TRC-458, low on power after mods done...

[mr_fx]

ok here is what I know...

My TRC-458 is low on power...

AM Ch 1 - Dead Key 3w - Swing 7.5w
AM Ch 20 - Dead Key 3.25w - Swing 7.5w
AM Ch 40 - Dead Key 3.3w - Swing 6.5w

USB Ch 1 - 8w
USB Ch 20 - 8.5w
USB Ch 40 - 8.5w

LSB Ch 1 - 8w
LSB Ch 20 - 8.25w
LSB Ch 40 - 8.5w


My buddy has a TRC-449 (same chassis, just a mobile version)

He is getting around 6 watt Dead key and 25+ watt swing on AM and up to 30 watts on SSB

(I personally checked both radios) Further more my radio got similar numbers before this mod


My TRC-458 is not doing so well on power after the broadband mod...

list of mods...

Variable mic gain
variable TX freq (external)
variable RF power
broad banding
full channel expansion


Another thing to note is this

READINGS TAKEN FROM DRIVER / FINAL

TRC-458

DRIVER off the key - Base .02 - Collector 0 - Emitter 0
DRIVER keyed up - Base ..72 - Collector 13.65 - Emitter 0
DRIVER whistle - Base .68 - Collector ? fluctuates - Emitter 0

FINAL off the key - Base .0 - Collector 0 - Emitter 0
FINAL keyed up - Base .68 - Collector 13.60 - Emitter 0
FINAL whistle - Base .48 - Collector 16-18v?? ? fluctuates - Emitter 0



NOW FOR THE TRC-449, which WORKS GREAT

DRIVER off the key - Base .05 - Collector .03 - Emitter .05
DRIVER keyed up - Base .86 - Collector could not get reading? - Emitter .17
DRIVER whistle - Base .89 - Collector could not get reading? fluctuates - Emitter .22

FINAL off the key - Base .05 - Collector 01 - Emitter .05
FINAL keyed up - Base .86 - Collector could not get a reading??? - Emitter .18
FINAL whistle - Base .90 - Collector could not get a reading??? - fluctuates - Emitter .23


you may notice the readings are WAY different here

 

[unit_399]

ok here is what I know...My TRC-458 is not doing so well on power after the broadband mod...

Explain the broadband mod that you did. Was L37 modified in any way?

 

[mr_fx]

Explain the broadband mod that you did. Was L37 modified in any way?

TRC-458 Variable RF output and Broadbanding mod's

 

[fnkycoldmedina]

i would first suspect the variable power mod since it did better numbers before modding it .try to undo those tx circut changes too .

 

[mr_fx]

I suspect it too... I have found a few other version of the broad band L37 mod and they DO NOT include the .05uf cap

 

[unit_399]

MrFX -

The broadbanding mod I use for the 858ssb chassis does not involve any capacitor changes. Utilizing the full windings in the coil is all that's required for good broadbanding. Also, RN's mod didn't mention that L37 MUST be retuned after the mod is done.
The RF Power control mod looks like it will work, but it may be installed improperly. Personally, I wouldn't use it because the amount of rf power at this point is very small, and running wires from L37 to a VR at the front of the unit can be lossy and reduce power..




When aligning the transmitter, it should be noted that the driver/final bias settings in the Realistic 858s is different than in the Cobras, Presidents, etc.
In the 449,457,458, set the driver and final bias at 15ma and 40ma respectively, not 30ma and 70ma as in the others.

Also check D23 in your rig. If a 220 ohm resistor is installed in the D23 position, remove it and replace it with a 1N914 diode (observe polarity). Then remove C87 (2.2uf/16v) and replace it with a 15uf/16v electrolytic. This will improve speech clipper performance (and AM modulation) considerably.

Good luck. 73s

- 399

 

[mr_fx]

well replacing the cap with a jumper did the trick... Radionut has updated his website

 

[mr_fx]

well maybe not... it was working great... now gets no transmit... (at least nothing on the meter...)

I was on a D-104 base mic when this happened, I usually have them adjust pretty low... for some weird reason this D-104 was turn all the way up... not sure if that could be the cause

NOW AM gets NO dead key BUT AM does swing

while SSB does not show any power out on the meter

 

[mr_fx]

well now it is working again... HOWEVER the drive and final are giving me weird readings, the collector voltage fluctuates between 4.2-6.8

but on teh other radio (trc-449, which is the same radio as this) it see 13.8 or so on the collector

 

[mr_fx]

the board must have a crack, I don;t know

 

[bob85]

how are you measuring collector voltage in tx?, hope its not with a multimeter,
collector and base are hot with rf, measure voltage where you test bias current on the cold side of the collector choke.

 

[mr_fx]

ok I undid the broadband and now it's alive... id a rough retune on the TX and it is making some power now...

 

[26FB156]

Why would you want so much swing on AM?
4W carrier your rig should swing up to 8W any more will just lead to distortion.
73,
Ian G1DRP

Sent from my GT-S5830 using Tapatalk

 

[mr_fx]

Why would you want so much swing on AM?
4W carrier your rig should swing up to 8W any more will just lead to distortion.
73,
Ian G1DRP

Sent from my GT-S5830 using Tapatalk

I have always set them up using the following formula:

C x 4 = S where C is AM Carrier and S is swing watts (pep)

I have heard some people say that it should be Carrier x 2... either way I have never had ANY complaints

 

[wavrider]

Cx4=S is roughly 100% modulation without using a scope, taking into account that the S= PEP meter readings of course the best way is to use an o'scope.