Discussion in 'Amplitude Modulation' started by KA5SDC, Apr 23, 2019.
I make do with a DX-60, when I can keep the smoke in
I do. Two deal breakers for the Apache:
(1) The lack of 160m capability. The Apache was touted as an "upgrade" from the DX-100, but they deleted the very band where, when the Apache was in active production, AM was still the dominant voice mode.
(2) The crappy (scratchy Apache) audio, most importantly that stupid 470k (R48) resistor to ground in the audio line between the mic and the 1st audio stage, that loads down and kills the low-frequency response of a crystal mic like the D-104, abetted by 510 pf coupling capacitors (C61 and C64) in the low-level audio stages. However, that and other audio issues (some shared by the DX-100) can be fixed if the owner is willing to dig into the transmitter and make appropriate circuit corrections.
Plus, I'll add a third:
(3) The modulator tubes, EL34s, although more robust audio tubes than the 1625s in the DX-100, are very expensive now bordering on unobtanium.
What makes this even less understandable is that the Mohawk has 160.
There is a mod to add 160 to the Apache, so it could have been done when the rig was designed.
It can be fixed rather simply, so not a deal-killer.
They're audio tubes, which is why the price is so high.
But the Apache modulator can be modded to use other tubes - in fact, that's a good idea, because in the original design the EL-34/6CA7s are pushed way beyond ratings. 6146, 807, 6BG6 are good candidates.
73 de Jim, N2EY
The Marauder is not a good AM transmitter, MUCH better for SSB. The Heath TX-1 Apache is a very good transmitter and much better if you change out 3-capacitors in the audio circuitry and then unplug the 6AL5 clipper tube. Here is the schematic:
The RX-1 Mohawk is a very good receiver. However, the 3rd gain control, the i.f. gain control, requires some "getting used to" because very few receivers have this additional control.
I have a DX-100, a Marauder, an Apache (plus 2-more that need restoration), and a Mohawk. My second transmitter, after getting my General Class license in October of 1959, was a DX-100 and it was my main HF transmitter until November 1967 when I finished building my first Heath SB-401 transmitter. I also have other AM capable transmitters including a WRL Globe Champion 350A (one of the last of these that was built according to Leo Meyerson as he told me not that long before he died) and a Hallicrafters HT-20 (s/n 11). The Apache or the Globe Champion 350A are the 2 that I use the most.
My Heath original "twins" station is shown in the last photograph at:
In the late 1950s, Heathkit sold the RX-1/TX-1 pair (Mohawk/Apache) for a bit more than $500 (plus shipping for about 150 pounds in 2 packages).
What you got once they were built was a nice 100-watt-class AM station for 80 through 10 (pre-WARC) that was also pretty good on CW. It could receive SSB, too - for another $90 or so you could transmit on SSB with the SB-10 adapter.
Better have a nice big STURDY desk to put them on, and a source of 110 AC good for about 600 watts peak. Mobile? Not unless you have a vehicle with a lot of room and an AC generator. And - they don't transceive, you have to zero beat.
Now fast forward less than 10 years to 1967. Heathkit is selling the SB-101 transceiver for $370. With power supply, about $400, add a CW filter for another $25 or so. Say $425 plus shipping for maybe 40 pounds.
Once built, you've got a nice 100-watt-class SSB/CW station for 80 through 10 (pre-WARC) It won't do AM, but it's easier to use than the TX-1/RX-1 combo, it transceives, and it's small and light enough for mobile use with the DC supply (another kit, cost $50 or so). Or you could set it up on a card table, with the power supply on the floor.
Any wonder SSB transceivers pushed AM separates aside in the 1960s?
heh heh. almost on the air.
With a rebuilt audio section they work AND sound very well into a 1000-1500W linear amp. Ive had a B model with VFO in the mix since the 90's.
Most low power tube AM gear has their share of weak points with most of it in the audio. A sleeper here is a Johnson Adventurer with the rare optional screen modulator. Unlike the small Heath DX's it has a rugged PS and a very stable WRL 755A VFO is used with it and some other rigs...I have absolutely no use for crystals on HF/MF since I got the General in 1956
The Eico 730 modulator uses a pair of EL34s, but they are modulating only a single 6146 in the 720 transmitter.
For some reason, 6146s have a reputation for making poor modulator tubes. They are used in the output stage of a lot of 100-watt class SSB rigs; if they make poor modulators, wouldn't they also make poor SSB linear amplifer stages as well? Distortion in a linear amplifier is particularly a problem, since it generates splatter and a broad signal.
My HF-300 transmitter works with a VFO or crystal, the old fashioned kind with the round holder that fits into pins 2 and 4 of a 5-pin tube socket, and I have a drawer full of crystals for it which includes most of the commonly-used AM frequencies. I occasionally run xtal control just for kicks, but mainly, it's good to have them on hand in case the VFO goes out, which would otherwise keep me off the air until I got it running again.
I think the vfo was much nicer in the Apache.
And the other issues are easy to fix.
I think I would want more power on 160 anyway, if I had room for a 160 meter antenna...
One need not take up a lotta room for a 160 radiator.
I have had great results using a Cushcraft MA160v.
Not very tall. Ground mtd.
Using mine also on 30 es 40m CW.