1971 Traynor Bassmaster MODS

The Traynor YBA-1 and YBA-1A Bassmaster are probably the most popular models of all the vintage Traynor amplifiers … designed and built by Pete Traynor in Toronto Canada in the 60’s and 70’s // they were meant as foolproof back-line replacements for Fender and Marshall amplifiers, which of course were in common use everywhere in North America at the time …

Because they resemble Marshall JTM45’s electronically speaking we tend to assume they we designed as “competing” guitar amplifiers … being also similar in design to the amp the JTM45 was derived from, ie., the Fender (Tweed) Bassman amplifier, which later became favored by guitar players … the circuit that produces a most natural rock’n’roll sound, but started out as a Bass amplifier … the Tweed Bassman



It’s pretty obvious upon scrutiny that these YBA-1 amplifiers were in fact optimized for Bass use … little things, here and there, that would prevent the amp from distorting for example give it away. Of course, the name might give it away too …

Later on, bringing the operating voltages up quite a bit (as in the YBA-1A) meant more clean power // a better Bass amp perhaps … the purpose of the “A” is similar to the YBA-3/YBA-3A thing, which means higher power in the Traynor line …

The YBA-1 operates at a B+ of about 445volts while the YBA-1A operates at a B+ around 540volts … personally, I find the YBA-1’s a little less harsh sounding, especially when used on guitar … but maybe that’s just me


a brief run-through of what’s under the hood …


The first thing to notice is how robust and well built these amplifiers are … with well laid-out powering and signal flow, not unlike the kinds of layouts seen in earlier American (Fender) and British (Marshall) made tube amplifiers …

The stock YBA-1 power supply was built using quality components, and the amp is wired together with extra strong cloth wire … the signal caps typically contain Mullard “mustard” caps, as seen in vintage Marshall and (other Canadian made) Garnet amps … they are regarded as smooth sounding, and not “metallic” as other types of signal caps might sound

One of the interestingly odd things we find in the chassis of a YBA-1 is a 150 ohm (20 watt) resistor on the main speaker jack … these are included as a safety, in case a faulty (open) speaker chord is plugged into the amp … this is something we don’t see in other amps


Although a good idea in some sense, the resistor will steal a little bit of power from the speaker … for a 16 ohm load it’s about 10%, for an 8 ohm load it’s about 5% … not a big deal, but generally I remove that resistor as it is not really “needed” in normal operating mode … nowadays, players are way more knowledgeable about these things anyway (at least after my coaching they are !)

The filter caps in early Traynor amplifiers are typically a little on the conservative side on the (main) B+ node … in this amplifier the ‘cans” are dual 40uF/450 Mallory caps // which is low on the B+ side and too heavy in the front for the preamp sections … a hallmark of, again, how a BASS circuit maybe should be filtered … wrong, both ways IMO, especially for guitar use


For general guitar use, I like to use a bigger cap on the B+ (47uF500v) and lower values on the front of the amp (22uF/500v) – same as I would on an older Fender guitar amp … the bigger cap on the B+ gives more punch and body when striking chords, and the smaller caps in the front helps keep the circuit feeling lively (not stiff like a Boogie)

The YBA-1 came with a fixed bias circuit … there are good reasons for making this variable // accommodating different power tubes and brands, power tube drift with use, taste, etc …


The stock signal path is clearly relevant as a Bass amp

An extra grid blocker cap in the PI circuit (defeating output stage distortion) … lower impedance levels in the PI circuit (dropping gain) … low impedance grid bias resistors (defeating output stage gain and distortion) … lack of grid blockers on the power tubes (like a JTM45), at least in the chassis shown here, is a bit of a surprise otoh … a Fender “Blackface” tone stack feel with exaggerated low-end (again good for a Bass amp, not my preference for guitar) … quality signal caps throughout – what we now refer to as Mullard “mustard” caps … good stuff overall, some needing change if the amp is to be used on guitar


The front end of the YBA-1 resembles that of a JTM45 with two bright-normal input channels … pretty plain-jane, and not considered so useful these days


The first thing to do is re-build the power supply circuit with “guitar” valued filter capacitors …


and while we’re at it, let’s clean up the chassis ground connections a little …


The bias circuit is easily made variable by replacing the 39k ohm resistor by a 50k 1watt pot … and the second 8uF/150volt cap to 100uF/63vdc in order to reduce hum on the bias line … as a result, it takes the bias circuit a little longer to charge up fully, but not too much … about 30 seconds or so,

So, as a precaution, I’ll advise the owner to wait a little before flipping the STANDBY switch … not a terribly unusual “tube amp quirk” anyway …


The front end is then modded to a more-useful Marshall 1959 Bright/Bass channel arrangement … I leave it exactly as in a Marshall so a patch chord in the front is needed the same way to dial in the massive bottom part …

Vintage NOS Mullard “mustard” caps are introduced as part of the mod and the 125uF/16v caps are doubled on the bass channel’s cathode … this way, the amp stays vintage sounding as much as possible … the tone stack is pure JTM45, with one 0.022uF Mullard signal cap replacing the 0.1uF tone cap, and a new 0.0022uF signal cap brought in … a pair of 0.33uF/160 mustard caps is used in the cathode circuit of the “bright” gain stage, and another pair used across the 820 cathode bias resistor in stage #3 to give the amp a more mid-rangey feel … something we see in the model 1959 Marshall amps


The owner asked to keep the current set of Telefunken 6CA7’s and did following some testing and playing … when I got the amp the power tubes biased in around 22mA/24mA and when I was done they sat the same … I swapped in a matched and balanced ECC83S from www.eurotubes.com in the PI position …





The amp sounds wicked … it has its own personality, aside from being wired as a YBA1-JTM45-1959-5F6A hybrid …

The only thing that I’m not elated about is the self-hum of the amp … despite star-grounding power supply circuit there was a slight amount of residual hum in the background when turning up the volumes, which I attribute to higher than usual leakage fields emanating from the power transformer … otoh, the original hum “at turn-on” is all gone now

Years ago I started The Traynor Amplifier Schematic Archive


I’d like to thank all the generous people who contributed …!!

5 Comments on “1971 Traynor Bassmaster MODS

  1. I want all the modification done to my yba-1, I’m from Northern ontario canada near sudbury, can you recommend someone

  2. Hi Sheldon, I build and customize amps right here in Sudbury. Im Jack’s Custom Amplifiers. You could email me at jacquesport@persona.ca. I modify many yba1s for people. Im a big fan of Traynor products. I personaly own 8 yba1s. I mostly get requests to change the circuit to ’72 plexi specs, Which sounds incredible.

  3. Wrt. variable bias supply mod: if you replace the single-diode rectifier with a bridge, you get more current and the bias supply will charge up and stabilize faster.


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