[Boatanchors] AR-88 comments, value?

Tue Sep 3 20:08:28 EDT 2013

    This is not my experience.  The AR-88 uses tubes which are capable at higher frequencies and also uses very low loss coils in the RF and antenna section.  I've measured sensitivity and noise of my receiver and find it stays good right up to 30 mhz.   Of course, its a single conversion receiver with low IF (455 khz in the standard model) so the image rejection is only fair.  Mine measures about at the spec or slightly better, about 200:1 at around 30 mhz. which is a bit less than 50db. Good double-conversion receivers like the SP-600 have substantially more.  The measured noise depends on the AVC configuration.  In the standard receiver its slightly better than 1 uV for 10db signal to signal plus noise using the widest crystal filter; about 3 khz. This is on a par with the SP-600.  When the set is configured for a reduction in the amount of AVC delay, as is standard in the F version, made for triple diversity, the noise falls due to running the RF stages at condiderably less bias. I measure around 0.6 uV that way but the overload characteristics are degraded.  Gain and noise level seem to be pretty constant over the entire range. 
    The 6SG7Y tubes used have slightly higher Gm than the 6BA6 but are semi-remote cut off.  This probably makes it easier to have full range AVC without amplification but I am not so sure of the IMD characteristics. The mixer is a 6SA7, a rather noisy tube.  However, I have tried substituting a 6SB7Y for it (drop in) with no noticeable or measurable difference.  Of course, the bias is too high for the 6SB7 so its gain is reduced but this may also reduce its noise contribution.  In any case, the RCA designers seem to have considered upper frequency performance with some care.  
     FWIW, my measurements were made after a careful alignment using a Hewlett-Packard 606-A.  I think they are reaaonably valid.  
     Both the RF tubes and mixer are superior to those used in the Super-Pro.  A side note:  the version of the Super-Pro that goes to 40 mhz and the post-war SP-400 differ from the lower frequency versions in that they use shunt feeding of the RF stages rather than series feed. This gets the DC off these coils presumably to increase the Q.  The losses in the coils and insulation is one of the biggest problems with maintaining good performance above perhaps 15 mhz.  National used plug-in coils in the HRO and a sliding coil box in the NC-100 and later receivers, Hammarlund used a peculiar knife-switch arrangement in the Super-Pro and RCA used low loss ceramic insulation in the bandswitch and polystrene formers for all RF and oscillator coils in the top three bands. Getting rid of excess losses is also the reason for the rotary turret in the SP-600.  Collins used a whole different approach to design in its receivers to accomplish a similar purpose.  


-----Original Message-----
>From: Bry Carling <bcarling at cfl.rr.com>
>Sent: Sep 3, 2013 4:28 PM
>To: boatanchors at mailman.qth.net, Al Klase <ark at ar88.net>
>Subject: Re: [Boatanchors] AR-88 comments, value?
>
>The AR88 is not so good above about 15 MHz from what I am told.  My friend owned one 
>and it dissapointed him since he was mostly interested in 15 - 30 MHz reception.
>
>
>On 3 Sep 2013 at 16:04, Al Klase wrote:
>
>> Ian,
>> 
>> The AR-88 is a much better radio in almost every way than an SX-28.
>> The 
>> latter was a high-end consumer product.  The AR-88 is a PROFESSIONAL
>> receiver, and may well have been the best general coverage radio in
>> the 
>> world when it was introduced.  Don't be seduced by the PP 6V6's in
>> the 
>> 28.  The single ended 6K6 in the AR-88 sounds better in side-by-side
>> tests on a quality speaker (Altec 604).  The reason is the the RCA
>> guys 
>> had a handle on negative feedback.  Reduced IMD results in better 
>> performance on noisy signals.
>> 
>> Richard K's price range is pretty good.  At the retail level, a
>> proper 
>> S-meter is a $200 adder.  I don't see any advantage to the LF model
>> unless you just hate the broadcast band.
>> 
>> Like any radio this age, TLC, i.e. recapping, is in order.  The
>> AR-88 is 
>> pretty straight forward to repair.  Recapping the front end on an
>> SX-28 
>> is a nightmare.
>> 
>> Go for it,
>> 
>> Al
>> 
>> On 9/3/2013 2:50 PM, Ian Wilson wrote:
>> > There is an AR-88 available (sort of) locally. Although
>> > arguably the last thing I need right now is another
>> > boatanchor receiver, the AR-88 is something special.
>> >
>> > No special tubes needed, I see. Would be interested
>> > in reports on how this stacks up against the SX-28, say.
>> > Also any suggestions as to what would constitute a
>> > "reasonable offer" assuming fair condition and no
>> > obvious major damage would be helpful.
>> >
>> > 73, ian K3IMW
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>> -- 
>> Al Klase - N3FRQ
>> Jersey City, NJ
>> http://www.skywaves.ar88.net/
>>