9R-59D Coil Pack
 

I am repairing TRIO’s 9R-59D with its poor receive sensitivity.

I found that both antenna terminals are shorted with a few resistance.

However, they seem not to to be like that, I suppose, when I look at its schematic.

So please let me know if the terminals of your 9R-59D are shorted or not.

Thanks in advance.

Re: 9R-59D Coil Pack
 

The schematic is here: https://forums.qrz.com/index.php?thr...to-fix.566471/
The aerial coils appear to be floating?

Re: 9R-59D Coil Pack
 

Are you using an ordinary DC Ohm meter?

It is good practice to have a low impedance DC connection from antenna to earth on a receiver. General coverage shortwave receivers were expected to be used with a simple long-wire antenna, and the DC path to earth prevents the build-up of static charge, and also provides a leakage path should it experience statically charged rain.

So the inputs to receivers are often a transformer winding to earth, or a tapping on an inductor to earth. It presents a latrge impedance at the frequency the receiver is tuned to, but it presents a low impedance at other frequencies and at DC.

I don't have the 9R-59D schematic, so I can't comment on what it shows. But it ought to have a DC path somehow. Antennae can just charge up and up until some component flashes over.

David

Re: 9R-59D Coil Pack
 

Ah, thanks, Bill.

There looks to be an error in that diagram (not an unusual thing to find) the input coils are indeed transformers and the antenna is switched to one of the input windings. The problem is that the other ends of those windings are grouped together and go nowhere other than to each other, and the input ends of the unselected windings are switched out of circuit.

This wouldn't work!

I expect there is a connection from the Earth terminal to the bottom ends of the input windings. This will make the receiver work, and you'll get a low Ohms reading between the Aerial and Earth terminals.

David

Re: 9R-59D Coil Pack
 

Thanks, Bill.

I thought antenna coils from antenna side should be floating from the chassis.

I also found that the resistance btw red antenna terminal and chassis was a little higher when the band switch was set to “A”. It’s about 7 ohms and at other bands, it’s about 5ohms.

Maybe this info doesn’t make sense, but if anyone can advise me a possibility of this issue, it will be very much appreciated.

Re: 9R-59D Coil Pack
 

If it has two antenna input terminals the schematic might be like the one in the 9R-59?:

http://www.rigpix.com/kenwood/trio_9r59_manual.pdf

EDIT: Post crossed.

Lawrence.

Re: 9R-59D Coil Pack
 

David,

Many thanks for your detailed comments.

I did cut the antenna line from the red terminal and tested again. But it’s still conducted to the GND with a few ohms.

I also tested that I connected only the red terminal to my DP antenna and its sensitivity was much better.

I am confused a bit. So let me understand more what you commented.

Anyway, thank you very much for your quick response.

Re: 9R-59D Coil Pack
 

I’m not sure if 9R-59 antenna schematic is like 9R-59D.

Here is the schematic of 9R-59D.

http://radiokobo.sakura.ne.jp/G/ham/9R-59Dkairozu.html

Re: 9R-59D Coil Pack
 

It looks to be different, that 9R-59D schematic has an error as has already been said.

Lawrence.

Re: 9R-59D Coil Pack
 

The lowest frequency band will have many more turns of wire and of thinner wire, so higher resistance on that band is to be expected.

David

Re: 9R-59D Coil Pack
 

Have we got the right model?

As far as I know the 9R-59 had an oblong tuning scale, whereas the 9R-59D, 9R59DE and 9R59DS models had twin main tuning and band spread windows.

If it's D or D* model I have one sitting on the bench right now and could check resistance readings.

9R-59 circuit is towards the ned of the attached service manual.

Re: 9R-59D Coil Pack
 

Reading from earth terminal to antenna terminal on a 9R-59DS. These readings will vary slightly depending on how clean the band switch contacts are.

A. 2.8R
B. 1.7R
C. 1.0R
D 1.3R

Re: 9R-59D Coil Pack
 

Graham,

Thank you for checking your receiver. Yes, mine is D* type one.

Now I recognize the rotary switches need to be cleaned up somehow, but shorted antenna terminals are OK and its schematic is wrong anyway.

So I need to prepare just a long wire for my 9R-59D or maybe I modify to float the GND side of SO239 connector to connect my dipole antenna of ham radio.

Thank you all. I’ll try to find other reason why the receive sensitivity is poor on my 9R-59D.

Re: 9R-59D Coil Pack
 

I believe there is a problem with the sealing compound used on the coils which causes them to lose 'Q' as it ages.

There are many 9R59D* threads on here. Have a look at them and you'll find a mention of this.

Attempts to measure the absolute sensitivity of my own receiver were not successful, as the test conditions aren't clearly defined.

Re: 9R-59D Coil Pack
 

Graham,

What I meant to say "my 9R-59D was poor receiving sensitivity" had actually two issues.

One, relating to my original question here, is when connecting my dipole antenna of Ham radio to the added SO239 connector, the voltage after 2nd IF (AGC D2 1N60 cathode side) will be at 20% than connecting only center of it.

Yes, it should be like that bcoz RF coils are autotransformers and DP antenna is not good for that, I understood.

Second is that the voltage of ACG (D2 Anode side) is getting gradually weaken to 0V, sometimes 30min after switch ON or sometimes within 5min.

I thought the diode D2 was deteriorated, but it seemed to be working well and the input from the 2nd IF to the diode is actually gradually getting down as time goes.

I am investigating on this second issue now.

BTW, I got a TX-88D which is the AM/CW transmitter of the same era of 9R-59D. It really looks COOOOL! Not switched ON yet bcoz I don't have its xtal.

I'm planning to build a DDS VFO for this TX88D and hope to be on the air soon.

Re: 9R-59D Coil Pack
 

Are there anyone out there who modified ANT coil to work fine with dipole antenna inserted BALAN in the 50ohm coax cable?

My understanding for the poor receiving sensitivity is caused by my BALAN-inserted DP and 9R-59D’s ANT coils construction which are also works as BALAN to avoid common mode noise from the antenna elements.

One solution is to replace my BALAN to so-called “Floating BALAN” or “common mode filter”, I suppose.

However, this takes much time and I wonder it may cause the worse SWR problem to my other transceivers.

Another mod is to float the SO239 female connector from the 9R-59D chassis.

This is good when using the 9R-59D as an standalone receiver, not connecting to a TX-88D transmitter because antenna comes through the TX-88D to 9R-59D and so the antenna will be GND-ed again at its remote connector which connects transmitter and receiver.

The best way I expect is to mod the ANT coils circuit not to be like an autotransfomer or balan.

If anyone did mod for this issue, please kindly advise me.

Thanks a lot!