DX-100 Transmitter · Volume 6
Reference
Everything in this volume is taken from a primary document - a Heath manual, a Heath catalogue or a Heath letter - and cited to it. Where two Heath documents disagree, both figures are given and the disagreement is noted rather than resolved by preference. The manual editions are listed with the evidence needed for a hosting decision: publication year, whether a copyright notice was seen on the copy examined, and whether a renewal search has been made.
6.1 Specifications
Table 1 — Specifications
| DX-100 | DX-100B | DX-100U (Daystrom Ltd) | |
|---|---|---|---|
| RF power output | 100-125 W phone, 120-140 W CW | 100-125 W phone, 120-140 W CW | 100-125 W phone, 120-140 W CW |
| Output impedance | 50-600 ohm, non-reactive | 50-600 ohm, non-reactive | 50-600 ohm, non-reactive |
| Output coupling | pi network, coaxial | pi network, coaxial | pi network, coaxial |
| Operation | crystal-VFO, CW-phone, local-remote | crystal-VFO, CW-phone, local-remote | crystal-VFO, CW-phone, local-remote |
| Band coverage | 160, 80, 40, 20, 15, 11, 10 m | 160, 80, 40, 20, 15, 11, 10 m | 160, 80, 40, 20, 15, 10 m |
| Audio output | 85 W, 300-3000 c/s | 85 W, 300-3000 c/s | 100 W, 300-3000 c/s |
| Power requirement | 115 V AC, 50-60 c/s | 115 V AC, 50-60 c/s | 95-150 or 195-250 V AC, 45-65 c/s |
| Standby | 150 W | 150 W | 150 W |
| CW | 400 W (intermittent) | 400 W (intermittent) | 400 W (intermittent) |
| Phone | 450-600 W | 450-600 W | 450-600 W |
| Cabinet | 20 7/8 x 13 3/4 x 16 in | 19 1/2 x 11 1/2 x 16 in | 19 1/2 x 11 1/2 x 16 in |
| Net weight | 100 lb | 100 lb | 100 lb |
| Shipping weight | 107 lb | 107 lb | 114 lb |
| Price when new | $189.50 (1955-58) | $189.50 (1959) | not established |
Sources: DX-100 manual, p. 66; DX-100B manual, specification page; DX-100U manual, p. 1; prices from the 1955 flyer, 1956, 1958 and 1959 catalogues.
Where the documents disagree. The launch flyer of early 1955 claims 125 W phone and 140 W CW as “actual r.f. output” and a 120 lb shipping weight; the manuals give the output as a range of 100-125 and 120-140 W and the shipping weight as 107 lb; the catalogues from 1956 onwards say “in excess of 100 watts on phone, and 120 watts on CW”. The 1959 catalogue’s DX-100-B body copy says the pi network matches 50 to 72 ohms while the specification table on the same page says 50-600 ohms; the manual supports 50-600. The launch flyer describes the 6146s as push-pull; every other document, and the schematic, has them in parallel.
6.2 Valve complement
Table 2 — Valve complement
| Valve | Function | Notes |
|---|---|---|
| 6AU6 | VFO | Clapp oscillator, electron-coupled; mounted outside the VFO box to keep its heat out |
| 12BY7 | crystal oscillator / buffer | modified Pierce with crystals; buffer and multiplier on VFO |
| 5763 | driver | screen voltage set by the panel DRIVE control; metered 0-50 mA |
| 6146 x 2 | final amplifier | in parallel, class C, about 740 V, sub-mounted on a shield plate |
| 6AQ5 | screen clamp | protects the 6146 screens if drive is lost |
| 12AX7 | speech amplifier | two resistance-coupled triode stages |
| 12BY7 | audio driver | triode-connected, into a 2:1 step-down transformer |
| 1625 x 2 | modulator | push-pull class AB2; an 807 with a 12.6 V heater |
| 5V4G | low-voltage rectifier | capacitor input, 360 V at 150 mA |
| 5R4GY x 2 | high-voltage rectifiers | in parallel, choke input, about 740 V |
| 6AL5 | bias rectifier | 75 V from a transformer tap |
| OA2 | regulator | 150 V to the VFO screen |
Fifteen valves in total. The DX-100U substitutes a 5U4G for the 5V4G, 6CH6s for both 12BY7s, and KT88s for the 1625s.
6.3 Frequency control
Table 3 — Frequency control
| VFO range | Bands | Dial spread (DX-100B manual) |
|---|---|---|
| 1750-2000 kc | 160 m | 4 in |
| (same range, doubled) | 3500-4000 kc, 80 m | 5 in |
| 7000-7425 kc | 7000-7300 kc, 40 m | 4 1/2 in |
| (x2) | 14.000-14.350 mc, 20 m | 2 1/4 in |
| (x3) | 21.000-21.450 mc, 15 m | 1 3/4 in |
| 6740-6807.5 kc | 26.960-27.230 mc, 11 m | 1 1/8 in |
| (x4 from 7 mc) | 28.000-29.700 mc, 10 m | 4 in |
Crystals may be used in the same ranges as the VFO output, and in addition in the 3500-4000 kc range for the appropriate bands (DX-100B manual, p. 3; Eckweiler).
6.4 Metering
Table 4 — Metering
| Meter switch | Measures | Range |
|---|---|---|
| DRIVER | driver anode current | 0-50 mA |
| GRID | final grid current | 0-10 mA |
| PLATE | final anode current | 0-500 mA |
| VOLTS | final anode voltage | 0-1000 V |
| MOD. | modulator anode current | 0-500 mA |
Normal operating figures from the tune-up: 5 mA grid current; about 250 mA anode current on CW and 240 mA on phone; modulator current about 50 mA unmodulated, peaking to about 125 mA on speech.
6.5 Iron and major components
The parts list names the heavy components, which is useful when a replacement has to be identified or a transformer rewound:
Table 5 — The parts list names the heavy components, which is useful when a replacement has to be identified or a transformer rewound
| Part number | Component |
|---|---|
| 54-30 | plate transformer (1800 V centre-tapped, 400 mA) |
| 54-31 | power transformer (low voltage, all filaments, bias tap) |
| 51-22 | modulation transformer |
| 51-33 | driver transformer |
| 46-10 | plate filter choke, 400 mA |
| 46-11 | low-voltage filter choke, 150 mA |
| 45-17 | line filter choke (nine off) |
| 45-13 | 47 ohm parasitic choke (two off) |
| 40-54 / 40-55 | 160 m and 40 m VFO coils |
| 40-62 / 40-63 | 20 m and 40 m slug-tuned buffer coils |
| 40-61 | 10-15 m driver coil |
| 40-59 / 40-60 | 160 m and 10 m plate coils |
| 25-34 | 125 µF 450 V electrolytic (two off, the high-voltage filter) |
| 25-10 | 20-20-20 µF 450 V electrolytic can |
| 26-20 | 11-35 pF differential capacitor (the VFO tuning capacitor) |
6.6 Related Heath equipment
Table 6 — Related Heath equipment
| Model | What it is | First seen | Price |
|---|---|---|---|
| SB-10 | single-sideband adapter, phasing type, 10 W PEP | 1959 catalogue | $89.95 |
| MK-1 | modification kit to fit the SB-10 to a DX-100 or DX-100B | named in a Heath letter of 13 August 1959 | not stated |
| VX-1 | electronic voice control, “designed primarily for operation with the DX-100” | 1958 catalogue | not recorded here |
| B-1 | balun coil kit, for feeding balanced antennas | 1958 catalogue | $8.95 |
| AC-1 | antenna coupler | 1954 catalogue onward | $14.50 |
| TX-1 “Apache” | the DX-100B’s successor as flagship | 1959 catalogue | $229.50 |
| RX-1 “Mohawk” | matching receiver | 1959 catalogue | $274.95 |
6.7 Manuals and documents
Free scans, with the evidence relevant to hosting. “Notice seen” means a copyright notice was actually observed on the copy examined, not inferred - which matters here, because the DX-100 assembly manual turns out to carry one. The back cover of the complete DLARC scan reads “Copyright 1956, Heath Company, Benton Harbor, Michigan”, with a printing date of 8-21-56 at the foot of the opposite corner; the other DLARC scan, whose cataloguer recorded “No Copyright found”, is a set of loose pages that does not include that cover. A first printing of 1955 has not been examined. No renewal searches in the Catalog of Copyright Entries have yet been made for any of these titles, so every hosting judgement below is provisional.
Table 7 — Manuals and documents
| Document | Heath number | Date on the copy | Copyright notice seen? | Renewal searched? | Free scan |
|---|---|---|---|---|---|
| Assembling and Using Your Heathkit Transmitter Model DX-100 (assembly manual, 68 pp., cover price $1.00) | none seen | printed 8-21-56 | yes - “Copyright 1956, Heath Company, Benton Harbor, Michigan”, on the back cover | no | DLARC, 88 images |
| The same manual, loose pages, 56 images | none seen | undated; back cover not present | not seen - the DLARC cataloguer recorded “No Copyright found” | no | DLARC |
| The same manual, other scans | - | - | not examined in detail | no | heathkitmanuals · second · third · fourth |
| Assembly and Operation of the Heathkit Transmitter Model DX-100B | 596-213 | Copyright 1958, printed 3/15/58 | yes - “Copyright 1958, Heath Company, Benton Harbor, Michigan” | no | DLARC, 163 images |
| Assembly and Operation of the Heathkit Transmitter Model DX-100U (Daystrom Limited, Gloucester; cover price 21/-) | none seen | undated; late 1950s | no US notice seen | not applicable in the same way; UK publication | VMARS manuals archive |
| Assembly and Operation of the Heathkit Single Sideband Adapter Model SB-10 | none seen | Copyright 1960, printed 9/28/62 | yes - “Copyright 1960, Heath Company” | no | Internet Archive |
| SB-10 manual, DLARC scan, with Heath correspondence of 1959 bound in | none seen | 1959 letters | not seen | no | DLARC |
| Improved Keying for the DX-100 (Heath modification sheet, 2 pp. plus figures) | none seen | undated | no | no | Internet Archive |
| DX-100 schematic sheet | none seen | undated | no | no | Internet Archive |
| DX-100 schematic and layout sheet | none seen | undated | no | no | Internet Archive |
The catalogues and flyers used throughout this dive are at World Radio History and are advertising matter: mid-winter 1955 flyer, Summer 1956 flyer, Christmas 1956 flyer, 1956, 1958, 1959 and May 1961 catalogues.
Further reading
- Bob Eckweiler, AF6C, “Heath DX-100 HF AM/CW Transmitter”, Heathkit of the Month #8, Orange County Amateur Radio Club, September 2008. The best short account, and the source for the DX-100/DX-100B differences as a list. w6ze.org
- Ken Brueschke and Michael Mack, “The History of the Heath Companies”, AWA Review 32 (2019), for the Viking II reverse-engineering account and the DX-100’s effect on Heath’s engineering department. Internet Archive
- Chas Gilmore, “H is for Heathkits and Hams”, EEJournal, part 1. A former Heath general manager on the 1950s ham line. eejournal.com
- Chuck Penson, WA7ZZE, Heathkit: A Guide to the Amateur Radio Products. Not online; quoted in the mailing-list literature for the DX-100’s loading arrangement and the factory modification kit.
- Doug Roth, WA3DSP, “Heathkit DX-100 Restoration” - the most thorough published rebuild, with measurements. wa3dsp.org
- Mark Bell, K3MSB, DX-100B restoration pages. k3msb.com
- wireless-girl.com, DX-100 restoration and modification notes, including the argument against the SB-10 conversion. wireless-girl.com
- Nostalgic Kits Central, DX-100 modifications, abstracting The AM Press/Exchange of May 1989. nostalgickitscentral.com
- Heathkit Virtual Museum, DX-100 and DX-100-B entries. DX-100 · DX-100-B
- The site’s Heath Company history dive, for the company context. heathkit.fubsypoly.com
6.8 Open questions
- No renewal search has been made in the Catalog of Copyright Entries for any DX-100 title. All four Heath manuals examined are pre-1964 publications, and three of them carry a notice (1956, 1958, 1960), so the hosting question turns entirely on renewal. That search is the next piece of work.
- The DX-100 manual examined is a printing of 21 August 1956. Whether the 1955 first printing carried the same notice is unknown; no copy of it has been examined.
- Production quantities are unknown. No Heath production figure for the DX-100 or DX-100B has been found in any source consulted.
- The exact changeover date from DX-100 to DX-100B is not settled: the B manual is dated 15 March 1958, but the plain DX-100 is the version in the 1958 catalogue, and one secondary account dates the B to 1957.
- The DX-100U’s production dates, price and the extent of Daystrom Limited’s redesign are not established; only the manual has been examined.
- CQ for October 1956, pp. 34-35 (Lloyd Jones, W6DOB) has been read only as quoted in a 2003 mailing-list posting bound into a manual scan; the original has not been consulted.
- The 1956 QST time-sequence keying article for the DX-100, referred to by later restorers, has not been located.
Sources
All sources are linked inline above; the manual editions and catalogue issues are listed in the two tables in this volume.
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