A Czech crystal company, Krystaly, Hradec Králové, a.s. is able to produce 20mm crystals.
The crystals are not clamped between stainless steel plates, like the wartimes
FT-171 or DC-35 versions. The crystal is round, with 20mm diameter. The contact
surfaces (very thin layer of silver) are applied on both sides, with a short
lead on each side. So the crystal is not swinging between 2 fix metal plates:
The whole system, crystal and contact area, is moving.
My friend, Karel, from
the Czech Republic and I, decided to give them a try. They offered the crystals
with a smaller contact disk, but we wanted to spread the current through a
larger area. They offered to produce the tools for larger contact disks if we
pay for it (laser cut masks) After some discussions between Karel and the company
we decided to order 3 sets of 6 crystals, with individually made 16mm contact
disks.
They resonate about 2 kHz too high in my Paraset and in the transistor
oscillator. Adding a small parallel trimmer helps tuning them down to the
claimed frequency. They adjust very nice over a large range before the
oscillation stops. Nearly no chirp, no jumps…I am really satisfied.
They only produce the crystals. They have no boxes/bases or holders left. You
get a disk with 2 leads on it. That's all. I use a round disk of phenolic board
as base and two 4mm plugs (19mm or 3/4 inch spacing, like FT-171). The lid (not
visible on the photos) is black POM tubing.
The design of the holder is from Karel. It uses two
slotted 0,2mm phosphor bronze strips to hold the crystal from the side without
blocking the oscillation. Don't pack them in foam to protect them. No
oscillation possible! With the slotted strips the disks are fixed on the side on
4 points. The electrical contact to the brackets has to be made by the applied
wires. Never try to ow what I am talking about.
A friend from Italy has made the first test-order. Now, because the tools are
paid for,
they take 12.- Euros per crystal. I can inform you if he is satisfied, when his
crystals have been delivered.
Don't expect them to proceed quickly. They don't have them on stock. They promised
to offer "custom vintage crystals" on their website soon. When more people
order, they will learn that it's worthwile to do it ;-)
Karel and I have no deal with that company. You have to do all correspondence
yourself.
On 15-12-2012 Carlo Strozzi, IZ4KBS
wrote down his experiences with these crystals:
Hi all,
I'm picking up this old message to let
everyone know that I also ordered a set of those large
crystals from www.Krystaly.cz, and it did take months to
have them manufactured, but eventually I got them
delivered yesterday. I have a set of useless QRG FT-171B
holders and I wanted to find a way to use them to host
these new crystals. With the help of a Dremel tool, I
enlarged the inner receptacle of the FT-171B case, then
I made a thin and "springy" metal clamp out of a tuna
fish can, made the two cuts that hold the quartz slab,
and here is the result (see attached picture). The metal
clamp is glued to the holder at the bottom, with a tiny
dot of Super Glue. Another (almost invisible) dot of
Super Glue was used to fix the bottom edge of the
crystal at the bottom, where it rests on the clamp, to
make sure it will never "rotate" onto itself because of
the vibrations; maybe this is an unnecessary precaution,
but it won't hurt, and it does not seem to prevent the
crystal from vibrating freely.
So it looks like that using FT-171B
holders with these crystals is definitely an option, and
a much easier/quicker one than building a custom holder
from scratch. By carefully designing the clamp, the slab
ended up having only three points of contact with the
clamp itself, at about 120° from each other, instead of
the usual four. As a matter of fact, the crystal in the
picture resonated at 7010.34 KHz with no holder, and at
7010.30 once placed in the holder as shown, so I believe
it remains almost as free to vibrate as if there was no
holder.
By zooming into the picture you may be
able to see further details, including the fact that I
did not cut the thin metal wires that come with the
crystal, in case I ever need to pull it from the holder
and reuse it in some other ways.
The guys at www.Krystaly.cz seem to
have learned from the first order done by Tom and Karel,
because I had ordered the crystal in the example for a
nominal QRG of 7010 KHz, but without specifying whether
it was series or parallel resonance. So they assumed it
was parallel, and they made the crystal for 7000 *series
resonance*, so that once placed in a parallel resonator
it had more chances to be close to the specified 7010,
and indeed their assumption proved correct. That's to
say that when these particular crystals are placed in a
typical tube oscillator, like the Paraset or a a similar
one, they will likey resonate about 0.14-0.15% higher
than their nominal series resonance. The actual QRG can
further be adjusted with the help of a parallel trimming
capacitor, as usual. I preferred not to place that
capacitor inside the holder, partly because there's no
room for it, but mostly because different tube circuits
are likely to require a different parallel capacity
value to resonate the crystal at the nominal frequency
it is intended for, so that capacitor has better be
placed in the circuit, not in the holder. In some cases
it may be desirable to put the capacitor in series with
the crystal, as opposed than in parallel, so again I
believe that the proper place for the capacitor is the
circuit, not the holder.
I have tested the crystal in the
picture with my Jones Push-Pull transmitter, where it
provides a good sounding note but it delivers less power
than a modern HC49/S or HC49/U crystal (about 30% less,
depends on crystals). I've only tested that on 40m, I'll
check also on 80m when I enclose one of the crystals for
that band. I believe that this is possibly because my
Jones TX is designed for low power, with the use of a
small 6J6 double triode, and these larger crystals
probably require a more powerful exciter to get the best
from them. I may try with a 6L6 one-tuber one of these
days, to see if my assumption is correct. Here you can
see my Jones Push-Pull, so that you get an idea:
I am glad to hear that the Crystals arrived, and you are
satisfied. I like your way to mount the crystal. It is
indeed not necessary to form 2 isolated brackets. Your
solution is nice. If you machine a slot between the two
4mm male connectors (between the screws inside the box,
but leaving an "island"
to fix your clamp, you will be able to add the trimming
capacitor (or fixed
ones) if you like. I can offer you to do that on my
mill.
The crystals I got were still too high, but the tuning
behaviour is nice, much better then with small crystals.
In my case I got more output with the Krystaly XTALs,
but the outputs drops a bit when you bring them down
with a parallel C too much.
Now, with those XTALs, the way to a "TRI-TET-TEN" is
open:
http://members.shaw.ca/ve7sl/tritet.html
I know you are in danger to get infected....;-)
I think it is a good idea to supply you valuable info's
on the Paraset reflector as well, Carlo!
yes, by removing more plastic inside the box is is
certainly possible to gain more space. As I said, I
prefer to place the capacitor in the circuit, but others
may want to enclose it with the crystal, and it can be
done, even with FT-171B holders, as you say. As you
noticed, I wanted to find a simple solution, also for
those who do not have special tools, hence the
single-piece bracket. It may be possible even to do away
with no bracket at all, by cutting a small groove in the
plastic block that separates the holder prongs, and
gluing the bottom edge of crystal in that groove with
the smallest possible dot of super glue. However I'm
concerned that if the box is dropped then the crystal
may fracture, even if it is very light in weight and has
almost no mass, so using the bracket may be safer, even
if it requires more work.
