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The prototype - click for larger views On this page I will describe various construction options and also show a list of possible parts. The circuit can either be built as a point-to-point circuit or on a PCB. My prototype was a point-to-point circuit built in a rather interesting box - see pictures on the right... That construction method has some advantages, the most important being that it's easy to modify the circuit after contruction. The disadvanteges are the size, and that circuits can be difficult to build that way, if the builder is not experienced... I have chosen to build my final circuit on a PCB - mostly because of size. The advantages of PCB construction is size and ease of construction. The circuit is much less flexible though, so modifications can be difficult to make.

I have just received the PCBs from the factory, and am in the process of assembling them. The PCB viewed from above is shown here. The actual size is 10cm*8cm. The lines that surround the top part of the PCB is a piece of aluminium plate that serves three pupposes. The first is as a shield, the second as a heatsink for the 5k and 3k9 resistors in the input stage, and the third as a mounting plate for the input tube. I have chosen this design to make the complete preamp as compact as possible. If there's more space available the input tube and the two resistors could also be mounted on the chassis. If anybody is interested in factory made PCBs they cost approx. $10 each.

Part list The parts list contains part numbers for some parts. That does not mean it's essential to use those exact parts, but those parts will fit the PCB. Other parts will work fine, but if you plan to use my PCB layout be sure to get parts with the correct size. I have specified 450V and 630V capacitors for some of the values. If your powersupply does not exceed 400V you could use 400V parts instead, which may be easier to get or cheaper. The voltage of my powersupply rises to about 430V on powerup, so I have chosen "safe" parts. The "K73-17" caps mentioned are Russian types that are sometimes available as cheap surplus on eBay. All resistors, except the two 10Ws, are metal film. The 10W resistors are low-inductance wirewounds. All the parts are available from Farnell Components and most are available from RS Components also. Both companies have branches all over the world (except in the US/Canada), but I am sure parts sources are easy to find in North America also... And just in case your wondering about the strange brand names - "Epcos" used to be Siemens, "BC Components" used to be Philips Components and "Vishay" used to be ERO...

Item	Quantity	Reference	Part	Lead spacing	Part number
1	4	C1,C4,C16,C20	100n 630V	15 or 20mm	Epcos B32652-A6104-J or K73-17
2	2	C2,C13	470n 630V	20 or 22.5mm	Epcos B32653-A6474-J or K73-17
3	2	C3,C14	1µ 63V	5mm	Epcos B32529-C105-K
4	1	C5	680p 400V	5mm	BC Components 2222 463 46801
5	1	C6	4n7 160V 1%	5mm	BC Components 2222 461 44702
6	1	C7	2n2 250V 1%	5mm	BC Components 2222 462 42202
7	1	C8	10n 160V 1%	5mm	Vishay MKP1837-310-161-G
8	2	C9,C19	10µ 450V	5mm	Panasonic ECA2WHG100
9	2	C10,C15	1m 16V	5mm	BC Components 2222 037 55102
10	1	C11	120p trimmer		BC Components 2224 808 31121
11	1	C12	22n 160V 1%	5mm	Vishay MKP1837-322-161-G
12	1	C18	100n 250V	10 or 15mm	Epcos B32652-A4104-J
13	1	C21	22u 450V	7.5mm	Panasonic ECA2WHG-220
14	1	D1	1N4448	7.5mm
15	3	JP1,JP3,JP4	2.54mm header	2.54mm	Molex KK
16	1	JP2	2.54mm header	2.54mm	Molex KK
17	10	JP7	1mm solder pins
18	1	K1	DIL-relay
19	1	L1	22mH,L10-02R	5mm	Toko 187LY-223K
20	1	L2	2m2H,L10-02R	5mm	Toko 262LY-222K
21	1	L3	4m7H,L10-02R	5mm	Toko 262LY-472K
22	1	R1	820R 0.75W 5%	12.5mm
23	1	R2	27R 0.75W 1%	12.5mm
24	1	R3	1M 0.75W 5%	12.5mm
25	2	R4,R5	47k 3W 5%	20mm	Meggitt RSS3
26	2	R7,R19	1k 0.75W 5%	12.5mm
27	1	R8	1k5 0.75W 5%	12.5mm
28	2	R9,R10	2k,RPOT-15H		Vishay T93YA
29	1	R11	2k2 0.75W 5%	12.5mm
30	1	R13	91k 0.5W 1%	12.5mm
31	1	R14	1k 3W 5%	20mm	Meggitt RSS3
32	1	R16	68k 0.75W 5%	12.5mm
33	1	R18	100k 0.75W 5%	12.5mm
34	1	R20	27R 0.25W 5%	10mm
35	1	R21	220k 0.25W 5%	10mm
36	1	R22	1k 0.25W 5%	10mm
37	1	R23	0R	12.5mm
38	1	R24	470k 0.25W	10mm
39	1	V1	Noval PCB socket
Parts not on PCB:
40	1		5k 10W
41	1		3k9 10W
42	4		150R 0.125W
43	1		Noval chassis socket

Comments? Questions? Just send me an e-mail! Mail: mcs@post5.tele.dk