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Old 8th Feb 2020, 1:45 am   #1
ORAWA01
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Default Freq. adjustment on regen receiver with Denco coils

Hi All

I got this vintage Maplin regen kit receiver for 80m. It seems tune between 3560khz - 3700khz.
I wanted it to tune either from 3500khz or 3700 kHz, so it would tune ham band CW or SSB DX signals.
I am wondering if this is possible to adjust on this simple rudimentary regen receiver. It uses 2x ICs, and 2x transistors and 2x Denco coils. Tuning is done by what looks like variable resistor.
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Old 8th Feb 2020, 3:02 am   #2
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Default Re: Freq. adjustment on regen receiver with Denco coils

I'm sure that such a change could be made, but it will be a million times easier to do if you find a circuit diagram.

B
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Old 8th Feb 2020, 4:29 am   #3
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Default Re: Freq. adjustment on regen receiver with Denco coils

If it has the following marked on the pcb

Maplin
80mtre
GB59P

Then the full article is in Maplin Magazine March-May 1984
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Old 8th Feb 2020, 5:56 am   #4
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Default Re: Freq. adjustment on regen receiver with Denco coils

That 1984 design https://www.americanradiohistory.com...1984-03-05.pdf ticks most of the boxes for the OP description but it has 4 transistors rather than 2.

Looks very much as if it was intended to tune the full 3.5-3.8MHz, so may just be a setting-up problem or component tolerances to blame if it isn't doing that.

B
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Old 8th Feb 2020, 10:49 am   #5
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Default Re: Freq. adjustment on regen receiver with Denco coils

That's the only one I can find in the Maplin mags that uses Denco Coils and is varicap tuned.

There are a couple of others but not 80m specific but they also use a variable capacitor and again, different number of transistors.
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Old 8th Feb 2020, 11:07 am   #6
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Default Re: Freq. adjustment on regen receiver with Denco coils

I will just add that in the parts list for that article, the PCB has part number GB59P. Sounds like it must be the same project.
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Old 8th Feb 2020, 11:13 am   #7
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Default Re: Freq. adjustment on regen receiver with Denco coils

Hi the components around t2 set the rx tuning range the pot rv4 is main tuning this varies the voltage across the ba102 d3 diode changing its capacitance. The
easy way to change this is to change the inductance of the coil t2 this is by ajusting the brass screw in the top of the coil noting its posision before so it can be put back if expected resaults are not acheived . Less inductance higher in frequency Denco coils have a wide range of ajustment.
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Old 8th Feb 2020, 11:31 am   #8
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Default Re: Freq. adjustment on regen receiver with Denco coils

Indeed, it says MAPLIN 80mtre GB59P on the PCB. And I see at least 3x transistors this morning under the morning Sunlight. But the last is TR4. I see TR1, TR2 and TR4, but cannot spot TR3 on the PCB.

I tried to rotate the top star like hat on the T2, hoping it would tune down a bit to CW part of the band, but it didn't. Tried rotating the hat of the T1, but hardly moved the freq.
The set was working OK on 3600khz SSb reception, lots of Russians were having their local net rag chewing, sounded like.

But it stops tuning at about 3570khz where digital noise is very loud. It also doesn't go up over 3695khz, so that I couldn't hear usual DX hunting strong stations from the continent at nights.
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Old 8th Feb 2020, 11:39 am   #9
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Default Re: Freq. adjustment on regen receiver with Denco coils

Quote:
Originally Posted by Bazz4CQJ View Post
That 1984 design https://www.americanradiohistory.com...1984-03-05.pdf ticks most of the boxes for the OP description but it has 4 transistors rather than 2.

Looks very much as if it was intended to tune the full 3.5-3.8MHz, so may just be a setting-up problem or component tolerances to blame if it isn't doing that.

B
That's the same receiver. Looking at the PCB closely, yes it is. Thank you. Thats is a real good article on the receiver. Thank you.
I thought it might be a regen, but learn that it is a DC receiver. It sounded very dynamic and clean on the band.
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Old 8th Feb 2020, 11:53 am   #10
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Default Re: Freq. adjustment on regen receiver with Denco coils

Hi its the brass screw that ajusts the coil the plastic star is to hold the coil to a chasis if not used in a holder. It should be the red coil this is the osc the aerial blue coil is wide enough to cover the 80mtr band hope this helps Mick
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Old 8th Feb 2020, 11:55 am   #11
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Default Re: Freq. adjustment on regen receiver with Denco coils

Quote:
Originally Posted by mickm3for View Post
Hi its the brass screw that ajusts the coil the plastic star is to hold the coil to a chasis if not used in a holder. It should be the red coil this is the osc the aerial blue coil is wide enough to cover the 80mtr band hope this helps Mick
Aha, got you. Will try that tonight when the band comes alive. Thank you Mick.
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Old 9th Feb 2020, 10:55 am   #12
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Default Re: Freq. adjustment on regen receiver with Denco coils

Yes, it did work treat. I rotated the copper screw on the red coil, and the tuning shifted to the cw part of the band. Thank you for the advice and info.

https://youtu.be/S0He4tqAJrQ
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Old 10th Feb 2020, 11:19 am   #13
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Default Re: Freq. adjustment on regen receiver with Denco coils

It is now tuning from 3480khz to 3810khz, tested with the general coverage sw receiver side by side oscillation.

This morning trying out the set in the 80m ssb top end of the band. Antenna was 20m long wire in the garden.

https://youtu.be/JMh2BV1UnlM
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