G'day, I have a DAK Mark X SSB Base Station.
After many hours of finding a dry joint and other problems I finally have it semi-running.
I have no RX on AM..almost no background audio.
When the output valve (tube) is plugged in a 2 watt resistor supplying the B+ rail (450 volts) gets red hot, I suspect an internal short in the tube.
I have found a circuit on-line but it only deals with the PCB and none of the chassis mounted parts, Id like to know what component values around the tube are, especially the fried resistor.
Also, would anyone have some ideas where to start on the no AM RX? I'd really love to get this thing up and running 100%
DAK Mark X
Re: DAK Mark X No TX output & no AM RX.
It as been a very long time since I last work on one but if I remember right, the PA valve is 6DG6 if so check PA tank cap 0.001uf at 2kv this is connect to pin 3 via 10 ohm 1 watt resistor also check the grid cap 0.01uf 1kv this is connect to pin 5. I have found that most problems with the PA stage are due to bad caps. As for on AM are you seeing any signal meter movement?
Rick.
Rick.
DAK Mark X
Thanks alot for the reply...yes found one of the caps you mentioned was bad so now just have to wait to source a new 6DG6.
On closer inspection the PCB appears to be a vary close variant of a single board Cybernet PLL02A Chassis (with a motorola equivalent PLL).
For example the radio had a "slide" put in which Ive removed and was the exact diode/resistor in the O2A radios.
I have very low level AM TX (working to the pre-driver stage) but cannot modulate the carrier (SSB audio is fine TX and RX)....there is no AM RX at all...nothing on the meter with a sig-gen connected....I recall from days gone by (I used to play around with this stuff in the 80's) a common problem was the mode selector in some radios but the DAK uses a huge OAK type switch and it appears in good condition so assume there must be some other problem...thanks again
On closer inspection the PCB appears to be a vary close variant of a single board Cybernet PLL02A Chassis (with a motorola equivalent PLL).
For example the radio had a "slide" put in which Ive removed and was the exact diode/resistor in the O2A radios.
I have very low level AM TX (working to the pre-driver stage) but cannot modulate the carrier (SSB audio is fine TX and RX)....there is no AM RX at all...nothing on the meter with a sig-gen connected....I recall from days gone by (I used to play around with this stuff in the 80's) a common problem was the mode selector in some radios but the DAK uses a huge OAK type switch and it appears in good condition so assume there must be some other problem...thanks again
Re: DAK Mark X No TX output & no AM RX.
Check the 10.24MHz is present at the second mixer this maybe the reason for weak AM. Seeing that you have a sig gen can you not scope through the RX stage to find the dead spot. I am not saying you should not replace the PA valve but are you sure it as failed as I have never need to change one. Also check the relay connects they maybe burnt. Is the PLL board a 471202?
Rick.
Rick.
DAK Mark X
Thanks for all your help Rick...Ive not repaired cb's for many years so am pretty rusty on all this.
Ok..this is where I am at.
(Im not worried abt TX at this stage)
SSB RX is perfect, cannot belive how sensitive and good audio is.
There is NO AM RX whatsovever....even 200uV direct from Sig-Gen there is nothing.....Its (to me) pretty hard to work on, have been trying to follow the mode switching but its so bunched up and one of the wafers switches high voltages (ouch)
Cannot find any markings on the PCB, but Its almost identical in appearance to a single board GE O2A set...The schematic I have is for the PCB only and shows no off-board wiring etc and is very hard to read....>Thanks
Ok..this is where I am at.
(Im not worried abt TX at this stage)
SSB RX is perfect, cannot belive how sensitive and good audio is.
There is NO AM RX whatsovever....even 200uV direct from Sig-Gen there is nothing.....Its (to me) pretty hard to work on, have been trying to follow the mode switching but its so bunched up and one of the wafers switches high voltages (ouch)
Cannot find any markings on the PCB, but Its almost identical in appearance to a single board GE O2A set...The schematic I have is for the PCB only and shows no off-board wiring etc and is very hard to read....>Thanks
Re: DAK Mark X No TX output & no AM RX.
Just found my copy of diagram and had a quick look over it. I would check Q43 this is the AM RX switching transistor, the emitter should be about 6.5 7.5vdc in the RX mode if this is missing then no AM RX.
Rick.
Rick.
DAK Mark X
8.6 Volts on the emitter of that transistor when mode set to AM.
I checked the main supply and its only 12.9 volts from internal PSU.
(I was thinking maybe the 8.6 due to a higher than 13.8 supply but no go)
I wish I had this set to repair 10 years ago when my eyesight was better, it took me an hour with a torch to find the correct transistor!!
Cheers
I checked the main supply and its only 12.9 volts from internal PSU.
(I was thinking maybe the 8.6 due to a higher than 13.8 supply but no go)
I wish I had this set to repair 10 years ago when my eyesight was better, it took me an hour with a torch to find the correct transistor!!
Cheers
Re: DAK Mark X No AM RX audio.
Check CF1 which is a 10.7 MHz filter this where the AM path starts, from hear it go through T13 to D22 / 23 to T14 and then to a CF which his 455 KHz and then off to Q27, 28, and 29 and the detector his D25 / 26. It could be one of the transistor are dead or detector diode. You should be able to detect the AM signal with a scope at D25 if not check with a scope at the Base of Q27. Low volts from the PSU maybe down to a bad cap or just adjustment check the PSU with a scope for ripple it will tell you if it's a bad cap. Hope this helps, let us know how you get on. I know what you mean about the eyesight.
Rick.
Rick.
DAK Mark X
Thanks again Rick....I'll try all that and get back to you here in a couple of days with the outcome, Ive become kind of obsessed with getting this thing running and have spent all day on it...have to do some paid jobs the next couple of days instead.
Ive found a couple of other problems, not sure if they are related.
The Squelch (on SSB) has almost no range, its either off or hard on and the adjustment pots (VR-9 + 10) seem to have no effect either.
The switchable AGC plays up a bit too, but I think thats just the front panel switch which has been re-wired (wrongly) at some stage.
The board is interesting, it appears very similar to single board cybernet, but the actual board qlty (thickness) and soldering is much poorer than any of these Ive ever seen.basically its just a giant box of air with a cheapy internal which was originally priced higher than most ham gear of the day...still it looks the goods and its rarity means its far too interesting to scrap, Ive thought of re-building it by putting another cybernet board inside but all the wiring would probably take me longer than fixing the bloody thing...cheers.
Ive found a couple of other problems, not sure if they are related.
The Squelch (on SSB) has almost no range, its either off or hard on and the adjustment pots (VR-9 + 10) seem to have no effect either.
The switchable AGC plays up a bit too, but I think thats just the front panel switch which has been re-wired (wrongly) at some stage.
The board is interesting, it appears very similar to single board cybernet, but the actual board qlty (thickness) and soldering is much poorer than any of these Ive ever seen.basically its just a giant box of air with a cheapy internal which was originally priced higher than most ham gear of the day...still it looks the goods and its rarity means its far too interesting to scrap, Ive thought of re-building it by putting another cybernet board inside but all the wiring would probably take me longer than fixing the bloody thing...cheers.