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G3ZJO > TECH 19.09.04 09:25l 82 Lines 2814 Bytes #999 (0) @ WW
BID : B70044G3ZJO
Read: GUEST OE7FMI
Subj: Dual Gate FET Mixer
Path: DB0FHN<DB0THA<DB0ERF<DB0FBB<DB0GOS<DB0ACC<DB0EA<DB0RES<ON0AR<IW8PGT<
CX2SA<GB7YFS<GB7COV<GB7COV
Sent: 040919/0802Z @:GB7COV.#29.GBR.EU #:62958 [Coventry] $:B70044G3ZJO
From: G3ZJO@GB7COV.#29.GBR.EU
To : TECH@WW
Hello Everyone
3 Bulls in one.
1.)
Does anyone know of a source for the 40673 Dual Gate MosFet. THE mixer we
used to use in converters / transverters.
Alternatively and probably preferably, has anyone used a modern substitute
in such a circuit.
I seem to remember the Yaesu FT101 mixer was a Japanese equivalent device
without gate protection diodes.
As they were 'popping off' 20 years ago I should imagine they are still
needing replacement in the surviving 101's.
2.)
We tend to think that solid state devices will go on forever unless pushed
over the limits.
Does anyone know of any problem with the Dual Gate Mosfet's manufacturing
process possibly in the past which causes premature death.
I have home brew transverters for 2m, 4m, 6m, and 70cm. (DL6HA remember
?).
The VHF ones use the 40673 mixer, actually a TI equivalent E1819 which has
diode gate protection.
The following must be more than coincidence.
I recently produced a convertor for 136Mhz WX sat use using a spare DL6HA
board and devices from the spares draw. The mixer device did not work, it
ran hot.
Well I thought fancy that, I have treasured a faulty 40673 / E1819 for all
these years as a spare.
Now out of stock I looked for a donor, the 2m transverter gets pressed
into service at times, so the 6m lost its mixer, it ran hot. The 2m mixer
device works on the new board when temp. substituted.
So we will shelve that project then, until we find a suitable mixer.
There is a lot of 4m activity locally now with new licencees and PMR rigs,
so out came the 4m transverter not used for some time. The converter noise
was undetectable. Yes the mixer was running hot.
I remember reading about 'the black death' in early bi polar transistors
and recently that a similar problem is expected with the latest
microprocessors due to the size of the internal structure. One molecule of
corrosion and its gone as it were. I do not remember anything about FET's.
3.)
As the older residents will notice I am fairly new to packet and
particularly to the BBS.
Well one has to get ones stimulation from somewhere. With very few
exeptions, (some stations are rarely active now), mention a dual gate
mixer on 2m or the local 70cm repeater and thats it, end of conversation.
I hope that 'non English speaking' readers can understand this, I am doing
my best to keep away from 'funnies'.
I follow with interest the comments about language.
I realised when writing this that Style comes into it. Authors write in a
developed style and can be recognised by their style.
Most letters from those who are learning English are Quaint, very good,
understandable, but Quaint. I can't do Quaint.
73 - Eddie, G3ZJO @ GB7COV
Message timed: 09:01 on 2004-Sep-19
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