Breadboarding a Vacuum Tube Trem Circuit

[martin manning]

I don't know that I'd recommend it, but it can be done. To support the 12AX7, I'm using a PCB noval socket with short pigtails soldered to a-g-k, and it is very stable. Longer leads are used for the filaments to get them out of the way. The power supply is a Triad 130-0, 130-0, 50mA flat-pack transformer feeding a FWB with 260V (CT is connected to the middle of the reservoir cap stack). With this light current draw B+ is ~380V. The filament is powered by a DC bench supply.

The circuit shown is a Fender-type tremolo with an LED in the plate circuit of the driver as discussed recently in another thread. Bringing it up with a Variac, the LFO starts oscillating at around 80V, and starts instantly when hit with full voltage. The phase shift caps are all 22n, and check out the small size of the first two- those are 630V rated stacked ceramics. The resistors are 1M5, 1M, and 1M, and in this configuration the LFO is running at 2.6Hz. There is no speed pot, but placing a 100k across the 1M5 increases the frequency to 6.1Hz.

[xtian]

Very cool, thx for sharing. I want to do similar so I can play with tone stacks.

[martin manning]

Surely breadboards like this are not made for use with high voltages, but it seems to work. Building up a couple of gain stages or a phase inverter for some actual measurements and listening tests seems feasible. For this trem circuit the simple power supply with FWB plus reservoir filter is fine, and it doest take up much space, but it has too much ripple for a preamp. There is room to squeeze in another RC filter, or perhaps the power supply could be built up in a separate enclosure with more filtering and other features. Another useful thing is small piece of aluminum angle with holes for pots and jacks that can be attached to the base.

[JazzGuitarGimp]

For years now, I've been thinking about building a bench supply with Hammond's highest voltage, highest current transformer, a large heat sink for the VVR's: one for B+, one for SCREENS, and one for BIAS, with switch-selected layers of filter caps and a switch-selected assortment of chokes. It would be a fun project, and it would be very useful.

[martin manning]

Once in a while I've seen Heathkit regulated tube bench supplies come up for sale. See e.g. http://www.w6ze.org/Heathkit/Heathkit_067_IP32.pdf Less capable, but similar to what you are proposing. For small signal tubes something simple and cheap would do.