Note: This page copied from original W7XXX Homebrew Forum
HAM Homebrew Amplitude Modulated radios
W7XXX all homebrew AM
Page 1 of 1• Actions !
W7XXX all homebrew AM
by W7XXX on Mon Dec 24, 2007 8:29 am
The All Homebrew AM Shack of W7XXX
Last edited by on Fri Feb 08, 2008 6:54 pm; edited 4 times in total
W7XXX- Admin
- Posts : 18
Joined : 24 Dec 2007
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 5:54 pm
The
"White Lightening SM300" transmitter. RF deck is single 813 in class C
with swing link final coil blocked from DC by a doorknob capacitor.
Output 300 watts. Modulator deck is pair 813's class B (wired as
triodes) with peak output of 450 watts. A negative peak limiting
circuit holds negative peaks at 100% and allows positives to go up to
140%. The power supply delivers 2kv at 500 ma continuous and peaks at
700 ma with no problem. The rectifiers are the Cetron 3B28 that has an
uncovered plate so they glow lavender. The PS has an inrush current
circuit of 2 seconds delay. No breaker, breaker to the undertaker here.
Last edited by on Fri Feb 08, 2008 7:09 pm; edited 2 times in total
W7XXX- Admin
- Posts : 18
Joined : 24 Dec 2007
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 5:55 pm
mtrs.6AG7
oscillator and 6146 final. Xtal controlled with jack for VFO, but I
robbed the VFO cabinet for the small receiver, so it is not usable. I
decided just to use it with xtals as I have all the most used AM freqs
for 75 meters. Below is the keying relay with a switch for checking the
exciter and adjusting the transmitter grid current. The dud 813 on top
is just for show.
Last edited by on Fri Feb 08, 2008 7:21 pm; edited 2 times in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 5:57 pm
AM rocks! The mirror is to see behind the exciter for changing xtals.
Last edited by on Fri Feb 08, 2008 7:23 pm; edited 2 times in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 5:58 pm
12AX7
preamp, 12AU7 driver, and 1614 finals class B (wired as triodes).
Output transformer has multiple taps from 4 to 500 ohms. 250 ohms
matched the UTC VM-1 mod xfmr used as the 813 driver transformer. Idle
current on 813 mod is 50ma, perfect for class B 813's. Balanced line
audio matches the Heil vintage looking mics.
Last edited by on Fri Feb 08, 2008 7:32 pm; edited 4 times in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 5:59 pm
The
copper tube houses a Heil matching transformer and a .05 mfd Black Cat
Sprague capacitor. Notice the 20k 3 watt WW resistors used to hook the
screen and control grids to convert the 1614's to triode use. The input
must go to the screen grid when using these smaller tubes. The 813
screen and control grid can be wired together for class B, but the
smaller tetrodes and pentodes require the dropping resistor.
Last edited by on Fri Feb 08, 2008 7:39 pm; edited 1 time in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 6:01 pm
The
"Moonshine DC13" receiver. Dual conversion with tunable IF (500-1200kc)
and mixer stage and xtal controlled 1st converter. 3 tuned (2
amplifier) stages of fixed IF at 455kc. Has 6V6 audio with feedback to
add presence to the AM signal. The noise limiter is a dual diode series
type. The two s meters were used to give a balanced look. The first one
reads the first tunable IF stage and gives a good idea of signal
strength to band noise ratio and the second one reads the avc action.
13 tubes with silicon rectifiers. B+ is 150 volts and 105 volts
regulated for stability. PS is overkill and never gets warm. No
noticable freq shift after 1 minute or so warm up. Bandwidth is a
little over 10kc, perfect for AM.
Last edited by on Fri Feb 08, 2008 7:59 pm; edited 3 times in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 6:03 pm
No
extra holes until I had to change the tunable IF design and frequency.
Also changed 1st converter to 2 tubes, 6BZ6 and 12AT7 from original 3
tubes which left another hole. Not pretty as I had planned, but it
works great. Also changed from larger Miller 132 kc IF transformers to
the smaller 455kc Nationals which left more unsightly holes. Originally
it had a plug in coil band switching on the 1st converter, but it
didn't work as well as I wanted so again more holes. Still haven't got
the BFO transformer installed.
Last edited by on Fri Feb 08, 2008 8:09 pm; edited 2 times in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 6:04 pm
No
awards for beauty here, but good receiver building procedure was used,
IE, no crossing grid and plate leads, keeping certain leads short, and
isolating circuits with space. I had some shielding planned, but it
wasn't necessary. On a smaller chassis shielding would become an issue.
Last edited by on Fri Feb 08, 2008 8:13 pm; edited 1 time in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 6:06 pm
The
"Mountain Dew DC8" Dual conversion 8 tubes. 6 tubes in basic receiver
and 2 in outboard converter. Has only one stage tunable IF and 2 fixed
tuned IF stages (one amplifier), but it still does an amazing job on
receiving AM. With the converter bypassed, it tunes the entire BC band
(550-1700) and picks up stations all over the West. It has a simple
noise limiter that helps knock off the sharp edge of static. Circuit is
similiar to the "All American Five" except it uses silicon rectifiers
and has an OC3 regulator for the mixer and osc stages.
Last edited by on Fri Feb 08, 2008 8:23 pm; edited 1 time in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 6:07 pm
The
SWR power meter. The detection circuit is from a military Collins unit
that I converted from 75 ohm to 52 ohm. Very accurate. Notice the Dow
Key antenna and rcvr B+ relay on the side
Last edited by on Fri Feb 08, 2008 8:27 pm; edited 1 time in total
Re: W7XXX all homebrew AM
by W7XXX on Tue Feb 05, 2008 6:16 pm
The
ugly rig with the 4 meters on the top is the start of the small xmtr. I
keep changing my mind whether it will use a 4D32 modulated by 807's
class B, or maybe a single 813 crystal oscillator, Heising modulated by
an 813 in class A for 100 watts out. The mics are the Heil balanced
line Pro Heritage and Pro Classic both outstanding copies of vintage
mics.