[TMC] TMC Multi-coupler help...Update..

[Jordan]

Ok.. I have replaced the FET device with the NTE452, and it works much better...

I removed the ECG-106 transistors, and replaced them with a pair of ECG-159
transistors, but this cuased more problems than it solved.. Apparently the
ECG-106 devices are a low to moderate gain devide, and the ECG/NTE-159 are a
medium to high gain device...They got much hotter and only added to the IMD...
The measured HFe of the ECG-106's are around 50, and the ECG-159's measured at
around 110....one of the two 106's actually measured very low, at around 20, and
is probably on it's last legs... this device was the one with the large
heatsink...

The unit is a godsend on 50-500 Khz with the BCB reject filter inline, and
actually adds about 5-10 db of usable gain on the lower frequencies...cleans the
BCB crud up to where it's non-existant....

I'm not quite finished, but I cannot find any ECG-106 or NTE-106 devices in
stock anywhere in Canada, an with the Holiday mail crush being what it is, I
will probably have to wait until after the holidays to order some from a U.S.
Distributor....

I would also like to add a couple more of the output boards, but they might be
pretty tough to locate... I would like to have 10 outputs working, and currently
have 3 boards giving me 6 outputs... I have 4 R-390A's and would like to feed
both the balanced and unbalanced inputs individually , and have a couple of
spare outputs for "spare" receivers, or for receiver comparisons....
73 de Jordan....

Jordan wrote:

> Ok.. well I am well into the repair of this unit... This unit appears to be
> somewhat unique in that it uses a FET front end device, and it operates on
> -26VDC from the internal power supply... It also uses common Drain circuitry
> due the negative voltage operation... I would think it uses a 26 Vdc
> potential for an increased dynamic range...The FET device , a 2N3823, Subs
> to an NTE-459 , and I managed to find two of these in the entire city....it
> feeds a pair of non-original ECG106 transistors which appear to be obsolete
> devices, but the recommended sub is an ECG/NTE-159... these feed the 2N2368
> buffer....
> Can anyone provide hints as to what the value of the -26Vdc source dropping
> resistor might be..? The replacement resistor is totally open, and the only
> bands left appear to be a red first band, a second band that could be either
> red,orange or brown... I think it may be red, as red/orange/x would be an
> odd value....
>
> The drain is bias above ground ( or below actually ), by a 1 K resistor...
> there is also a slight bias applied to the gate through a 1.2M and 120K to
> ground divider , in series with a 50K ohm 10 turn pot....
> Looking at the circuit, I can't think of a reason for it to cook so severely
> without damaging other components, and it is located right next to the 1K
> drain resistor which has been replaced as well, but there is no sign of the
> board being burned...
> The unit was tried and found to be functioning very poorly, and that may be
> due to the open resistor alone, or the FET device may be shorted, although
> FET VOM testing does not show any shorts....any ideas...???  73 de
> Jordan....
>
> Jordan wrote:
>
> > I'm looking for docs and or a manual for a TMC , or even someone who
> > could verify a few component values for a TMC Solid State HF Receiver
> > Multi-coupler...
> > The unit I have is Labelled as a TMC 6806 Multi-coupler, but that is
> > probably not the "Official" ID....
> > This unit uses a JFET RF device in the pre-amp board, a 2N3823, followed
> > by a pair of unmarked ( unreadable ) transistors, and finally a 2N2368 (
> > Buffer?) on the preamp board before the signal goes to the individual
> > dual BNC output boards....
> > I have pictures of the unit , and the board in question if that is of
> > any help...73 de Jordan....