[Collins] Collins ham gear redesign

[Carl]

> I've been following this thread and you and Gerry win the "Big dick" 
> contest


My 47 yr old GF already knew that (-;


> so zip up....the guy in Texas wins the wannabe contest
>
> I have an S-line with 62S-1 , R-390A and a TenTec Omni6+
>
> Once upon a time I had a 75A3.......changed mixers added a product 
> detector in the FM socket...there is no changing a sows ear into a silk 
> purse


AMEN to that. The contingent at the CCA and elsewhere that fanatically 
believe Collins could do no wrong notwithstanding.
I havent gone beyond a full overhaul with my A3 but it will get several mods 
before it becomes a daily driver. The first will be 6ES8 Pullen mixers and 
product detector and then tackle the AGC for AM as well as SSB/CW since it 
came with CW and SSB filters but will mainly be used on AM.

A 32V3 was also part of the one owner package and that will get some work to 
the audio to remove the narrowed audio harshness plus the distortion over 
80% modulation.

No visible mods or extra holes.


> Bonafides a BBA in accounting and an MBA in Finance....Infantry 
> MOS...lotsa time in Ham Radio
>
> BTW I've never heard Carl on VHF


Well, I could answer that if I knew your call and location.
Why so secretive?

Carl
KM1H


>
> -----Original Message----- 
> From: Carl
> Sent: Tuesday, July 08, 2014 2:14 PM
> To: geraldj at netins.net
> Cc: collins at mailman.qth.net
> Subject: Re: [Collins] Collins ham gear redesign
>
>
> ----- Original Message ----- 
> From: "Dr. Gerald N. Johnson" <geraldj at netins.net>
> To: "Carl" <km1h at jeremy.mv.com>
> Cc: "Glen Zook" <k9sth at sbcglobal.net>; <collins at mailman.qth.net>
> Sent: Monday, July 07, 2014 6:33 PM
> Subject: Re: [Collins] Collins ham gear redesign
>
>
>>>>
>>
>>>> What would you have designed differently?
>>>>
>>>> I think I would searched for a remote cutoff pentode for the 75S IF
>>>> with more gain than the 6BA6 so the two stages didn't have to be
>>>> run up at their power dissipation limit to get the desired gain and
>>>> I would have complicated the power supply to have a 250 or 300 volt
>>>> output for a more common 6AQ5 output stage that was cathode biased
>>>> instead of fixed biased from the fragile bias supply to have gotten
>>>> the desired audio power with less heat from the output tube. I
>>>> would have never used a selenium rectifier for the bias supply
>>>> either.
>>>
>>>
>>> There were plenty of better tubes than the 6BA6 by the time the 75A4
>>> came along. The use of a single triode was a poor choice for a mixer,
>>> a dual triode such as the 12AT7 would offer more conversion gain and
>>> a high degree of overload handling followed by improved gain
>>> distribution..
>>
>> Ah, the mixers. The 75A receivers used pentagrid mixers that have a few 
>> known characteristics. Easily overloaded, and very noisy.
>
> ** I found that out the day I bought my just purchased A4 into the R&D lab
> at National. It soon had 7360's in both mixers with a 6GM6 RF amp and some
> gain redistribution; its a very robust receiver that I still use. With
> recent reproduction and cascaded 800Hz filters it outperforms any ricebox
> Ive ever tried for digging under the noise on 160/80 CW
> There is something to be said for a premium level non synthesized radio 
> with
> no detectable phase noise and "artifacts" present in modern gear. That was
> also my reason for the TS-830's as expanded below.
>
>
>>
>> The 6U8 and 6AU8 in the S-line were not great choices either.
>
> ** The 6U8 was failure prone, the 6U8A fixed that and the 6EA8 fixed the
> remaining problems and was used in applications for many years as a
> workhorse tube. While a few say they werent interchangable I havent run
> across any examples and the swap was either beneficial or no change. In my
> CE-100V and 200V, for example, the 6EA8 had better performance to 30 MHz 
> and
> emission stayed high a lot longer.
> It certainly would not be my choice in a receiver signal path however.
>
>
>
> I traced
>> the noise sources in my new S-3B (it spent a year on its side out of the 
>> case after I moved to Texas) and found that the second mixer was the 
>> primary noise source because the gm of the pentode of a 6AU8 was low, and 
>> as a mixer it was way lower. That limited the dynamic range of the 
>> receiver on both ends. I installed an adapter holding either a 6688 or 
>> 7788 from Amperex with 50,000 umhos in place of the 6AU8 with 4000 umhos 
>> and then was able to drop the signal into the second mixer seriously.
>
> ** Those are serious tubes with a short life and hard to tame as Racal 
> found
> out. Serious overkill for HF.
>
>
>
>> With a nuvistor 2m converter in front of it, I took the signal from the 
>> 600 watts of W5WXV at about 20 miles from showing about 20 spurs in 200 
>> kHz down to three and one of those was where he was supposed to be and 
>> the other two were close to the noise level. I did take the receiver gain 
>> a little further down than was great on HF but I didn't hurt the system 
>> NF with the 2m converter out front.
>
> ** I still have Ameco 2 and 6M nuvistor converters somewhere and also a
> W2AZL 417A 2M converter I built in 66 and preferred over the Ameco. A few
> years ago it produced a 1.2dB NF at the NEWS Conference which is better 
> than
> most rice boxes.
>
>>
>> A ham at Rippey Iowa who sold prop pitch rotors and remote antenna 
>> switches also sold a drop in replacement for the first mixer using a 
>> double gate MOSFET. He didn't agree that the second mixer was the 
>> limiting factor, but then if he didn't see it raining he would not 
>> believe it if I told it was raining. George McKercher was his name. He 
>> drove a pair of 4-1000A on HF with his S-line. With the plate variac at 
>> half voltage he only peaked at 1 amp and 3 KV on the meters when chasing 
>> DX with a visitor present in the shack.
>
> ** These days some use a commercial 1200-1500W amp as a driver stage for a
> real tube!
>
>
>>>
>>>
>>> OTOH Collins didnt have a decent AGC for any mode on any model until
>>> the 75S3C. I modified both of my contest grade R4C's using that
>>> circuit plus added a Medium position.
>>
>> The 3B and 3C were the same receiver except for the extra crystal board 
>> until very late production. I never noticed a problem with the AGC in my 
>> May 1964 3B. I copied that dual time constant filter to the Q-5er.
>
>
> ** Back then there was no Internet and all I had was a S3C on loan with 
> its
> manual.
> The NCX-3 and NCX-5 also have a superb receiver path and AGC which I didnt
> appreciate back then as I had no use for transceivers with limited 
> features.
>
>
>>>
>>> The 75A family was even poor on AM for ham use, other brands were
>>> much better; heck my 1941 SX-28 or NC-200 is much better. The HRO-60
>>> is a dream to use as a battle conditions AM radio. The A4  AGC was a
>>> joke on CW/SSB and was one of the first things I changed with mine in
>>> 65.
>>
>> There is a problem with the 75A-4 and replacement tubes. I have a project 
>> very slowly in the works to compare RCA 6DC6 to ECG 6DC6. They give an 
>> A-4 wildly different AGC characteristics with the ECG tubes acting more 
>> like 6AH6, sharp cutoff at a lower bias voltage than the RCA or ordinary 
>> 6BA6. Abd that also changes the S-meter calibration significantly.
>
>
> ** Likely remarked 6AH6's. Relabeling was a big business back then but the
> 6DC6 never impressed me in any Collins or Hallicrafters. My favorite swap
> has always been the 6GM6 in the 7 pin family if performance above about 15
> MHz was important, it varied by radio. In a NC-300 the 6GM6 improved 10M
> sensitivity over the stock 6BZ6 by about twice comparing several of the
> hottest NIB of both, but since the AM 10dB SNR was already below .25uV you
> need a good location and a highly directive yagi in order to benefit. 
> Since
> I have both it is the usual go to radio on 10AM only, I use my TS-950SD 
> for
> CW/SSB.
>
>
>>>
>> Lots of more recent ham gear has had hardly working AGC. Icom used
>> to advertise their amplifier as blowing the receiving operator back
>> from the operating table, which it did with their receivers (One IC I 
>> used for FD one time appeared to have no AGC at all. Its owner bought a 
>> TS-440 after that and it was so different the day he got it he stayed on 
>> the air for 24 hours.) AGC of the FT-857 is so good that audio is no help 
>> at pointing 10 GHz dishes. Aiming is much easier with the AGC turned off.
>
> ** For HF I progressed from the 75A4/100V plus 75A4/200V to a pair of C
> Lines, a pair of TS-930's, pair of TS-940's, and currently a TS-950SD and
> one of the highly modified 940's. I might get a TS-950SDX if a good one
> shows up. Ive tested a lot of the so called premium rigs and cant find any
> reason to get one. Having 2 complete stations with amps and a switching
> matrix that permits any rig to use any antenna Im quite satisfied. Maybe 
> if
> SDR improves a lot more I might be tempted but at 73 I might be drooling 
> in
> a rocker before that happens (-;
>
> I use 3 modified TS-830's as the IF platforms for 6M and above. Currenty 
> to
> 2304 but gear is available to 10 GHz.
> For several years I was supplying 24 GHz mixers and amps to the EME and
> contesters around the world using rejected modules at work that didnt meet
> the Po or gain specs at 23 or 26 GHz and when retuned/peaked for a narrow
> range they exceeded specs at +33dBm.
>
> Carl
> KM1H
>
>
>
>
>
>> On 7/7/2014 2:53 PM, Carl wrote:
>>>
>>>> One of the first mods I made to my new S=3B was to replace the BFO
>>>> adjustment pot that was switched at the CCW end of rotation with a
>>>> pot with a push pull switch. So when I set the BFO frequency for my
>>>> likes (or for narrow shift RTTY) I could switch to SSB and back
>>>> without having to go through the setting process again. I don't
>>>> know why it wasn't built that way from the beginning, unless the
>>>> engineers never used a modern TV set with a push pull switch. I had
>>>> no trouble at all buying the better switch and pot assembly in a TV
>>>> parts store.
>>>>
>>>> The filters of those days had a lousy time response turning
>>>> lighting into extended crashes and power line noise into continuous
>>>> noise (as seen on a scope that I connected to the jack I added to
>>>> the end of the receiver IF strip). A few years later I used a
>>>> vintage Q-5er with converter and wired up my receiver/TX patch
>>>> panel so I could use either the Q-5er or the S-3B or both with my
>>>> transmitters. Often on 75 meters I could copy through thunderstorms
>>>> with the Q-5er and couldn't with the S-3B because of that filter
>>>> ringing. The Q-5er selectivity came from loosely coupled ferrite
>>>> core IF transformers at 85 kHz and had a more Gaussian amplitude
>>>> response with a fine time response. Lightning came through as
>>>> clicks, not crashes. The modern Collins mechanical filters offered
>>>> as options in the Yaesu FT817, 857, and 897 don't ring nearly so
>>>> much.
>>>
>>> Thats why I like to use a NC-300 or HRO-60 under those conditions.
>>> One with a 80 KHz IF and the other brute forcing it with a load of
>>> 455kc IF circuits. The Collins R-390 is another decent storm radio
>>> but not the 390A. The USN RBB and RBC by RCA is perhaps the peak of
>>> electrical storm radios but I havent used a R-390 at sea. Yeah, I
>>> have those also (-;
>>
>> 390 and 51J-3 should be better than 390A and 51J-4 because of the lack of 
>> vintage mechanical filters. I have a 390A at the barn that the previous 
>> MARS member never got working, mice and moisture have probably not 
>> improved it in the last 15 or 20 years. I'm no long in MARS but MARS 
>> didn't take back any of the equipment though I asked them to, especially 
>> the 6' rack TMC independent sideband receiver with 100 tubes. A squabble 
>> over a repeated signature for it is why I left MARS though I was Iowa 
>> newletter publisher and technical coordinator. Its still with me but 
>> filled with mouse nests, I don't think I want to apply power.
>>
>> I have a 51J-3 with product detector and better AGC added by an ISU 
>> professor, W0PFP who is now a SK. I'm not sure I've turned it on since I 
>> moved. It was working good except its RF stage will oscillate on the 3 
>> MHz band if peaked. It has a white panel that was tan with pipe smoke 
>> when I got it.
>>>
>>> Another USN radio is the mid 30's RAK and RAL regens, the peak of
>>> regen development. It uses an audio peak limiter as a form of AVC
>>> that is extremely effective and easy on the ears. I used a RAL often
>>> at sea for hamming and have the pair here also. The RAK (it tunes
>>> 15-600kc) is better on CW only and feeding a 455kc IF or building a
>>> crystal controlled down converter into it would be an interesting
>>> experiment.
>>
>> The RAL and RAK were used on liberty ships through WW2 based on the 
>> design philosophy of nothing new, only proven designs and if the operator 
>> was careful there was no leaked LO for enemy subs to detect. If the 
>> operator let it oscillate it had two Rf stages to cut down that radiation 
>> but probably wasn't perfect.
>>>
>>> Carl KM1H
>>>
>> I don't know if the modern fancy SDR have come to it yet, but an SDR 
>> needs
>> two AGC loops. One to protect the D/A converters from overload and 
>> another to control the audio level. The front end AGC is seeing wide band 
>> signals, how wide depends on the specific design, so if that is the only 
>> AGC, a strong signal a distant frequency can be pumping the audio level. 
>> There needs to be a post detection AGC, like the limiter of those regens 
>> that works on only the audio to the user. I suggested that to one of the 
>> SDR gurus in 2006 and he hadn't though about that at all.
>>
>> That audio level pumping can come from using a narrow audio filter after 
>> the RF AGC in most any receiver. Makes the audio or DSP filter relatively 
>> useless on a crowded band. Yes, AGC ought to be derived after ALL the 
>> selectivity but I sometimes use a passive low pass filter on the speaker 
>> wire to cut down on post filtering wide band receiver noise, a problem 
>> when the filter is followed by two mixers and 7 stages of wide IF that 
>> contribute almost as much noise as the front end passes through the 
>> filter. Plus the noise artifacts of the DSP audio filter.
>>
>> I have a 2m transceiver that has two filters on the IF strip, one at the 
>> mixer (its single conversion with a VCXO for the LO), and one right 
>> before the product detector. Its called a Hohentweil.
>>
>> If it had a good tuning range the Hohentweil would be an interesting VHF 
>> transceiver and IF for microwave. Not all the Minnesota area tranverters 
>> are rock stabile and sometimes there's a want to shift 2 or 2.5 MHz to 
>> allow more than one direction of contacts from the central hill top 
>> location at the same time. And as I work on higher bands a 432 or higher 
>> first IF would be beneficial in image rejection without lossy complex 
>> millimeter wave filters.
>>
>> 73, Jerry, K0CQ, Technical Adviser to the Collins Radio Association
>>
>>>
>>
>>
>> -----
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>
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