Another AL-80A plate choke

[NM7G]

I've read plenty about AL-80A choke resonance problems and recommendations to replace the original pl. choke with an AL-80B unit. Here's where I'm baffled: Photos I've seen of an AL-80B show a plate choke with three separated windings. One ham reported a 17m resonance in his 80A, but his plate choke was one continuous winding (ostensibly something Ameritron did with the earliest serial number amps), later changing to a different choke. The plate choke in my (S/N 2014) AL-80A, has FOUR windings on a ceramic form that otherwise looks much like the 80B unit. Has anyone else had a 4-winding choke in their 80A, and from where did it come? Is it from some other Ameritron amp or otherwise? I'm reluctant to try the amp on 17m or 12m until I get this sorted out. Thank you!

[W1QJ]

It seems that someone already changed your AL-80A choke to the AL-80B choke. I've sold many AL-80B chokes to AL-80a and SB-1000 owners. Have more to sell.

[K1ZJH]

Isn't Ameritron selling one plate choke for all of their model amplifiers at this time?
I just picked up one direct for a good price, thanks to advice from KM1H.
Pete

[NM7G]

I guess my question was unclear. I have a plate choke in an AL-80A (S/N 2014) that's not like the "one size fits all" for $20 that MFJ is selling. P/N 10-15197 has three windings spaced along the form (per the photo on their site), and mine has four windings. I found no part number on the choke in my amp. Photos I've seen of an 80B choke look like the 10-15197 in that both have three separated windings, so mine appears not to be for an AL-80B. My choke does not look like a homebrew job.

So, my question is this: Did some AL-80As ship with a choke with four separated windings? If my 80A wasn't shipped with the pl. choke that's in it, and it's not the universal choke (P/N 10-15197), then a prior owner replaced the original choke with an unknown type choke, or Ameritron was experimenting with different chokes. I'd like to know the choke belongs in the amp.. It definitely doesn't look like p/n 10-15197 on MFJ's web site, but it's possible they forgot to update the web photo.

I don't know the choke I have belongs in the amp. I'll call MFJ if no one has heard of this before.
Gary

[K1ZJH]

Yes, they did.

http://cgi.ebay.com/ws/eBayISAPI.dll...m=110727765186

Too bad Tom, W8JI isn't actively posting right now, he would be the man to ask about the AL-80A.

Pete

[W1QJ]

The AL-80A was a long running amp design. It started before the WARC bands were introduced. So the earlier model AL-80A amps had one continuous winding to satisfy 160-10 meters. Later when the WARC bands were introduced a newer plate choke came in the amp to satisfy the WARC bands. That choke was a space wound choke. Later, when the AL-80B came out it too had a space wound choke that was a bit different. I don't know the reason for it being different than the first run space wound chokes in the late AL-80A amps. Obviously for some reason Tom changed the design to a 4 section space wound unit. I can only guess why the design was upgraded and I will make that guess and say that perhaps the 3 section design worked just fine on the WARC bands except in cases where perhaps the owner of the amp ran high power RTTY or digital modes and the choke heated up and failed only on those modes. Another guess might be that the WARC bands did not all come about at the same time. If a WARC band was added later than the production of the amp, then a change would have to be made to the plate choke if there was a resonace close to the new WARC band. It could also be that Tom just simply improved a bit. Don't forget when the WARC bands came into play the radios and amps all had to change to satisfy the need. I am sure that sent the manufactuers scrambling. NO? In fact, not too many amps specifically have individual WARC band positions on them. Some do and some recommend sharing a regular band.

[K1ZJH]

I've read that the early choke has a series-resonance the 17 meter WARC band.

Pete

[KM1H]

It simply boiled down to having to re engineer the choke a few times until they got it right by using customers as their testers....typical for that outfit. Glad youre satisfied Pete, I buy lots of those chokes now for retrofits in several amps, cant beat the price. Before I wouldnt touch them and wound my own which was time consuming.

Carl

[K1ZJH]

Thanks for the tip Carl. And it will fit will no mechanical issues.

Pete

[NM7G]

It simply boiled down to having to re engineer the choke a few times until they got it right by using customers as their testers....typical for that outfit. Glad youre satisfied Pete, I buy lots of those chokes now for retrofits in several amps, cant beat the price. Before I wouldnt touch them and wound my own which was time consuming.

Carl

O.K., thanks guys. Now I know this choke likely came from Ameritron in the amp., and I saw the 4-space-wound on eBay. My first thought when I saw that the 80B uses a 3-space-wound is that it mounts horizontally, so undoubtedly stray capacitances are different in the 80A and 80B, perhaps (???) accounting for the 3 versus 4 configuration. Frankly, I'm skeptical about them selling one choke for all amps for that very reason. Resonances can't be the same in all amps, but then maybe none of them are harmful resonances with p/n 10-15197. This issue wouldn't be a big deal for me, but I like the WARC bands a lot. Since Tom hasn't made an appearance, I'll call MFJ and ask if I should replace my choke with the "one-size-fits-all" model. Really appreciate your help!

Gary