[Boatanchors] AR-88 Update

[EP Swynar]

Hi Joe,

If you want to really help the selectivity of that receiver, grab an old
Heathkit Q-multiplier at the next Hamfest you might visit, & incorporate it
as a permanent part of your set-up...

I did just that very thing here. My Heath QF-1 has an insulated "...chicken
wire" connection simply wrapped around the plate pin of the first IF
amplifier tube...the coax lead to the pin comes through a vent slot at the
back of the enclosure, permitting the access lid to stay shut all the time.

The only issue I had in this regard was the fact that my AR-88LF has an IF
up around 735-KHz, vs. the "standard" 455-KHz design of the QF-1 --- no
problem, I simply reduced the electrical values of the fixed mica caps in
the Heathkit's Colpitts circuit, & re-aligned it. That did the trick.

The results have been most gratifying.

The flexiblity of a Q-multiplier merely enhances the existing selective
"agility" of the stock receiver. It is an inexpensive,  worthwhile addition,
and one  which may be quickly & easily removed, thus returning the rig to
"original" condition in no time at all...

~73~ Eddy VE3CUI - VE3XZ


***************************


---- Original Message ----- 
From: "Carole White-Connor" <carolew at bellatlantic.net>
To: <rca at mailman.qth.net>
Cc: <boatanchors at mailman.qth.net>
Sent: Saturday, August 04, 2007 9:01 PM
Subject: [Boatanchors] AR-88 Update


> About a month ago, I posted for some help on an AR-88 I had just bought.
Thanks to all who
> responded. Your suggestions were very helpful. I'm wrapping up the
restoration of this set and it
> has turned into a real keeper.
>
> This set is different from the AR-88 schematics that I have seen because
it has a 6V6 push-pull
> audio. That became a problem because what was under the chassis did not
always match the
> schematics I had.
>
> When I started, my first problem was the dial. The tuning knob would turn
somewhat and the
> variable cap turned somewhat but the dial was frozen. I soaked the gears
with WD-40 but it didn't
> help. I dropped the front panel and the dial worked perfectly. It turns
out there was friction
> between the dial and the front panel. I couldn't see what was warped or
bent so I took the
> coward's way out. I placed a nylon washer between the retaining brackets
and the front panel. The
> miniscule bit of clearance solved the problem. The set now tunes as
smoothly as an SP-600.
>
> This set had been heavily modified. The rectifier tube and socket were
gone. In their place, a
> prior owner had installed a circuit board with diodes and dropping
resistors. The work was very
> professional. Also, the prior owner had installed a very large output
transformer with 8-ohm
> output impedance. This output transformer was so large that it covered
half of the hole where the
> rectifier socket had been. Again, the work was very professional.
>
> The non-professional modification was three oil-filled caps hanging
precariously under the
> chassis. I checked the voltages on these caps at start-up and during
operation. All were under 400
> V so I placed the hanging oil-filled caps with modern 10 mfd/450V units.
There was also a
> four-section capacitor can on top of the chassis. It looked to be of 1950s
vintage. I replaced the
> four caps with modern electrolytics. One of these can sections was open.
When I replaced it, it
> cleared up an annoying distortion problem.
>
> With new electrolytics in place, the radio played like a dream. I imagine
the new output
> transformer was a high-priced replacement. I can't believe a stock AR-88
would sound this good.
> (I'm using an inexpensive Radio Shack stereo speaker).
>
> This set had been worked on several times in the past. The workmanship
ranged from pretty good to
> crappy. The caps in the set ranged from bath-tub caps, to black beauties,
to ceramic discs. The
> ceramic discs measured good so I left them in place. I replaced the black
beauties as a matter of
> course. Not surprisingly, all leaked. Several sections of the bath-tub
caps were leaky so I
> replaced them all. Surprisingly, only two or three resistors had drifted
up in value. I replaced
> those.
>
> The end result is a tremendously sensitive receiver with a killer audio.
Selectivity could be
> better but I'm learning to make due with the variable selectivity
settings. This set does not have
> a cabinet. However, it plays so well and looks so good that I'm thinking
of buying a $150 Hammond
> cabinet from Fair Radio.
>
> I thought you all  might enjoy this story.
>
> Joe Connor
>
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