Discussion in '"Boat Anchor" & Classic Equipment' started by AF6LJ, Jul 11, 2014.
Run it into ur KILLERWATT!
It is real stable on seventy five meters...
Forty and twenty are another matter......
There were several HF SSB transceivers made that went beyond the typical 100 watt level. Swan, Hallicrafters, Drake, National and some others made higher-power rigs, all the way up to the Hallicrafters SR-2000 which ran the old 1000-watts-DC-input legal limit.
There were three problems with such rigs:
1) The increased power added cost and complexity to the rig and power supply.
2) In many but not all versions, TV sweep tubes were used in the final. They were inexpensive back-when, but today are expensive and can be difficult to find.
3) When used with a linear amplifier, the extra power capability is wasted.
Still, some hams liked having a little extra power (which amounts to a couple of dB) rather than running an amplifier.
Might be fixable.....or you may decide to go the X-Lock route.
Note that the rig uses the same VFO range on both 75 and 20. So if it is stable on 75 it is stable on 20.
For those not familiar with the 350 and similar Swans, here's how they cover the 5 bands without a lot of complexity:
The IF is 5.175 MHz (approximately). Single conversion all the way. The filter is optimized for USB, and that sideband is used on all bands in the IF.
For 80/75 meters (3.5 to 4 MHz), the VFO tunes 8.675 to 9.175 MHz. Because the VFO is above both the input and output frequencies, the sideband inverts, and the rig is on LSB on 80/75. (Note that the tuning direction does NOT invert).
For 40 meters (7.0 to 7.3 MHz), the VFO tunes 12.175 to 12.475 MHz. Because the VFO is above both the input and output frequencies, the sideband inverts, and the rig is on LSB on 40. (Note that the tuning direction does NOT invert).
For 20 meters (14.0 to 14.35 MHz), the VFO tunes 8.825 to 9.175 MHz. Because the VFO is below the and output frequency, the sideband does NOT invert, and the rig is on USB on 20. The same tuning range is used on both 80/75 and 20
For 15 meters (21.0 to 21.45 MHz), the VFO tunes 15.825 to 16.275 MHz. Because the VFO is below the and output frequency, the sideband does NOT invert, and the rig is on USB on 15.
For 10 meters (28.0 to 29.7 MHz), the VFO tunes 22.825 to 24.525 MHz. Because the VFO is below the and output frequency, the sideband does NOT invert, and the rig is on USB on 10.
This design eliminates multiple conversions, and gives the "right" sideband on each band. (The LSB/USB tradition had been set in amateur radio long before Swan went into business).
The Big Problem with this conversion scheme is that you have a VFO operating on multiple ranges, with bandswitching, and some of the ranges are pretty high up in the HF range. Making a such a VFO and having it be stable and affordable was quite a feat with the technology available. Thus the drift reputation.
The Elecraft K2 uses a similar heterodyne system, with the IF slightly lower (around 4.9 MHz.) The K2 achieves excellent stability by means of a PLL system.
Thanks EY! I do have a linear (that needs about 60W) but can't run it yet because the antenna is in the attic and I don't feel like lighting the house on fire. All the parts for nice outdoors system are here and slowly going together. Other than that, I love repairing things, and there's PLENTY of room on the radio bench even after I finish up the next few projects! (DX60B with SX99 receiver right after new antenna farm)
I can see the future and it looks more like Sue's radio bench! I said 6FL, I meant 6LJ... sorry! Blame that on small children and no sleep.
The excessive drift on twenty could be due to changing band switch contact resistance.
I have already thought this all the way though, and have decided to deal with the drift on the other bands at a later date.
For starters a better switch will have to be found for VFO band switching. One that is sealed would be ideal.
Temperature compensating the VFO for each band is easy enough and there are a number of ways to accomplish this. Compensating caps are but just one. I have almost a decade of experience using temperature dependent resistor networks biasing varactor diodes, that is the "other way" and it is very effective.
Ether way that issue is on the back burner for now since the band I use most often is stable enough...
In fact if 75 is stable but 20 is not it's almost guaranteed to be the switch. Some contact cleaner, or even just rotating the switch several times could fix it.
Another approach would be to use little DIP relays instead of a switch. 3 would be needed to cover all 5 bands.
But a shot of cleaner may be all that's needed.
That bad 12BA6 may have been a real rig-saver. From the pics (more please!) it appears that the whole thing was just left alone for years, rather than being golden-screwdrivered into multiple problems!
More pics when I get back, getting ready to head out to the Post Office and do a little shopping.
Using dip or reed relays is a good idea. I would rather go for a sealed switch first, less work and would keep the radio closer to stock.
Like I said above I would be more amiable to using an external DDS for the higher bands.
The relay idea is only if the switch can't be fixed and a replacement is unobtanium.
I bet the X-Lock could be implemented in a 100% reversible fashion, with less cost and effort than an external VFO.