Drake SPR-4 Shortwave Receiver

[xrunner]

So here she is - the fully restored Drake SPR-4 in it's rightful place on my radio desk.

Now, back to Ebay! 

[Kosmic]

So here she is - the fully restored Drake SPR-4 in it's rightful place on my radio desk.

Now, back to Ebay! 

Good job, look really good 

[bd139]

Indeed. Excellent work 

[Specmaster]

Looks really good there, what's next?

Sent from my POT-LX1 using Tapatalk

[xrunner]

Thanks a lot guys. 

I found an MFE3007 dual-gate MOSFET the SPR-4 uses for the rf amplifier transistor on Ebay (NOS) for cheap, so I got it in reserve in case needed someday.

What's next? As far as a project not sure. However, 6 meters is really alive in the day now so I might just use what I have for a while LOL. Just this week I worked three new DX entities on 6m - Belize, Costa Rica, and St. Martin using the homebrew beam. We had a high windstorm last week and it looked like one element of the beam was bent by the wind but it was only torqued at the screw joint. I got up there and was able to tap it back with a garden tool. After the season I'll take it down for the winter and look at making some of my own mechanical improvements. It needs to hold the elements a bit better. I see the 3D printer involved in some way. Some of the fittings are already made by a 3D printer my friend's friend made for this project. He made them out of PETG which is tougher than PLA.

I designed my own style of antenna end-insulator right after I got the 3D printer. I don't like most of the types you can buy. I want my antenna wire to pull straight out of the insulator and not wrap around and/or tie in knots. I installed them this spring on two different fan dipoles. Two are printed in gray and two in white. The material is PLA. I want to see how they hold up after the blazing heat of the summer. Some say they will get soft and stretch. That is what I will find out. So far, they look just fine. If anyone wants the CAD for the insulator to use or mod let me know. Hmmm ... might ask DAVE if he can add .stl as a file attachment type (or could be zipped I guess).

[xrunner]

I received a PM regarding the file I used to print the dial numbers. I will attach the Open Office file here for anyone who might need it. The font and spacing should be OK. Edit the file with your specific band details. But you must use clear adhesive "paper" to print it.

[carlos2007]

Hello,

Interesting post, I am going to align my SPR4 but I see that the OP only made the 50 Khz  and 5645 khz if alignment. What about the preselector and injection alignment (mixers circuits) , local oscillator.....?

I would be very pleased if somebody could explain the rest of steps since is not very clear.

I have came across with a website that explain the rf amplifier and mixers more in detail:

http://www.dashdist.com/1u2u/SPR-4/improve/improve.php
I attach an old invoice that came with the SPR-4 I have purchased
 
   

 

[Smoky]

That's a cool looking radio. Great job Xrunner

[xrunner]

That's a cool looking radio. Great job Xrunner

Thanks. 

Interesting post, I am going to align my SPR4 but I see that the OP only made the 50 Khz  and 5645 khz if alignment. What about the preselector and injection alignment (mixers circuits) , local oscillator.....?

What about the preselector and injection alighment do you want to know? It's been 5 years but I only made posts about the steps I thought needed explaining if I did it differently from the service manual, or that I thought needed more explanation. Just because I didn't post about every step doesn't mean I didn't do them.

The only problem I ran into was that I didn't have several of the accessory xtals, probably because they weren't available.

[carlos2007]

Thanks for the prompt answer. Is the rest of the alignment difficult? Did you find any remarkable problem in the rest of alignment?

 By the way I am a bit confused about  the 50 khz LF filter alignment there are four transformers, T11 to T14, are adjustable but they have a small spring and I am not familiar with this type of adjustment.

 How is the method for aligning this type of slug, do I have to pull out the spring or just turn it? Spring or white and red discs need to be  hold? Photo is attached.


 Regards.

[xrunner]

Thanks for the prompt answer. Is the rest of the alignment difficult? Did you find any remarkable problem in the rest of alignment?

Not that I can remember, but it was 5 years ago. 

By the way I am a bit confused about  the 50 khz LF filter alignment there are four transformers, T11 to T14, are adjustable but they have a small spring and I am not familiar with this type of adjustment.

 How is the method for aligning this type of slug, do I have to pull out the spring or just turn it? Spring or white and red discs need to be  hold?

Well you caught me off-guard with that question. I couldn't remember pulling any springs so I took mine apart. OK, what these are is a coil of very hard wire that can be turned not pulled. Sort of a miniature version of the coil that goes into your sewer when they snake it. On the end the coil is flattened so that you can use a tuning wand with a slot on one end. You have to adjust these with the case ON from the back of the receiver and without using metal tools. You might have to buy a set of plastic tuning wands if you don't have any ... but ...

It looks to me from your pic that a gorilla has got hold of yours and mucked around with the end of that coil, perhaps twisting it or trying to turn it with a pair of pliers or something. I think they ruined the flattened part so a tuning tool might not work now. I'd have to think about what to do if the end is ruined, maybe some readers here will have an idea. 

[carlos2007]

I know now because it lacks a a bit of sensitivity, maybe last owner tryed to calibrate it without propers tools. I have two SPR'4s and the other has a very good sensitivity in all bands but needs an alignment too,

This one that has the springs broken is almost new in minty condition, however the other looks like older and well used but works quite nice.

Just an idea, could work if a small solder tin drop cover the spring? Or could enworsen the spring?

[Wallace Gasiewicz]

These cans with the "spring" adjust are found in many older HAM radios/  The "spring" is connected to a tuning slug which tunes a coil.  They are usually held in place by wax or glue at the top.  I do not know if this Drake used anything to hold the adjustment.    Collins and Yaesu seemed to be fond of these things also.     In a lot of tuners they are "ganged" together.     
The "spring" is essentially a screw adjustment attached to a ferrite "slug".  It does not matter it the end is flattened or not. Sometimes the thing is so sensitive that touching the spring can change the alignment.  Mostly you can attach a hemostat to the spring and it does not affect anything until you turn it to tune the radio..

[carlos2007]

Yes. I will touch them very carefully maybe a slight turn will be enough. The preselector has 5 similar transformers but the movement is up and down.

[Wallace Gasiewicz]

The tuning coils in the picture are the same thing but they are ganged together and adjusted with the tuning dial.   To align these coils the red stuff on the top needs to be removed and then the coils can be fine tuned by turning the coil.  After everything is aligned, you are supposed to glue this back to secure it.