[Hallicrafters] SR-2000 Audio additional comments

[James Liles]

Good evening Richy:

Forgot to add step two,

ALL tests using the 14Mc band!

Clean all tube sockets with a between tooth dental brush and Deoxit.  Then 
while in receive mode wiggle all tubes and if you hear any static or 
abnormal behavior, clean them again.

Then switch to transmit and tune the radio up in low power mode into a dummy 
load then switch to receive.

Now make a strap out of copper sheet about 3/4 of an inch wide and long 
enough to fit around the 12BY7A with a 1/8 inch gap.  Remove the 12BY7A and 
fit the new tool/sensor to fit snugly around the tube.  Drill a small hole 
at the top end large enough for a #20 wire and solder a one inch piece of 
wire to the new sensor using high temp silver solder.  The reason for the 
wire is to attach a scope probe and to dissipate the heat a bit otherwise 
your probe will melt.  While your at it make one for the 7 pin tubes ---  
we'll use that for other measurements later.  These sensors provide an 
approximately 2pf NON-INTRUSIVE sensor into the radio.  Use them on any 
tubed radio.

The SR-2000 transmit circuits can be completely aligned without turning the 
High Voltage on using the 12BY7A sensor.

For this test we will simply go to transmit tune with the HIGH VOLTAGE OFF 
and attach a scope to the 12BY7A measuring the signal with a 10X probe. 
Peak the pre-selector and increase the RF drive until the scope says 12 
volts p/p.  The 8122's won't draw grid current until approximately 18 volts 
p/p but you won't hurt them even if you exceed 12 volts because they use a 
10K grid leak resistor to protect the 8122's from excessive overdrive as the 
radio runs in the AB1 mode.

While in transmit mode HIGH VOLTAGE OFF --- watching the scope, wiggle all 
tubes except the 8122's checking for output variations on the scope.  Any 
anomalies, clean the socket again.

The sensors will be used in many many more service processes but this 
completes our previous post.

A closing note:
If you have a spectrum analyzer you might consider acquiring an HP 8447D or 
8447A preamp --- 20db to 25db gain to put in front of the spectrum analyzer. 
This configuration will enable you to visualize the radio from the receive 
RF amp to the final drivers.  The configuration that I use is an HP 8447D to 
an HP 8568B spectrum analyzer.  Using that configuration and injecting 3uv 
into the antenna lead on 14Mc, the sensor placed on the 12DK6 receive RF amp 
will paint 70uv in a properly functioning SR-2000, 400, or 400A.

We use it throughout the radio to verify the performance of each stage.

More to come and if it's too much, just delete it.  I started three years 
ago to write a service manual and am two years late so I thought it best to 
get the important stuff out in small pieces.

Kindest regards and a very Merry Christmas and Happy Holiday season


 ----------------- ORIGINAL MESSAGE ------------
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From: "James Liles" <james.liles at comcast.net>
Sent: Tuesday, November 23, 2010 10:34 AM
To: <hallicrafters at mailman.qth.net>
Subject: Re: Hallicrafters Digest, Vol 82, Issue 25

> Good morning Richy:
> The function switch is very seldom the problem.  The switch is mounted on 
> a plate that is riveted to the chassis and has become loose and oxidized. 
> The early radios used screws.  I would stop any repair work now and do the 
> following before you replace the function switch.
>
> Drill one of the rivets out that hold the function switch plate and 
> install a screw and star washer using Penetrox copper particulate compound 
> (Copper butter --- like that used on the aluminum elements of an 
> antenna) --- the zink compound is OK but I prefer copper.  Then do 
> this ---- you are going to hate me for this one but the payback is 
> immense.  Remove every screw in that radio and reset with a dab of 
> Penetrox.  A handy device to administer the Penetrox is an 18 gage 
> surgical syringe.  You say I can't afford that device ---- wrong, they 
> cost $.26 at your local pharmacy and while your there buy a 28 gage 
> version for Deoxit administration.  Now place a drop of Deoxit on every 
> star washer that lives under a rivet and use a small hammer and narrow 
> screwdriver to tap the star washer as you would try to turn a wheel to 
> reset it.  VOILA you have just fixed %95 of the problems that will occur 
> with the SR-2000, SR-400, and SR-400A etc.
>
> Any radio that uses an aluminum chassis will have the same problems.  You 
> can tell whether a radio has been stored in the garage where temperatures 
> vary wildly or in the closet.  The garage kept radios always seem 
> impossible to make work properly or are forever squirrely.  The SR-2000 is 
> probably the most affected of all because it absolutely demands chassis 
> continuity without unexpected chassis loops.  This is because of it's 
> inherent power and collocation of components.  The above procedure is a 
> permanent fix.
>
> One of the most common complaints with the SR-2000 is "I can't neutralize 
> that radio and if I could, it would be goofy tomorrow"  Again, the above 
> procedure is a permanent fix.
>
> BTW, L15 and L16 are best adjusted with a sweeper.  Don't understand the 
> comment regarding the effect on the audio --- they have to be way off to 
> affect audio quality.
>
> Good luck and don't give up on that radio.  A Merry Christmas and Happy 
> Holiday season to you and yours --- Kindest regards Jim K9AXN
>
>> Message: 1
>> Date: Mon, 22 Nov 2010 12:01:57 -0500
>> From: ss409ss at aol.com
>> Subject: [Hallicrafters] SR-2000 Audio
>> To: Hallicrafters at mailman.qth.net
>> Message-ID: <8CD587E1B405088-1F8C-280E9 at webmail-d073.sysops.aol.com>
>> Content-Type: text/plain; charset="us-ascii"
>>
>>
>>
>>  Thanks Walt and Jim,
>>
>>   I had to remove the case to get at L-15 and L-16. The advancement of 
>> those two controls yielded muddy audio from the speaker so I moved them 
>> back and checked the test point with a freq counter. I also set the 
>> carrier null while I was in there. I found that the function switch was a 
>> big issue with this one, the radio emits a carrier in ssb, pulling 
>> slightly on the switch and it goes away, also if the switch doesn't have 
>> the same tension on it, the USB osc will drop out on occasion.
>>
>>  I am currently working on that function switch, I took many pictures 
>> then I took it out and all apart, cleaned it, reset the wipers and 
>> contacts and put it back in. I am head scratching on the wire placement 
>> for a few of the connections but this was late last night so I went to 
>> bed and figured I would get up with a clear head and finish it up looking 
>> at my pics, the problem is the bottom wires that I couldn't get at with 
>> my camera. I did mark all of them down on paper as I took it out but you 
>> know how that goes..lol  Regards, Richy N2ZD
>
>