Washington 858pll low power

[ExitThirteen]

Since the D858 SSB chassis already has a built-in compressor circuit, you are correct, no need for anymore compression. Mod #3 (the D46 mod) really isn't necessary, it just helps bump up SSB output in some radios. Mods #1 & #2 are your best bets for tailoring your SSB ALC so you can use a power mic if you wish, without the mic audio circuit going bananas, a common issue with this old chassis.

Let me know how it all works for you!


~Cheers~

 

[unit_399]

LiquidH8-
I'd like to add to Exit Thirteen's suggestions. The 858PLL chassis utilizes a speech clipper circuit to raise the average modulation. This was Uniden's most sophisticated clipping circuit, and should be left as is. The signal from the mike amp (IC3) is clipped by the back-to-back diodes D21 and D22. With high audio drive, the audio output from the diodes is a constant 1.3 volt peak to peak almost-squarewave. TR20 re-amplifies the clipped audio to a level sufficient to drive the output modulator (IC4) to 100%+ modulation, and low-pass filter L10/L11 rolls off the harmonics generated by the clipping. I like to bump the value of C87 from 10uf to 15uf/16V. This adds some compression to the clipping for a smoother sound. As you've found out, these rigs have so much audio that an amplified mike is unnecessary. 73s

- 399

 

[liquidh8]

Yeah, mod 3 I may not use, though I will try it just because, I have an amp I run so really not needed. Mod one and two I will definitely try. Just have have some more room in the mic gain control when I am running the transistor amp, it is so sensative every little back noise i picked up, included the cooling fans of my amps.


Unit 399, I appreciate that theory of operations, it helps clarifythe cicuit for me. I'll try that out too!

 

[liquidh8]

Update.

Mod one seemed to help a bit, I am using a stock Cobra mic right now, I have a CA-75 power mic I modded some time ago, but the PTT switch is being a little goofy.

Mod 2 I did and undid, didn't seem to make a difference in my case? I had 2 friends pretty close to tell the difference, one on an ICOM, the other using a ranger 2950.

Mod 3, that really woke it up believe it or not. Nice mod I've never seen before, thank you .

Mod Four, I did but I don't know what difference it made. I didn't have a 15uF cap, so I paralleled a 4.7uF cap on the trace side.

I can't hook up the scope yet, since I never got around to building the RF sampler for the coax. So I don't really now what it looks like after said mods, but I know what I am told, it is loud, clean and punchy.

Thank everyone for their input and help! Especially unit_399 and exitthirteen!

 

[ExitThirteen]

Glad it's up and working!


Just remember, on Mod #1, you can change the value of that resistor up to 2.2k. The higher the resistor value, the more TR16 limits modulation.

Mod #2 is mainly used for high powered mics, like the D104 or the Turner "Plus" series of desk mics. Mine is setup with a 220 ohm resistor, instead of the 470, since I run a D104. You can play with this resistor value also. In this case, the lower the resistor value, the more it limits modulation.

Mod #3 can really wake up a radio that has sluggish SSB output. You may have to re-tune CT7 a little bit, but this mod really helps on some radios (like yours and mine).

Keep us posted if you do more experimenting.


~Cheers~

 

[liquidh8]

I may try putting a pot in there for mod one, just so I can play with it to get what I need.

mod two is still up in the air. I have a mic I may try to get to work with it.

Mod 3 is a keeper, CT7 required very little adjustment. I will post results of any further testing.

For a few days I am just going to talk on it. Again, thank you for the knowledge!!

231PA

Jim