Old uniden Grant PC-196aa board

[Handy Andy]

As yes, those "Dual Mixer" FET's - kinda like the Tetrode - With a Pentode Attitude - only in Solid State



The Tetrode by pinout only...



Due to the Direct connection to the Substrate - you have some better control or "stray" RF Capacitive effects of the free electrons found in a Tetrode, but these are confined to the substrate.

Doesn't mean it was "fool proof" just more robust but unable to serve larger current amplifier designs without some strikes against performance due to the "dual Gate" design of the 3SK45.

Fun little part though - Noisy (as in touchy prone to "oscillate"), but fun...

 

[Robalo]

Like this type off filter

 

[Robalo]

2-FT2 filters in series

can you explain this please

 

[Dmans]

Robalo,
The information supplied in the attached is Unit_399's work. It is VERY informative on these models (858 SSB's). Specifically the FT-2 information is page 12 of the info.

Many thanks to Unit_399!

73
David

 

[Handy Andy]

Thanks from Me Too - 399!
Excerpt from article ...


Credits to 399

 

[Robalo]

I was looking for that info on line . Thank you

 

[Robalo]

thank you Unit_399 for this info.

If you try to increase the channel display brightness, you take the chance of overdriving the LEDs, and causing them to fail. Sometimes, the display is dim simply because the red plastic in the channel display window or the LEDs themselves are dirty. This is a 35 year old radio, and there is probably a lot of dust in there. Other times, the channel display will go dim because of dirty contacts in the channel selector. Before modding the circuit, try rotating the channel selector clockwise through all 40 channels several times, and see if the display brightens up. These are sealed switches, so you can't use contact cleaner on them. If this helps, then the switch is the problem, and the best way to try and cure it is to ALWAYS rotate the switch in the same direction. In this case, Clockwise. VR17 is actually a dimmer control used in some models, and adding it will not make the display brighter. If the brightness hasn't improved after several turns of the selector, and the window and LEDS are clean, then remove R151 and replace it with a 6.2Kohm resistor and a 1 Kohm resistor hooked in series. Don't use a lower value that this, as you'll smoke the display for sure. Good luck and 73s.

- 399

 

[Robalo]

the clarifier is very nice on this unit, and is has been done this way. The parts have been removed. The R119,D29,D30 AND R118 goes from 27.379 mhz center 27.385 to 27.3875. The center of the clarifier is at 2 oclock pictures coming up.

 

[Robalo]

The clarifier parts location

 

[Robalo]

After the HIGH POWER MODIFICATION FOR UNIDEN 858 SSB CHASSIS
whats the driver and final ma measurements please. ca not find cobra 139xlr service manual . thank you 73' s

 

[Dmans]

Robalo,
The service manual states 40Ma for the driver and 70Ma for the final.
(Personally I would reduce both of those figures about 10Ma each.)

73
David

 

[Dmans]

A couple of quotes from unit_399's page:

The Sam’s for the Cobras and the Presidents Washington and Grant, as well as the Cobra service manuals, call for a driver bias of 40 ma, and a final bias of 70 ma.

The final transistor, which ran very warm anyway with the specified 70ma bias current, started burning out from the heat generated by excessive key down times.

Go gently when setting the bias. More is not always better. (I.e.-Power supply issues?)

73
David

 

[Robalo]

i got 40 ma at driver and 0.08 ma at final something is wrong. thanh you for fast answer

 

[Robalo]

The problem was R205 out of range now is 1 ohms, driver is 30ma and final 60ma but istill swing 12 watts pep on ssb. AM 4 WATTS DK pep 18, SSB 12 watts alc does not do more mmm. if i peak ssb i get 18 w but on am less than 1 watt ?

 

[Robalo]

parts location