833 Modulators
BE 150-a 8 CH mixing console
Grant, W4BVT, with home brew 4-1000A transmitter
Collins 51-j Receiver
Built 1951
Restored by Grant W4BVT
Built 1951
Restored by Grant W4BVT
4-1000A transmitter,
modulated by a pair of 833's
modulated by a pair of 833's
Left of the operating pos,
on the right of the transmitter.
on the right of the transmitter.
Guest position
Operating
position
position
Front
view
of the
4-1000A transmitter
right
before it
was put
on the air
the first
time.
view
of the
4-1000A transmitter
right
before it
was put
on the air
the first
time.
Transmitter Construction
It is a 4-1000a modulated by a pair of 833's.
The 833's are driven by an external pair of 4-125's as AF driver for max headroom.
Peter Dahl mod transformer and Peter Dahl 833 driver transformer.
I built my own 833 sockets for low profile and max pin cooling. I also specially built low noise ac to dc fill supplies for the 833's. They weigh less than a pound each, are 99% efficient, and 4 inches wide by 6 inches long by 1.5 inches thick. Regulated 10 vdc and 0 noise at 60HZ or 120, filtered very well at the noise range it switches at, so no rf hash can be present. Standard switchers won't work.
The 4x1 fill supply is a standard CT fill supply for the 4x1.
Plate supply is Gates bc-1t plate trans with a 16 h swing choke with a 10mf oil cap. The modulator feeds from that, then there is a 10 h choke and a 8 mf cap that feeds the mod reactor. This gives the modulator and rf section separation and provides the extra voltage drop needed for the 833 to have a bit more voltage than the final. That is necessary for good modulation.
The HV wire is 15kv 14 ga. stranded silicone and the lv wire is Teflon covered silver wire. The sequencer and overloads are also home brew old-school style, mostly Mercury relays at various speeds. The big mercury relays are 60 amps. The transmitter has emi filters as well at 60 amps. All the big ac stuff came from a few old stoplight control cabinets.
The impedance is matched from 833's to the 4x1, and the turns ratio of the mod transformer is 1.4 to 1, so it is all good stuff. All the coils and caps are broadcast spares or pulls from various radio stations. The 833's are new and the 4x1 is a strong pull.
I now run 833c's as the new a's have much more distortion in AF service; the old US tubes don't do bad, but the new china a's do suck in the modulator, and the c's have lots more plate dissipation.
I use a pr-40 main and a re-20 guest mic into a broadcast electronics 150-a 8 ch mixing console into a crl AGC-400, then a PMC 450, then into the transmitter. The audio gear is fed ac by a home brew ac filter and isolator system.
The board and the processing are 1990 's tech and still do well. The audio iso transformer is hooked up before the station ac voltage regulator and runs at full voltage.
Besides the audio chain and the main plate supply, the stations ac voltage is regulated by a 30 amp 1% adjustable regulator. I fire up the whole station at 111 volts per leg and turn it up to 117vac-118vac per leg after warm up.
The main plate supply voltage is variable and reduced for legal limit operation through a big 50 amp 240 variac , switched with the 60 amp mercury stop light relays.
The station is operated by push button start and stop controls located at the operating position. Ppush one button and the whole station comes on in sequence, another button to shut it all off. The transmitter is keyed by toggle switch on the same panel.
The whole station is grounded in the star configuration with 3 inch strap used at the transmitter.
Lots of old and nos parts mixed with some new stuff.
Thanks for your time looking at my creation,
Grant
W4BVT Ham Radio Station
Internal shot of the 4-1000A RF deck. It is a bit neater now, but you get the idea--big parts!