858 ssb chassis RECEIVE MODS NEEDED !!

[Zman]

Can i get them at Radio Shack?

 

[Zman]

By gosh i found some in my stash i forgot i had. LOL

 

[Robb]

Can i get them at Radio Shack?

Doubtful.
Check out the 1N6263 on Google. Think I bought 200 and paid ~$20 for the lot. You can probably buy less/pay less. Nothing wrong with having spares. This is my second batch/buy. Gave some to locals and put them in every CB or 10m radio I have. Worth it - IMO! The first batch of 50 I bought went pretty fast.

The 2999e (IMPORTANT: the 'e' designation is critical - they have the highest gain/lowest noise). But not all radios will benefit from swapping to these. You will need a digital volt/ohmmeter that has a 'hfe' ('transistor gain') test function. If the transistor that you took out has a much smaller hfe/gain than the 2999e (test both transistors to find out); then you should use the 2999e. If the hfe is nearly the same; then don't bother with the 2999e.

Mass producing radios by Uniden/others meant that some of these stock transistors did well; while many others just weren't up to snuff. That is when this 2999e transistor will show improvements.

The 858 chassis radio will be best served with the stock transistor. JJ found all of this out - and you reap the benefits of his experience, knowledge, and testing - by trusting his judgement.

 

[Zman]

Doubtful.
Check out the 1N6263 on Google. Think I bought 200 and paid ~$20 for the lot. You can probably buy less/pay less. Nothing wrong with having spares. This is my second batch/buy. Gave some to locals and put them in every CB or 10m radio I have. Worth it - IMO! The first batch of 50 I bought went pretty fast.

The 2999e (IMPORTANT: the 'e' designation is critical - they have the highest gain/lowest noise). But not all radios will benefit from swapping to these. You will need a digital volt/ohmmeter that has a 'hfe' ('transistor gain') test function. If the transistor that you took out has a much smaller hfe/gain than the 2999e (test both transistors to find out); then you should use the 2999e. If the hfe is nearly the same; then don't bother with the 2999e.

Mass producing radios by Uniden/others meant that some of these stock transistors did well; while many others just weren't up to snuff. That is when this 2999e transistor will show improvements.

The 858 chassis radio will be best served with the stock transistor. JJ found all of this out - and you reap the benefits of his experience, knowledge, and testing - by trusting his judgement.

Please reread my last post...

 

[721 Crazy Canuck]

Just did this mod to my TRC 458. The resistor alone cut my white noise by almost a full s-unit. I also did the diodes and transistor with pretty good results.

 

[giboni]

It is an old Post. I wanted to share a simple installation Mod for the receive.

I had a Ureka moment when re-capping/repairing my CP2000B. The CPI Base/Mobile

It uses the 8 pole SSB filter for both AM & SSB. The 858 Chassis uses 1 Monolithic 7.8MHZ

crystal filter on AM & a 7.8 MHZ I believe 8 pole crystal filter on SSB. Sooo. I had a rusted 138xlr not salvageable. Salvaged the 8 pole filter.

Put it in my Cobra139XLR in place of the monolithic. Wow. Mind boggling channel rejection now on AM. Slight loss in sensitivity.

Their is another long thread on the gain 2sc2999 versus 2sc1730.

I have all the second generation 858 AM/SSB Base Stations. Including early 858 late 858 Madison. Robyn 520D, Teaberry Stalker 202, Cobra 139xlr,Trc457, trc458 & President Washington.

So I slowly Gathered the Sam's 127, etc. Slightly different tune-up/alignment procedures. To the point. All books are USED. All had notes in the margins.
Various issues with this chassis. All had notes about Tr5 being shorted.

Looked on CBtricks. technical bulletin to warranty shops. Change Tr5 (2SC1730) to

2SC784. TCH B #1211

Found them but too expensive $1.00 each minimum 10. But did find a German/Euro equivalent BF255 very reasonable.

Wonder if 399 can figure out the Gain of the 2Sc784 & BF255 ? Could not find data on it.

Now back to the 7.8 MHZ Ladder Filter replacing the 7.8 MHZ monolithic.

CBC international lou Franklin has not carried his 7.8 Crystal filter in years. But I found the schematic online for it.
I'm bread boarding this circuit to apply gain to the new(used) filter I installed.

I can then start plugging in different UHF,VHF transistors including the maligned

2sc2999 & hear the differences ! Nice info 1 meg hmm. too bad those links are dead.

You can still purchase N.O.S. 7.8MHZ Fliter. Internet search. 19.00 + shipping. One caveat is that

they are obviously 2.4KHZ band-pass. You will have to make sure that on AM you are dead center

on frequency with the Clarifier. With this receive Mod I went to a 10 Turn pot for the clarifier. Worth

it believe me. It sucks getting splashed by Skip Stations. Now I barely get any adjacent channel interference even from locals a mile away running 600 watt foot warmers.

I have now collected 8 pieces of this filter. To redo my collection of course !

Lastly. Of course. Vintage rigs like this almost always in my recent experience require an alignment.

After a complete RE-Cap with Quality 2000hr + low esr caps a couple of the Radios were still spot on.

I went through the trouble and expense of assembling the equipment.

Best John

 

[Needle Bender]

It is an old Post. I wanted to share a simple installation Mod for the receive.

I had a Ureka moment when re-capping/repairing my CP2000B. The CPI Base/Mobile

It uses the 8 pole SSB filter for both AM & SSB. The 858 Chassis uses 1 Monolithic 7.8MHZ

crystal filter on AM & a 7.8 MHZ I believe 8 pole crystal filter on SSB. Sooo. I had a rusted 138xlr not salvageable. Salvaged the 8 pole filter.

Put it in my Cobra139XLR in place of the monolithic. Wow. Mind boggling channel rejection now on AM. Slight loss in sensitivity.

Their is another long thread on the gain 2sc2999 versus 2sc1730.

I have all the second generation 858 AM/SSB Base Stations. Including early 858 late 858 Madison. Robyn 520D, Teaberry Stalker 202, Cobra 139xlr,Trc457, trc458.

So I slowly Gathered the Sam's 127, etc. Slightly different tune-up/alignment procedures. To the point. All books are USED. All had notes in the margins.
Various issues with this chassis. All had notes about Tr5 being shorted.

Looked on CBtricks. technical bulletin to warranty shops. Change Tr5 (2SC1730) to

2SC784. TCH B #1211

Found them but too expensive $1.00 each minimum 10. But did find a German/Euro equivalent BF255 very reasonable.

Wonder if 399 can figure out the Gain of the 2Sc784 & BF255 ? Could not find data on it.

Now back to the 7.8 MHZ Ladder Filter replacing the 7.8 MHZ monolithic.

CBC international lou Franklin has not carried his 7.8 Crystal filter in years. But I found the schematic online for it.
I'm bread boarding this circuit to apply gain to the new(used) filter I installed.

I can the start plugging in different UHF,VHF transistors including the maligned

2sc2999 & hear the differences ! Nice info 1 meg hmm. too bad those links are dead.

Best

Good stuff, makes me want one.

 

[357]

 

[loosecannon]

this is a cool mod, but where in the heck did he get 50uV for an S9 reading?

every SAMS ive ever looked at had the S9 adjustment at 100uV.

i've never heard of a CB radio being made with a meter that sees an S9 reading with 50uV of input.

im wondering where the piece of paper he is referencing came from?

anyone ever tried this?
LC

 

[ExitThirteen]

I have been doing the L4 mod for many years. It does indeed work nicely, especially with your R43 mod, LC.

Using a friend's signal generator, I was able to dial it down to the lowest it would go, at .032uV and my President Washington was still able to pick up the audio tone. No S meter reading, but it still picked up the tone. The L4 mod is a legit mod that works. Keep in mind that if this mod is done, the AGC may need adjustment as well.

~Cheers~

 

[Yeti Communications Ltd]

actually not a "new" mod i have seen this in 858 chassis for over 30 years now and i have preformed it a few times myself ...changing the fet to a later one can improve it a bit also ...personally i prefer to take the extra coil and 2 pole filter from a base unit (and some of the better mobiles and add it to a mobile unit also to gain a bit of selectivity having all the gain in the world does not make up for good selectivity

 

[357]

this is a cool mod, but where in the heck did he get 50uV for an S9 reading?

every SAMS ive ever looked at had the S9 adjustment at 100uV.

i've never heard of a CB radio being made with a meter that sees an S9 reading with 50uV of input.

im wondering where the piece of paper he is referencing came from?

anyone ever tried this?
LC

Swizz says:
100uV is an old S-meter Level in (EMF). The new S-meter Level is measured into 50ohms
μV (50Ω)
https://en.wikipedia.org/wiki/S_meter


I did the mod on my 449 but my noise floor went from 3 to 7 s-units.
Weakies were doing 9 s-units. Re-calibrating the S-meter didn't help.

There must be another step like exitthirteen says with the AGC?

 

[loosecannon]

I have been doing the L4 mod for many years. It does indeed work nicely, especially with your R43 mod, LC.

Using a friend's signal generator, I was able to dial it down to the lowest it would go, at .032uV and my President Washington was still able to pick up the audio tone. No S meter reading, but it still picked up the tone. The L4 mod is a legit mod that works. Keep in mind that if this mod is done, the AGC may need adjustment as well.

~Cheers~

thanks for the feedback!

i too have seen this mod since the old Secret CB days, but always thought it was used in broadbanding the radios for more coverage.
the impedance mismatch thing was a new one to me.
someone much smarter than me stated that there really isnt a mismatch with RF, only DC, as the reactance here is about 1500 ohms.

next time i come across an 858 SSB unit, i will give this a try and see how i like the results.

i also agree that adding the extra coil and monolithic crystal filter really cleans this chassis up.
LC

 

[giboni]

Ahh the 357 Post is just a black rectangle. Sooo. I am in the dark as to this "Fet" change.

And which FET ? & to what later Fet Part #? The broad-banding mod I am aware of. R43-L4 & RC Mods .Okay how about an explanation. Shotky's ?

Best

 

[loosecannon]

not sure why you cant see the video, but it might have to do with your individual forum settings.

go to youtube.com and do a search for: upd858 chassis: sensitivity enhancing

and you will find this video by a person called SWIZZRADIOS

you may already know of this mod, as its bee around for a long time.
LC