From poking around the band modules on the AUX-7 I acquired,
they just seem to be diodes connecting pin 1 to everything else,
right? Is there any reason I can't just roll my own with 1N4001s
or something similar?

The two modules on the board I have appear to be TI parts,
labelled BC1206. I have searched high and low but I can't
find a data sheet, or any reference at all, to a TI part
bearing that number. Anybody have an idea what those might
be?

Cheers,

--lyndon

P.S. I have two band modules covering 0-1MHz I would be willing
to swap for some WARC coverage :-)

The resistors I replaced were 2 watt 47 ohm carbon composition resistors just like the one's that exploded. I am still perplexed as to why these would run so hot as to burn up. All items in that circuit checkout perfect. I realize that 1000pf instead of 1520pf ceramic capacitors shouldn't make that much difference.? The Door knob are rated at 7.5kv so should be good. I did find a poor solder joint on one of the parasitic resistors but it had good mechanical connection.? Have repaired that.? I will look into some of the other type of resistors.? Thanks

73? Bob

Probably not a huge issue. The L4B uses a pair of .001 uF (1000 pf) in parallel for .002 uF. So the value can vary a bit. The pair of 760 pF would be 1520 pF total. Fix your parasitic suppressors first.

It sounds like your resistors may be inductive. Metal composition are suggested here:



Also suggested are Ohnite OX or OY ceramic composition.



73

-Jim
NU0C

On Wed, 24 Apr 2024 13:11:23 -0700
"K6OXN Bob via groups.io" <bobk6oxn@...> wrote:

Ok while running at the lower CW hv, I noticed a distinct smell of burning resistors. Took the amp case off and found both of the Parasitic resistors from the Plate in the Plate Choke to be burned.

Ok while running at the lower CW hv, I noticed a distinct smell of burning resistors. Took the amp case off and found both of the Parasitic resistors from the Plate in the Plate Choke to be burned. I am trying to determine why and what could be causing the excessive current in this circuit.? Was not transmitting for more than a minute before turning the amp off. C39 and C40 have been replaced with 500pf door knobs and test good on my meter. C41 is a door knob 47pf that also measures good. RFC 5 seems to be ok along with C44 and C45. The Tuning coils all look good and no arcing showing in that area.? I am unable to determine why the Resistors are getting so hot. Should not be that much current thru the chokes as far as I can tell.? Open to all advice.

Hans, G0UPL , designer of the? VFO I used in my TTR-7 digital VFO has sent a link to an excellent white paper he wrote on the Si5351A phase noise. Well worth the read at:

?

73,
Dale W4OP

Using the dummy load the L7 tunes just fine with the Plate knob just past mid on the 40 meter band. It tunes just fine as best I can tell. I am using the 7610 and in CW mode on the L7. Running about 400 watts out with 50 watts in. Getting some type of electrical smell when xmtting suspect the Parasitic choke resistors.? Will have to take the amp out and look it over. Since both the 7610 and TR7 both seem to be taking out the parasitics, along with the Load cap reading 0, I suspect something in the plate tuning area of the amp. Will have to see how to tune 40 meters and inspect the tuning coils. HV is about 1800 volts in CW. I inspected the Band switch and coax to it, with nothing seen.? Will keep everyone informed.

73? Bob

It could be a couple of things. The L7 has a two section Load cap. Only half is used on the high bands. The second section is switched in parallel by the band switch for 20m through 160m.

There are also fixed padder capacitors that are switched in parallel with the load variable on the lower bands. C48 is added in parallel on 80m and C49+C50 added to that on 160m.

If you are noticing this on 40 you may have a band switch issue or stressed solder joints in the tank circuit. Does the Tune pointer line up about where you expect? How does it tune (into a dummy load) on 20, 40, and 80?

73

-Jim
NU0C

On Wed, 24 Apr 2024 08:58:12 -0700
"K6OXN Bob via groups.io" <bobk6oxn@...> wrote:

I just noticed that my L7 after for possible parasitic oscillations,, I note that the Load adjustment is only good when setting is about 0. I don't remember but that does not seem correct. I have tuned amp on several 40 meter freqs just doesn't seem right.? Any suggestions?? Thanks in advance.

73? Bob

This is all related to the replacement of the Parasitic Chokes and the Plate coupling capacitors.

Here you go.

The complete re-drawn (Orcad) L-4PS schematic is in the 'Files' area of this , at?/g/DRAKE-RADIO/files/L-4B%20Orcad%20schematics%20-%20Factory%20and%20modified/Drake%20L-4PS%20Factory%20Wiring.pdf. I've also posted a re-drawn schematic of the complete L-4B RF Deck there.

Mark - AD7EF

Same place in my L4B and L7 manuals.

73

-Jim
NU0C

On Wed, 24 Apr 2024 13:09:28 -0400
"Ken, WA2LBI via groups.io" <wa2lbi@...> wrote:

The two circuit breakers are circled in the attached schematic.

Ken
WA2LBI


On Wed, Apr 24, 2024, 10:20 Jim VE7RF via groups.io <jim.thom=
[email protected]> wrote:

On Tue, Apr 23, 2024 at 05:56 PM, Jim Shorney wrote:

Look again. It's there, just easy to miss.

Still can't find it. And I have 4 x manuals for the 4 x l4b's. its not
on the L4PS schematic.

--

73

-Jim
NU0C

On Wed, Apr 24, 2024 at 07:20 AM, Jim VE7RF wrote:

Still can't find it.? ?And I have 4 x manuals for the 4 x l4b's.? its not on the L4PS? schematic.

Jim;

The second circuit breaker is between the bottom leg of the center-tapped input winding and the screw-terminal... it's drawn at a 45 degree angle.

In this copy of the schematic, it's just below the 'BRN/BLK' marking:




It's a bit more apparent in my re-drawn copy of the L-4B PS:



Mark - AD7EF

I just noticed that my L7 after for possible parasitic oscillations,, I note that the Load adjustment is only good when setting is about 0. I don't remember but that does not seem correct. I have tuned amp on several 40 meter freqs just doesn't seem right.? Any suggestions?? Thanks in advance.

73? Bob

This is all related to the replacement of the Parasitic Chokes and the Plate coupling capacitors.

开云体育

I was thinking the other day "I wonder what was actually happening"?

This was in the late 70's, a common among DXers and Contesters was a dirt cheap thing to do to make your signal just jump and stand out in pile-ups.

My particular setup.
Plain TR-4
AC-4 power supply
Shure 444 Mic.

Like the D-104 the Shure 444"s frequency response was incredible with all Drakes.

Now this is my question of what is actually happening. I'll say what the Modification was at the end.
But doing this "Mod" you can immediately see the plate amp meter being MUCH more aggressive,
jumping far higher than usual, so power is either higher or more "Full".

Listening on the air It had the exact sound of a processed signal made by a external speech processor
like the "Vomax" unit. but at a FAR cheaper cost. Adjusted for Inflation the Vomax today would cost $412.00!!!!

Looking at a scope it also seems to look just like the vomax signal. Still "Peaky" but fuller.

It did not sound distorted at all. Or the sound of a bad flat-topped signal.

But the "Punch" it had was incredible! To a S meter and to the "Ear"
it seemed pretty equal to like a modern rig running maybe up to 10 db of compression.

But it seemed "Clean" Never got a complaint about splatter or distorted signal,
?if anything you got compliments on how great the audio was.

I never even thought to try to figure out what this "MOD" was actually doing,
all I knew was it worked, and worked GREAT with never a hint of anything negative from anyone.

What was this "MOD"?? On the AC-4 Power Supply is a Jack for the ALC for when running with an amp.
This Jack is connected to the amp,,, well you all know what it is for.

But this "MOD" was simply inserting a shorted out RCA plug into that jack on the AC-4 shorting it out.

That's it!

The Drake Is now retired, But I got to wondering, has anyone else done this "MOD" from the 70's
and even maybe still does it today?

And even more what was actually happening?

Joe WB9SBD

On Tue, Apr 23, 2024 at 05:56 PM, Jim Shorney wrote:

Look again. It's there, just easy to miss.

Still can't find it.? ?And I have 4 x manuals for the 4 x l4b's.? its not on the L4PS? schematic.??

Works fine, a 9/10 cosmetically, built like a tank. Asking $250 plus shipping. Photos and video here:



Please contact off=line if interested.

73,
Randy, KS4L

FT8 is pretty hard any any amplifier running at or near maximum ratings.? It would be like running RTTY.

I have heard that the failure rate for imported 3-500's? is somewhat higher than the originals.....
--

73/Rick

W4XA
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