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I've got a Heathkit AR-29 and need some parts for MPX board

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Posted on October 2, 2020 at 19:54:34
redpackman@aol.com
Audiophile

Posts: 5
Location: Minnesota
Joined: October 2, 2020
 No, it's not the chip. I believe mine is working. I have two broken coils on my MPX board. The one I really need is the L-307 which I believe is the 70 mH low pass filter. Marked 40-957. It's shattered. I could also use a L-304 which is the 20 mH Low pass filter, but I've patched it together with some instant glue an hope it holds. It is marked 40-956.

If you don't have either of these could those of you experienced in Heathkit (I'm brand new after I got this cast-off unit which works well except the MPX section) where I might find these parts.

I could also use an FM Antenna plastic bracket (the piece that fits AROUND the antenna and is bolted to the arm extending from the receiver (mine broke at that point).

Any help would be appreciated.

 

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RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 2, 2020 at 22:30:34
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 I'm guessing you need micro (μ) henry inductors, not milli (m) henry parts.

Look here for parts quite close to the values specified.


Eli D.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 01:06:45
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 You are right about Mouser, quality stuff and not too bad on prices. Realize that they, Digikey and Newark are now part of Element 14. They do have different stuff still.

Still, you are never going to find one that fits exactly. You might have to drill the board or bend the pins. However it doesn't really matter at those frequencies.

Actually you can wind your own. The formula is online somewhere for turns and diameter. But you need a core and that is where a parts place can come in handy. You have to find that first to get the permeability of it for the calculation.

After that use an LCR meter to check the value. If necessary you can add or remove turns.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 01:16:14
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 https://www.mouser.com/ProductDetail/Bourns/5730-RC?qs=vBs3sXYVMrCNkvRob8YzvQ%3D%3D

They got a cheaper one with axial leads but assuing it is on a circuit board this is better.

They don't seem to have the 20uH, Digikey shows up. I hate ordering sit from two different places.

If you glued the 20uH together it is definitely not in spec.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 01:30:34
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 HA, Mouser can't seem to find it but Google found it, AT MOUSER ! LOL

https://www.mouser.com/Passive-Components/Inductors-Chokes-Coils/_/N-5gb4?P=1z0wpjl

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 09:53:08
redpackman@aol.com
Audiophile

Posts: 5
Location: Minnesota
Joined: October 2, 2020



Here's the schematic for the AR-29 and also a file that zooms in on the problem components just so we're all on the same page as far as the right fixed inductors and their tolerances. My problem components are L-304 20 mH inductor/filter and L-307 70 mH inductor/filter. I'm a total novice at this, so forgive my ignorance.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 13:44:25
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 The "arrows" on the inductor symbols indicate adjustable.

It seems my guess about μH. was wrong. FWIW, I was thinking RF parts, but those chokes are part of a 15 KHz. low pass filter.

Can photos of the parts, with a coin for scale, be posted?


Eli D.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 15:33:54
Jim McShane
Dealer

Posts: 5910
Location: Chicago
Joined: January 13, 2003
 Just FYI -

Mouser is owned by Warren Buffett - it's a Berkshire-Hathaway company. And Digi-Key is a privately held company.

The information above is sourced from Dun & Bradstreet.

Finally, Newark Electronics is a part of the Avnet group of companies. In the Newark logo it says it's an Avnet compnay.

So the 3 firms are not related.

Edited to correct typo...

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 15:39:43
rivervalley817
 I for one miss the old MCM Electronics

ah well,

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 16:15:13
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 MCM was owned by the same folks as Newark. For whatever reasons (profit among them), MCM was "folded" into Newark.

Go to Parts Express for some of the stuff that used to be sourced from MCM.


Eli D.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 18:41:39
rivervalley817
 thank you Eli. I have PE already bookmarked. I order from them via Amazon to cut / consolidate shipping costs

regards,


 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 20:42:09
redpackman@aol.com
Audiophile

Posts: 5
Location: Minnesota
Joined: October 2, 2020



Here's a photo showing the damage.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 20:44:39
redpackman@aol.com
Audiophile

Posts: 5
Location: Minnesota
Joined: October 2, 2020



Here's a photo with the coin you suggested so you can get an idea about size.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 3, 2020 at 22:02:32
Eli Duttman
Audiophile

Posts: 10455
Location: Monroe Township, NJ
Joined: March 31, 2000
 Sure appears to be mH. sized and adjustable.


Eli D.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 4, 2020 at 02:36:18
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 https://www.google.com/search?q=element+14+compaies&rlz=1C1AOHY_enUS781US781&oq=element+14+compaies&aqs=chrome..69i57j0.8490j0j8&sourceid=chrome&ie=UTF-8

They say element 14 so they are affiliated somehow. That doesn't require they be owned.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 4, 2020 at 06:31:24
stellavox
Audiophile

Posts: 413
Joined: June 23, 2004
 First of all, try bypass the whole circuit (both broken coils) with a piece of wire and see if the channel comes back to life. If not something else is also wrong.

A large reason for the use of this filter was to keep the 19Khz (and 38Khz) multiplex signals out of the audio output because, when used with a tape recorder, it caused audible intermodulation problems with their bias oscillators. If bypassing the broken coils restores the channel AND you can't hear any other "artifacts" you could just stop there and enjoy.

20 and 70 millihenry variable inductors are relatively LARGE values - but then again you are "only" working at 19 Khz. Miller and Millen used to make these "air wound" adjustable coils but you can only probably now find them surplus. In the pic, it looks like the stock coils were wound inside ferrite cores which helped reduce their size.

Depending on how far you want to go with a repair, you could try putting in FIXED value inductors, which should be available from Mouser/Digikey and make the parallel caps variable. In any case, when repaired you'd have to "tune" the filter, which would require some kind of an audio oscillator to send it a signal and a way to look at the output (like with an oscilloscope) so you could null out the 19K as well as possible.

In any case - Good Luck

Charles


O yeah, regarding the antenna - if it's a "loopstick" - a 6"? ferrite rod with coil(s) wound around it - you could try looking in the miscellaneous drawers in the the hardware section of your local store - look for a plastic cable clamp that would fit around it and then figure out how to attach the screw end of the clamp to a bracket of some sort or maybe glue it to whatever's left of the original bracket

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 5, 2020 at 12:26:45
Jim McShane
Dealer

Posts: 5910
Location: Chicago
Joined: January 13, 2003
 Their only relationship is that they are all distributors/sellers of electronic parts. They are competitors, along with Allied and Arrow and some other smaller firms.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 7, 2020 at 11:45:05
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 I was thinking after seeing the picture. Then I consulted the impedance nomograph and those are indeed milliHenries, not microHenries.

Still Mouser has them, not to bad price for the small ones. The big ones for use in power supplies for tube equipment are quite pricey and won't fit the board anyway - but I bet they never saturate. :-)

I am seeing three bucks, six bucks. They are fixed but it is specified ad really, to ust adjust them to that inductance ? Why ? Nobody else seems to use adjustable inductors in their pilot and carrier filters.

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on October 18, 2020 at 05:06:50
JURB
Audiophile

Posts: 2056
Location: North Ohio
Joined: May 29, 2016
 So what happened with this thing ?

And BTW that is actually a pretty good filter.

Of course nothing beats a pilot canceller. There are engineering difficulties implementing them There hs to be a filter anyway so there is a phase shift. That means a whole nother PLL. I kinda wish there was a sort of universal add on for that. They got one for some wideband IF old FMs that get noise due to the digital data running with the signal, so why not this ?

Anyway, equivalent coils can be had, so where are we at here ?

 

RE: I've got a Heathkit AR-29 and need some parts for MPX board, posted on April 21, 2022 at 17:24:30
hkaplan131@gmail.com
Audiophile

Posts: 1
Location: Phoenix,AZ
Joined: April 21, 2022
 I found a part that is useable for L306 on the AR-29 from DigiKey. It is a 22 mH adjustable coil that can be used in place of L306. The cap across the coil will need to be removed from the broken coil and soldered to the PCB. Her are the details of the part -
Digi-Key Part Number
4161-CTCLNSF-T1034Z-ND
Manufacturer
Central Technologies
Manufacturer Product Number
CTCLNSF-T1034Z
Description
22.0 MH VARIABLE COIL

The large value inductance for L307 is no longer available.
Detailed Description
22 mH Adjustable Inductors 70 @ 79.6kHz Radial

 

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