[Milsurplus] BC-684 rf chain

[W7QHO@aol.com]

In a message dated 6/22/03 3:36:22 PM, cosmoline@aa4rm.ba-watch.org writes:


> Anyone have one out there?
>=20
Marty,

Yes we have a. SCR-608 at Ft. MacArthur where I volunteer.   Complete with=20
everything including antenna mount and mast sections.   Have an 808 too, not=
 as=20
nice but restorable.   I have the TMs for all three systems.

=A0=20
>=20
> Curious re 3-digit xtal numbers & multiplier scheme compared
> to BC-604 & 2-digit xtals which does things this way
>=20
> =A0=A0 1619-1619 osc. & class-C amp into saturable reactor where
> =A0 =A0 =A0 =A0 =A0 =A0=A0 9th harmonic picked
>=20
Another 1619 (V102) here called the rectifier.   Ninth harmonic picked up at=
=20
the plate of this tube.=20

> =A0=A0 1619 tripler
>=20
> =A0=A0 1619 doubler
>=20
Actually, a doubler followed by a tripler stage.

>=20
> =A0=A0 1624 straight-thru final
>=20
> Channel 48 would be 20mcs +4.8 mcs =3D> 24.8 mcs.=A0=A0 Multiplier, per ab=
ove, is=20
> 54
>=20
> Note '604 RF chain with all the 2.5V quick-heat tubes comes right out
> to 12.6 vdc for the series string.=A0 Neat
>=20
>  ---------------the '684?----------------
>=20
>=20
> =A0=A0 1619-1619 osc. & class-C amp into saturable reactor where
> =A0 =A0 =A0 =A0 =A0 =A0=A0 12th harmonic picked
>=20
Again, a 1619 "rectifier" follows the reactor and the 12th harmonic is picke=
d=20
up at the plate of this tube.

> =A0=A0 1619 tripler
>=20
> =A0=A0 1619 doubler
>=20
Yes, in the 684 the tripler DOES come first.

> =A0=A0 1624 straight-thru final
>=20
> Channel 348 would be 34.8 mcs - & note xtal fundamental is 483.333mcs.=A0=
=A0=20
> Multiplier, per above, is 72
>=20
Yes, that's exactly right right for the BC-684.   I suspect the two vs. thre=
e=20
digit numbering systems were to distinguish the xtals that went with each se=
t=20
since both use the same holders.    The one hundred xtal set for the BC-604=20
spaned 370.370 to 516.667 KC.   The 684 set spanned 386.111 to 540.277 KC. B=
oth=20
TMs include tables listing each xtal's fundamental frequency, channel number=
=20
and final output frequency.   As one might expect, a number of xtals in each=
=20
set could be used in either system For ex. the xtals for cnls 7 and 276=20
(383.333 KC fundamental), 13 and 284 (394.444 KC findamental), to name a few=
.   Of=20
paticular ham interest, channel 22 and 296 xtals (411.111 KC) both give an=20
output frequency of 29.6 MC IN THE BC-684.

>=20
> I've never seen a BC-684 or it's TM.=A0 Guess from the tiny sample of xtal=
s=20
> for same vs. '604 that few of this art'y version were built.=A0 Guessing t=
he=20
> BC-659 2-way served most of art'y guys needs.=A0=20
>=20
Actially, I believe quite a few SCR-608/628s (BC-684 xmitter) were built, an=
d=20
in my travels I've seen about an equal number of the two and three number=20
series crystals turn up.   The 608/628s were used in mobile artillery vehicl=
es.  =20
Also, the Navy used them on their ships to talk to BC-659s on the shore.  =20

Interesting that you got the BC-604 to work on the 72nd harmonic.   Did you=20
have to modify any of the tuned circuits, or were you able to do this within=
=20
the available range of adjustment through the multiplier chain and PA?

Dennis D.   W7QHO
Glendale, CA



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