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 Post subject: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Mon 05, 2018 10:55 am 
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Joined: Sep Mon 05, 2011 1:42 pm
Posts: 814
Location: Philadelphia, PA
Hi -

The vernier for the VFO on my Heathkit HW-8 is slipping so that I can't tune down to the last 25 kHz of the band. I know that there is a direct replacement available (https://tinyurl.com/ycx9l652) but it's very pricey. Does anyone have any tips about how to fix this issue?

Thanks -

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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Mon 05, 2018 2:13 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 5171
Dan,

Usually the problem on these is the reduction drive has so much torque capability that people end up breaking the capacitor trying to turn it too far. Is your drive actually slipping before it reaches full mesh?

If it is slipping before full mesh check that the capacitor isn't binding due to a bent plate or debris buildup in the bearings. It should and must move reasonably freely for the reduction drive to work. You may need to get some oil into the rear thrust bearing which can usually be done by putting a couple of drops at the shaft/bearing/rear frame interface.

Any chance there is a misalignment somewhere when the kit was built putting excess stress on the drive or capacitor? Examine and make sure everything lines up correctly.

If the capacitor is turning freely but the reduction drive still slips it is probably repairable. I have never gone into the specific HW-8 drive (mine fortunately works fine) but I have repaired several similar ones where you have to bend back the "ears" that hold it together and then clean and lubricate the reduction mechanism. You might be able to find a replacement reduction drive that will fit; Dan's small parts carries an exact replacement for the HW-9 but I don't know if he or someone else might have the same replacement for the HW-8 at far less than the price of the reduction drive and capacitor.

If your capacitor is OK and it is just the reduction drive I would at least attempt to repair it. I have repaired numerous drives like this and all have come out in workable condition. It isn't the most fun you will ever have but it isn't as bad as most dial restringing tasks.

Rodger WQ9E


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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Mon 05, 2018 2:33 pm 
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Joined: Jun Mon 22, 2015 6:21 pm
Posts: 205
Location: Bath, Maine 04530
I have also had to repair my HW-8 tuning cap. The plates were pulled out of the shaft. I pounded them back in place with a ball peen hammer and they stayed with out adding any glue or locktight. The problem comes from the amount of torque from the reduction drive. I made stops to prevent this from repeating it self. Here is a picture showing the stops. The one on the bottom is hard to see but it's the same as the top one. Doing it this way will let you make adjustments and center up the dial. Hope this will help someone. Carl

PS I am a retired machinist and the ball peen hammer is a very small one we make for fine tuning. HI HI

Don't know why the picture came out so small. I'll try it again.


Attachments:
HW-8 VFO.jpg
HW-8 VFO.jpg [ 22.49 KiB | Viewed 270 times ]

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Last edited by Cwebs on Feb Mon 05, 2018 6:52 pm, edited 1 time in total.
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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Mon 05, 2018 2:41 pm 
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Joined: Jun Mon 22, 2015 6:21 pm
Posts: 205
Location: Bath, Maine 04530
Let's try this. Now that is better
Set the reduction drive so the two set screws are at 12 and 3 o:clock and replace the 12 o:clock one with the longer screw. This will let you set the dial. If you use the 3 o:clock one you won't be able to get at the other set screw. Set the two stop screws befor you replace the unit and you should be close. Carl


Attachments:
HW-8.jpg
HW-8.jpg [ 126.05 KiB | Viewed 268 times ]

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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Tue 06, 2018 4:02 pm 
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Joined: Sep Mon 05, 2011 1:42 pm
Posts: 814
Location: Philadelphia, PA
Roger and Carl, thanks for your replies.
I realize I misspoke in my original query - the issue is that I can't reliably tune to the first 25 kHz of the band - in other words, the tuning cap won't open all the way.
The capacitor is okay - none of the plates are bent or loose, and I can gently get it to open all the way by applying pressure with my fingers.
I think I may try to get the reduction gear apart and try to clean and lub it.

Thanks again -

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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Tue 06, 2018 4:09 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
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If the capacitor is rotating smoothly and the slippage is only over the last part of the range it might be possible to loosen and rotate the reduction part of the mechanism 180 degrees to see if that takes care of the issue before you take it apart. If it is slipping it probably needs attention but you might consider the non-invasive rotation alternative if that is possible given the mechanical setup of the HW-8. It has been too long since I have been inside one of these to note whether or not a 180 degree rotation and re-installation of the reduction mechanism is possible.

Rodger WQ9E


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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Tue 06, 2018 4:16 pm 
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Joined: Jun Mon 22, 2015 6:21 pm
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Location: Bath, Maine 04530
rsingl wrote:
If the capacitor is rotating smoothly and the slippage is only over the last part of the range it might be possible to loosen and rotate the reduction part of the mechanism 180 degrees to see if that takes care of the issue before you take it apart. If it is slipping it probably needs attention but you might consider the non-invasive rotation alternative if that is possible given the mechanical setup of the HW-8. It has been too long since I have been inside one of these to note whether or not a 180 degree rotation and re-installation of the reduction mechanism is possible.

Rodger WQ9E

Rodger, I think to do that would mean backing off the two set screws and turn the cap shaft 180. If he turns the mounting screws 180 that won't change the contact area to the unused area. I might be wrong...Carl

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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Tue 06, 2018 4:38 pm 
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Carl,

Having now had coffee I agree with you :) I would leave the mechanism in place, loosen the set screws, and try a new range on the reduction drive. It is a 360 degree continuous rotation so he might find that the issue is from wear to a specific point on the shaft and/or ball bearings and setting it up so that a different point of rotation is used might cure the problem.

The drives RME used on their 4300/4350 and matching VHF 126 converter are famous for problems made worse by RME's instructions to increase the pre-load on the mechanism if it slips. I have dissected a couple of these and the problem appears to be a soft center shaft compared to those used in other mechanisms (like those by Johnson). it might be possible in the RME setup to turn the shaft down slightly and then go up one size on bearings but I haven't tried that process.

Rodger WQ9E


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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Fri 09, 2018 12:58 pm 
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Joined: Sep Mon 05, 2011 1:42 pm
Posts: 814
Location: Philadelphia, PA
Disaster. I was applying a tiny bit of oil to the capacitor when my oiler basically exploded. Not too much oil got on the circuit boards, but enough that I'm afraid to power the radio up. Guess I'll just try it very slowly on the variac.
And my efforts to disassemble the reduction drive pretty much failed, so I'm on the lookout for a replacement VFO assembly.
Some blame shifting - the previous owner of this HW-8 replaced the VFO knob with a very heavy metal knob - I suspect the extra weight has the root cause of the problem.

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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Fri 09, 2018 1:35 pm 
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Dan,

Oil is generally not conductive but clean it off so that it doesn't attract dust/debris buildup. With the low voltage HW-8 I seriously doubt if you have done any damage other than cosmetic/cleaning.

When something gets wet that shouldn't I often use WD-40 (WD stands for water displacer) as first aid and what remains after the lighter distillates of WD-40 evaporate is the light oil that is mixed in.

As I recall, and looking at the photos kindly provided by Cwebs, you have a little bit of spare space in a HW-8. You may be able to find a suitable substitute without finding a HW-8 parts unit and one of the commonly found reduction knobs may be a good "guts donor" to provide a reduction mechanism as replacement. Maybe one of the small Jackson drives would fit.

Rodger WQ9E


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 Post subject: Re: Heath HW-8 VFO Vernier Slipping
PostPosted: Feb Fri 09, 2018 2:44 pm 
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Joined: Jun Mon 22, 2015 6:21 pm
Posts: 205
Location: Bath, Maine 04530
Like Rodger said, I also use WD 40 for cleanup as well as cleaning out pots when noisy. Tip the rig so everything will drain out onto rags and let it dry . It might leave a little wax coating but no problem. If you are mechanical you should be able to repair the cap but a try won't cost you anything. Go for it. Let us know how you make out and a picture of the cap will help. Carl

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