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G8MNY > TECH 10.03.23 12:00l 93 Lines 4799 Bytes #999 (0) @ WW
BID : 42480_GB7CIP
Read: GUEST
Subj: AM TRF Radio
Path: IW8PGT<LU4ECL<ED1ZAC<GB7CIP
Sent: 230310/0809Z @:GB7CIP.#32.GBR.EURO #:42480 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Nov 08)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
In a recent construction contest, we all had to build this QUASAR project kit
No 3063 "One Chip AM Radio". Here I have redrawn the circuit in a more logical
way.
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÂÄÄÄÄ>+9V
4K7 5K6 ³ ³
ÃÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿ ³ ³/BC +³100u
1K ³ ³ ÃÄÄÄ´ 548 ===
ÚÄÄÄÄÂÄÄÄÄ´ ³ 10K _³_ ³\e ³
100K ³ ³ ³ u47 ³ \_/ 6R8 ³
Rod ³ ÚÄÄÁÄÄ¿ ÃÄÄÄ)Ä´ÃÄÄÂÄÄ150KÄÄ´ ÚÄÄÄÄÄÄ)ÄÄÄÄÄ´ ³+ 100u
ÚÄÄÂÄÄÄ)Ä´MK484³ ³ ³ ³ ³ 820K _³_ ÃÄÄÄÄ)Ä´ÃÄ>LS
||( ³_ ³ ÀÄÄÂÄÄÙ ³ ³ ³ ÚÄÄÄÄ´ ³ \_/ 6R8 ³
||( ³/| ³ ³ ³ ÃÄÄ¿ ³ ³/ ³ ÃÄ´ÃÄÄÄ´ ³/e ³ 8ê
||( === ³ ³ === ³ _³_ ÀÄ´BC548 ³ ³n47 ÃÄÄÄ´ BC ³
||( /³ ³ ³ u1³ ³ \_/ ³\e ³ u47 ³ ³/ ³\558 ³
ÀÄÄÁÄÄÄ´ ³ ³ === ³ ³ 10K<Ä´ÃÄÄÁÄÄÄÄ´ ³ ³
160pF ³ ³ ³u47³ _³_ 100 ³Log BC³\e ³ ³ ÚÄ>LS
=== ³ ³ ³ \_/ ³ ³Volume 548 ³ ³ ³ ³
u47ÀÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄÁÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÁÄ>0V
Construction was easy, about 30 min to do a good job. Most kits work OK.
The Tuned Radio Frequency Rx is fairly sensitive, but the high RF gain in this
not flat & there is a tendency to get RF oscillation at the high frequency end
of the band. Selectivity is surprisingly good. N.B. the IC runs at 1.2V
maintained by the 2 diodes. 1.5 of an LED is a bit too high. The 1k load & 100k
bias are said to be the optimum values for the IC's detecting & AGC action.
The AF amp is very poor, why they did not use an IC I don't know. The 1st class
A stage in run on next to no voltage so it distorts. The following class A
driver stage has too little standing current to drive the output NPN BC548 to
deliver +ve current swings into the 8 ohm LS.
There is no LW option, Ideally a 2nd coil on the ferrite rod is needed.
MY IMPROVEMENTS
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÂÄÄÄÄÂo\ÄÄ>+9V
³ ³ bootstrap 1K ³ ³ ON
4K7 ³ ÚÄÄÄÄÄÄ´ ³ ³
ÃÄÄÄ¿ ³ +³ 3k3 ³/BC +³100u
1K ³ 10K === ÃÄÄÄ´548 ===
ÚÄÄÄÄÄÄÂÄÄÄÄ´ ³ u47 ³ ³15u _³_ ³\e ³
100K ³ ÃÄÄÄ)Ä´ÃÄÄÂÄÄ150KÄÄ´ ³ \_/ 6R8 ³
Rod Cd ³ ÚÄÄÁÄÄ¿ ³ ³ ³ ³ ÃÄÄÄÄÄÄ)ÄÄÄÄÄ´ ³+100u
ÚÄÄÂÄÄÂÄÄ)ÄÄ´MK484³ ³ ³ ³ ÚÄÄÄÄ´ 820K _³_ ÃÄÄÄÄ)Ä´ÃÄ>LS
||( ³_=== ³ ³ÀÄÄÂÄÄÙ ³ ³ ³ ³ 10K ³ \_/ 6R8 ³
||( ³/|³ ³ === ³ ³ ÃÄÄ¿ ³ ³/ ³ ÃÄ´ÃÄÄÄ´ ³/e ³ 32ê
||( === ³ ³ ³n82³ === ³ _³_ ÀÄ´BC548 ³ ³n47 ÃÄÄÄ´BC ³
||( /³ Rd ³ oLW ³ u1³ ³ \_/ ³\e ³ u47 ³ ³/ ³\558 ³
ÀÄÄÁÄÄÁÄÄ´ \ ³ ³ === ³ ³ 10K<Ä´ÃÄÄÁÄÄÄÄ´ ³ ³
160pF ÃÄÄÙ ³ ³u47³ _³_ 100 ³Log BC³\e ³ ³ ÚÄ>LS
=== ³ ³ ³ \_/ ³ ³Volume 548 ³ ³ ³ ³
u47ÀÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄÁÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÁÄÄÄÄÁÄÄÁÄ>0V
Oscillation at HF end of MW.
By adding a light damping CR across the tuned circuit stops the oscillation,
the Cd is kept very small, a 10pF, & Rd = 330k did it OK without degrading the
performance.
1st AF amp distortion fault.
Running this AF amp from +9V gives lots more unclipped gain, but the
unregulated DC feed can lead to instability with a high gain output stage, so I
cut the track to the pot & added a 10k in series to attenuate the gain a bit.
Bootstrap.
I added a bootstrap to the output by changing the 5k6 for a 1k from +9V & a 3k3
to the NPN base, with the centre tap connected to a new cap to the output NPN /
PNP. This provides a lot more +ve output drive current, without increasing the
standing current & also increased the gain.
LS.
Using a higher 32 ohm LS reduces the LS current by 4, but I did not have one &
had to make do with the 8ê, which worked OK once boxed up.
LW.
Adding a switched 820 or 910pF gave tuning over 1 LW station @ 198kHz OK. I put
it across the unused 60pF tuning cap section & switch both in circuit to gain
the max tuning range. It is not very sensitive done this way, switching the
coil to a bigger one would me much better!
ON OFF
I added an ON-OFF switch too.
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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