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Author Topic: Suggestions for Collins 75A-4 Headphones?  (Read 1044 times)
KY6R
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Posts: 35




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« on: October 15, 2018, 07:58:45 AM »

The headphones that sound great on new rigs (8 ohms) do not sound good in the Collins receiver. I'm guessing there are old "cannonball" headphones - but which are not very comfortable. Maybe wire up an impedance matching transformer for my headphones - or maybe just find different headphones?

What do you use?
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KM1H
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Posts: 4792




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« Reply #1 on: October 15, 2018, 08:25:16 AM »

The stock A4 does not have very good audio and unless a full overhaul of paper caps and some resistors was done it will even sound worse.
Disintegrating foam inside the mechanical filters create their own distortion problems.

I have had my A4 since 1965 and use mainly the Heil headsets as it is not used on AM.

Carl
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G3RZP
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Posts: 1159




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« Reply #2 on: October 15, 2018, 12:05:26 PM »

Carl,

I suspect that none of the mechanical filter manufacturers figured that the 1960s manufactured filters would be still be in use 50+ years later. There could well be a problem waiting to emerge with crystal filters of that era that used solder sealed HC-6/U or HC-49/U crystals.

Strange to think that it can be easier to get parts to keep a 1938 National HRO working than a 2008 rice box with through hole integrated circuits.....
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KD0REQ
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Posts: 2364




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« Reply #3 on: October 15, 2018, 02:32:27 PM »

if I had that kind of money, I'd think about 600 ohm phones. highest grade would be something from the aircraft phone makers like David Clark,
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KM1H
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Posts: 4792




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« Reply #4 on: October 15, 2018, 03:00:50 PM »

Quote
Strange to think that it can be easier to get parts to keep a 1938 National HRO working than a 2008 rice box with through hole integrated circuits.....

I know what you mean Peter and recently finished a 1941 SX-28 for a customer. A breeze compared to those ricers.

Carl
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W1BR
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Posts: 4163




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« Reply #5 on: October 15, 2018, 03:15:36 PM »

I had to replace and remove foam that turned into chewing gum in the mechanical filters in my JRC-515.  The problem wasn't only in vintage Collins filters.
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KM1H
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Posts: 4792




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« Reply #6 on: October 15, 2018, 03:24:02 PM »

The ones in the R-390A are particularly nasty and that radio is one of my favorites for SW and Ham AM using the 6 and 12 kHz filters and an outboard hi fi amp.

My HRO-60 is has too sharp IF filtering for BC quality audio.  The last thing I want to listen to is space shuttle or aircraft bandwidth AM or even SSB.
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W8RLC
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Posts: 127




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« Reply #7 on: October 15, 2018, 05:12:42 PM »

I had to replace and remove foam that turned into chewing gum in the mechanical filters in my JRC-515.  The problem wasn't only in vintage Collins filters.

Are you saying that the old foam actually caused an issue with the filter?
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G3RZP
Member

Posts: 1159




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« Reply #8 on: October 16, 2018, 12:28:22 AM »

Same foam problem with Kokusai mechanical filters, and very well known to owners of KW Electronics transceivers. In those filters with peizo-electric transducers, very often the foam produced acid which etched away the silver plating on the transducers.
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W1BR
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Posts: 4163




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« Reply #9 on: October 16, 2018, 06:15:35 PM »

I had to replace and remove foam that turned into chewing gum in the mechanical filters in my JRC-515.  The problem wasn't only in vintage Collins filters.

Are you saying that the old foam actually caused an issue with the filter?

Yes.  Massive losses.  The foam turned into a gummy mess.  I did an article on the problem for
Popular Communications Magazine many years ago.
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W8RLC
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Posts: 127




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« Reply #10 on: October 16, 2018, 07:11:40 PM »

Thank you for the information. I was not aware of the problem. I guess I am lucky that my 75A4 is working well, hopefully at some point there were some filters produced that used something that did not break down. Do you remember the year and month of the article?
« Last Edit: October 16, 2018, 07:15:06 PM by W8RLC » Logged
W1BR
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Posts: 4163




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« Reply #11 on: October 16, 2018, 08:18:41 PM »

Thank you for the information. I was not aware of the problem. I guess I am lucky that my 75A4 is working well, hopefully at some point there were some filters produced that used something that did not break down. Do you remember the year and month of the article?

My experiences related to the Japanese filters used in the JRC, I am not that familiar with the Collins 75A4 filters.

I wrote for them monthly for almost twenty years... lost track of what and when and I ditched the entire hard copy collection of those magazines last year during a cleanup. 
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G3RZP
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Posts: 1159




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« Reply #12 on: October 17, 2018, 01:35:25 AM »

As the foam problem appeared in R390 filters, I would reckon it's a fair bet that it will happen with those in the 75A4 and coming up, the 618T.
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KM1H
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Posts: 4792




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« Reply #13 on: October 17, 2018, 09:00:19 AM »

R-390A Peter, the 390 uses LC filters. Ive already had to rebuild a 800 Hz A4 filter which is actually older than most R-390A production runs.

Carl
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K0RS
Member

Posts: 1109




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« Reply #14 on: October 17, 2018, 12:48:25 PM »

I'm afraid Carl is right, the A4's audio isn't the best.  I heard an A4 side-by-side with an NC-183D and the difference was dramatic.  To make things worse, the W3HM modified (I believe that's what you have) A4 is very tiring to listen to.  I had one and reminded me of the early solid state radios with their harsh response.  I preferred my stock 75A4's audio.
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