TRC-458 compared to TRC-433

[KG6YGE]

The TRC-433 (not touched inside) has more sensitivity and audio clarity than my TRC-458.

Background-

I found a 458 at a local thrift for $10.00, so I have my first CB radio since 1975. It had no mic, so I bought a TRC-433 on eBay for $15.00 plus shipping, since it came with mic too (realistic 21-1175 with pre-amp).

While waiting for it to arrive, I got the service manual for the 457-458 and peaked the receive side, using the 1/2 wave vertical dipole using the EZNEC demo software.

Both radios are sensitive, but the modulation and demodulation of the TRC-433 is simply better than the 458, at this time.

I have read through the tips and tricks for the TRC 449-457-458 series, but nothing is focused on just muddy reception. The clarifier does work, and I have verified its operation.

Does the 433 have a better diode detector than the older 458? Any other thoughts, besides a general recap?

I have been through all the alignment steps in the SM, except for injecting a 100 pps 1usec pulse in the mic input circuit and tweaking L1/L2 for max output at TP#5 (noise blanker section), but I plan to do that today.

Thanks

Charlie in Nothern VA.

 

[2RT307]

Sometimes, it's just the radio. I've had two of the same rigs that one received better. Maybe one was made on a Monday!

As old as the 458 is, it probably could use a recap. They have very good receivers in them though, but I can't remember which board it had in common with the Cobras and Unidens. 139XLR base, maybe? Lots of guys know better than me, and I think I've seen Exit Thirteen do a lot of posting on this generation of radio. Maybe he will chime in here for some specifics that can help you.

73,
RT307

 

[Zman]

I have a 432, cousin to the 433, and it does seem to talk better than some of my other radios but comparing it to my 458 it does not hold a candle audio and receive wise....

 

[Eastside]

Hate din plugs.

 

[KG6YGE]

I found the RS manual from CB tricks for the TRC-449 is better written than the Sams TRC-458/457 SM, so still fiddling..

http://www.cbtricks.com/radios/realistic/trc_449/graphics/realistic_trc_449_sm.pdf

With the vertical 1/2 wave dipole with the lowest point about 7 feet off the ground, getting contacts from Mexico (pacific side), Great Lakes, Louisianna, Central California, Arizona, mostly on ch 6. This is with #14 speaker wire, and about 30 ft of RG-58U back to the radios. The TRC 433 contacts are just easier to understand, both radios are about the same on sensitivity.

 

[KG6YGE]

Anyone with a TRC 457/458/449 that has aligned and or modded theirs ?

 

[slprydk]

Anyone with a TRC 457/458/449 that has aligned and or modded theirs ?

I have done plenty, 457, 458, 449, 138XLR, 139XLR, 858 Madison's, 858 Washingtons, Robyn 520D's, and others. This chassis has lots of channel, TX and RX mods available. The 457 I have right now has been converted to blue clock and channel displays, has the 2sc2999 receive mod, and sounds really good with an old non amplified Turner CS-3.

Jim

 

[Zman]

The standard 858 PLL like the ones that SLPRYDK mentioned all are great, however, the older 858 chassis that the Couriers and Teaberrys use plus my Midland 78.893 SUCK on AM but work well on SSB!!!!

 

[KG6YGE]

I have done plenty, 457, 458, 449, 138XLR, 139XLR, 858 Madison's, 858 Washingtons, Robyn 520D's, and others. This chassis has lots of channel, TX and RX mods available. The 457 I have right now has been converted to blue clock and channel displays, has the 2sc2999 receive mod, and sounds really good with an old non amplified Turner CS-3.

Jim

Thanks Jim. I looked up TR5's specs (2sc1730L) and the NF is in the 4 range, and Hfe ranges from 40-100, while the 2sc2999 is 2.2 and as a little higher Hfe (current gain...100-200 for the e model), so that looks like a good mod for me to try. Plan to do that one first, then the diodes (1N60Ps - D10-D11) in the am detector.

Plan to keep the original parts, and compare the before and after against the TRC 433 sitting on top of it. I'll post the results.

Niose Figure of the receive chain is set by the first stage, and gain of the 858's TR5 is a function of the Hfe of TR5 times the turns ratio of the coil the collector it is connected to transferring power to the following stage. The DC set point of TR5 is set by the voltage divider network resistors (R15, R12 and R10), but these are bypassed at the small signal amplification frequency of 27 MHz. At DC, the effective gain is -Rc/Re, or 220/1000, about -0.22, as modified by the AGC coming through R13.

This site was a working cascade two stage model you can use to see how the NF of the first stage sets the character of the receiver chain. Some have noted better performances with the TR5 changeout than others. There is a vairance in the Hfe in the original 2sc1730L model, as well as for the 2sc2999e model, and they almost overlap at their limits. More typically, an improvement will be noted.

http://www.minicircuits.com/applications/mcl_nf_calc.html



Charlie

 

[kf6jim]

Do these three radios use the same main board?

 

[KG6YGE]

No. The 433 is about 15 years newer than the fabled UPD858 based uniden. It is a remarlably good little base, that is as sensitive as the 458 on AM.

I haven't done the 2SC2999e mod to the 458 yet, for one reason. Addiction to SSB (namely ch 38 LSB). On SSB, the 458 lets me hear the 11 meter world about 3000 miles in radius. The audio qulaity in SSB is outstanding, meaning phone like clarity at times, from stations in Texas and Ark. An using only 12 watts (measured), I have gotten through as far as Tennessee and Arkansas, with a 1/2 wave vertical dipole in a tree.

I was not getting good results in tuning the 458 until I built a proper, shielded 50 ohm load. More coupling into the chassis than I realized with the cover off.