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Re: [Amps] Clipperton L soft

To: "Joe Subich, W4TV" <>
Subject: Re: [Amps] Clipperton L soft
From: Alek Petkovic <>
Date: Fri, 21 Jul 2017 11:28:36 +0800
List-post: <>
It is plausible that the previous owner has changed from a doubler to full wave rectifier.

From the Clipperton L manual, the anode voltages, at idle, are 2700V for the high and 1800V for the low.

If you halve these values, as is the case when you change from the doubler to full wave and then allow for the change in the value of the metering resistors, the 700V reading on the meter sounds fair.

73 and good luck.
Alek. VK6APK

On 21/07/2017 7:51 AM, Joe Subich, W4TV wrote:

> Here's what I see;
> On CW, the Vp meter shows 700 volts.

700 Volts sounds awfully low.  The Clipperton L used 4 x 572B tubes with
a plate voltage (unloaded) of 2300-2400V in SSB and 1500-1600V in CW as
was typical in the SSB/CW switching of the day.

Perhaps someone converted the amplifier for 4 x 811A tubes and changed
the power supply to a half wave rectifier instead of a voltage doubler.
Check the tubes then carefully check the power supply.


   ... Joe, W4TV

On 7/20/2017 5:58 PM, Kelly Taylor wrote:
Hi all,

Just trying to diagnose a weak Clip L.

Here's what I see;
On CW, the Vp meter shows 700 volts.
The transformer, when isolated, reads five ohms to the low-power tap and eight ohms across the entire secondary The filter caps each start out showing short then gradually charge to then read the 100k of the parallel resistor.
The diodes read low resistance forward and out of range reverse.
The "fuses," two delicate resistors in series with the plate choke, and the choke itself, read very low in resistance Thinking I shouldn't trust the internal meter, but wary of servicing it live, I checked the values of the three resistors in series acting as a divider for the meter (each is off by 30%). The meter shunt resistor, again, isolated, reads within one per cent of spec.

I don't want to drop $300 on tubes only to find nothing's changed, and don't want to drop $100 on a Harbach kit only to find it was just the tubes all along.

Someone's been inside here before me; the electrolytics are not factory and there's some not-entirely-professional soldering, but the connections all seem fine electrically.

Is the off-spec condition of the meter dividing network just a diversion from bad tubes?

There's no evidence of any component having let out its smoke.

73, kelly, ve4xt

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