The AM Forum

I have thrown in the towel on eliminating strong birdies in a Drake R4B receiver that is in good electrical and physical shape.  I spent a month trying to hunt down the source.  The Birdies occur on all bands, very strong at 3893 Khz. Strength of the birdies is varied with 80 and 40 meters have multiple birdies that rival the crystal calibrator.  Spurious harmonics (50 Khz Oscillator?) seem to be apparent as real signals at V1 (RF amplifier 6BZ6) and V2 (Mixer 6HS6).  I can go into the testing, component removal/tests, and blood, sweat and tears, but result is a good receiver with a whole suite of unwanted signals on every band which is problematic on 80/40 operating frequencies of interest.  Although my education was in electrical engineering, I was not a design engineer but I still grasp at  the fundamentals.   I am retired at 72 and struggling a bit to relearn and remember or intuit and need to seek Elmers and references that can direct my attention to the source of the problem.  Problematic is the tight spacing of wiring and components, so I always worry about causing more damage that I fix.  I have the references on the Drake Mods, troubleshooting, and the pictorials of components and circuit boards to no avail except knowing the territory to do the checks.

I have basic equipment with a scope, signal generator. and an SDR Play I could use as a spectrum analyzer as well as VTVM/multiuse VOM.

I am missing something - I had an R4B in 1970 and it was a very good receiver with no birdies of the magnitude I have found in an operational restore of this one.

I know of restorers that would likely get it given enough time and money, but hope I can get some new thoughts and direction to pick this up again.

Thanks in advance

Bob, NS7H

Bob,

My friend Mark WB0IQK recommends getting on http://wb4hfn.com/ and contacting them for phone support. Mark would have gotten on here himself but is having trouble with this board recognizing his password again.

Good luck.

you might try some ground enhancing / connection improving methods.  a little bit of red de-oxit on tube pins and then working the tube straight in / out helped solve some similar type problems in a 32s1 tx.  any ground lug connections may be suspect as well  - often can be resolved by loosening the mount and then retightening.  good luck 73

Hi Bob,

I agree with prior post...

However,
 
Sounds like a stage is oscillating that is not supposed to be... That said, I would make a little current loop pickup and use a SA and see if I can find the offensive stage. I would pull all tube stages that are a KNOWN source of LO. You are looking for those stages, IF, mixer, RF, audio etc... that are normally gain stages, that are now operating as an LO which should not be the case.

I would take the simple approach first, namely find the source of unwanted LO.

Alan W4AMV

Bob,

At present, I listen on a Drake TR7 and I have the same problem you are experiencing.  Recently I flipped all the breakers in the house off except for the radio room.  The "birdies" disappeared.
Our home is a very rich RFI box.
73,
Chuck

You didn't mention - birdies with or without antenna connected? You also might try shutting down each electrical equipment one at a time to see if it makes any difference. TV's, modems, computers, even modern ovens or any modern appliance have all sorts of oscillators in them that can radiate harmonics all over the place. Years ago my neighbor had a TV that radiated a strong signal on 80 meters. Always new when he turned that TV on.