[Boatanchors] AR-88 comments, value?

Tue Sep 3 23:16:22 EDT 2013

I agree.  In my experience the AR-88 is the only receiver of that era  
that performs well on 10M without an external converter or preselector.

Dennis D.  W7QHO
Glendale, CA

****************
On Sep 3, 2013, at 5:08 PM, Richard Knoppow wrote:

>    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 le
> ss 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/
>>>
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