[time-nuts] Oscillator temperature compensation...

[Joseph Gray]

Burt,

Thanks for the information. I thought that the tolerance was supposed to
100 Hz, as You said. As far as I know, this is the original crystal that
came with the rig when NMSU bought it. I will spend more time working with
the rig this weekend.

I am looking for a solid state LPB transmitter, if you are interested in
selling yours. I have just worked out a trade to another Amateur for a
carrier current line coupler.

Joe Gray
W5JG



On Fri, Jun 21, 2013 at 11:47 PM, Burt I. Weiner <biwa at att.net> wrote:

> Joe,
>
> As was mentioned earlier, U.S. AM broadcast tolerance is +/- 20 Hz.  Many
> of the LPB low power transmitter were used for TIS/HAR service.  The
> tolerance for that service is +/- 100 Hz.  I've maintained several of these
> stations, including the 100 watt system on 530 kHz at LAX Airport.  The
> transmitters were made by LPB, were all solid state, and stayed within 5 Hz
> for years without any adjustment.  It's been a real long time since I
> worked on any of the tube version of these, but >200 Hz sounds like
> something has gone wrong.  It may be a defective crystal or some component
> in the oscillator circuit.  To your knowledge, is the crystal that's off
> frequency a LPB supplied crystal?  The LPB's were also used for broadcast
> transmitters, particularly at daytime stations that had very low power
> nighttime authorization.  Used that way they had to maintain their
> frequency within the +/- 20 Hz tolerance, which was never a problem with a
> good crystal.  They are actually pretty good transmitters and are capable
> of 125% positive peak while keeping the negative peaks at 95% or less when
> driven with a real audio processor.  I have one of the 30 watt solid state
> transmitters and one exciter board.  I also have one that is an amplifier
> only that I'm able to drive to about 15 watts out with my bridge generator.
>
> LPB went out of business a few years ago and left a lot of customers who
> had pre-paid for their equipment holding the bag.  I was one of them.  It's
> a shame because they really are good transmitters.
>
> Burt, K6OQK
>
> At 09:26 PM 6/21/2013, time-nuts-request at febo.com wrote
>
>> >> I have an old AM transmitter that has three 6AL11 compactrons. The
>> crystal
>> >> is a fundamental, cut for 660 KHz. I don't have a schematic for this
>> thing,
>> >> but I believe that one half of one 6AL11 is used for the oscillator.
>> >>
>> >> The problem is, the frequency decreases as the rig warms up. It will
>> >> eventually stabilize, but the final frequency is over 200 Hz low. Not
>> as
>> >> good as it should be. I think the original specification was well under
>> >> half of that.
>> >>
>> >> I have replaced the electrolytic caps. The others are mostly
>> silver/mica
>> >> with a few ceramics. I checked all of the resistors and only found one
>> that
>> >> was out of tolerance (I replaced it).Three NOS tubes were installed.
>> There
>> >> are no tunable components in the oscillator section. Only the output
>> >> section has anything tunable.
>> >>
>> >> I know that there are many Amateurs on the list and I'm sure many know
>> more
>> >> about old tube rigs than I do. Does anyone have a suggestion as to
>> what the
>> >> trouble might be?
>> >>
>> >> Joe Gray
>> >> W5JG
>>
>
> Burt I. Weiner Associates
> Broadcast Technical Services
> Glendale, California  U.S.A.
> biwa at att.net
> www.biwa.cc
> K6OQK
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