Wednesday, November 2, 2016

1973 Fender Twin Reverb with rare JBL speakers

I played a Twin through high school. They're big, heavy and torture to take around. I'll never forget loading mine up in the back of my dads station wagon one night and he drove me to band practice (a Go Go band called Currency back in 1985!) and we took a corner and heard a crash. I was worried about my precious tubes. In Actuality it took out a window and the amp was just fine.....

About this amp. It's a nice one. This was a custom order one loaded with original JBL speakers and has the original foot switch.....

I'd never choose these speakers myself but when I do hear them I understand why someone would. Clean, big and bright. I actually like them in a black/silver panel Fender amp.

The complaint on this one was muddy sound, noisy intermittent reverb. It had some bad caps, needed a good cleaning, fresh output tubes and a NOS 12AT7 reverb driver tube. Never use a new 12AT7 in this position. They don't last and there are plenty of cheap 12AT7 tubes about....Sylvania, RCA, Telefunken, GE, anything but JJ or Sovtek!

This amp was also literally 7 resistors and 1 capacitor away from the original black panel circuit. I converted it. That's a part of that muddy tone one heard with these early 70's amps. It's worth it. The amp plays with a more open sound. Also re-wire the bias circuit so you can actually bias the amp. Get rid of that 'balance' arrangement.

Silver panel schematic:

Look at the phase inverter. That's where the "silverness" happens. Change it up to:

You may also change the 2 resistors in the power supply, but I prefer to leave those alone. A hair warmer in my experience.

You don't see many of these about here in NYC. Most of us prefer Deluxe Reverbs or Princeton Reverbs for these tiny clubs. So the prices are largely dependent on region. Some places you can get one for a bargain. You can buy one of these hand made amps for the price or less than a new reissue! Leaves me to wonder what the point is in those reissue amps. They are nice, but not quite as nice as one of these. Something to consider......

Idea on value:

One like this with JBL speakers can command a high price, the rest, great amp for the money!


Update on this: Client wanted a fresh set of preamp tubes as well. I'm a "if it ain't broke don't fix it" kind of guy but complied. When you change an entire set of tubes sometimes problems can arise. In this case one did. The tremolo started going 'tick tick tick tick'. No biggie. Simply put a .1 600V capacitor across the neon bulb tremolo 'bug' from the 10 Meg resistor to ground. I have little idea why this works, I'm just glad Jeff Bober showed me this trick 25 years ago! Saved me a lot of time over the years. I watched another tech painfully decline this and his customers Twin just kept coming back to solve the problem. The situation got tense. I told him this but he saw no logic in it understandably but he wouldn't even try it. I wasn't the tech at this shop and knew by suggesting this I was merely causing tension so I backed off. The customer backed off too and went elsewhere.....

Amp sounds great. Those JBL speakers have a richness to them. That's why they work so well for me. Clean but good, complex clean.

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