needs... Btw, in the single channel version of this mod the discarded gain stage can be used, in conjunction with a relay circuit, to give a 2 channel switching amp that produces a jaw dropping 70's overdrive and compression.... (JC (jc@lynx.bc.ca))