Jeff,
> Tough for me to imagine because the device's switching speed is going
> to be the low tens of nS range - and the rest of the "ham stuff" with
> respect to switching is going to be in mS increments. I can't quite
> follow the conclusion that the circuit would necessarily need to be
> modified as a result of the part differences.
I worked with John "Doc" Sheller (now K8RR) on the QSK-1500 some
30 years ago. I distinctly remember that the MC14011BCP requirement
was added to the "service and technical manual" after the units
were shipped due to the timing problems discovered when other
manufacturers' devices were used at U3.
John designed the circuit on a breadboard and just happened to have
Motorola parts when he did it. The values of R4/C4 were selected to
work with the TS-930 (or TS-940) that he owned at the time. It was
only after the unit was in "production" (all the boards were stuffed
and soldered by hand) that the critical nature of U3 came to light.
While I have not studied the differences between the Motorola and
other designs, I would suspect the input clamping in the Motorola
design effected the charging rate of C4.
73,
... Joe, W4TV
On 7/7/2010 8:31 PM, Jeff Blaine AC0C wrote:
> Joe,
>
> Thanks for the comment.
>
> Tough for me to imagine because the device's switching speed is going to
> be the low tens of nS range - and the rest of the "ham stuff" with
> respect to switching is going to be in mS increments. I can't quite
> follow the conclusion that the circuit would necessarily need to be
> modified as a result of the part differences. If I were looking at a
> nearly $250 investment required just to get two of these obsolete parts,
> I sure would want to give it a try. But that's me.
>
> In looking at the data sheet the thing I noticed was a lot of hype on
> the Mot sheet about additional diode clamps. I can believe that the
> circuit may not ensure that part is properly bypassed and the designer
> relied on the input clamps to keep things from getting the gate oxide
> blasted.
>
> Good luck to Lon in his adventure!
>
> 73/jeff/ac0c
> www.ac0c.com
>
>
> --------------------------------------------------
> From: "Joe Subich, W4TV" <lists@subich.com>
> Sent: Wednesday, July 07, 2010 7:17 PM
> To: <amps@contesting.com>; <k5jv@kingwoodcable.com>;
> <keepwalking188@yahoo.com>
> Subject: Re: [Amps] QSK-1500 chip
>
>>
>> > Would a CD4011B instead?
>>
>> Probably not. The QSK-1500 functioned only because of the specific
>> properties of the MC14011BCP when used at U3B and C.
>>
>> It has been nearly 30 years now and I can't remember if the specific
>> requirement was because of the output properties of U3C or the input
>> properties of U3B but those two gates plus D1, R4 and C4 are a crude
>> pulse stretching circuit with a very fast attack time (allowing the
>> PIN diodes to switch before the transceiver can generate RF) and
>> holding the diodes in the transmit state just long enough after the
>> key was released for the transceiver to stop producing RF but still
>> releasing quickly enough so as not to overly delay the overall return
>> to receive.
>>
>> If one needs to replace U3 and can not find an MC14011BCP, the circuit
>> between pins 8/9 and pin 4 will need to be replaced by one that takes
>> a logic high (+12) when the key is closed and produces a logic high
>> (+12V) output that remains high for about 10 - 15 ms after the key
>> is opened. Using another "4011" type of quad NAND will most certainly
>> require a significant amount of cut and try to find new values for D1,
>> R4 and C4 to achieve the proper timing characteristics.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>> On 7/7/2010 7:31 PM, Jeff Blaine AC0C wrote:
>>> Would a CD4011B instead? I know the TI chip is still available and has
>>> diode clamped inputs. $0.40 at Mouser.
>>>
>>> 73/jeff/ac0c
>>> www.ac0c.com
>>>
>>>
>>> --------------------------------------------------
>>> From: "kingwood"<k5jv@kingwoodcable.com>
>>> Sent: Wednesday, July 07, 2010 2:59 PM
>>> To: "Amp Reflector"<amps@contesting.com>
>>> Subject: [Amps] QSK-1500 chip
>>>
>>>> Greetings to all,
>>>>
>>>> I have located a source for the, hard to find, Motorola MC14011BCP
>>>> chips. The only problem is that I must order 25 of them to get the
>>>> price
>>>> anywhere with reason.
>>>>
>>>> Does anyone have an interest in these chips? There are two of them
>>>> in the QSK-1500. The manufacturer marked on of the a absolutely
>>>> critical
>>>> for proper QSK timing. If I get enough interest, I will order them and
>>>> will sell 20 of them for $10, each, including shipping to the
>>>> original 48.
>>>> First come, first served.
>>>>
>>>> 73 de Lon, K5JV
>>>>
>>>> Lon W. Cottingham
>>>>
>>>> 1110 Golden Bear Ln.
>>>> Kingwood, TX 77339
>>>>
>>>> 281-358-4207
>>>> 281-795-1335 Cell
>>>>
>>>> _______________________________________________
>>>> Amps mailing list
>>>> Amps@contesting.com
>>>> http://lists.contesting.com/mailman/listinfo/amps
>>>>
>>>
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>>
>>
>
>
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