My Drake SPR-4 now Stuck in Mute

[K6IC]

My venerable Drake SPR-4  (really a solid-stated R-4) failed to recover from Mute function while in use the other night.  The symptom is that there is no audio,  and the S-Meter is at full scale,  just as it is during the Mute function.

Cycled the power, and still sutck.  Turned off the RX for about 10 mins,  and all was OK until the next transmission,  where it has NEVER recovered.  I Do not have the Service Manual for it,  and not even the schizmatic.  It is possible that I've roasted the front-end,  as only use a 115 VAC Dow Key relay.  One set of  aux contacts on the Dow runs the mute,  the others  short the speaker output (on transmit). There is no sequencing ... flip the transmit toggle switch which applies 115 VAC to the Dow and away we go.    Unplugging the mute cable has no effect -- still stuck.

The transmitter is a Dixie 100 B.  I assume that the Mute drives the AGC to the point of cutting-off the RF and IF amps  ... or perhaps it is different in an all Solid-state RX (?) .     Advice  appreciated  73  Thanks,   Vic

[WQ9E]

Vic,

The SPR-4 requires that the mute jack be shorted for receive so it is possible you have either a cable or relay problem.  Removing the cable would definitely not make it work.  Try sticking a shorted RCA plug in the mute jack.

Rodger WQ9E

[K6IC]

Hi Rodger,

OH !!  Been  SSSSOOOOOO long since setting up this RX,  had forgotten this.   The back of the DX 100  is very difficult to access,  so cannot see the Aux contacts.  This sounds a bit more promising.   Guess that there was a shorted plug that I removed oh so many years ago to add the Muting function.   Will give that a whirl and look at the Aux contacts on the relay.

73  Thanks again,    Vic

[K6IC]

Hi again Rodger,

OK  you were correct about the Muting function.  Shorting the Mute jack,  indeed,  did restore the RX function.   AND burnishing the the Aux contacts on the DowKey relay made everything function perfectly,  ...  again.

Almost never use this AM operating position,  but when I do,  it is to take a net,  every three months.  So sometimes something has borken from dis-use.

So  Thank You again.   I shudda remembered the ploarity of the Mute.
73  TU  Vic   K6IC

[WQ9E]

Vic,

You are welcome and I am glad that solved the problem!  If the SPR-4 only had the independent bandwidth selection and passband tuning like the rest of the 4 line it would be my favorite receiver-even without that it does a nice job.  I built one of the crystal replacement synthesizers (as described in QST) and it is a really nice general coverage receiver.

73, Rodger WQ9E

[K6IC]

Hi Rodger,

I got this Radio,  used,  in about 1973.  Got it from Gilfer Assoc,  and they set it up, covering most ham bands,  and quite a few SW BC bands.   For what it is,  it has been a very nice radio for decades.

That synth sounds like a nice addition.   73  Thanks again for the quick,  correct solution,  Rodger.     DE  Vic

[WQ9E]

Hi Vic,

For future reference, here is a link to the website from the designer of the synthesizer: http://www.geocities.com/hagtronics/r4.html

And a link to the board and major active components available from FAR circuits:  http://www.farcircuits.net/vfo1.htm

There are separate "kits" for the SPR-4 and R-4 series since the premix scheme is a bit different on the two Drake receivers.  I ended up with 3 of the kits, 1 for the SPR-4 and a couple for the standard 4 line since I have several 4 lines.  At the time I put mine together (4 years ago) the additional passive components, display, and misc. parts ran around another $45 per unit over the basic cost of the FAR board and included parts.  Mine all worked fine although I did have to do a little cleanup on one of the FAR boards before I started.  They definitely are still a nice addition to Drake line to provide full general coverage and are much less expensive than trying to find an FS-4 on ebay.  The display also helpfully tells you which band to select and the preselector setting for a given range.

Rodger WQ9E