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Anode systems should have series-resistance to limit peak current in the event of a tube arc or failure. That series resistance should always be in the anode lead between the filter capacitors and RF choke. A diode clamp should be installed to protect meters, especially the grid meter since the grid is in the normal path of any internal tube arc.?

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Could you explain to me what this means A diode clamp should be installed

Thanks

No problem Hal!

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Gentlemen,

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My apology.

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I was thinking you were talking about Grid

Bypass circuits of caps and chokes instead

of Anode Bypass.

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As a compliment, the W8JI program of

analyzing and preparing Anode Chokes

is topnotch in the Land.

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Hal Mandel

W4HBM

Dear Everett et al,

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There are those that believe a Pi-Wound, or even

a Solenoid-Wound inductor is the Saving Grace of

QRO amplifiers.

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And there are those who think that monsters are

really hiding in their granddaughters’ closets, and

that hidden, destructive parasitic oscillations

reside, ready to lash out on unsuspecting operator

equipment.

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Both camps are correct. RF energy behaves more like

sub-atomic particles riding waves of phase change

DC energy, excited somehow in more direction

than only one, and possible at the very same time.

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Modeling software is only a test to see if something’s

kosher or not at a readily recognizable set of params,

so what, and why did my amplifier, after hours and

hours of QSY everywhere and outside antenna follies,

decide to go, “BINK!” and leave me with a $5,000

set of ceramojunk? “ Parasitic Oscillations,” the

well-remembered AG6K would say, while his close

friend(s) would say, “Hogwash!,” and both were right?

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(I still have small rolls of Nichrome 30 and Nichrome 60

if anyone needs any.)

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The circuit recommendation to avoid hi-impedance

pathways is achievable by a method to bolster the ampacity.

Using something with a wide bandwidth helps.

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Most Pi-W’s use microscopic wire.? Some Grid Anomalies

may induce a bolt of juice in them tubes, there, of Just

How Many Amperes Wre You Thinkin’?? Bazillions?

You may be right, but how long was that for?

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In that infinitesimal slot your Pi-W’s windings are going

to heat up, maybe in more than one place, and what’s

next? Current Down, Voltage Up: Goombye Grid.

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It might as well be mentioned a nice fat slug of copper

wire in between every G1 tube socket and chassis ground

for as short a distance as possible makes a reliable

addition to the design of all.

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Tetrode rigs, especially Grid-Driven behemoths, need

great bypassing on their tube sockets. Now thems are

serious monsters under the bed.

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Hal Mandel

W4HBM

I was told that the original RF-choke could cause oscillation.

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Thanks Dave.

Always “good” to hear the issues!

In the L7 the RFC3 was ok (no issues in 15 years)

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I found the RF-choke I used :

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Thanks

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225 ?H; that's a big value indeed. I thought you wound it yourself on the original mandrel.

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Why did you have to change this ?RF-choke?

From my own experience in blowing up two of those, is that RFC3 RF-choke purchased from RF-Parts is resonant on 30 meters when used in a 3-tube (8874) Alpha 76A amplifier.? Use in other amplifiers may differ.?

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73,

Dave, w6de

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I found the RF-choke I used :

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Francois,

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> I remember the green capacitor (B) but not (A).

** Your capacitor 'A' went with your old RF choke.

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Yes, you are correct.

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Hello,

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> Do you have the service manual of this amp?

** No, I don't have the service manual for this amp. If you could share it with me, it would be appreciated.

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> I remember the green capacitor (B) but not (A).

** Your capacitor 'A' went with your old RF choke.

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A= 47 pF

B= 307 pF

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Thanks for the images of your modifications; they can be very useful to me

Fran?ois, here are the exact capacitors I used to replace C41 and C42 in my L7:

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** Thank you these items are very valuable to me, even though I can't source them directly from RF Parts Company. Now I see exactly what these capacitors are ?doorknob type

--

F1AMM

Fran?ois

Hi Francois,

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I did not document my changes and sold the amp a few years ago.

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I remember the green capacitor (B) but not (A). That could easily be a memory leakage on my side but I couldn’t find it on the pictures before the restauration. .

I don’t know the values of the (B) capacitor but replaced it with doorknob type (red).

The red wire to the capacitor is spark-plug wire.

On the attached picture you can see the new RF-choke was placed.

When I looked at the photo’s I made, I saw I did change the indicator assembly as well.

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Do you have the service manual of this amp?

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> The only thing I changed was the RF-choke and a replacement for the green pcb like 160m capacitor (by door knob types).

> I only opened it once a year to remove the just. That was all.

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Hello

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I am weak in technology (I am 75 years old). It seems to me that you are pointing out the two curious plate capacitors A = C41 (47 pF) and B = C42 (307 pF).

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Could you give me, precisely, the replacement capacitors that should be supplied. A url would be welcome.

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> Why do you want to see these tubes all the time?

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The reason is in this message

/g/ham-amplifiers/message/40898

> It seems your lid or top sheet metal has been changed. Mine has holes and I can see the tubes.

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I recently bought this L 7 (about $1000) from an OM who used it very little. It has the serial number 672.

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On this device, the air is sucked from the bottom of the case by a kind of scoop. It is a propeller fan that extracts the air at the top. The power supply box is marked L7PS

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The PA cover seems original; it is the same color as the other panels (yellow anodized aluminum)

Why do you want to see these tubes all the time?

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It is the most reliable amp I’ve had.

You can push this amp to all its limits and beyond, it just won’t die.

Even when it starts to stink like burning socks.

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I used 2x 3-500ZG, for hours and hours, daily, for 15 years.

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The only thing I changed was the RF-choke and a replacement for the green pcb like 160m capacitor (by door knob types).

I only opened it once a year to remove the just. That was all.

Use it, push it, don’t worry about the colour of the tubes. Just stay within the current limits and you will be fine.

(make sure the ventilation is running . ?)

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Great amp.

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