Oscilloscope Clock II - Further Development Notes

Introduction

My scope clock 2 uses a DG7/32 CRT - this is my reference design and I have modified it to suit other CRTs. Only CRTs that I have tested the scope clock with (and I present photographs and movies below) will be shown. But the design should work with many similary tubes.

Key CRT parameters
Parameter DG7/32 DP7/5 2AP1 E4103/B/4 DH3/91
Final Anode
volts		 500 800 500 — 1000 1000 500
Focus Anode
volts		 0 — 120 200 — 300 125 — 250 ? auto
Grid (note 1)
volts		 -50 — -100 0 — -50 -30 — -60 -25 -16 — -54
X sensitivity
mm/V		 0.35 — 0.43 0.16 0.13 — 0.26 0.10 0.19
Y sensitivity
mm/V		 0.22 — 0.28 0.26 0.11 — 0.22 0.09 0.22

Note 1: for extinction of an undeflected, focused spot

scope clock 2

Left to right, DG7/32, DP7/5, 2AP1, E4103/B/4 and DH3/91

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2AP1 CRT

Gallery

Hover the mouse over these screenshots for more information:

scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2

Power supply changes

This tubes permit operation at a slightly higher anode voltage than the DG7/32 reference design but close enough to make any changes to cathode voltage unnecessary. The required grid voltage is lower (as a negative voltage, i.e closer to the cathode voltage). The required changes represent a simplification of the reference design as the grid supply voltage doubler is no longer required.

DP7/5 CRT

Gallery

The DP7/5 has a short blue phosphor and a long persistence greenish yellow phosphor. These photographs were taken with the correct exposure to show the blue colour (one only) but then over exposed to show the long persistence afterglow. The afterglow is subtle as shown with the room lights on when it disappears. But the blue colour itself is very appealing.

Hover the mouse over these screenshots for more information:

scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2

Power supply changes

This tubes permit operation at a slightly higher anode voltage than the DG7/32 reference design but close enough to make any changes to cathode voltage unnecessary. The required grid voltage is lower (as a negative voltage, i.e closer to the cathode voltage). The required changes represent a simplification of the reference design as the grid supply voltage doubler is no longer required.

E4103/B/4 CRT

This is an old WW2 British CRT made by GEC. The tube diameter is about 38mm and the usable screen is some 25mm in diameter. There is little information available on it but I did get it working from this information.

I have two of these old CRTs and unfortunately they both have some points where the phosphor is burned.

Gallery

scope clock 2 scope clock 2 scope clock 2 scope clock 2

Power supply changes

Perhaps this does illustrate how flexible the clock design is as with only a little adaptation I had the CRT working in about an hour. The two changes I had to make were to reduce the grid blanking voltage to -21V by changing the grid supply transformer to a single 15V RMS winding and to supply the tube with a 4V 1A heater supply (I did this using PWM control of a MOSFET from the 6.3V AC supply, more on this technique later). The CRT is suppose to require an anode voltage of 1000V but I tested it using the 800V available.

DH3/91 CRT

Gallery

scope clock 2 scope clock 2 scope clock 2 scope clock 2 scope clock 2

Power supply changes

This tubes permit operation at a slightly higher anode voltage than the DG7/32 reference design but close enough to make any changes to cathode voltage unnecessary. The required grid voltage is lower (as a negative voltage, i.e closer to the cathode voltage). The required changes represent a simplification of the reference design as the grid supply voltage doubler is no longer required.

I have no intention of making a scope clock 2 using a DH3/91. The purpose here was to test the CRT and present the photographs and movies above. For this reason a separate power supply PCB design with the parts omitted has not been developed. It is only necessary to replace C14 with a link and omit D12. Also, the tube deflection is asymetric with deflection plate D1' connected to the final acceleration anode connection (pin 2: g2, g4, D1'). This means that one connection to the collector of the final deflection amplifer transistor is omitted. On review, I think some further tweaks to the PSU might be worthwhile. But I have demonstarted the CRT in operation.

Power supply schematics and boards

These tubes permit operation at a slightly higher anode voltage than the DG7/32 reference design. The required grid voltage is lower (as a negative voltage, i.e closer to the cathode voltage). The required changes represent a simplification of the reference design as the cathode supply voltage reduction and the grid supply voltage doubler are no longer required. Other changes are as noted.

These board are reduced version of the DG7/32 design; I have not renumbered them so the parts are not sequentially numbered but have an exact correspondence with the previous design.

The Eagle files can be downloaded here.

I found myself missing the right sort of base for the 2AP1 CRT so I quickly made one:

Power Supply Board Parts List

Power Supply Card
Part Description Farnell Code Rapid Code Dimensions
C1 100u 16V 1236662 2.5mm lead spacing
7mm diameter
C2 2200u 16V 9692215 This part is 25V
7.5mm lead spacing
16mm diameter
C3 10u 16V 9451480 2.5mm lead spacing
5mm diameter
C4, C5 & C6 100n 9750983 5mm lead spacing
2.5mm x 7.5mm package
C7, C8 & C11 220u 400V 8813582 10mm lead spacing
25mm diameter
C10 1u 630V 1200810 27.5mm lead spacing
13.4mm x 31.6mm package
C13 1u 250V 9693980 2.5mm lead spacing
7.5mm diameter
C15 100u 250V 1673472 7.5mm lead spacing
16mm diameter
R1 390 5% 0.25W 62-0360
R2 1k trim pot 9354298 Bourns 3362P series; brightness control; see note 2
R3 330 5% 0.25W 62-0358
R4 10k 5% 0.25W 62-0394
R5, R7, R12 & R16 470k 5% 0.25W 62-0434
R6 1M8 5% 0.25W 62-0448
R10 500k pot 9354395 Bourns 3362P series; focus control; see note 3
R17 DP7/5: 1M 5% 0.25W
2AP1: 680k 5% 0.25W		 62-0442
62-0438
D1 & D2 1N4001 9564993
D3 UF1G 1625267
D4 1N4148 9565124
D5, D7 & D9 1N4007 9565051
D11 1N4004 1843708
Q1 BC327 9558489
Q2 ZTX558 9526676
IC1 78L05 1014073 The pcb layout shows TO220 package; the L device is adequate
IC2 6N137 9994866
X1 Connection to CRT heater see note 1
X2 Blanking input from digital card see note 1
X3 External brightness control (if used) see notes 1 & 2
X4 Connection to CRT cathode, control grid and focus anode see note 1
X5 Connection to analogue card see note 1
X6 External focus control (if used) see notes 1 & 3
X7 Connection to transformers wire links or else see note 1
X8 Connection to digital card see note 1
X9 Unused connection see note 1
socket for IC2 8 pin DIL socket 22-0107

Notes

  1. 0.1" pin header strip with everyother pin removed; wires soldered and covered with heatshrink tube
  2. The brightness control (R2) can be either a 1k trimpot on the PCB or an external mounted 1k pot connected using X3
  3. The focus control (R10) can be either a 500k trimpot on the PCB or an external mounted 500k (or 470k) pot connected using X6
2AP1 CRT Base
Part Description Farnell Code Rapid Code Dimensions
Mill-Max Receptacle 11 required Mouser (UK link) part 575-03900
X1 CRT connection to Analogue and PSU cards 0.1" header pin strip with every other pin removed

Transformer Board Parts List

The board is optional. See schematic for 115V or 230V operation.

Transformer Tidy Board
Part Description Farnell Code Rapid Code Dimensions
Transformer A 230V RMS 10mA, 13.5V RMS 200mA, 6.3V RMS 1A Transformer TRA800 from
Ask Jan First
Transformer B 2 x 22V RMS 1.6VA 9531360 note 2
F1 0.5A 26-0167 20 x 5mm holder
X1 Transformer B wires see note 1
X2 Mains supply screw connector, 5.08mm spacing, 3 way
X3 Outputs to PSU PCB see note 1
X4 Transformer A wires see note 1

Notes

  1. 0.1" pin header strip with everyother pin removed; wires soldered and covered with heatshrink tube
  2. The test with the E4103/B/4 CRT used a 1 x 15V transformer
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