[Boatanchors] REAR88 mods.

[David Knepper]

Anyone interested in my CR-88?
PLEASE CALL FOR PRICE.

Phone number on the CRA homepage.

Thanks

David Knepper, W3ST/W3CRA
Publisher of the Collins Journal
Secretary of the Collins Radio Association
www.collinsra.com
Join today
----- Original Message ----- 
From: "Brian Goldsmith" <brian.goldsmith at echo1.com.au>
To: <boatanchors at mailman.qth.net>; <joeconnor53 at yahoo.com>; "'RCA 
Equipment'" <rca at mailman.qth.net>
Sent: Sunday, January 17, 2010 2:51 AM
Subject: [Boatanchors] REAR88 mods.


>
> Joe wrote:-
>
>
>>I'm working on a heavily modified AR-88 that I bought a few years ago.
>
> ****** G'day Joe,you should be so lucky!
>
>
>
> >I am trying to understand what some of these mods were designed to do and
> where they came from.Some are basic, for example, the 5Y3 was replaced 
> with
> diodes and a new output transformer was added so an 8-ohm speaker could be
> used.
>
> *****  The new output transformer was probably not added so an 8 Ohm 
> speaker
> could be used.I'll bet the original burned out and a replacement was found
> to be made of unobtainium,any old port in a storm etc.
>
>
>
>>Some are weird. The audio output was changed from a 6K6 to a 6V6.
>
>
> ******** Quite common as the AR88LF used a 6V6.Also,a  replacement output
> transformer would be much easier to match a 6V6.The change of tube meant a
> change of grid bias and this was easily achieved by interchanging R44 (160
> Ohm) and R43 (100 Ohm).
>
>
> Along the right edge of the set (in front of the power transformer), a 
> 6SN7
> and a 6K6 were added. I'm sure I'll find more as I probe further. The
> workmanship is so good that it would be easy to confuse the mods with
> factory work. This leads me to assume that the former owner knew what he 
> was
> doing.
>
> ****** A picture would be worth a thousand words.Looking from the front
> panel along the top right edge,the original tube lineup was 6H6 (V8),6H6
> (V9) and 6SQ7 (V10).
> Are these tube types still there?
>
>
>>The set is gorgeous and works well with two weird problem: with AF Gain
> wide open, it sounds great. If I back the AF Gain to a half-way position,
> the set motorboats. Thus, I am leaving the audio gain fully open and am
> using the RF gain as my volume control.
>
>
> ****** You will need to gut all of the original "bathtub" type multi 
> section
> paper capacitors and replace the innards with modern polyester types.
>
>
>> The second odd-ball problem is that the radio has far more gain with the
> Selectivity Switch in the No. 2 position. It should have more gain in the
> No. 1 position.
>
> ****** The different gain from Sel 1 to Sel 2 is normal.In Sel 1 the IF
> transformers have a double humped pass band,in Sel 2 etc the response is
> peaked and has slightly more gain.
>
>
> >It motorboats with Selectivity set to the No. 3 or No. 4 positions.
>
> Any insights and help would be appreciated.
>
>
>
> **** See above about gutting and restoring ALL the bypass caps.
>
> I have taken the liberty of posting this to the original list and to the 
> RCA
> Equipment list where a number of 88 afficonados hang out.
>
> Regards to all,Brian G.
>
>
>
>
>
>
>
>
>
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