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Author Topic: Search a Collins 75A4  (Read 822 times)
DG2AT
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Posts: 20




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« on: November 04, 2018, 03:47:52 AM »

Hi,

would like to buy a restaurated Collins 75A4. Anyone know where i can ask or looking for?
Tnx for any helpful hints.

73, Jan
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AC2EU
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Posts: 1455


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« Reply #1 on: November 05, 2018, 06:27:47 AM »

I think "restored" is what you meant.
Here's one on ebay that looks to be in excellent original shape , but NOT listed as restored.
https://www.ebay.com/itm/Collins-Model-75A-4-Receiver-Amateur-Bands-/202471461760

You may have to find one like the above, then have someone do the restoration.
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N2DTS
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Posts: 951




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« Reply #2 on: November 06, 2018, 11:31:16 AM »

Not worth the money they pull down, but very nice looking.
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KM1H
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Posts: 4796




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« Reply #3 on: November 06, 2018, 12:51:30 PM »

If you want a frequency meter buy a Collins, if you want to be able to hear the weak ones buy a National and get much better audio included; and if you want automatic tuning of the band buy a Hallicrafters or Hammarlund.

Ive owned a much modified 75A4 since 1965 and it is the best Ive ever used for digging into the noise on 160 and 80 CW DX signals.

Carl
Ham since 1955
National Radio 1963-69
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AD4U
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Posts: 2537




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« Reply #4 on: November 08, 2018, 05:27:37 AM »

No help here trying to find a 75A4 but I ditto the above comments.

A friend K4IVK gave me his 75A4 when he went into a nursing home. Since I got it for free, I sent it to Howard Mills to be updated and restored. Howard installed ALL the factory updates and (with my OK) he installed modifications that he recommended. My 75A4 only had the 3.1 KHz filter. Howard added the true Collins 2.1 KHz and 500 KHz filters.

I can imagine how wonderful a 75A4 was in the 1950's when used beside other receivers of the era. WOW!

IMO and On The Air (not in a lab) on 160-80-40 meters my 75A4 will "hear" anything that any modern ham receiver will "hear" and will "hear" better than most.

I don't own any of the $10,000 whiz bang rigs on the market today, but my 75A4 will still "hear" just about anything any of my other 40 rigs will "hear" on 20-15-10 meters and better than most on the lower bands.

If you find a good one, you won't be sorry.

Dick AD4U
« Last Edit: November 08, 2018, 05:30:02 AM by AD4U » Logged
KM1H
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Posts: 4796




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« Reply #5 on: November 08, 2018, 06:57:43 AM »

Quote
I don't own any of the $10,000 whiz bang rigs on the market today, but my 75A4 will still "hear" just about anything any of my other 40 rigs will "hear" on 20-15-10 meters and better than most on the lower bands.

If your into BA's and have the test equipment for those then the 75A4 is much easier to refurb than many others for a fraction of the cost. The real money spent is for making it look new which many dont care about since they want to actually use them regularly and not have to worry about getting a little scratch.

I like to use a slightly souped up HRO-60 and 75A3 on 10, 12 (60 only) and 15 AM and they will equal or beat any SS rig Ive owned or repaired/evaluated since the noise figures are all way up in the ~12-15dB range. Then toss in phase noise and other crud along with a marginal audio stage.

Carl
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N2EY
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« Reply #6 on: November 08, 2018, 10:00:13 AM »

No help here trying to find a 75A4 but I ditto the above comments.

I can imagine how wonderful a 75A4 was in the 1950's when used beside other receivers of the era. WOW!


Collins' first amateur receiver was the 75A prototype, circa 1947. It was revolutionary for its time, and Collins followed up with the 75A-1, -2, -3, and -4. Each was smaller and lighter than its predecessor.....a 75A-1 weighs 57 pounds, a 75A-2 weighs 50 pounds and a 75A-4 weighs only 35 pounds. A 75A-4 weighs 61.4% of what a 75A-1 does.

The 75A-4 sold for $595 when introduced, and rose to $695 by the end of its run. That's just the receiver with one mechanical filter - add an accessory filter and the reduction knob for about another $75.

Think about what those mid-1950s prices amount to in 2018 dollars.....

There are improvements to the 75A-x receivers that improve the performance even more. One popular mod is a 6GM6 in the RF amp, a 6ES8 in the first mixer and a pentode 6EA8 in the second mixer. (6BA7s are the best of the pentagrid mixers, but noisy).

73 de Jim, N2EY
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AC2EU
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« Reply #7 on: November 08, 2018, 12:27:23 PM »

No help here trying to find a 75A4 but I ditto the above comments.

I can imagine how wonderful a 75A4 was in the 1950's when used beside other receivers of the era. WOW!



The 75A-4 sold for $595 when introduced, and rose to $695 by the end of its run. That's just the receiver with one mechanical filter - add an accessory filter and the reduction knob for about another $75.

Think about what those mid-1950s prices amount to in 2018 dollars.....


73 de Jim, N2EY

Sounds like it was the "whiz bang $10,000 rig" of the 50's .
I think you could buy a new car for about $1500 back then.

The more things change, the more they stay the same, eh?
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KM1H
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« Reply #8 on: November 08, 2018, 02:49:08 PM »

Quote
Think about what those mid-1950s prices amount to in 2018 dollars.....

There are improvements to the 75A-x receivers that improve the performance even more. One popular mod is a 6GM6 in the RF amp, a 6ES8 in the first mixer and a pentode 6EA8 in the second mixer. (6BA7s are the best of the pentagrid mixers, but noisy).



Those inflation formulas need to be taken with a grain of salt as the buying power of the US Dollar varied. As a HS teenager I was able to buy quality US ham gear with no problem and only had part time low paying jobs.

Yes, Ive been mentioning the 6GM6 for many decades now ever since its use was suggested in QST around 1964. I elected to use 7360's from another 60's article in both mixers in 1965 after evaluating just the first mixer mod and find them just about overload proof.  The 6ES8 is a good tube but it seems very few take advantage of its semi remote cutoff characteristic and apply AGC to the grid. The 6ES8 was the only consumer grade twin triode Im aware of that did that.

In tests Ive run Ive found the 6BY6 (developed specifically for the FM band) to have less noise than the 6BA7 but they are not interchangable without a bit of work. National appeared to find the 6BZ6/6BA7 low noise sweet spot in the NC-300/303 while the 6DC6/6BA7 in the 75A4 is a poor performer in comparison. Swapping in a 6GM6 in the 300 here resulted in only a meaningless .15uV improvement.

Collins had the commercial/military mind set and didnt push high sensitivity performance nor ham requirement AGC as it wasnt that important. It wasnt until the 75S3 that they built a great ham receiver; BUT the 200 kHz tuning range was a huge mistake IMO.


Quote
I think you could buy a new car for about $1500 back then.

My parents bought a new 1952 Plymouth Cranbrook sedan with the deluxe radio for $2200 IF I remember correctly. After that they went to Buick and Olds and their last one was a 69 Olds 98 sedan. Dad had decided buying new was a bad idea and bought 2-3 year old more upscale trade in puffs from the dealer and never regretted it.

Carl
« Last Edit: November 08, 2018, 02:57:24 PM by KM1H » Logged
WA4JQS
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Posts: 277




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« Reply #9 on: November 08, 2018, 02:54:25 PM »

I agree they hear very well. I used a few 75A4's in the Navy very nice receiver my dad WA4LLK sk. left me his 75A2 it still has the the green tag and the allen's hanging inside. He had also bought a RME sideband adapter for it.. why he never got the matching speaker i have no ideal. but the Hallicrafters big reflex speaker sounds great. I dont think he ever changed a tube in it either.. i turn it on and tune around on 80 and 160 everyweek or so and it hears just as well as my Kenwood ts950sdx and TS 870's.
I did recap the RME this summer as it started humming on me. the big 4:1 spinner knob is something else.. thought a few times about selling it but change me mind.. but at 72yrs now guess i should really think about finding it a good home..
73 Tony WA4JQS
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