RECEIVER STC R1082
RESTORATION (DIARY)
(Dec. 2006 - Sept. 2008)
1. Initial condition, objective
2. Restoration
3. Final check
4. Later additions
5. Measurement tables
1. Initial condition, objective
The receiver R1082 has the model number 10D/8415 and my receiver has the serial number 15589. I bought it on eBay in November 2006. The receiver was in original condition, no changes had been made. Coils for the bands D, E, F, K and L were included together with some spare coils for those bands. The specified frequency coveradge is L 470 - 785 and K 785 - 1200 kHz, of which the lower band has connection for a D/F add-on, and F, E, D 4000 - 8500 kHz.
The objective was to clean the set, check and change any faulty components and make a function check. As the receiver is a simple straight design no alignment is needed. I also plan to get a VU33 valve, a protection diode over the antenna input, the valve is missing in my receiver.
2. Restoration
1. The valves were removed and all components checked, see table 1. R6, R11 and R16 were faulty, to be changed later, see par. 6 and 7 (061202).
2. One of the contacts in the LT power switch was broken, was fixed by joining the halves with a copper strip. see photo.
As I wanted the LT to be switched on from the external power supply the switch was adjusted to be permanently on. The HT
switch was shorted to chassis, some isolation pieces were missing. I found them loose in the case (!), they were mounted in place.
The LT/HT switch now worked as I wanted, the LT is switched on with the power supply and the HT with the receiver switch.
(061203).3. The receiver was cleaned, fine cleaning of the engraved text will be done later (061203). (Cleaning of the text with a toothbrush and soap as well as a thorough cleaning of the panel and chassis was done 070130).
4. The case was cleaned and fixing hooks were moved from the bottom to the side where they were missing. A peace of board was fastened under the case as a stand, the holes for the removed hooks were used to fix it in place. Coils for bands E and K were claened, to be used for the initial tests (061228).
5. The valves were checked physically, two had loose bulbs fixed with old tape, were fixed with new tape. V1 type VR18 was
very loose, perhaps some of the leads was broken? (061229).6. Resistor R16, which was broken, was bypassed with a 100 kohm 1W resistor, hidden under the original resistor, see photo (070112).
7. Both potentiometers R6 and R11 for volume and reaction were faulty and were changed to new Bourns 50 kohm 2W Cermet pots (1/4”), see photos (070126). I am planning to open the old ones and try to repair them or build the new ones into the old cases.
8. An external power supply was designed, see Accessories, the valves were inserted one by one and the LT and HT current was measured, see table 2 (070126).
9. The valves V3 to V5 (AF stages) were inserted and the amplification was checked with a 1 kHz input signal from an AF signal generator and the output was measured
at the phones connector with an oscilloscope and with a 20 kohm load. The signal levels and the stage amplifications are
shown in table 3. The values seem resonable, the AF part works well with high amplification (070129).10. The dial lamps were missing, small axial lamps 3V 50 mA were soldered in, gave sufficient light.
11. The valve voltages were measured in normal use, see table 4.
12. Aerial, ground and phones were connected and the receiver was tested on bands E (shortwave 49 m) and K (medium wave BC). It was working quite satisfactorily! (070130).
3. Final check
1. The coil frequency coverage was measured with a RF signal generator and counter,
see table 5. Anode coil D gave much too high frequencies, the spreading capacitor showed 27 pF instead of the nominal 200 pF, it was changed. All coils were now cleaned.
(070201).
2. Listening tests were done on all avaliable bands. The receiver was performing very well on all bands! The sensitivity and above all the selectivity were not as good as with the R1155, there is a real development step between the two although the designs are only about four years apart. The best sensitivity and a fair selectivity was found when the feedback was close to oscillation and the RF volume was low.
With a good aerial it was very pleasant to listen to short- and medium wave BC stations with the restored receiver!
I now decided the restoration was successfully finished! (070202).
4. Later additions
After a tip from my friend Maurie Camps in Coleambally, Australia, who is also restoring an R1082, I found the VU33 valve at Chelmervalves in England. The valve is only a protection diode across the antenna input and not necessary for the function of the radio, but it is nice to have the receiver complete. See photos below. The valve is sitting very tightly in a special socket with a screw locking one of the valve pins to avoid the valve loosening when flying in rough condiditions and making hard landings! The locking screw can be seen just above the valve designation V6 in the photos (080901).
I have also disassembled the faulty potentiometers and put the new cermet potentiometers inside the original case. They now look original but they work fine, can stand higher power and are noise free! See photos below (080908).
5. Measurement tables
Table 1
Component checks
Spec Real Spec Real
R1 0.5M 0.57 C1 10p 220
R2 0.5M 0.59 C2 50p 220
R3 0.75 0.90 C3 300p var 47-383
R4 0.5M 0.52 C4 200p 193
R5 1.5 1.5 C5 200p 250
R6 0.05Mpot broken C6 0.5u 0.54
R7 0.1M 0.11 C7 300p var 26-360
R8 0.25M 0.28 C8 0.5u 0.5
R9 0.02M 0.022 C9 200p in coils
R10 0.1M 0.107 C10 100p 124
R11 0.05Mpot broken C11 10p 20
R12 1.0M 1.08 C12 0.5n 0.33
R13 2.0M 2.4 C13 1n 3.9
R14 0.5M 0.57 C14 2u 2.03 >2M
R15 2.0M 2.0 C15 0.5n 1.0
R16 0.1M broken C16 1n 0.78
R17 0.2M 0.36 C17 1n 1.14
R18 150 151 C18 2u 2.4 >20M
R19 150 151 C19 4u 4.2 >8M
R20 0.5M 0.55 C20 2u 2.4 300 //
R21 5000 6006 C21 100p 94
Table 2
Filament current per valve, voltage Uf = 2.13 V
V1 130 mA
V2 95 mA
V3 88 mA
V4 85 mA
V5 220 mA
Accumulated anode current, voltage Ua = 126 V
Idle 2.8 mA (with coils, without valves)
+V1 4.4 mA
+V2 4.8 mA
+V3 5.1 mA
+V4 6.4 mA
+V5 12.3 mA (total in normal use)
Table 3
Audio frequency amplification, input 1 kHz for 10 Vptp out in 20 kohm at phones connector.
Uin Uout F Rem.
AF-stage 3 V5 0.8 Vptp 10 Vptp 12 times
AF-stage 2 V4 70 mVptp 10 Vptp 145 times ca 12 x 12 times
AF-stage 1 V3 7 mVptp 10 Vptp 1430 times ca 10 x 12 x 12 times
Table 4
Valve electrode voltages, normal listening, to chassis
Rör Uf- Uf+ Ua Ug Usg
V5 0 2.0 109 -2.8
V4 0 2.0 40 -1.4
V3 0 2.0 60 -1.0
V2 0 2.0 30 -0.5
V1 0 0.2 115 -0.4 0-28 var w vol
Ufil = 2.0 V Ifil = 0.56 A
Uanode = 118 V Ianode = 10 mA
Table 5
Frequency span of the anode coils (the frequency determining coils, green) in kHz.
Coil Spec f low Spec f high Real f low Real f high
D 7000 8500 6500 9900
E 6000 7000 5000 8100
F 4000 6000 2940 6800
K 785 1200 708 1670
L 470 785 360 900
More on WWII receivers
Top of page
Home
Updated September 25th 2009