opening up the Uniden/President Washington audio

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sh450
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opening up the Uniden/President Washington audio

Post by sh450 »

I was wondering if anyone would be able to share any info on opening up the audio band width on either version of the Washington Base(older 858 PLL, or newer 8719 PLL)? I have one of each. This would be a great help. Thanks!
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Post by Goldfinger »

Uniden Washington 8719:

http://www.cbtricks.com/radios/uniden/w ... 19_sch.pdf

Change C121 to a 3.3 uF 16 volt electrolytic or tantalum. Observe polarity.
Change C86 to a 1 uF - 2 uF mylar or metal film.
Change C82 to a 1 uF - 2 uF mylar or metal film.
Change C119 to a 10 uf 50 volt electrolytic. Observe polarity.
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Post by Goldfinger »

President Washington 858:

Similar schematic: http://www.cbtricks.com/radios/cobra/13 ... lr_sch.jpg

Change C69 to a 10 uF 16 volt electrolytic (if it isn't already).
Observe polarity.
Change C61 to a 1 uF - 2 uF mylar or metal film.
Change C77 and C78 to 2.2 uF electrolytic or tantalum. Observe polarity.
Change C83 and C82 to 1 uF mylar or metal film
Change C84 to a 3.3 uF 50 volt electrolytic

need more treble?

Change C73 and C75 to .01 uF ceramic disc
Change C200 and C201 to .001 uF ceramic disc
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sh450
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Post by sh450 »

Thanks Goldfinger!
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Post by Sickpuppy22 »

I have some question's regard this audio mod, a friend of mine has a trc 457 upd858 pll, which is roughly the same as the washington radio.

He asked me if i could find out anything about opening up the audio chain for a little more hi fidelity.


Now my question is i've read at a couple of places that the trc 457 has a built in equalizer that limits the low end and that it may have to be removed or modified aswell to pass more low end.....or will this mod suffice to give him a tad more hi fidelity on his Transmit?
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Post by tecnicoloco1 »

Check the schematics C-73 and C-75 are part of the EQ,unless you by-pass the EQ you won't need to replace this caps.

Have fun,the mod works great either by-passing the EQ or with the EQ inline.

Thanks to Goldfinger for sharing this information.
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Post by wraithpc »

By-passing EQ:

Remove L10, L11, C71, C72, C73 and C74. Connect a wire between the emitter of TR20 and the old junction of C71 and L10.
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Post by Sickpuppy22 »

Thanks for the heads up, i think i will do it first without bypassing the EQ as he is using a silver eagle as a mic for now.
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Post by Goldfinger »

I have done plenty of radio's without bypassing the EQ and they come out sounding good. Changing C73 and C75 to smaller values DOES change the high end response with the EQ intact. if you bypassed the EQ, then changing these caps wouldn't do anything.
This choke-cap circuit is actually there to smooth out the clipping transients caused by the diode clipper circuit just before TR20, not as much for frequency shaping.
You have to be careful adding too many lows to any radio with a mod transformer as they don't have enough core to respond well below 100 hz.
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Post by Sickpuppy22 »

Thanks Goldfinger, i have one last question for you.

The values and parts to be changed will changing the type of cap say
metal film to tantalum have a dramatic impact or will it be arlgiht if i cant
get a hold of the exact caps listed here?
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Post by Goldfinger »

In the electrolytic (polarized) areas you can stick with electrolytic if need be. I just use the tantalum's because they sound slightly smoother, but the difference is subtle. Any non-polarized cap can be used in the areas I stated to use Metal film... polypropylene, mylar, non-polarized electrolytic, etc. I usually use NTE mylar caps because they sound nice and the electronics shop in my town carries them. The most important thing is to stick with the capacitance values listed and just find what you can "capacitor type" wise.
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Post by 479tx »

How do these mods sound with a non-hifi mic like a Silver Eagle d104?

Does it still enhance the sound?

P.S.

On the TRC-457, two components are different (for all realistic model 858 radios) for whatever reason than the original design (that the 139 xlr, etc. use) - D23 is a resistor - replace this with a 1n914 diode (observe polarity) and c87 was reduced from 10uf to 2.2uf, parallel a 10uf across the back of the 2.2uf at c87. The above two mods REALLY wake the modulation up on AM and apparently make the AMC circuit just like other 858 models.

I think the clipper circuit (d21/d22) actually works pretty well, I haven't tried disabling it, does it get really nasty with a d-104?
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Post by Goldfinger »

Yes, widening the transmit still enhances the sound even with a D-104. I hi-fi'd a Uniden Madison for a local here and at the same time I changed some caps on the amplifier board inside his TUG-8 D-104 so it would respond a lot lower. That combo sounds awesome. Huge audio!

I just posted the info on widening a D-104 HERE
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Post by 479tx »

Sweet! That's what I'm going to do on my 457.

Can you still sound OK with the d21/d22 combo bypassed (mine is w/ a 4.7 resistor in between) as long as you don't overdrive the mic?

The thing wouldn't make much audio until I did that.
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Post by 479tx »

Oh yeah, and did you do the two "want more treble" caps on his Madison?

Thanks for the info and all you contribute goldfinger!
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Post by Goldfinger »

Yeah, the modulator has plenty of power on the 457 chassis so it can go loud without clipping the audio amp out.

The Madison I did was the 8719 chassis and I did change C182 to a .01uF for a little more TX and RX highs. I also used a .002uF for C75.
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Post by 479tx »

Goldfinger wrote:Uniden Washington 8719:

http://www.cbtricks.com/radios/uniden/w ... 19_sch.pdf

Change C121 to a 3.3 uF 16 volt electrolytic or tantalum. Observe polarity.
Change C86 to a 1 uF - 2 uF mylar or metal film.
Change C82 to a 1 uF - 2 uF mylar or metal film.
Change C119 to a 10 uf 50 volt electrolytic. Observe polarity.
The above changes are for TX only right?

And the two option changes below are for additional highs?

C182 to a .01uF for a little more TX and RX highs.
I also used a .002uF for C75.

Thanks!
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Re: opening up the Uniden/President Washington audio

Post by redlght »

Change C121 to a 3.3 uF 16 volt electrolytic or tantalum. Observe polarity.
Change C86 to a 1 uF - 2 uF mylar or metal film.
Change C82 to a 1 uF - 2 uF mylar or metal film.
Change C119 to a 10 uf 50 volt electrolytic. Observe polarity.

Is that the whole rx/tx audio mod for an 8719 washington?
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Re: opening up the Uniden/President Washington audio

Post by Goldfinger »

redlght wrote: Is that the whole rx/tx audio mod for an 8719 washington?
No, just the transmit
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Re: opening up the Uniden/President Washington audio

Post by redlght »

Can i have the rx mod also? Thanks
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Re: opening up the Uniden/President Washington audio

Post by Goldfinger »

Receive:

C91, C28, C108, C110 - change to 2.2uF mylar, polyester or non-polarized electrolytic
C25 - make smaller in value for more highs


Receive and transmit:

C111 - make smaller in value for more highs.
This cap affects both receive and transmit. If you make it smaller for more transmit highs, you may not need to make C25 smaller for more receive highs.
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Re: opening up the Uniden/President Washington audio

Post by redlght »

Thanks your golden goldfinger.
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Re: opening up the Uniden/President Washington audio

Post by redlght »

Any problem using Metallized Polyester MKT Film Capacitors instead of mylar and what does raising C119 to a 10 uf 50 volt do.
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Re: opening up the Uniden/President Washington audio

Post by Goldfinger »

Yes, metalized, polypropylene, monolithic, pretty much any non-polarized cap of at least 25 volts or higher is fine.
C119 is just the last cap in the transmit audio chain, It needs to be higher in value also to pass the bass.
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