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Old 14th May 2024, 9:16 pm   #1
Phil G4jhs
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Default Codar Multiband 6 info

I recently got hold of a Codar Multiband 6 (No coils) and I am in the process of restoration. I do have a set of the Denco 9 pin dual purpose coils green range but read somewhere that there are changes to be made if you want to use them with this radio? Does anyone have any info regarding this coil mod or any other info that would help me in my quest.

Kind regards
Phil
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Old 17th May 2024, 10:55 pm   #2
frsimen
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Default Re: Codar Multiband 6 info

Hello Phil,

A belated welcome to the forum

Looking at the construction information for the Multiband 6, the wiring to the valve holder for the plug in coils matches the pinout for the coils given in the Denco data for Green coils.

I've seen the same comment on line about the coil modification, perhaps whoever built that version made a mistake in the wiring. Denco green coils should work without modification. If you can't get the circuit to oscillate, swapping the wiring to pins 3 and 4 should sort that problem out.

Paula
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Old 20th May 2024, 12:22 pm   #3
Phil G4jhs
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Default Re: Codar Multiband 6 info

Hi Paula,
Thank you for the info. I was thinking along the same lines looking at the info for the Denco green coils. Regarding your comment on pins 3 and 4 for regeneration I take it that you mean reverse the connections to 3 and 4? The circuit diagram that I managed to get hold of is slightly different to the wiring of this RX. Connecting an antenna gives no signal but if I inject a signal I can detect it albeit very faintly. Will be spending more time on it shortly.
Kind regards
Phil
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Old 20th May 2024, 7:17 pm   #4
frsimen
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Default Re: Codar Multiband 6 info

Hello Phil,

If the regeneration isn't working, the phase of the regeneration winding is probably not right. Reversing the connections to pins 3 and 4 on the valve base (not on the coil!) will correct that. It does sound as if something isn't working properly. Check the AF stages first, then worry about the detector stage. If you fit a MW coil, you should be able to hear the detector oscillating on another MW radio. That will prove that the coil phasing is correct. If it doesn't work, maybe the FET has been damaged, or wired incorrectly.

Paula
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Old 20th May 2024, 9:49 pm   #5
Phil G4jhs
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Default Re: Codar Multiband 6 info

Hi Paula
I did order a couple of FETs on the off chance it is damaged. The audio stage seems ok, i do have output into a 8ohm LS and also into my headphones when i inject a signal but as soon as i get the chance i will swap the connections on pins 3 and 4 and see what happens if no progress i will change the FET and check the components around it. I will let you know how it goes.
Many thanks
Phil
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Old 24th May 2024, 3:22 pm   #6
Phil G4jhs
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Default Re: Codar Multiband 6 info

I have stripped the PCB from the metal work and cleaned the copper ground plane that goes underneath the metal work, really filthy. Replaced all the rusty self tapping screws with cheese head screws and nuts. I also changed the coil connections 3 and 4 over with no apparent improvement but then found that the B9A coil holder has an intermittent connection so have ordered a new one.
The FET that I got hold of is a 2N3823. is this a good swap for the original 2N3823E / PN3819E ? my knowledge of FET's is limited. What does the E denote?
Regards
Phil
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Old 24th May 2024, 11:08 pm   #7
frsimen
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Default Re: Codar Multiband 6 info

Hello Phil,

Back in the 1970s, the 2N3823 was in a 4 lead TO-72 case. The 2N3823E was the same transistor in a TO-92 package and these were cheaper.

I expect your modern day 2N3823 is identical to the 2N3823E and will be in a TO-92 package.

Paula
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Old 25th May 2024, 10:47 am   #8
mickm3for
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Default Re: Codar Multiband 6 info

Hi details of coil on page 11 dont know if a mod coil pin 9 to earth pin 8 to aerial pin 5 to tuning cap +gate of fet pin 2 to ground/earth pin4 to react cap pin 3 to fet D Mick
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Old 25th May 2024, 12:41 pm   #9
Phil G4jhs
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Default Re: Codar Multiband 6 info

Hi Mick. Many thanks for your input, I do have some info on the green Denco coils but I did get some info a while ago that said that there was a mod for the Codar Multiband 6 but the way the B9A is connected looks oOK for the green coils so a bit mystified on that one. still work to be done on the next rainy day

Cheers, Phil.
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Old 25th May 2024, 1:40 pm   #10
Phil G4jhs
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Default Re: Codar Multiband 6 info

This is a circuit diagram that I managed to get hold of. there are differences between this diagram and the circuit of my Codar radio, the supply voltage is one of them and some component values are very different.

Waiting for a replacement B9A valve holder before I can go any further.
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Old 25th May 2024, 2:44 pm   #11
mickm3for
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Default Re: Codar Multiband 6 info

Hi I have lashed up a version of this it works with an MPF102 in TR1 location the 2N3819, the pin of the coil junction with the 60pF react cap is pin 4 the RFC is 2.5mH.

Mick
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Old 25th May 2024, 3:09 pm   #12
Phil G4jhs
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Default Re: Codar Multiband 6 info

Hi Mick, it is good to know about the mpf102 i shall keep that in mind. once again thanks for your help.
Cheers
Phil
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Old 25th May 2024, 3:53 pm   #13
mickm3for
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Default Re: Codar Multiband 6 info

Hi the radio will run on 9V or 12V some mods during production ie around the Drain of TR1 the regen part. Resistor 860 ohm was changed to 2k2 the 0.012 across it changed to 0.01 and the 10uF changed to 1uF and a 9V supply.

You should have 9V ish on the S of the FET to ground, reading the 9 pin socket from the pin end clockwise continuity from P2 to P5 this is the main tuning winding from P3 to P4 this is the feedback winding and from P8 to P9 this is coupling for the aerial.

Mick.
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Old 26th May 2024, 5:12 pm   #14
Phil G4jhs
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Default Re: Codar Multiband 6 info

Hi Mick
Just had time to check some voltages. First off on this radio negative and ground have no connection between them but in the circuit diagram they have so the voltages are as follows on T1.
8.4v on D to -ve
3.2v on S to-ve
1.7v on G to -ve
1.17v on S to ground
Any thoughts on this?
Cheers
Phil
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Old 26th May 2024, 6:11 pm   #15
frsimen
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Default Re: Codar Multiband 6 info

The S to ground and S to -ve surely should be the same. Check that the negative is connected to the ground point. The gate should be at 0V, whether measured to negative or to ground. Are you sure the FET is connected correctly? Mixing the gate with either the source or drain connection could cause some odd voltages to appear.

One think I've noticed is that the circuit diagram you posted earlier does not match the wiring instructions I've seen for the Multiband 6 kit. The wiring to the valve holder for the coil is wrong in the circuit. When you fit your new socket, check that the wiring matches that of the Denco coil otherwise you the radio won't work.

Paula
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Old 27th May 2024, 10:47 am   #16
Phil G4jhs
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Default Re: Codar Multiband 6 info

Hi Paula, There is no physical connection between -ve and ground. I measured the resistance between the two and it is 400ohms. The build instructions do not show any link between the two as far as I can see. They have also had notes written on them one saying Earth 7.6v?
The coil connections look ok and match the Denco information that I have but still waiting for B9A to turn up.
I have not had the FET out yet but hopefully i can spend more time on the radio this week.
Regards
Phil
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Old 27th May 2024, 11:18 am   #17
mickm3for
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Default Re: Codar Multiband 6 info

Hi is pin 9 and pin 2 of the coil to -ve or ground chasis Also is the tuning cap and react cap to -ve or ground and is there a conection between pins 9 /2 and the moving plates of thuning cap/ react cap Mick
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Old 27th May 2024, 2:06 pm   #18
Phil G4jhs
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Default Re: Codar Multiband 6 info

Hi,Pins 9 and 2 are to ground and the connection to moving plates and ground is good and the tuning cap and reaction cap are connected to ground.
There is no connection between ground and -ve apart from a 400ohm resistance somewhere. If i get chance today or tomorrow i will replace the FET and see how it goes .here are a few pics for perusal.
Regards
Phil
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Old 27th May 2024, 2:10 pm   #19
Phil G4jhs
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Default Re: Codar Multiband 6 info

The wiring of the radio is exactly as i received it but i will tidy it up a little.

Phil
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Old 27th May 2024, 4:17 pm   #20
mickm3for
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Default Re: Codar Multiband 6 info

Hi looking at layout the FET is an N channel so it requires d to be + and s to be - but other transistors are PNP so e + . I have looked at layout / circuit the negative to the osc FET stage is via pin 8 of the AF module through a 470 ohm (within the LP1153 to pin 5 this is ground so your 400 ohm reading is correct DO NOT SHORT PIN 8 AND 5 and do not short - ve to ground as damage to LP1153. Take readings around the FET from ground NOT battery negative mick
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