[Boatanchors] Modified AR-88

[mac]

Joe,

My guess would be that a previous owner added a push-pull audio output  
stage using a pair of either 6V6s or 6K6s.  (No idea why you now see  
one of each.) The 6SN7 would be the phase inverter.  Motorboating  
usually means bad or too small decoupling caps in the B+ circuits.

The AR-88 is reasonably roomy under the chassis.   Suggest you get an  
original  schematic and do a little reverse engineering to dope out  
just what  mods have been done.

Dennis D. W7QHO
Glendale, CA



On Jan 16, 2010, at 3:58 PM, Joe Connor wrote:

>
> I'm working on a heavily modified AR-88 that I bought a few years  
> ago. 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.
>
> Some are weird. The audio output was changed from a 6K6 to a 6V6.  
> 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.
>
> 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. 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. It motorboats with Selectivity set to the No.  
> 3 or No. 4 positions.
>
> Any insights and help would be appreciated.
>
>                                Joe Connor
>
>
>
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