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 Post subject: Re: Quartz Crystals
PostPosted: Nov Fri 10, 2017 3:59 pm 
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Joined: May Tue 16, 2017 3:03 pm
Posts: 99
Location: Potomac, MD 20854
Tom Herman wrote:
K3STX wrote:

FWIW, my transmitter is a 6AG7/807 MOPA, about 50 watts output so I am beatin' that rock hard. Maybe I should try a real FT-243 before I go muckin' around with my power supply.

paul


Paul,

I have a fairly good selection of 75 & 40M FT-243's: If you're good in the callbook (QRZ nowadays!), I'll be happy to send you a real FT-243 so you can see how they work for you.

-Tom


I have one on the way from AF4K, will let you know if that is the problem. If so, I might be learning how to grind crystals soon. :D

paul


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 Post subject: Re: Quartz Crystals
PostPosted: Nov Sat 11, 2017 4:08 pm 
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Joined: Jul Tue 21, 2009 1:38 pm
Posts: 690
Location: SW WA state
Well, I've run a whole bunch of crystals through the RFL-459A, and found impedances all over the place, with an HC-6/U at 430 Ohms, and similar ones at just over 20 Ohms... The FT-243's tested today ran anywhere from 44-140 Ohms...
I haven't seen any ironclad correlation between holder types and crystal impedances, other than transmitting type FT-243's seem to average lower impedances that later, smaller crystals...
Typically, the hermetically sealed xtals tend to be closer to actual channel frequency than the FT-243's are.
I have not tried running any of the crystals at higher currents than 20 mA: That may be a way of seeing just what they are capable of doing.
I can measure up to about 100 mA crystal current, and at an average of 30 Ohms, that's about 3/10 of a watt of drive power, which is probably way too much for most crystals.


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 Post subject: Re: Quartz Crystals
PostPosted: Nov Sat 11, 2017 4:53 pm 
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Joined: Jun Sun 19, 2011 2:31 pm
Posts: 4802
Tom,

The crystal current is largely dependent upon the circuit in which it is used. The 6AG7 (and its miniature counterpart the 6CL6) became one of the common types for MOPA transmitters because of this tube's ability to generate a fair amount of drive with very low crystal current and a FT-243 works beautifully in the circuit and in most rigs with this circuit the smaller HC-6/U will also perform well.

I believe it was Bill Orr who published a circuit for a single tube transmitter using a 4-1000A as the oscillator/output tube and it took extremely careful adjustment of this rather impractical circuit to avoid destroying the crystal; RCA had a slightly more practical circuit using an 813 which used a pilot lamp in series with the crystal to both indicate crystal current AND act as a fuse to protect the crystal. Of course the RCA circuit would destroy the operator if he avoided the strong caution about using a proper keying relay since it is keyed in the 1,500 volt lead to the screen dropping resistor which is a lot more serious than the minor annoying tingle cause by the Johnson (and similar) differential keying circuit which puts a fairly high but current limited negative voltage across the key. My Valiant helped me become fully awake a couple of mornings when I forgot and got across the straight key terminals.

Rodger WQ9E


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 Post subject: Re: Quartz Crystals
PostPosted: Nov Sun 26, 2017 10:54 pm 
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Joined: May Tue 16, 2017 3:03 pm
Posts: 99
Location: Potomac, MD 20854
rsingl wrote:
K3STX wrote:
Very interesting. I have a Post called "Keying my MOPA" in which I describe frequency drift in the first few seconds after I apply B+ to the oscillator tube. My thought was it was a voltage regulation problem, but all my "FT-243" crystals are HC6/U stuffed into FT-243 cans by Brian. Maybe that is more what is going on here.

FWIW, my transmitter is a 6AG7/807 MOPA, about 50 watts output so I am beatin' that rock hard. Maybe I should try a real FT-243 before I go muckin' around with my power supply.

paul


Paul,

I would bet those crystals are your problem....
Rodger WQ9E


And right you are! I just got two REAL FT-243 crystals. My test is to turn on 6AG7 oscillator and apply B+ to my 807 at the same time (with switch) and then begin sending DITS immediately and following frequency shift.

ALL of my HC49-stuffed-into-FT243 holders drift down in frequency a few hundred hertz or so for the first second or two. Then they stabilize. But after this BIG drop some continue to drop a very little bit during the transmisstion. But the big shift is when I first key oscillator/amp. If I do not transmit for the first 3 seconds there is almost no perceptible shift. Some of these crystals are better than others, and some REALLY stabilize nicely after that first second or two.

I have bought some HC-49 crystals off eBay for ($4 for 3 crystals) and I stuffed my OWN FT-243, they work well too.

paul

One of mine (7058 kc) drifts BADLY and chirps badly. This is the one I use the most. (USED to use the most).

The real FT-243 crystals are perfect.


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 Post subject: Re: Quartz Crystals
PostPosted: Nov Sun 26, 2017 11:50 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 31403
Location: Maryland 20709, USA
For anyone interested, Surplus Sales of Nebraska has a lot of crystals, here:
http://www.surplussales.com/Crystals/index.html

No affiliation, just a satisfied customer going back many years.

- Leigh

_________________
73 de Leigh W3NLB
http://www.AtwaterKent.info
Click "Grebe Stuff" for Synchrophase info


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