Dear Everett et al,

?

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

a Solenoid-Wound inductor is the Saving Grace of

QRO amplifiers.

?

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.

?

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.

?

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?

?

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

if anyone needs any.)

?

The circuit recommendation to avoid hi-impedance

pathways is achievable by a method to bolster the ampacity.

Using something with a wide bandwidth helps.

?

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?

?

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.

?

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.

?

Tetrode rigs, especially Grid-Driven behemoths, need

great bypassing on their tube sockets. Now thems are

serious monsters under the bed.

?

Hal Mandel

W4HBM

Gentlemen,

?

My apology.

?

I was thinking you were talking about Grid

Bypass circuits of caps and chokes instead

of Anode Bypass.

?

As a compliment, the W8JI program of

analyzing and preparing Anode Chokes

is topnotch in the Land.

?

Hal Mandel

W4HBM

No problem Hal!

?

?

?

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.?

?

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

Thanks

> A diode clamp is simply? a pair of REVERSE connected diodes, […]

?

Does the following diagram correspond to your proposal?

?

?

What is the green diode used for?

--

F1AMM

Fran?ois

>That clamp diode is typically a single diode.

http://radiojim.exofire.net/pages/Glitch%20diodes.html

Yes, a “single diode path” would have made it clearer.

Thanks for the clarification. What I understood is that these diodes are used to protect the galvanometers in the event of an arc in the PA

I am still studying a way to cook my 3-500Z which have not been hot for at least 15 years. The idea is to cook at high current with a low anode voltage, without HF.

?

The maximum rating of the cathode current is not clear in the Eimac specifications. There are examples with a current of 0.4 A (for one tube).

·???????? Does this current (0.4 A) seem acceptable to you?

·???????? Can we go beyond that?

This requires a grid voltage of around +30/+40V 100 mA. So 4 W and the tube is given for 20W

?

I am considering using, temporarily, another transformer, with a lower secondary voltage, upstream of the doubler.

?

Is this a bad idea?

Dear Francois,

?

Attached, please find a great book about tubed amplifiers.

?

’73,

?

Hal Mandel

W4HBM

> Attached, please find a great book about tubed amplifiers.

?

Hello

?

Thank you for this communication.

?

Even if it does not answer my question, this document is very interesting, both at the technological and implementation level.

?

I reformulate my initial questions:

·???????? What is the maximum anode current (reasonable) for a 3-500Z tube

·???????? What maximum current can be used in a Drake L 7 to bake the tubes (not in RF operation), compared to the transformer capacity for example.

?

I measured some characteristics of the HV transformer (measured in short circuit)

·???????? Transformation ratio

o?? In CW: 2.95

o?? In SSB: 4.14

·???????? Resistance brought back to the secondary

o?? In CW: 13.4 ?

o?? In SSB: 18.6 ?

?

?