Hammarlund SP-600 JX-6

[W2TRH]

Hello All, i recently got ahold of a SP-600 JX-6 receiver. I checked every tube, all where ok and cleaned the tube sockets as well. The receiver worked well at first but now the audio got hotter and any am stations i listen to are distorted with the AVC switch on. Anybody have an idea what might have "let loose"  that has worked on these?, thanks for your time,
                                                     Steve

[n2bc]

Probably not a quick fix if it has not been re-capped.  Have you peeked under the chassis?  Look for "black beauty" caps, they are infamous for shorting.

Grab your favorite search engine, you find lots of info like this:

http://www.hammarlund.info/SP600svc.htm

[WBear2GCR]

I was over at Steve's and we fired up the SP-600. The RF gain control does not have any effect.

Steve could probably use some tips for troubleshooting in general, and in particular starting with this issue.
For example, referring to the schematic, what voltages to look for, and where.

And maybe how to locate/identify those schematic points inside the radio.

                 _-_-

[MikeKE0ZUinkcmo]

Congratulations!!

The JX-6 is a plane vanilla version of the radio.  I strongly recommend you print out, double sided, the Anthology, and buy a print copy of TM11-851.   There is a lot to study in that receiver. 

Mine had fallen victim to several "field engineers" so my first task was to return it to stock, and start over.   Doing a complete re-cap will require extensive dis-assembly but the result is worth the effort.

[w8fax]

Mine was all stock when I got it and it was working but not too good. Replacing ALL the caps is the first part of it. I found many of the black beauties defective. Burnt, split open, etc. Sometimes it is a REAL challenge to get at some of them.  Next came switches. Clean. I believe the caps and switches are the main thing to start with.. BTW, the power caps, I think they called them "bathtubs" can be gutted and a new cap put inside if you wanna keep the "old" look. Take your time....be careful. There is a ton of stuff on the internet about these rigs. Part of the fun is the fact that the thing is so heavy so moving it around is tuff. I find that placing rigs on mouse pads turned upside down helps with sliding but not much can help in the lifting...lol

[WBear2GCR]

For sure a download and printout of the Anthology (preferably printed in color) is a must. I did it.

In Steve's situation though, and if it were my receiver I would start with the non-working part, since it does receive in a reasonable fashion now. Once you pull a bunch of stuff out and replace it, you've got a ton of "variables".

So, what Steve needs to get rolling is a bit of hand-holding on the basic aspect of correlating the functionality of the RF gain switch with the components that it is associated with and how that circuit operates, and how to identify those parts in the unit. Steve's pretty good at building from scratch, but I don't think he's done much troubleshooting on existing units - but I'm not certain of that.

So maybe if anyone knows that RF gain control and how it operates, maybe run-down here would get him down the track a bit...

                  _-_-

[w1vtp]

It would be helpful if we knew what the symptoms are.  From what I can determine right now the AVC line is no longer "working."  That has to be a relatively simple issue.  Question: does it work in the "CW" mode?  Is there some RF control in that mode?  The AMFone world wants to know   

[WBear2GCR]

Turning the RF gain control has no effect. Meter is about at the 50dB mark, may or may not respond to received signals from that point.

BFO functions, it receives in CW mode. Afaik no change in the way the RF control operates.

                      _-_-

[w1vtp]

Turning the RF gain control has no effect. Meter is about at the 50dB mark, may or may not respond to received signals from that point.

BFO functions, it receives in CW mode. Afaik no change in the way the RF control operates.

                      _-_-

I'm thinking this problem will end up not being a biggie.  Maybe one end of the pot has opened up

[n1ps]

Hi Steve,

Not that familiar with the 600, but a couple ideas.   I dont believe the RF gain control is in the circuit with the AVC on, looking at the sp600 print.  When AVC off the gain control provides neg bias for the front end from the V20 rectifier, the more negative the less gain as delivered to the IF amps.   So does the gain control work when the AVC is off?  Its important because it tells you that the problem is either at or after the AVC switch. 

With the AVC on it sounds like there is no or little AVC action.  With a strong signal the first tubes are getting overload. Some likely suspects are:
1. Resistor chain for the AVC starting with R111, R60 and R61.  They should be with 15-20%.
2. Confirm the RF gain control works with the AVC off.  With strong signals you should be able to control the overload distortion manually.  If the gain control does not affect the gain (AVC off) then the problem is at an individual stage.  V6, V7, V9 and V10 are AVC controlled at each grid via a series resistor.  Check each one.
3. The AVC switch.  Its a DPDT with one side switching AVC and the other controlling the meter.  Ohm it out.

A place to start if you haven't fixed it as yet.


p

[W2TRH]

Good Evening Gent's, my apoligies for not responding sooner, i want to thank you all for taking the time to responed to my qestion. The jx-6 i have is stock, i have seen my share of equipment that has been "field Engineer fixed" for sure. When i first powered if up it worked great, did it slow on a variac , only after about two day's of using it, did it start to have issues, i am making a list of sugested parts and will check the pot's as well, anymore sugestion's will be welcome of course, a soldering iron in hand, a pile of parts, and a snow day from work will get it going again, 

[w1vtp]

Hi Steve,

Not that familiar with the 600, but a couple ideas.   I dont believe the RF gain control is in the circuit with the AVC on, looking at the sp600 print. 
With the AVC on it sounds like there is <snip>...


p

The RF gain is in the circuit when AVC is selected.  I just ran my  SP600 and if I turn down the signal goes down  and eventually away

Al

[WZ1M]

Its been a long time since I tangled with one of these but I had a similar problem with my JX-1. It was the resistor across the AVC switch that was causing the problem. Like I said, been a long time and I mite be leading you down the wrong path.
Regards,
Gary

[Todd, KA1KAQ]

Could be one thing or several things causing your problem. Tubes that test good in a tube tester can end up working poorly in a circuit. Not often, but not unheard of, either.

In all but the later models (can't recall the model#), caps were a known problem throughout the radio, as mentioned by Mike and others. Later models used disk caps and other, improved components. Trying to fix just one symptom without addressing the overall issue of defective/aged components on one of these beasts can leave you chasing your tail and frustrated.

I'm not big on the shotgun approach, but this is one receiver than will truly benefit from a thorough cleansing before you expect too much of it. I'd go through it a stage at a time starting with PS and replace caps, testing after each stage, and check resistors along the way.