Traynor YGM-2 (Yes, a YGM-2!!)
One of the slightly more rare of the late 60's Traynor combos is the short lived YGM-2 Guitar Mate. This is similar to a YGM-3, but with Trem and NO reverb. Odd. It has the same power section, and very similar bias/preamp/phase inverter arrangement. It also was loaded with a single 12 (originally a Marsland, but long replaced with the 12 out of an Ampeg Jet, I'm told).
The amp came in with some bad history. It had had several trips into another reputable shop, yet always came out "sounding like total garbage". I wondered what could be so wrong that wasn't spotted. Sometimes that just happens, especially if you've stared at it for so long. Can't see the forest for the trees as it were, but someone looking over your shoulder can instantly say "ah, look, a bad ground", or whatever. Happens to the best of us.
I plug it in at the shop and after warm up, the first note through the thing literally sounded like distorted, muffled, crunchy garbage. Completely unreasonable. I shut it down, and put it on the bench.
The work done to it was nice. Can cap replacement, and an Orange Drop coupling cap. Several resistors were replaced with very high quality flameproof metal films. All the tubes were brand new. Bias was resistor fixed.
I first went about my usual battery of tests under signal. Wiggle this, tap that. Immediately I got some strange stuff when moving the 1st preamp tube around. HF oscillations, noise, angry waveforms... I immediately cleaned the tube socket and reseated the tube. All the weirdness was gone. Banging and wiggling around wouldn't do diddly. Great! Then, what I had was an EXTREMELY cold bias. Giant crossover notch.
In typical Traynor fashion, the amp circuit was quite different from the one and only published schematic available online. The schematic showed the tubes as being cathode biased, but the amp had a bias tap and supply. It was pretty typical, with the caps replaced the way I like to do it: a 10u @ 100V as the primary, and a 100u @ 100V as the reserve. Since this thing has a bias wiggle trem (the best sounding, IMHO), the bias supply goes right to the trem pot, and gets wiggled by the trem oscillator. Since the pot could fail open, there is a failsafe 1M resistor from the raw side of the bias supply directly to the bias feeder resistors. Opps! There was a mistake in the wiring here, and the raw side of the bias BEFORE the 1M was connected, thus dumping the full RAW bias voltage on the tubes. Move the wire, and add a trim pot for adjustment, and whamo! The thing biases up nice and clean. Doing around 22 watts clean as a whistle!
Opps! I ran out of 20K resistors doing the YRM-1, and had to series connect two 10Ks.
Now that the amp is working wonderfully on the bench, I tried it out with my test speaker. Sounded like a dream. Exactly like they always do. Beautiful fat and sparkling clean, and creamy overdrive when pegged.
I put it back in its home and connected it to its Ampeg speaker, and tried that. Sounded like crap run over twice. The speaker is totally toast. How was that missed? It's beyond me.
The owner has a new driver on order, and will install it himself when it arrives. He's also going to fully seal up the back which sounds simply kick-ass on these units.