[HBR] Another Receiver Project -- HBR-4, Part 5

[Dan Merz]

Hi Walt,  I don't know if my experience was any better than yours as far as
ordering crystals but I was happy with what I got.  I ordered from MH
Electronics,  one each of replacement crystals for a Mackay 3010 receiver in
range of 50  to 60 Mhz,  at $15 each.  For my need,  I sent them an example
crystal since I wasn't sure what spec to use.  They have an online request
for quote form,  again essentially an email request form.    I didn't do any
price comparisons with IMC but I seem to recall looking at their site - I
seem to recall someone on the 390 reflector recommended MH,  good luck ,
Dan
----- Original Message ----- 
From: <waltah at earthlink.net>
To: "HBR Receiver List" <hbr at mailman.qth.net>
Sent: Monday, July 26, 2004 9:45 AM
Subject: Re: [HBR] Another Receiver Project -- HBR-4, Part 5


> I have only one of the crystals I need because Yaesu jiggered the
> conversion scheme for lowest cost and eliminated the crystals for
> 80 and 20, changed the scheme to use a crystal that's no good for
> me on 40, and my parts set was owned by a CB'er who changed
> the 10 meter crystals for his band.   So all I've got is 15 meters.
> But that's enough to get the oscillator working.
>
> I have ordered the rest of the crystals for it -- five HC-49/U, ranging
> 18 Mcs-42.5 Mcs for now, with space for a total of 11 bands -- FT-
> 101 bandswitch.
>
> I contacted ICM where I have in the past bought crystals for such
> projects.   Unfortunately the website is a lot more cumbersome for
> ordering than it was the last time round and they seem indisposed
> to fix that.  Basically you must simply email them with a list of
> what you want.
>
> Does anyone know a reliable supplier of '1 each' quantities of
> crystals who has an up-to-date ordering process?   Guess I'm kind
> of spoiled by places like AES and online metals.
>
> Lessons relearned while working on the transplanted TEMPO One
> (Yaesu FT-200) VFO:
>
> 1.  Even small 'jumpiness' of frequency -- like stable at one
> frequency for 10 seconds, then a jump of 30 cps, and stable there
> for 15 seconds, then a hop back -- means a bad part breaking
> down.
>
> Voltages in a vacuum tube VFO will be higher than those in a
> bypolar transistor one, even if there isn't any plate voltage on the
> tank circuit, because the circuit Q is higher.   (Losses in the
> biasing circuits for the transistor and in the transistor itself are
> higher than in a vacuum tube circuit.)   Never trust those small
> silver mica caps that Yaesu uses so freely.    It's best to replace all
> the SMs in the VFO box with the best NP0 ceramics you can find.
>
> (Four other frequent causes of 'jumpiness' -- (1) VHF or UHF
> oscillation -- all tubes worthy of VFO use will do this and one
> should start with a 100 ohm resistor connected at the grid with a
> 1/8" lead.   (2) Inadequately filtered B+.    (3)  Tube with an internal
> short or loose internal structure -- very light tapping of the tube will
> expose this.  It is best to have at least three VFO tubes on hand
> for initial testing.   (4) For Hartley or Colpitts circuits, heater to
> cathode leakage -- the biggest disadvantage of these circuits.)
>
> 2.  Yaesu's scheme was to build a good VFO, populate it with
> inexpensive caps, then reduce the drift with temp compensating
> caps.  As a result, replacing Yaesu's silver micas with NP0
> ceramics will give you a VFO with way too much temperature
> compensation.   The original basic non-adjustable TC capacitor (7
> mmf, N750!) should be replaced with an NP0 at the same time the
> silvered micas are done.
>
> They'd have been money ahead if they had started with good caps
> and used a fixed temperature compensating cap, value chosen at
> the end of the design process, rather than cheap caps, two TC
> caps, and an air-variable differential cap to allow adjustment.
> Especially since the differential cap was always set to mid position.
>
> Walt
> KJ4KV
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