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Vacuum tube 'down converters'

Discussion in '"Boat Anchor" & Classic Equipment' started by KB2FCV, Dec 6, 2010.

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  1. KB2FCV

    KB2FCV Ham Member QRZ Page

    On my SX-101A I notice it has an band marking for a converter for either the 6 or 2 meter band (as well as a converter spot on the band selector). I'd love to find a vacuum tube converter. What sort of converters are out there that will put out the 30-34.5 MC that the radio wants? I'd love to find something but I haven't a clue as to where to begin looking or who made them. Any ideas / suggestions?
  2. KL7AJ

    KL7AJ Ham Member QRZ Page

    Keep your eyes peeled for vintage converters made by AMECO. They usually had Nuvister front ends and were real hot receivers.

  3. KB2FCV

    KB2FCV Ham Member QRZ Page


    Thanks!! I'll keep my eye out for one. I did a little research and looked up Ameco, sounds like with a little work you could set them up for whatever IF output you need with not too much difficulty. That will be neat to have that working.

  4. KQ6EA

    KQ6EA Subscriber QRZ Page

    They've been turning up on eBay quite often in the last several weeks.
  5. WB5WSV

    WB5WSV Ham Member QRZ Page


    I have a couple of Ameco converters I have yet to use. I have a 2M one that uses Nuivsters and I believe it downconverts to 10M, so getting it to the range you want would likely not be too hard. I am going to get my trusty old NC-155 running again and try out that converter.

    I have another very interesting Ameco 6M converter that uses tubes and as near as I can tell runs 12V on both the filaments and B+ and downconverts 6M to the AM broadcast band! Why anyone would want that I have no idea.

    Another outfit that made them was International Crystal. I have one of their tube-type 6M converters that I was told was for 2M, and since my NC-155 already has 6M I never used it.

    Also consider some military surplus Guard Channel Receivers, such as from the ARC-27 and ARC-34. They are designed for 220 MHZ and up and have IF outputs down in the HF range. I have an ARC-34 guard receiver I paid 50 cents for years ago, and Fair Radio has been selling ARC-27 guard receivers for years now for under $20.

    Have fun!

  6. K1ZJH

    K1ZJH Ham Member QRZ Page

    Make sure the converter is equipped with the proper crystal for the IF
    range you are looking for! IFs in the 28, 14, 7 and 30MHz ranges were all very popular. Unfortunately, the correct crystal is probably worth than the converter today.

    Look for names like Tapetone, Janel, "W2AZL," Tecraft and even EF Johnson. Johnson made a small 6N2 converter (six and two meters combined) in a small package. Again, it came from the factory with 3 or 4 IF range options. The correct 6N2 converter for the 30.5 MHz IF is either 250-43-4 or 250-43-42. Unfortunately most sellers on eBay are flippers and don't have a clue what IF range the converters are for, so you may have to ask for the crystal frequencies and work the math.

    You'll also have to consider the power supply. Some, like the Amecos, will need to steal power from the receiver or a separate supply. Converters like the 6N2 and a few others, have their own built in AC supply. National also made converters for specific receivers. I'm not sure if the NC303 used the same IF range for VHF converters as the SX-101?
    For a Hallicrafters rig, the companion HA6 and HA2 transverters might be worth looking at; but they will be ham band IFs--they can be pricey if in good condition. I see you also own a HT-32A and a SX-101A; I am restoring a pair myself. I am eventually to modify a Johnson 6N2 transmitter to work as a transverter on 6 and 2 mtrs, along with the 6N2 converter, to have a really vintage VHF station.

    Pete k1zjh
    Last edited: Dec 6, 2010
  7. KL7AJ

    KL7AJ Ham Member QRZ Page

    Hi \robert. Such things were made to convert them to car radios! Gonset made a similar device as well.

  8. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    The weird tuning range of the SX-101A and NC300/303 allowed tuning all four MHz of the two meter band on a single slide rule scale. However most of us using these receivers "back in the day" didn't bother using those scales, we used a 28 MHz tuning range (L.O. at 116 MHz in the converter, so 28.00 MHz = 144.00 MHz receive frequency) to get better calibration and resolution and make SSB and CW signals easier to tune in.

    So if you want a converter, don't sweat it if you don't get the 30+ MHz I.F. version, it's not that great anyway.:p
  9. K9STH

    K9STH Ham Member QRZ Page

    Ameco made converters for all sorts of frequency ranges including the 6-meter and 2-meter amateur radio bands. The converters for the 6-meter and 2-meter ranges came in 2 different versions. The CB-6 and CB-2 used "normal" miniature tubes with the r.f. amplifier being a 6ES8 and the CN-6 and CN-2 which used Nuvistor tubes. The 6ES8 tubes are not that common but the 6BQ7 is the same tube and are readily available. The Nuvistor converter was also available that covered the 220 MHz band (now 222 MHz).

    The Nuvistor converters have a slightly lower noise figure than those using the 6ES8. However, either model converter works very well. I have at least 15 of the Ameco converters, both the miniature tube front end and the Nuvistor front end.

    The Hallicrafters SX-101 Mark IIIA and the SX-101A had a converter band that covered 30.5 MHz to 34.5 MHz calibrated for 6-meters and 2-meters. The National NC-300 and NC-303 had a converter band in the same frequency band that was also calibrated for 6-meters and 2-meters. Heath, in the RX-1 Mohawk, used 22.0 MHz to 26.0 MHz for the converter band.

    There are other tube-type converters made by various manufacturers that are also available. These include ones made by National, Heath, Johnson, WRL, International Crystal, and several others as well as all sorts of home brew converters.

    Being somewhat of a "converter junkie", I have between 30 and 40 converters made by several manufacturers (including Ameco, WRL, Heath, International Crystal, Tecraft, Gonset, RME, as well as home brew) for the HF bands, for 6-meters, 2-meters, 222 MHz, and 70 cm. With the exception of the Heath XC-6 and XC-2 which were designed to be used with the RX-1 Mohawk, most of my converters use either the 10-meter band (28.0 MHz to 30.0 MHz) or the 11/10-meter bands (26.0 MHz to 30.0 MHz) as the intermediate frequency. Since my Collins 75A-1, 75A-2, and 75A-3 receivers have full coverage between 26.0 MHz and 30.0 MHz, I often use that particular range.

    Glen, K9STH
  10. W3JN

    W3JN Ham Member QRZ Page

    The 6ES8 is one of the only remote-cutoff triodes and is completely different from the 6BQ7, although they share the same basing and might sub for each other in cases where there's no AGC.
  11. K9STH

    K9STH Ham Member QRZ Page


    There definitely is no AVC/AGC in the Ameco converters and the 6ES8 and 6BQ7 work interchangeably in those converters.

    Glen, K9STH
  12. KL7AJ

    KL7AJ Ham Member QRZ Page

    Yeah, I imagine a remote cutoff triode would be a rarity indeed. I'm not sure if anyone really understood dynamic range in the 1950s! HI!

  13. K9STH

    K9STH Ham Member QRZ Page


    The old tube substitution manuals show the 6BQ7 as a replacement for the 6ES8. The RCA tube manuals show the 6ES8 as a variable Mu and the 6BQ7 as a medium Mu. There are various tubes listed as "remote-cutoff", "sharp-cutoff", and "semi-remote-cutoff". But, the 6ES8 is not listed as any of those, at least by RCA.

    The maximum transconductance of the 6ES8 is about twice that of the 6BQ7. However, the "typical" operation is shown considerably less. The 6ES8 can take up to 550 volts when not operating but that drops to 180 volts maximum when drawing plate current whereas the 6BQ7 and 6BQ7A are rated at 250 volts.

    A "typical" noise figure of 6.5 dB is given for the 6ES8 (when operated in a television tuner) but none is given for the 6BQ7. In actual use I haven't measured any real difference between the two types. Most of my tube manuals are RCA. I do have some manuals from other companies but those are older editions and they don't have the 6ES8 listed.

    Glen, K9STH
  14. W5RKL

    W5RKL Ham Member QRZ Page

    Some of the older converters provided an output in the AM broadcast band for mobile installation. In a mobile installation, the AM broadcast receiver provided the IF and audio section.

    An example of such a converter is the RME MC-55 80 to 10 meter tunable converter. I used the MC55 powered by a homebrew power supply, feeding a BC-312N receiver during my mid 60s Novice days. It worked very well.

    The MC-55 did not have a BFO signal for CW or SSB reception. Most mobile installations operated "AM" back in the days these types of converters were popular.

  15. K9STH

    K9STH Ham Member QRZ Page


    I have an RME MC-55 converter as well as a Gonset VI. Also have a solid state International Crystal converter for 6-meters that uses the AM broadcast band for the i.f. (Mobilette 61 model). Then there is a home brew solid-state 6-meter converter with an AM broadcast band output. That converter is unusual in the fact that it operates from 22.5 volts and has a battery holder mounted on the back of the converter!

    One of my 432 MHz converters was built at the ARRL laboratory back in the early 1970s. I got it from a former QST VHF column editor. That converter is solid-state. Also have the Nuvistor 432 MHz converter that was built as the example in the old RCA "Ham Tips". It was the "cat's meow" back when it was designed.

    Also have a home brew 2-meter converter that uses an 8 MHz crystal in an overtone circuit for the injection. This converter uses the 7 MHz range as the i.f.

    RME made tunable converters that used 7000 kHz as the i.f. frequency. Those converters are larger than many of the tube-type receivers. I have an HF-10-20 which converts the 10/11, 15, and 20 meter bands down to 40-meters and a VHF-152 which converts the 10/11, 6, and 2 meter bands down to 40 meters.

    There is a lot of history in VHF and UHF circuit designs that can be found in converters built over the years.

    Glen, K9STH
  16. W3JN

    W3JN Ham Member QRZ Page

    I've also seen tube sub manuals declare a 6AU6 as a sub for a 6BA6, so I don't take too much stock in those. Perhaps in some situations but generally not a good idea. 6ES8s are pretty easy to find.

    You can sub all kinds of tubes and they'll work, after a fashion. That, however, doesn't mean the tubes are the same.
  17. WA2CWA

    WA2CWA Ham Member QRZ Page

    The Ameco nuvistor converters actual model numbers were CN50 (6 meters), CN144 (2 meters), and CN220 (220 MHz). They were available in both kit and factory-wired versions.

    Pete, wa2cwa
  18. KM1H

    KM1H Ham Member QRZ Page

    The nice thing about the 6ES8 is you can extend the receivers AGC ine to the converter.

    Ive done similar to RME DB-22A's that now run a single 6GM6. All those extra tuned circuits virtually eliminate images to those single RF stage 455 kc IF radios.

    I have the HA 6 and HA 2 as part of the HT-32B/SX-115 station but they are not in use. I have another HA-6 with some RX path mods in regular use with a TS-830 driver; its the best contest and weak signal setup Ive ever used.

    The NC-300 is setup with Tapetone 50 thru 432 converters and the 2M W2AZL converter I built around 63 measured a 1.8dB NF at a VHF/UHF conference measuring test....not too shabby even today.

    The main station uses updated Microwave Modules xverters for 144 to 1296.

  19. KL7AJ

    KL7AJ Ham Member QRZ Page

    There's a debate as to whether that's a nice thing or not, at least nowadays! The best dynamic range is to be had when the front end has JUST enough gain to overcome subsequent noise, and FIXED at that level! converters of old tended to have too much front end gain for best dynamic range!
  20. KM1H

    KM1H Ham Member QRZ Page

    Since very few ever tried applying AGC to a converter any meaningful debate is debatable:rolleyes:

    Without a NF meter and equipment to do overload tests its a shotgun method at best to change the tubes gain from what is specified by the tubes manufacturer for best VHF performance.

    Gain distribution is a touchy balancing act that most radio manufacturers could never get right at least at the ham level. Adding a converter just made it worse during openings or contests.

    My preference for a 6ES8 is as a Pullen mixer.

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