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Post by Dr. Rigamortis on May 5, 2008 13:14:33 GMT -5
From reading on here and then having two Mark IV's of my own, and talking to friends with Mark IV's, it appears that there is defiantly a problem with the receivers loosing their sensitivity. I would say this is directed more toward Alan, who rebuilt one of mine some years back, but is there a common problem with them just not hearing well? I can hear, it is just low...youhave to turn the volume WAY up, then the squeal will drive you out of the room. I know of three Mark IV's that are all acting the same way. I have put new tubes, had it lined and even replaced the 6DS4's... still no improvements. What say you?? Anyone know?
Thanks,
Josh
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Sandbagger
Administrator/The Boss 
Posts: 6,250 
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Post by Sandbagger on May 5, 2008 14:11:38 GMT -5
From reading on here and then having two Mark IV's of my own, and talking to friends with Mark IV's, it appears that there is defiantly a problem with the receivers loosing their sensitivity. I would say this is directed more toward Alan, who rebuilt one of mine some years back, but is there a common problem with them just not hearing well? I can hear, it is just low...youhave to turn the volume WAY up, then the squeal will drive you out of the room. I know of three Mark IV's that are all acting the same way. I have put new tubes, had it lined and even replaced the 6DS4's... still no improvements. What say you?? Anyone know? Thanks, Josh I noticed a similar issue with my MKIII. The sensitivity is just a little off. Even when aligned for a single frequency, the sensitivity is something like .7 uV. Is this indicative of weak Nuvistors? I've checked over parts (but not the tubes yet don't have a tube tester), and is this common? |
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Post by mark4 on May 5, 2008 18:15:18 GMT -5
Not usually. I have (3) Mark IV/IVA's and a Mark III. One of them had low sensitivity brand new out of the box. It was that way form the start. Check the voltage supplies in the receiver. Also check the voltage at the 10 watt zener. A low output will affect sensitivity. Also has anybody tweaked the IF transformers? Should only be aligned by someone who knows what they are doing! Resistors and caps could have changed value also causing this problem. And you may have low output from a transformer. on the IF board or front end board. Yikes! I have seen old III's and IV"S with to much gain! The older radios prior to a MarkII had IF transformer problems with age. Do to the design.  |
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Post by giboni on May 6, 2008 5:59:37 GMT -5
Recently have been researching SAW ceramic and crystal lattice filters.Possibly the answer short cut would be to add a cheap solid state OP board and related parts as the first stage in the If chain?Hams who run real old stuff from the 40s 50s do this to their receivers.I like my M4a and M3 but rarely used them because of this problem.Worked on my Tram and used that most of the time. 73s John    ;D |
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Post by mark4 on May 6, 2008 16:17:00 GMT -5
Well, Design it and post it here!
I'm sure some will use it.
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Post by mark4 on Jun 30, 2008 8:46:07 GMT -5
Just a follow up note:
From the many browning MarkIV's I have repaired.
Other than alignment and tube replacement. It is no fault of the design in low sensitivity issue. Many other things can cause this.
But low voltage supplies is a big one.
That's why we recommened a 100,000 mile tune up.
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Post by Dr. Rigamortis on Jun 30, 2008 9:54:59 GMT -5
Well I'm not going to butcher up an almost new looking Mark IV by putting in some board. It came out designed the way it is, and thats how it will be repaired. If you want to take something out and put in a board you can on yours. I think it was a pretty good design they had myself. Here we are about 30-40 years later and some of these radios are still going with out any repairs. I cant wait till some of these export radios are 30-40 years old and see how they are holding up. Most will be in the scrap boxes I bet.
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Post by mark4 on Jun 30, 2008 13:02:20 GMT -5
That is why I posted the follow up note!
No matter what advise one may give or how much experience a tech may have. Someone will always hack up a radio regardless.
And I doubt that is going to change!
You can only decide how to take care of your own equipment.
If someone wants to hack up their own radio.
They have to live with the result.
Most of the time a trashed radio.
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Post by Tombstone (R.I.P.) on Jun 30, 2008 18:20:53 GMT -5
Hmm.....I had trouble awhile back with low sensitivity on my R27 receiver. I aligned the thing according to the service manual with no luck and then I noticed that a couple of IF transformers were loose in their clamps, I straightened that out and sill no improvement. I then checked voltages to no avail. I sent the receiver to Greg Barket and it came back like new. Don't know what he did to it. Seems like some of the Brownings had sensitivity problems after a lot of mileage.
Tombstone
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Post by mark4 on Jun 30, 2008 18:32:14 GMT -5
Here's the deal.
Radios before the MarkIII or late model MarkII had a different designed IF transformer.
These became a problem with age.
Hence sometimes low sensitivity.
Many other things can cause this problem also.
As for the MarkIII and IV there is no design flaw causing low sensitivity. But anything can go bad on a 30+ year old radio.
Including a bad IF transformer. Nothing here is bullet proof!
I have never had to do any crazy mod to fix low sensitivity in a browning. You could change out all of the IF transformers and still have low sensitivity. If that's not the problem! The real fix is knowing how to track down where the real trouble is. I have seen crazy problems that I fixed. And called Barkett to see if he has ever come across it. Most if the time the answer was no.
And he has had the same experience. It's just not as easy as some people would like to believe. When a radio is sick. The failure is not always the same part. Even with the same symptom. I wish it were that easy.
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