Home-brew A.F. signal generator, 10 Hz to 1 MHz, 5 switched ranges + V.F.O.
Dates from 1982 (vintage home-brew).

Internals, photo. #2

Home-brew A.F. signal generator, 10 Hz to 1 MHz, 5 switched ranges + V.F.O.
Dates from 1982 (vintage home-brew).

Outputs: sine-wave (full & variable level to 1v. r.m.s. max.), square wave (variable level only to 1v. peak - peak), and TTL (0v/+5v.).
Mains 230-v.a.c. powered.

Oscillator is a Wein bridge oscillator using a 2N5457 F.E.T for amplitude stabilisation. Three LM318 op-amps.; LM316; SN7406N; LM340T-5; LM340T-12; LM320T-12.
I make no claims as to the purity of the waveform. Its purity is predominately determined by the uniformity (or lack of it) of the law of the variable resistance twin-gang pots. that are used to determine the variable frequency. These are 5 kΩ log. + 5 kΩ reverse log. ganged. However, this item of test kit was designed to meet the need for a simple A.F. generator primarily for basic testing of audio equipment plus the provision of a clock source for TTL / logic circuits.
The full circuit diagram is available from me: please enquire on the Forum.

Other photos. in this series show internals and resultant waveform at 1 kHz.

Submitted by Al. / Nov. 23, 2012 //

Zetagi PSU model 1220 S: cct. diag of regulator cct.
See main photo. for full description.

Submitted by Skywave, Nov. 16, 2012 //

Item name: Zetagi PSU model 1220 S.    
Country of origin: Italy.
Vintage: mid. 1990's (estimate).
Brief manufacturer's spec.: Adjustable & regulated O/P voltage, 3 → 20 v.d.c.; current up to 25-amps. Has electronic current overload protection (foldback). Input voltage 220 - 240 v.a.c., 50 Hz.

Picture comments.
Above pic. shows this unit on 'soak test' after repair, during which the front panel meters were replaced by non-standard units. The white box with the square meters is an adjustable low-voltage, high power resistive dummy load.

Brief technical description.
Conventional linear regulated transistorised PSU. Uses four 2N3055 power transistors as the series pass elements. Uses an L200 5-pin PSU-controller i.c.
The manufacturer's spec. is rather optimistic! You can get that rated current is you don't mind a huge amount of ripple on the O/P! I found the maximum O/P current to be in the region of 20-amps. And even at 10-amps. O/P, the heat-sinks for the power transistors became FAR too hot!

Maintenance notes.
This unit should not be confused with the earlier offering from Zetagi: model 1220. That unit has a similar spec., is much older and does not use a regulating int. cct. Its comparative performance is unknown to me.
In the 1220 S, the rectifier reservoir capacitor consists of eight 2200 uF 25-v. units wired in parallel, producing about 18,000 uF in total. These have a habit of deteriorating over time, especially the one very near to the L200 heat-sink (which gets very hot). Usual repair is to replace all of them with 105°C units.

Photo. and comments submitted by Skywave, Nov. 16, 2012 //

HP 1715A 200 MHz dual-channel oscilloscope.
(Refer to the main photo. for item description)