Image: shortened wires and ferrite beads between HPF and LPF.


--

73

-Jim
NU0C

I got kind of busy last week. ?In replacing R3 in the AC-4, I decided to isolate C3 and C4 from the circuit and use a DC PS to condition both of these electrolytic capacitors, starting with a resistance measurement with the VTVM (1.5 VDC); individually, within 30 minutes they were up to 50 Mohm. ?Then overnight, they were up to 150 Mohm and climbing. ?I noticed C4b would drop a little to 75 Mohm then increase back to 150 Mohm; I interpret this as a clump of non-ionized electrolyte being uncovered and taking ?time to ionize the solution with a consistent open dielectric gap; nice that all of that is automatic, just applying a potential difference with the correct polarity. ?C4b had not been conditioned otherwise, all others had been. ?This AC-4 appeared to be completely factory with their practice of laying a component lead or wire against a terminal, then applying A LOT of solder; no good mechanical joint was created before soldering. ?Solder must have been really cheap then. ?The good part was it was really easy to unsolder all the connections. ?C4 was found to be a shiny aluminum can with C4b a 100 uF in lieu of 80 uF. ?The rest of the electrolytics were covered with canary yellow cardboard: all Mallory. ?C5 a and b were found to be 40 uF in lieu of 20 uF.
Leakage current measured for C3 and C4 follows.
C4a: 3.4 uADC constant. ?Capacitance measured 122.5 uF.
C4b: 4.1-4.4 uADC hopping around. ?Capacitance measured 124.2 uF.
C3: 3.4 uADC. ?Capacitance measured 121.8 uF.

With these caps about 20% greater than nominal capacitance ?(nothing surprising), the average DC voltage rises a little higher due to longer RC time constant of the RC filters.
Ambient temperature for slow conditioning up to rated WVDC was 78 deg F; the base of the can was a few degrees higher (handy IR thermometer).
With input voltage set to 120 VRMS, the following UNLOADED outputs were as follows.
650 VDC nominal, 720 VDC measured.
250 VDC nominal, 295 VDC measured.
BIAS -46.5 to -100 VDC, steady.
Filament voltage measured 14.87 VRMS.

I expect all these voltages will decrease much closer to nominal when loaded with the transceiver or transmitter. ?I also expect a significant rise in input line voltage will produce a significant rise in output voltages, loaded or unloaded. ?Probably the best thing to do is use an auto-transformer with the AC-4, as these are clearly unregulated power supplies. ?

I’m cleaning up and repairing a DC-4. ?The input voltage must be 12.6 VDC, as 13.8 VDC has shown to produce much higher than desired output voltages, with little to no sagging of 12.6 VDC filament voltage. ?Perhaps an AC-DC switching power supply, and the DC-DC power supply (DC-4) is a better solution in order to regulate the input voltages to these radios. ?Using late technology, modest priced good quality and noise-free switchers that adjust to 12.6 volts DC are available. ?I’m going to investigate this scheme. ?There are many attributes to using this power supply scheme.

One other note: A sign of a good functioning electrolytic capacitor is observed after conditioning, or regular use. ?With the capacitor isolated from circuit, discharge the cap with a homemade shorting probe and approximately 10 kohm resistor in series (keeps the v= Ldi/dt air breakdown sparks from occurring). ?Count to 20 connected to the cap. Have your voltmeter with lower voltage scale ready and attach it to the leads immediately after removing the shorting probe. ?The DC ?voltage should immediately and continually rise from zero on its own to some value being a reasonable percentage of the rated working voltage. ?A fast rate of immediate rise indicates you should EXPECT it to be in good operating condition.

73,
Michael, N4KZO

开云体育

Does this help?

73

Stan
KM4HQE

On Mon, Apr 22, 2024 at 03:50 PM, Paul K6PO wrote:

Here's what I have in my files:?
--
73, Paul K6PO

Hi Paul,


Thanks for the quick reply!!

Yours has the BRN and BRN/BLK the reverse of mine(which is wrong!)

I was to the point where I was going to open up my working L-4PS to see how it was wired!!?

Not sure where I found what I have in my picture.? Although I thought I got it from BAMA, when I looked at what they have,? none of the schematics there have any wiring color-codes shown on them. Must've found it somewhere else!

I discovered it when I started wiring up my rebuilt Hallicrafters Loudenboomer? (single 3-400/500) Power supply.

After I acquired an L-4PS plate transformer, I decided to dump the old Radio Industries INC full-wave (CT),? Mercury Rectifier, swinging-choke? stuff for the Drake style voltage doubler.

I'm going to run it on 120AC and will never use the low-voltage connections that Drake used for CW/TUNE

In fact, I'll probably also just hard wire my L-4B to stay in the SSB position since it's really no longer needed.

thanks again!


--

73/Rick

W4XA
*Every post is created using Linux

Many thanks Jim, I'll look in eBay to get some beads.?
73 de Raoul CE3RY

Here's what I have in my files:?
--
73, Paul K6PO

I will have another look later, as I have to open up a rig. The two HPF spares that I have did not have beads on the ALC board. I have found examples with beads on both ends of the red wire between the HPF and LPF, and another with a different wire beaded as well. I may have pictures somewhere.

As for the bead itself, 4A6 is the name of the bead that Drake commonly used. I researched it and the exact nature seems to be known only to Tektronix and the US government. But I did find some possible equivalents, and I purchased a some via eBay some 8 years ago that look exactly the same. So they must be the same, right? Kidding... Below is the sum total of the notes I took at the time. Don't ask me to explain any of it, it's been too long. :)
_____

4A6 bead.

E52-3N3Y-1G0 Krystinel Corp
111-00201-062 Amperex Electronic Corp
56-590-65/4A6 Amperex Electronic Corp
84127-35 Dla Land And Maritime
60-1037-03 Crane Electronics Inc.
84127-35 Defense Electronics Supply Center
Dla Land And Maritime
190SA168 Eaton Corporation, Eaton Motor Site
9170-0894 Agilent Technologies Inc., Hewlett Packard Co
FL0004F Scientific Radio Systems Inc
57-1634 Stackpole Corp The
276-0532-00 Tektronix Inc.
276-0532-00-BA Tektronix Inc.
276-532 Tektronix Inc.
5950-00-916-8080 Bae Systems Information And
British Sarozal Ltd
Bristol Electronics has 400 of Ferroxcube 56-590-65/4A6

Special Features: Ferrite; single thru hole 0.047 inch (1.19mm) dia.; 0.118 inch (2.997mm) lg; 0.138 inch (3.5mm) dia

FB43-101 Ferrite Bead

AL=600 +/- 20 %
OD = 0.138 in / 3.5 mm +/- 0.2 mm
ID = 0.051 in / 1.3 mm +/- 0.10 mm
HT= 0.128 in / 3.25 mm +/- 0.25 mm

RFI Suppression 5 - 500 MHz


_____

73

-Jim
NU0C



On Mon, 22 Apr 2024 13:54:26 -0700
"Raoul Meunier via groups.io" <rmeunier@...> wrote:

Beads have also been found on one of the wires connecting to the ALC board but I need to look at one to tell you which. A: Pending until I hear from you.

--

73

-Jim
NU0C

Wow! A lot of good information, thanks!

Jim, I'll reply based on your comments:

1. "Did you also add a ground strap at the other corner where there is an empty screw hole in the inner chassis wall?"? A:?Yes, that was something I had already done based on the information you provided some time ago in one of the threads.

2. "Also don't overlook the grounding of the ALC board. The two screws are a mechanical ground connection to the HPF module."? A:I did this a few days ago, not only cleaning the mating surfaces but adding star washers in between them on each side. This assures good connections.

3. ?"2^nd?Mixer shields over L701 and L703."?A:?The board in this TR7 does not have the shields. Fortunately, they are easy to make and install.

4. "Parasitic oscillation of the dual gate FET Q702 in the 2nd mixer board."? A: This is totally new to me. I will proceed based on the information from PA0TRT that you provided.

5. "For 10 Meters I have uploaded an Upconverter alignment tip from K8AC to the group Files section."? A:?I’m afraid I could not find the file. However, I have the information in my TR7 book, so I peak C418 for maximum power on 10m at the end of the Tx alignment.

6. *Very carefully* measure the base voltage of the drivers and finals in RX. It should be very close to zero volts. A: Done and ok.
   

7. "I don't know if this will be helpful or not but I noticed that in later version Drake shortened the wires between the HPF and LPF modules and added several ferrite beads. A: Both, the shortening of the wires and the beads, are pending.

8. Beads have also been found on one of the wires connecting to the ALC board but I need to look at one to tell you which. A: Pending until I hear from you.

I'll put my brain and hands to work to fix numbers 3, 4 and 7. Number 8 is pending.? For the beads I'll use what I have in my junk box; unfortunately, I have no idea of the material they are made of. This is becoming a compendium of information to fight the 40m oscillation. Certainly a keeper.

Thanks and until soon.
73 de Raoul CE3RY

?

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.??