#ng51

Starting from the left, there are four small pots in a group. The lower pair are the input level controls for the two jacks below them. I modified this a little (this belongs to me, so I’m not knocking anybody else’s gear around). I’m normally dead against ‘mods’ of all kinds on vintage gear. The people who built these things in the first place were experts, with the odd genius in there somewhere. I think it takes a mountainous ego to ’improve’ them, especially as our current thinking is totally alien to the thinking of the ’50′s and ’60′s. On this machine, the gain was just too much for the output of current guitar pickups, so I altered the input resistor arrangement slightly. That was all, so nothing extensive.

The two small pots above the level controls are tone filters and a little confusing. There’s a bass clef sign to the left of centre on the pots, and a treble control to the right. But…..they mean that the bass is CUT to the left, and treble CUT to the right. So they have the opposite effect to the way we might expect. The three large controls along from that are:-

                             Repeat volume (adjusts the echo level); Sustain (controls the number of repeats); Tone (controls the tone of the echo signal.)

Next to that there is a jack input for line level (when used in an FX loop or auxiliary output on a mixer) and then a five pin output socket (DIN socket). There are two different output levels available from this socket, ground is the centre pin, the left pin is a line level out put and the right pin around 100 millivolts so the same sort of value as a mic, if you’re using it as an in-line effect into an amp, for instance. The three pin DIN socket above that is the footswitch.

Apart from that we’ve got a bank of four buttons. Power on, and two motor speeds. One other control is not obvious. The centre (sustain) control has a pull-switch arrangement which switches in an extra head giving a very fast echo.

   At the back there’s the mains supply input. This is original but a lot have been swapped for IEC (kettle) sockets. The voltage selector has so many voltage tappings you could probably use it on Mars.

There are quite a few parallels between what we see above and the idealised diagram of the last blog. The differences are these:-

The tape travel is in the opposite direction, so all the heads are in reverse order so far as their position within the unit is concerned. There are three record heads, and this makes it possible to vary the output of each repeat. The two playback heads can be switched from single to double giving a double echo as required. The roller furthest left is a single one (double in the iealised version) because the tape tension is much more accurately adjusted by the tension roller and spring on the left side of the unit in this case. Also the black rubber roller pinches the tape (pinchwheel) onto the capstan, so that’s a more effective design also. The head with ‘X’ marked is an addition. Its a permanent magnet and just cleans up the tape erase to the Nth degree. Another thought about the tension roller is that its face MUST be perpendicular to the chassis. The arm to which  it is connected I’ve often seen bent. Or should we say, not quite straight (back to the second hand car trade trade). If this is not really well aligned, the tape will move around and maybe even drift off the heads altogether at the extreme. 

Everything should be scrupulously free of grease (even grease from your fingers, so careful when you handle the tape).

This shows the various presets, and if they’re not set at least somewhere near it might not work at all. The hum balance is probably the easiest to set approximately. Except its dead easy to sustain third degree burns from the valves as you’re doing it. Turn all the echo controls off, and turn the amp up till you can hear hum. By adjusting the hum balance preset (it moves the centre tap of the heaters effectively) you’ll get to a low hum spot. A pair of long nose pliers (genlty used) can save your fingers. The output signal can be set approximately by plugging your guitar (etc.) into the amp, noticing the sort of level you’re getting, then going for something like that while adjusting the pot. Handy if you’ve got three arms for this sort of thing. The controls would all be off except for the input pots which would be 12 o’clock.

The delay level is a bit more of a guess. With tone full on, echo volume at about twelve o’clock, sustain off and any one of the top pots (they’re the echo volumes) fully on and the other two off, set the delay level so that the echo signal is about the same as the dry signal. Easiest on the middle head (so middle repeat vol, on others off ) but a matter of personal choice really. 

Here’s a last parting shot before I remove to the water hole. (Tea hole). On this last pic you’ll see a heavy twisted black and white cable. There’s a good reason for this, but you can improve matter just by tightening down bolts. The transformer is bolted to the main chassis and the main earth (ground) is connected to that. As the heaters have a centre tap to ground (via hum balance ) any problems with the chassis connection between the transformer (that’s the big brown thing on the left of the pic, with wires all over it) is big bad news for hum and background noise. The heavy black/white cable actually straps the main and the sub chasis’s together, so the electrical connection of the frames isn’t really important. If that’s not done, slacken the screws off to the transformer chasis, and then tighten them down again. It will shift any claggy accumulations and refresh the ground connection.

I feel a much deserved tea coming on, or possilby something stronger when the sun is over the yard arm.