HR-10b Project

Discussion in '"Boat Anchor" & Classic Equipment' started by W7UUU, Feb 13, 2016.

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  1. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page


    Most of the AF4K crystals are NOT actual FT-243 types. Instead, Bry uses old FT-243 holders and installs HC-49/U size crystals inside. These crystals usually, but not always, work fine with circuits designed for the original FT-243 type crystals. However, the smaller crystals cannot handle the current that the FT-243 types can handle. This can produce chirping, and even complete failure, especially when those crystals are used with transmitters.

    Glen, K9STH
    WA2LXB likes this.
  2. W9GB

    W9GB Ham Member QRZ Page

    Bruce Stock, AB7YD; Brian Beezley, K6STI; and Jim Hanlon, W8KGI
    wrote a series of articles about the Heathkit HR-10(B) receiver, a decade ago.

    Electric Radio, Number 171
    Electric Radio, Number 172
    Electric Radio, Number 231 (August 2008),
    Electric Radio, Number 232
    Electric Radio, Number 234 (November 2008), page 26
    This article changes the resistors in the ANL circuit for clipping at 90% modulation,
    instead of 70% modulation with factory design.

    R26 : 120k ohms —> change to 200k ohms
    R30 : 270k ohms —> change to 200k ohms
    Bruce noted that HR-10 used 6EA8 mixer,
    but National’s NC300 used the 6BA7 for a similar receiver design for higher frequencies.
    Jeff, K6JCA : Heathkit HR-10B Improvements

  3. N2EY

    N2EY Premium Subscriber QRZ Page

    The 6BA7 is perhaps the best of the pentagrid mixers - and it's noisy. That's why the HR-10 and many other receivers don't use pentagrid mixers.

    With a noisy mixer, the usual solution is to have an RF stage with lots of gain. This works, but it's a trade-off of noise vs. dynamic range.

    73 de Jim, N2EY
  4. WA2LXB

    WA2LXB XML Subscriber QRZ Page

    Thanks for those links.

    I've been discussing Viking II mods with AB2RA and she has found that 'improvement' design modifications, even those that have been published, are often advertised to have effects that are either not reproduceable because the mod lacked measurements that prove the design change actually works as stated or that they create new problems.

    It's been an interesting journey, where she's installed and then removed some of the V2 mods published in ER when they didn't perform. I believe she's got a new article coming up that provides metrics after successful mods are made. This is good for us V2 owners because when she's done my V2 will benefit from her proven upgrades.

    I'm just glad that it's taken Dave so long to get his HR-10B on the air because I want to have a Heathkit Novice Rig QSO with him on CW and AM before he gets it all working and sells it!
  5. N2EY

    N2EY Premium Subscriber QRZ Page

    It's not well known for some reason. There was an article in that QST or one soon before that showed the special makes-fundamental-FT-243s oscillate-as-overtones oscillator circuit as a Tech Correspondence or H&K, and the converter was the result.

    For 40 meters, using 10.5 MHz as the crystal won't work unless the receiver tunes below 3.5 MHz. The solution is a 3.6 MHz rock, which results in a 10.8 MHz output and the band tunes from 3.8 MHz.

    Some BC-454 ideas:

    1) Selectivity can be improved by making the second IF regenerative. There was a QST article about this (March, 1960). Very simple mod.

    2) If you don't mind a bandspread can be greatly improved by replacing the tuning capacitor with one from a BC-455 and adding fixed padding capacitors. The BC-454 cap is about 140 pF per section and the BC-455 is about 62 pF per section. Some realignment will be required and you'll need a new dial, but if my math is right the result will be a tuning range of about 3 to 4 MHz, and a tuning rate 1/3 that of the original BC-454.

    3) There are two kinds of audio output transformer in the ARC-5 receivers. The older, "original" kind has no terminal 6 and provides only high-impedance output (4000 ohms or so). The newer, "B" kind has terminal 6 and provides either high-impedance output or about 600 ohms output (by moving the output wire to terminal 6). This is useful when driving passive audio LC filters and headphones designed for "600 ohms".

    4) To simplify heater requirements, the various 12.6 volt heater tubes can be replaced with their 6.3 volt equivalents - except for the 12A6.

    For some strange reason, the 12A6 and 6A6 are completely different tubes. The 12A6 is a power pentode with octal base while the 6A6 is a dual triode with a Medium 7 pin base (same as the 1625). The 6-volt-heater-equivalent of the 12A6 is the 6K6GT. Same pinout and everything. Don't waste time looking for a metal 6K6, they don't exist.

    5) If you can use a 12K8Y tube instead of a "plain" 12K8, stability may be improved. The "Y" indicates a mica-filled-bakelite base.

    73 es GL de Jim, N2EY
    W7UUU likes this.
  6. N2EY

    N2EY Premium Subscriber QRZ Page

    A word about mods.....

    I think that in the vast majority of cases the first step in doing a modification is to get the set working in "100% stock" condition. Part of this should include checking voltages, resistances, etc., against expected values.

    All too often, a "mod" is done to "fix a problem" that results from a parts failure rather than a design deficiency.

    @W7UUU encountered an extreme case of this in a HW-16 that had been extensively modified. Upon removing all the mods and restoring the unit to stock condition with good parts, it performed amazingly well!

    73 de Jim, N2EY
    WA2LXB likes this.
  7. W1BR

    W1BR Premium Subscriber QRZ Page

    If one is really ambitious you could add two 85kc IF transformers and convert the 1st IF (was it around 1400kc or so?)
    with a simple mixer and LO. I'd be tempted to dump the RF stage and try light coupling between the two tuned
    RF stages. Even the NF of a 6K8 should be passable on 80 meters. That would free up the 'SK7 RFA socket for use
    as a converter between 1400 (or whatever) down to 85 kc.

    As Jim suggested, it would also be easy to add some regeneration to improve Q, and a notch filter is pretty easy
    and effective at 85kc as well.

    One other possibility to deal with cost of crystals for a down converter is to find an old, junker Lafayette HE-73
    that is beyond restoration. It will supply the crystals, power transformer and some other useful parts to make
    a 20/15/10 down converter for a BC-454. They seem to go for silly prices on ePay, but I am sure they are out
    there, rusting away in barns and cellars.
    WA2LXB likes this.
  8. WA2LXB

    WA2LXB XML Subscriber QRZ Page

    Good point...I've used the DX-60 with the AF4K crystal on CW, but I haven't used it in the Viking on AM yet. If it blows a head gasket or gets all chirpy I'll let you know:eek:

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