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Author Topic: Fine tuning upgrade for old heathkits?  (Read 1098 times)
KD0ZGW
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Posts: 1055




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« on: July 11, 2019, 03:21:26 PM »

Just getting into old heathkits.  I enjoy using the old rigs but wish the tuning wasn't so dang fussy even after an extended warm-up.  No doubt I am spoiled by recent hardware as I've only been a ham a few years but it would surprise me if no one has ever produced an upgrade.

Specifically ;looking for upgrade(s) for HW101 & SB301 if it exists.

thx in advance to anyone taking the time to reply.

KD0ZGW
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KX4QP
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Posts: 404




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« Reply #1 on: July 11, 2019, 03:37:00 PM »

Electronically, it shouldn't be hard to add -- just a small-value variable cap with one or two stages of reduction between knob and shaft so it takes a long time to tune across the range.

Making that fit on the front panel seems like a fantasy, at least on my SB-102 (the HW-101, as I recall, has several vacant spaces where you could drill for another knob).

Alternatively, I guess you could replace the main tuning drive with one that adds another reduction stage and has a fast-transit knob (I've seen that kind of knob setup on ham rigs, but I don't recall what brand).  Seems like a pretty big project to do that to an HW-100 or SB-100 family transceiver.  I'm not familiar with the SB-301, but I'd bet it isn't any easier there.

FWIW, I don't find the tuning on my SB-102 especially picky, but to date I've only been listening on 80 and 40; it might run past signals more rapidly down on 10m (I wouldn't think so, since it tunes the same 500 KHz range there as on 80 and 40 -- but I haven't gotten any signals on that band in the two hours of listening time I've got in so far).
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KM1H
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« Reply #2 on: July 11, 2019, 05:26:51 PM »

What is the as built tuning rates in kc per turn using old terminology?

Carl
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VK6HP
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Posts: 544




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« Reply #3 on: July 11, 2019, 06:48:44 PM »

I believe it's 100 kHz per revolution, if my recollection is correct.  The SB-102 I restored has gone to a new home after being sighted by a keen collector, so I can't easily check it.

While the tuning rate is fast by modern standards, I've never had any real problem in practice.  One thing I wonder from the OP's post is whether his radio might have any of the infamous Heathkit warble in the tuning.  One way to check the tuning smoothness is to tune slowly past the calibrator signal in SSB mode. The audio note should change slowly and smoothly, with no jumping or irregularity.  The radio should also be able to be tuned to a given beat note and remain stable, give or take some long-term drift.  If you find the tuning jumpy, or the beat warbling, the LMO needs a mechanical overhaul involving restoration of electrical continuity in the LMO tuning capacitor.  See http://nebula.wsimg.com/d6a8106142d2492dec285d95be47aaf6?AccessKeyId=D1250C433DB440D6B60D&disposition=0&alloworigin=1

The only comment I'd make is that the solid state LMO in the SB-102 is considerably harder to access and work on than the earlier tube types.  But I've done it, and it worked out well.

73, Peter.
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KM1H
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« Reply #4 on: July 12, 2019, 10:06:31 AM »

I considered the 25 kHz of 3 of my TS-830's to be excessive but those are also used as IF's for VHF to microwave weak signal transverters. Working CW DX pileups on 6M for instance prompted me to add an outboard Jackson Brothers 6020 miniature 10:1 drive to the front panel. No holes involved, just a bracket pushing down on the table for stability.

Since tuning excursions are quite narrow, even on SSB, it was not a hindrance. 

OTOH my TS-940 and 950SD had selectable tuning rates and I was most comfortable with 10 kHz for HF use.

Carl
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G3RZP
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« Reply #5 on: July 12, 2019, 10:25:54 AM »

Under 25kHz/turn on my HW101
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KX4QP
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« Reply #6 on: July 12, 2019, 03:46:25 PM »

Under 25kHz/turn on my HW101

I've got an SB-102; it's 100 KHz per turn of the indicator dial, but that's something like three turns of the actual tuning knob -- there's a planetary reduction and I'm not sure what its exact ratio is.  Certainly doesn't seem too fast when I'm trying to get the other end of a band, though...
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VK6HP
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« Reply #7 on: July 12, 2019, 08:13:56 PM »

Thanks.  That fits my recollection of using the SB-102 better but I couldn't get the dial and tuning knob picture out of my head.  Even looking at the manual just now, it's not much help.

Reworking the warbling solid state VFO tested my patience, but it improved the tuning smoothness dramatically.

With smooth tuning action (and no backlash) you can forgive a lot.  Like Carl, I use 10 kHz per revolution on my "day" radio (TS-890S) but slip easily back to the faster rates of the classic radios like the TS-830S and Collins 75S-3B.

73, Peter.
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VE7DQ
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Posts: 270




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« Reply #8 on: July 13, 2019, 07:55:56 PM »

Unless Heathkit changed the design between the SB-100 and SB-102, the main tuning is done with a pinch wheel driving the kHz dial.  The friction is adjusted by moving the collar bushing that retains the shaft for the tuning knob.  They are known to slip.

There's not much room there to retrofit a planetary drive in front of or in place of the pinch wheel.  I believe it would be an interesting engineering exercise however... 
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KX4QP
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« Reply #9 on: July 14, 2019, 08:04:16 AM »

My SB-102 has an obvious and consistent reduction between knob and dial -- it's something in the range of 3:1 or 4:1 -- with near enough to zero backlash.  It's not slippage.  As far as I can tell from photos, the knob, dial, and escutcheon are original type.

I've seen photos and video of several different kinds of knobs on SB- and HW- family transceivers.  Either this is a favorite item to retrofit, or Heath sold different knobs (and presumably drives) at different times.
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VE3WGO
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Posts: 449




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« Reply #10 on: July 14, 2019, 11:01:23 AM »

The tuning dials on my SB-series (301, 101, 102, etc) is about 22.5 kHz per knob revolution.  Those dials look very nice when the lighting is adjusted right.  I am thinking of getting some yellow or green coloured LEDs to improve the appearance a bit more.

I never tried it, but I think a good way to get fine tuning without damaging the radio or digging into the LMO, is to put a tuning cap across the heterodyne oscillator crystal, or some similar form of tuning network there, to turn that oscillator into a VXO.  Those crystals range from 12 to 38 MHz, and that is high enough to pull nicely with a paralleled small variable cap of a few pF. 

In the old ARRL VHF manuals, the popular VXO project there got somewhere around 50 kHz at 50 MHz with 50 pF across the 8 MHz crystals, so you could scale accordingly (like maybe for 5 kHz use a small variable cap of around 10 pF in the heterodyne oscillator circuit).  Of course doing this might adversely affect the frequency stability of the receiver a bit, and the fine tuning range will vary with each band because the crystals vary in frequency over a 3 to 1 range, therefore the capacitor's parallel effect will also vary.

But it might be worth a try.

The heterodyne oscillator is V19A (12AT7) in the SB-101, and V4 (6AB4) in the SB-301.

In a transceiver, if the parallel cap could be somehow switched in by a small relay or voltage controlled diode switch to keep stray capacitance low, then the variable cap becomes an RIT control of sorts.

73, Ed


I could get spoiled with fine tuning.  My Icom IC-9100 in CW mode with the tuning rate set to 1/4, has 0.125 Khz per knob revolution (yes, 125 Hz!).  that is good for the super narrow CW filters.
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WN1MB
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Posts: 4




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« Reply #11 on: July 15, 2019, 02:14:10 PM »

I don't understand the OP's concerns, unless there's a defect in the mechanics or a flakey component or wiring.

The HW-101 and SB-series rigs have excellent tuning rates and is very smooth. If you want to experience fast tuning, try an HW-8! Now those babies need some attention. heh.

I suspect the switchable or variable tuning rates on newer rigs may have spoiled the OP and others.
« Last Edit: July 15, 2019, 02:16:29 PM by WN1MB » Logged
W5RKL
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Posts: 1113




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« Reply #12 on: July 15, 2019, 08:06:17 PM »


The HW-101 LMO has a tuning ratio of 6:1. This is accomplished by 2 series connected Jackson Brother Ball drives.

There are a few mods to the HW-101. I tried a few and wasn't impressed by any of them.

If you really want your HW-101 to stand out, why not fully restore it with all new components, new wiring, thoroughly
cleaned chassis, new relays, and all new hardware. I built an HW-101 from scratch, took me 3 months of searching for
all the parts needed to build the HW-101. It turned out great, stability better than factory specifications. Click the link
below to see the fully restored/build HW-101 from scratch.

https://w5rkl.com/heathkit-hw-101-complete-rebuild/

I'm currently working on my second HW-101 full restoration. It's about 85% complete. Click the link below
to see the current state of restoration of the second HW-101.

https://w5rkl.com/restored-heathkit-hw-101-2/

73
Mike W5RKL
https://www.w5rkl.com


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KM1H
Member

Posts: 5491




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« Reply #13 on: July 16, 2019, 06:42:49 AM »


The HW-101 LMO has a tuning ratio of 6:1. This is accomplished by 2 series connected Jackson Brother Ball drives.

There are a few mods to the HW-101. I tried a few and wasn't impressed by any of them.

If you really want your HW-101 to stand out, why not fully restore it with all new components, new wiring, thoroughly
cleaned chassis, new relays, and all new hardware. I built an HW-101 from scratch, took me 3 months of searching for
all the parts needed to build the HW-101. It turned out great, stability better than factory specifications. Click the link
below to see the fully restored/build HW-101 from scratch.

https://w5rkl.com/heathkit-hw-101-complete-rebuild/

I'm currently working on my second HW-101 full restoration. It's about 85% complete. Click the link below
to see the current state of restoration of the second HW-101.

https://w5rkl.com/restored-heathkit-hw-101-2/

73
Mike W5RKL
https://www.w5rkl.com

The 4511/DAF Jackson is already 6:1 and was soon replaced by the Oren Elliott Products much cheaper version. Those are still in production and used by Ameritron and others. Also in the MFJ catalog. OEP also produced the VFO cap with the built in reduction of 4:1 in other products.

Carl
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G3RZP
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Posts: 1313




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« Reply #14 on: July 16, 2019, 08:39:32 AM »

Didn't the HW101 tuning cap have a built in reduction drive as well? about 1.5:1?
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