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GM7HUD > SIX 22.12.05 01:22l 66 Lines 4405 Bytes #999 (0) @ WW
BID : 893173GM7HUD
Read: GUEST
Subj: CB to 6m conversion 9
Path: DB0FHN<DB0FOR<DB0SIF<DB0EA<DB0RES<DK0WUE<I0TVL<CX2SA<GB7YFS<GB7LGS<
GB7ESX
Sent: 051221/2224z 71798@GB7ESX.#31.GBR.EU $:893173GM7HUD [Witham, Esx]NNA V3.1
*CB TO SIX METRES * Part9 - The Transmitter section continued
*Anyone is free to use the following information for private use on the
provision that it is not used for commercial purposes . Permission is
granted by the author , ZR1EV , to publish and or distribute all or part of
the following on the condition that recognition is given to the author . In
the case of it being used in a newsletter or magazine , a copy of the
aforementioned should be sent to the above adress.*
We are now done with the "encapsulated" small coil formers and the rest of
the work can now be done without the aid of a magnifying glass (HI) .
Locate and remove T6 . This tuned interstage coupling transformer is wound
on a white plastic former and a lot of care should be excercised not to
overheat any of the pins , as the former may deform from the heat and
render it useless . The tuned primary of the transformer , can easily be
identified . The primary coil is wound from clear enamel coated copper wire
and the 1 turn secondary winding is wound using green enamel coated copper
wire .
Leaving the secondary winding as is , proceed to remove 2 turns from the
"top" of the winding , untill you are left with 5 turns on the former .
Form the free end of the wire with a small "longnose" pliers and feed it
through the hole in the base of the former where the original lead was fed
through . You will now notice thet the secondary and primary windings are
spaced too far apart (by the thickness of about two windings). "Pull" the
secondary winding lower down on the former (by pulling in the secondary
pins with a small pair of pliers) until the two windings touch . Trim the
pins to length and using a small hobby knife , scrape the insulation off
the pins and tin . Reinsert the transformer , solder back into the PCB and
replace C47 with a 27pF Disk ceramic capacitor .
Replace C49 with a 120pF disk ceramic capacitor . Replace L6 with a coil
consisting of 13 Turns wound onto a 1.5M ohm 0.5W carbon resistor . Replace
C52 with a 47pF 50V disc ceramic capacitor and C53 with a 120pF 50V disk
ceramic capacitor . Remove L7 and remove turns until you have 1.5 turns on
it . Prepare as with T6 and replace . Replace L9 with a coil made up as for
L6 . Modify L11 for 2.5 turns , L13 for 3.5 turns and L201 for 1.5 turns .
If you have difficulty locating L201 , you will find it (airwound coil)
between point (31) on the main chassis and the inner conductor of the
antenna socket . (some rigs have L201 and C201 omitted). Change C51 to 22nF
Replace C54 with an 82pF 100V disc ceramic capacitor , C55 with a 330pF
100V capacitor , C184 with a 68pF 50V disc ceramic capacitor and C201 with
an 18pF 100V disc ceramic capacitor . As "all coils are not wound equal",
You could experiment with slight changes in capacitor values for maximum
performance with minimum spurious output . C56 is fitted to some chassis ,
and can be removed in this mod . L13 is an air-spaced inductor with self
supporting windings , and can be streched or compressed for maximum output
When you notice that the peak tuning on T4 and T5 occurs when the slugs
are about the middle of the formers , you could INCREASE the capacitor
value across the primary by a few pF . The correct point for the cores are
about flush with the top of the screening cans . The same applies for the
Reciever coils , T8 and T9 with the exception of T7 . T7 should be tuned
for the loudest signal , not the loudest "hiss". This is important for a
good s/n ratio , so you can dig out those really weak signals on the band .
I have found that this occurs when the slug of T7 is a couple of turns from
the "bottom" of the coil former . If you cannot get this condition , try
changing the value of C100 by a couple of pF .
The rig should now "run up" smoothly . All of the rigs I have done so far,
exceeded the original specs on 27Mc on the reciever and practically always
got in excess of 10W PEP out of the transmitter (recomended PO) . If you
have a "lazy" 2SC1969 (Did a conversion once where I could do what I liked,
but could not get more than 8W PEP... Replacing the final did the trick),
You could try replacing the final with a 2SC1307 . These devices seem to
have more gain at 50Mc . See you in Part10 (final)
73 de Andy GM7HUD
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