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Author Topic: Drake SPR-4 has extra board with 3 IC's wired to volume control  (Read 784 times)
K1YTG
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Posts: 486




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« on: October 07, 2018, 02:24:53 PM »

I picked up the Drake SPR-4 and opened it up to find it does have the calibrator board and the noise blanker board .  Each plugged into sockets on the top of the chassis.
But there is also and extra board mounted on its edge way to the left on the top of the chassis.  It has 3 IC's in sockets on that board.  It is controlled by a rotary switch mounted on the front panel that had 4 positions. 
Shielded wires go to the Audio Gain control.  Looks like the audio has been sent to this board to be processed and then the altered audio is sent back to the gain control.

Is anyone familiar with this modification of the Drake Receiver?

Thanks,  Norm
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AD8CC
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Posts: 25




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« Reply #1 on: October 07, 2018, 03:19:22 PM »


Probably an agc modofication.  Not seen one with a single control, but it could just be a variation of this 2-switch version:


 

Sean AD8CC
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G3RZP
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« Reply #2 on: October 08, 2018, 03:45:04 AM »

What are the IC part numbers?
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K1YTG
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« Reply #3 on: October 08, 2018, 04:02:29 PM »

947  LM324N

17943  CD4016CN

7943   CD4049CN  these are the numbers on the IC's

There is also a switch labelled AVC with wires going to the power supply board.

The rotary control sounds like it is controlling the selectivity curve.

Less sound gets through as the control is turned clockwise.  Increasingly it sounds pinched as the control is turned.

Norm
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KM1H
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« Reply #4 on: October 08, 2018, 05:37:05 PM »

Well, they are all 1979 dates and all standard IC's you can look up, just copy and paste into Google
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G3RZP
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« Reply #5 on: October 09, 2018, 02:05:55 AM »

LM324 is a low power quad op-amp.

CD4016 is a quad bi-lateral switch.

CD4049 is  hex inverting buffer.

Could be an audio filter and some form of audio derived AGC.

What is the final IF of the SPR4? If it is down around the 50kHz mark, then the board could be a synchronous AM detector and AGC
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W9AC
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Posts: 117




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« Reply #6 on: October 10, 2018, 04:50:19 PM »

CD4016 is a quad bi-lateral switch.

And the more common CD4066 is a suitable replacement for the CD4016.  The main difference is that the 4066 has a lower "on" resistance. 

Paul, W9AC
« Last Edit: October 10, 2018, 04:53:18 PM by W9AC » Logged
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