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November 14, 2015

Repair of a Traynor YGL3 Mark 3 Guitar Amplifier and Accusonic Reverb Tank

This post is about a fun, relatively easy repair/restoration project on a classic piece of electric guitar/music gear: a Traynor YGL3 Mark 3 amplifier. The YGL3 is a vacuum tube -based piece of rock/music history. This project grew out of the Repair Cafe event in the Campbell River Sportsplex last month that I was a volunteer repair person for. A new friend, Joedy W, had brought this amp in to the Repair Cafe, but I didn’t have the time or the parts during that busy day to do the full repair. After I got back from some travels, we were able to re-connect yesterday and I could get to work on the amp. The whole repair/restore operation had four distinct elements to it. This was a pretty interesting project for me because I had never worked on a musical instrument amp before (that I can recall), but the repairs needed were fairly easy, requiring diagnosis mainly by observation with ears and eyes and ultimately just one test instrument, an ohmmeter.

Traynor YGL3 Mark 3 amplifier

The Patient: Traynor YGL3 Mark 3 amplifier

There were a few symptoms/problems when I first got to listen/look at the amp: extremely noisy output from the “effects” input channel, mostly hiss/static rather than 60Hz hum (the “clean” input channel worked OK, no noise.), and the crucial reverb effect (crucial to Neil Young, anyway, and many lesser-knowns) wasn’t working. The noise was bad enough that the amp effects channel really wasn’t very usable.
A couple of safety items to note first in case you end up working on a similar unit yourself: these amps are big, HEAVY, and somewhat awkward to carry. Weight is around 60-80lbs, thanks mainly to the magnets on the 2 big speakers plus the hefty power and output transformers, so be careful lifting them. Fortunately Joedy brought the thing over on a moving cart. Second safety note: this ain’t puny low voltage solid state circuitry. This is serious-voltage tube equipment, with hazardous voltages for tube anodes and cathodes and elsewhere, sometimes stored in high voltage capacitors. Lots of electric shock hazards that one can get a dangerous jolt from, so Be Careful! Plus the tubes get HOT in normal use. I take no responsibility if you decide to work on an amp like this yourself.
First up: reverb wasn’t working at all. I had briefly started diagnosis and repair attempts at the Cafe by replacing an obviously leaking electrolytic capacitor in the reverb circuit, but that didn’t cure the no-reverb  problem. The heart of the reverb system in these amps turns out to be a famous Accusonic unit, a “reverb tank’ with  input and output transducers and 2 springs each about 40cm long for acoustic delay, housed inside an metal box inside a thick soft case
Accusonic Reverb Unit

Accusonic Reverb Unit

Quick resistance checks of the Accusonic (after disconnecting it from the amp circuitry) found Reverb unit input had continuity at about 165 ohms, but output side showed open circuit, apparently an occasional problem with these units. In this unit, I quickly noticed there was a visibly broken wire adjacent to one of the solder lugs on the  output side connector. The fix was simply to solder a new connection to the lug. That entirely fixed the reverb problem. Now the Traynor has great reverb that Neil Young might enjoy.
Accusonic Reverb Unit

Accusonic Reverb Unit close-up

So, good reverb, but still the intolerable noise was present from the effects channel -repair not yet complete. Inspection of the schematic
Traynor YGL3 Mark 3 schematic

Traynor YGL3 Mark 3 schematic

showed 2 potential problem areas on the effects side: the V4 and V2 tubes, both 12AX7A. One half of V4 is used in the Reverb, and the V2 is used in pre-amplification for the effects side. We had earlier tried a swap of the V4 with no success, so today I replaced the V2 tube with the one from my parts bin. Success! No more noise, and a great sounding amp. The tube in question was the 12AX7A/ECC83 dual-triode tube -a very common part in its day. I even had a couple of spares left over from repairs of my father’s hifi Dynaco amp that was from approx late 1960’s, that had been sitting in my parts bins for 30+ years; another case to help me almost justify my parts hoarding to my relatives.
Circuitry View

Circuitry View

Finally, the master volume potentiometer was another source of noise when rotated – just a poor contact that needed cleaning. After applying some contact cleaner and rotating the control aggressively for a while to help the cleaning, that problem was solved too.
End result is an essentially fully restored Traynor YGL3 Mark 3 amp, now “gig ready” as Joedy describes it :-). A fun, relatively easy repair. Rock on!

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