[R-390] R390 progress

Tue Apr 26 02:15:40 EDT 2005

Hi,  I was surfing on Medley's site and see he says getting into the xtal
box is quite a job - I'll explore other things before going there.  I pulled
the two oscillator tubes,  6AJ5's according to the manual and markings on
the radio.  (What a job to get those little guys out of the cramped box -
resorted to tongs with tape to get some traction - I see why I need those
missing tube pullers !!)  But one of mine was a 6AK5.  Both tested ok and
the 6AJ5 is apparently the same tube as the 6AK5 designed for low plate
voltage.  They indicate about the same gm when tested according to the
Hickok settings for 6AJ5,  which puts low voltage on with my tester.  Does
anyone know if the 6AK5 performs reasonably well in place of the 6AJ5 in a
390?  I don't think I have extra 6AJ5's but I have enough 6AK5's to sink a
very small boat.  I think I searched my boxes for most of the 390 tubes when
I first got it - may have to go searching again,   Dan. 

-----Original Message-----
From: Bob Camp [mailto:ham at cq.nu] 
Sent: Monday, April 25, 2005 7:58 PM
To: Dan Merz
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] R390 progress

Hi

I have never torn into the crystal "box" on a 390 so I am just assuming it's
set up the same way as the 390A. If so then it's not terribly hard to get
into. While you have it open I would at least pull each crystal out and
re-seat it.

There is a test point that will let you figure out if the oscillator is the
issue. That should give you a pretty good idea how to track the problem
down.

I'm still betting on an oscillator problem. You could be correct in saying
that your bandswitch is out of synchronization.

	Take Care

		Bob Camp
		KB8TQ

On Apr 25, 2005, at 10:50 PM, Dan Merz wrote:

> Bob/others,  I pulled the crystal oscillator chassis out of the 390
> (non-a)
> and got it open down to the heater surrounding the crystals and then 
> reconsidered.  I started thinking maybe it's the position of the 
> switch like someone mentioned relative to the 390a - I decided to 
> check that before tearing into the heater.  I put it all back together 
> and now found 7 to 8 Mhz worked most of the time - good enough to hear 
> at least one ham mid-day.
> But I then checked all the bands using the crystal calib and found all 
> bands worked but noticed 4-5, 5-6, 6-7, 7-8 and 8-9 Mhz were quite a 
> bit weaker receiving the marker compared to the other bands.  I would 
> say 7-8 is not working very well but seems to mostly work.  
> Occasionally it seems to not work.  I tweaked the appropriate  caps 
> and tuning rods a bit at 4.6 and 7.8 Mhz but this didn't seem to 
> strengthen reception much.  I'm wondering what to try next to find the 
> problem.  The high bands seem to work ok judging by being able to peak 
> the background noise and picking up signals on the ones where there's 
> some activity.  That's as far as I got.  Is tearing into the heater 
> box surrounding the crystals straightforward ? - the manual I have 
> doesn't show that detail or the position of various crystals within 
> the box.
> I guess I should check the condition of the oscillator tubes,  duh !!
>
> I got the line meter to work by putting the missing jumper back on the
> 11/12
> positions on the rear - seems to be ok now.  The dial calibration was 
> correctable from the front panel,  or very nearly so. I'll deal with 
> that later.
>
> I appreciate all the help and advice,  Dan.
>
>
>
> -----Original Message-----
> From: Bob Camp [mailto:ham at cq.nu]
> Sent: Monday, April 25, 2005 4:23 AM
> To: Dan Merz
> Cc: r-390 at mailman.qth.net
> Subject: Re: [R-390] R390 progress
>
> Hi
>
> Sounds very good so far!
>
> I would definitely check the crystals for the dead bands. They may 
> simply have come loose in their sockets.
>
> The easiest fix of all is the 10KHz offset on the readout. Just center 
> up the zero adjust, slip the counter and you're done.
>
> 	Take Care
>
> 		Bob Camp
> 		KB8TQ
>
>
> On Apr 25, 2005, at 2:54 AM, Dan Merz wrote:
>
>> Hi,  I listened to the R390 tonight for the first time after 
>> repairing
>> -
>> more to go.
>> So far:
>> Put 12BW4's in place of 26z5's that were missing and rewired the 
>> sockets Added two 75 ohm-10 watt resistors below the rectifier 
>> sockets in place of missing 47 ohm resistors - a trial to start with,  
>> seems ok Jumpered pins 4/5 to 2/7 and used 12BH7 in place of missing 
>> 3tf7 Straightened a badly bent twinax female antenna socket Wired a 
>> replacement power connector obtained from Fair Added a missing knob, 
>> also from Fair Cleaned gear train in place with mystery oil
>>
>>
>> The radio worked once I realized the previous owner had used enameled 
>> magnet wire on some added wiring on the rectifier sockets - my 
>> connection to it looked good but only connected after I did some 
>> scraping to get rid of that enamel !!
>>
>> It appears to be reasonably aligned and  reads about 10 khz high on 
>> both ends of the 1000 khz range.  So far only one dead band found up 
>> to 20 Mhz
>> which was as high as I checked.   7 to 8 Mhz is dead.  I haven't
>> cleaned any
>> switches so hopefully that's the problem but only one other band 
>> showed any sign of intermittent connection.  The line meter appears 
>> dead.  The carrier level meter appears ok.
>>
>> I still need a male twinax connector for the antenna socket - one 
>> listener indicated he had one but I'm having trouble getting more 
>> info from him to pay him so he can send it.  One other response 
>> offered an IBM server cable with two connectors that were said to 
>> fit,  so that's my backup source at this time.  My local electronics 
>> junk collector couldn't help me on this one.
>>
>> Roy Morgan indicated he would provide a drawing/description of the 
>> fan he installed on his R390 to cool the 6082 tubes.
>>
>> I was relieved that the radio worked and pleased that it's working so 
>> well at this point.  The seller said it played weakly - at this point 
>> it is better than that in my opinion and I haven't messed with the 
>> tuned circuits at all or changed any of the tubes.  I suspect that 
>> the haywired resistors that were stuck in the 3tf7 socket were part 
>> of the problem before.  I removed the i.f. chassis to jumper the 
>> ballast tube pins and was pleased at how nice it looked underneath there.
>>
>> Now I have to study the manual a bit to see how the alignment goes on 
>> the 390 vs. the 390a - more similar than different I suspect,  Dan.
>>
>>
>>
>>
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