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 Post subject: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Sun 28, 2019 8:20 pm 
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Joined: Jan Sun 06, 2013 2:14 am
Posts: 343
Location: Butler, PA
Does this look burnt?


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Dan W3DKY
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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Sun 28, 2019 8:23 pm 
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At the risk of sounding like a jerk, you may try the "smell" test. It does look a little dark...

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Sun 28, 2019 8:51 pm 
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What about the bubbles inside

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Sun 28, 2019 10:21 pm 
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The RF choke in the photo doesn't look quite right to me either.

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Sun 28, 2019 10:29 pm 
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I might need another one just for parts.

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Sun 28, 2019 10:30 pm 
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Do you have an RLC bridge, so you can measure the inductance?

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Mon 29, 2019 1:49 am 
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The tube socket looks a bit discolored also ... I think anything in that circuit would be suspect from the appearance of heat damage as far as I can tell from the photo .... I agree on the choke as well ... it looks kind of ... odd

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Mon 29, 2019 11:13 pm 
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Location: Butler, PA
Can I take a resistance test on the choke? I do have have a device that might measure inductance.what is the difference between the 32a and the 32

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 12:26 am 
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Greetings to Dan and the Forum:

I would just replace the choke. It looks to have been burnt and the cocked winding section is indicative of a large current spike mechanically damaging the winding. A replacement shouldn't be that hard to find or expensive. Perhaps someone who has a similar radio would be good enough to measure his for you.

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 2:24 am 
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I would guess the resistance of the choke would tell you nothing at all unless it read open. The phenolic coil form might be discolored from the adjacent tube heat, maybe. Are the tubes toast? I would not worry about the tank coil unless the form is actually burnt, or the coil turns are crusty in which case you could either rewind it or clean them with a toothbrush and alcohol, or metal polish and then wash off what does not wipe off with alcohol.

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 4:14 am 
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Thanks so much for all your help with this. I will take a closer look at the sweep tubes in the morning. The rfc is 1.1 mH if anyone has one for sale let me know if this is allowed. I have a B&K 700 but need to recap before I use it. I will try to make an inductance measurement also.

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 6:05 am 
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Greetings to Dan and the Forum:

I have a similar-looking choke that measures 2.7 mH. This should do if the wire size is big enough. The leads are quite short, you will have to splice onto them. However, you can have it for the cost of postage. I think the post office is getting extra money now for padded envelopes in first class; I will have to pack it up and let you know.

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 6:55 am 
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Jthorusen wrote:
I think the post office is getting extra money now for padded envelopes in first class; I will have to pack it up and let you know.

They've been doing that for years now, Jim. Anything that has to be hand cancelled. Figure about $3 & change for postage.

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 11:33 am 
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Thanks for the offer Jim but this rfc is freq sensitive and is 1.1 mh in the parts list

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 7:02 pm 
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Hi Dan!

I took a quick look at the schematics for all three Heathkit mono-banders. All of them (75 meters, 40 meters and your 20 meter radio) use the same 1.1 mH choke. Its just a choke.... it decouples RF and keeps it out of the B+ line. Since the same choke is used on all three bands, it doesn't seem to me to be value critical as long as it is equal to or greater than the original specification.

There are cases where the choke can exhibit self-resonance and cause parasitics, but since both your choke and mine have multiple stacked Pi-wound windings, this is unlikely to be a concern.

The principal thing would be to ensure that the wire size is large enough to handle off-resonance plate current for the PA. That's where the choke I have may be inadequate; you would have to compare it to your existing choke.

However, since the same choke is used in all three radios, there ought to be one from a parts radio out there somewhere.

Good Luck,

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 7:10 pm 
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Location: Butler, PA
Thanks I just won a hw-32 on eBay for an offer of 50.00 plus shipping. Now I will have a parts machine plus tubes. I have some chokes in my junk box plus I can buy 2.5 my everywhere. Let me look around and c what I have. Thank for that research
73

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: Apr Tue 30, 2019 9:40 pm 
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Location: Butler, PA
Is the Hw-32 a grid driven tetrode or a grounded grid cathode driven amp?

When you are reading about tank circuits like my L4 coil and my final tune cap 5-50 pf do all of these descriptions mean the same thing or the same car cap?

Final tune cap
Plate tune cap
Tank tuning cap
Output cap
Load cap
Antenna coupling control

Thanks

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: May Sun 05, 2019 12:25 am 
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I found two new rfc plate chokes in my parts box. Which should I use.
1) 988 micro Henry 3 pi
2) 2.53 mh 4 pi
The one I need is a 1.1 mh 4 pi

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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: May Sun 05, 2019 4:41 am 
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If it were my transceiver I would give the 988 ( 1mhy) choke a try. It should be close enough to do the job. Chokes larger than required sometimes cause strange tuning effects in a final amplifier. I ran a HW32A for many years here and found it very reliable on a HB power supply.


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 Post subject: Re: HW-32A Tank Circuit L4 Coil
PostPosted: May Sun 05, 2019 4:50 am 
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Okay I rebuilt a hp-23a last year. The strange thing is that all three mono benders use the same size choke

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