Well,

I went back to the MAMA manual (Both the PDF and the DJVU files)

It appears I dod not get the above picture from BAMA asw the schematic there has no identification of the primary winging connections either.

Don't know where I got it now.? Still looking.? But the fact remains, the BRN/BLK and BRN in the above picture is reversed.
--

73/Rick

W4XA
*Every post is created using Linux

Howdy all,

This question has probably been asked before,? but I am having a little trouble with the plate transformer primary connection identification.


I have 2 plate transformers removed from original L-4PS power supplies.


I also have a complete very nice condition L-4B that I have the original manual for, but it appears that DRAKE didn't bother? to include the transformer primary color-coding? in the power supply schematic!!? So I got the the below picture from BAMA.





When check the primary windings using an ohm meter, there's infinite resistance between the BRN/BLK & YEL wires.

BUT I get "normal resistance BRN--YEL

THEN, I get? what I would call "normal" resistance between BRN/BLK -- BLUE? and then DOUBLE? between BRN/BLK -- GRN

This tells me that the above schematic has the BRN and BRN/BLK reversed

The rest of them are correct.(normal resistance between BLK/GRN--YEL/GRN)


I clearly did NOT the memo.....

Anyone else seen this?


--

73/Rick

W4XA
*Every post is created using Linux

I have no idea. You would have to check the manual. It is a 3N204 in the TR7.

On Mon, 22 Apr 2024 13:06:09 -0600
"Bill Leonard N0CU via groups.io" <billincolo73@...> wrote:

Is this FET the same device that is used in the R4-C mixer circuit?
Bill N0CU

--

73

-Jim
NU0C

The following files and folders have been uploaded to the Files area of the [email protected] group.

• /[drakelist] Oscillation in TR7 (2nd Mixer FET).pdf

By: Jim Shorney <jimNU0C@...>

Description:
A note on TR7 2nd Mixer self oscillation, from PA0TRT via Drakelist.

The following files and folders have been uploaded to the Files area of the [email protected] group.

• /Drake TR7 Up Converter Alignment.pdf

By: Jim Shorney <jimNU0C@...>

Description:
An Upconverter alignment tip from K8AC for better 10m transmit output.

Another change to the 2nd mixer that was not included in the VE7PS list is a shield over L701. Most boards will have a shield over L703. Very early boards will have neither. Also notice that early boards have fewer springy copper ground tabs.

For 10 Meters I have uploaded an Upconverter alignment tip from K8AC to the group Files section.

73

-Jim
NU0C

Here is another somewhat obscure point regarding the 2nd Mixer. I also saw it inked in to a paper service manual that I came across so I know there are at least two people have done this. :)



Also don't overlook the grounding of the ALC board. The two screws are a mechanical ground connection to the HPF module.

73

-Jim
NU0C

On Sun, 21 Apr 2024 23:15:44 -0700
"Raoul Meunier via groups.io" <rmeunier@...> wrote:

Thanks Jim, Kam and Gary for your comments and pictures, very explanatory!?I definitely need to do more work after looking at those ferrite beads over several wires.
Today I added a ground strap to the rear HPF board with good results. I was able to increase the pre-driver pot to get 60 watts on 10 meters and no oscillation on 40 meters, loading the 4-band Yagi antenna. However, when I went through the tuner to reduce the SWR, the scary oscillation immediately started, so I reduced the pre-driver pot to get 50 Watts on 10 meters. I can go through the tuner with no problems now, on 40m.
For some other reason, I can't get more than 60 Watts on 10 meters (using the Dummy Load).
I'll look for those ferrite beads and install them.

Thanks again!
73 de Raoul CE3RY

The oem Drake plate block caps in the L7 are failure prone. They went cheap, and used a pair of disc ceramic caps.? When they fail, they typ fail shorted.... which will take out the .82 ohm HV fuse.?

You might want to also check the safety choke across the load cap as well. It could have easily failed open during a HV fault condition.?

?The pair of 500 pf @ 7.5 kv rated HEC ceramic doorknob caps you installed is the correct component for the plate block cap assy.??

Did you also add a ground strap at the other corner where there is an empty screw hole in the inner chassis wall?

73

-Jim
NU0C

On Sun, 21 Apr 2024 23:15:44 -0700
"Raoul Meunier via groups.io" <rmeunier@...> wrote:

Thanks Jim, Kam and Gary for your comments and pictures, very explanatory!?I definitely need to do more work after looking at those ferrite beads over several wires.
Today I added a ground strap to the rear HPF board with good results. I was able to increase the pre-driver pot to get 60 watts on 10 meters and no oscillation on 40 meters, loading the 4-band Yagi antenna. However, when I went through the tuner to reduce the SWR, the scary oscillation immediately started, so I reduced the pre-driver pot to get 50 Watts on 10 meters. I can go through the tuner with no problems now, on 40m.
For some other reason, I can't get more than 60 Watts on 10 meters (using the Dummy Load).
I'll look for those ferrite beads and install them.

Thanks again!
73 de Raoul CE3RY

--

73

-Jim
NU0C

Thanks Jim, Kam and Gary for your comments and pictures, very explanatory!?I definitely need to do more work after looking at those ferrite beads over several wires.
Today I added a ground strap to the rear HPF board with good results. I was able to increase the pre-driver pot to get 60 watts on 10 meters and no oscillation on 40 meters, loading the 4-band Yagi antenna. However, when I went through the tuner to reduce the SWR, the scary oscillation immediately started, so I reduced the pre-driver pot to get 50 Watts on 10 meters. I can go through the tuner with no problems now, on 40m.?
For some other reason, I can't get more than 60 Watts on 10 meters (using the Dummy Load).
I'll look for those ferrite beads and install them.

Thanks again!
73 de Raoul CE3RY

开云体育

Collins had the same issues originating from the use of tube socket mounting screws as grounds for critical RF circuits, especially in KWM-2’s and S Lines. A lot of problems were repaired by simply loosening these screws a bit and retightening them.

Check your VOX again.

Already tried that, but I want back and tried again. Worked through
pretty much every permutation of gain and anti-vox possible. No joy.

--lyndon

Hi Raoul,

This happened to my TR7 last year. The oscillation was fixed by tightening every single chassis screw. They came quite loose over time.

Good luck and 73....

Kam, VA6CA?

RF Parts and Fedex came thru. Received the replacement Parasitic Choke resistors.? Ordered a spare set also and also 2 door knob capacitors 500 pf 7.5kv plate capacitors. Built up a small 2 strip copper attachement to hold the capacitors and rebuilt the chokes.? Also I forgot of course the .82 ohm fuse resistor in the PS went pop also. Replaced it and after a tenative slow power up checking things the L7 is back amongst the living.? Drake sure built an Armour plated PS and Amp. Is working just fine now on 40 meters my preferred band with 60-70 watts in from a TR7 I get a nominial 1 kw out of the L7.? Thanks for all the info and the help from our files and photo sections are also helpful.? Now to see if Karma has forgiven me.

73? Bob

That's the best explanation I have for what's going on around
here :-P

The T-4XB was tuning up okay (100W out), but only putting out about
15 watts on CW. I swapped V1, and all that did was drop the power
output on tune to 60W. So I hauled it off to the bench for a closer
look.

Meanwhile I dragged the T-4/R-4 off the shelf and set those up.
The T-4 tunes up fine on 15 (100W out), but on CW, while it sends
dits just fine, when I send a dash it drops back into receive mode
after about 1.5xdot time. I thought it might be the keyer, so I
plugged in the bug, and sure enough, hold down the dash paddle and
I get maybe a couple of hundred milliseconds of transmit, then the
T-4 goes back to receive mode.

For the brief moments when it does transmit, the waveform looks
perfectly normal.

Will somebody please tell me W.T.F. is going on here? Because I
don't have even the beginnings of a glimmer of a clue.

BTW, the T-4 got the full WB4HFN treatment right before it came to
me, which makes this even more baffling.

Also, I haven't tested SSB because my 90-degree microphone plug
collides with the bottom lip of the cabinet. A very expensive
S830 is now on its way, so I'll be able to solve that with a
pigtail in a couple of days.

--dazed and confused