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Author Topic: putting in a switch for 800 volts (plate supply) in a PS23 or hw-101?  (Read 2197 times)
AD5IW
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Posts: 15




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« on: September 25, 2014, 05:21:47 AM »

I'm working on the transmitter of a hw-100 and now need to neutralize the finals.  The best method is to disconnect the plate and grid voltage to the finals (a pair of 6146 tubes).  The grid is easy - just unsolder a single resistor lead. 

However the plate wire goes directly from the back connector to the choke (located in the finals compartment) - and is not easy to unsolder.  So I ended up disconnecting the 800 volt lead in the power supply (PS23).  This works but it is not easy to solder it back in (cramped area).

Is there a switch or shorting block that I could install - either on the power supply or hw-100?  This would make it easy to check the neutralization several times will working on the transmitter section.

Thanks,

Paul
AD5IW

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K8AXW
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« Reply #1 on: September 25, 2014, 08:22:33 AM »

No switch.  Just lift the anode connections from the tubes.  Be sure that when you re-install the top cover (with just two screws) that the free anode leads don't touch anything.

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G3RZP
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« Reply #2 on: September 25, 2014, 09:11:40 AM »

You should never run a beam power tube - or a pentode - with screen volts and no plate volts. That over dissipates the screen grid.

I think Al, you mean disconnect the HV feed to the plate choke. If you pull the leads off the top caps, then neutralisation will be crazy.
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KG6YV
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« Reply #3 on: September 25, 2014, 12:35:16 PM »

The switch to enable cold neutralization in most transceiver simply remove screen voltage from the finals, like in the Kenwood hybrid transceivers.

FYI
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K8AXW
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« Reply #4 on: September 25, 2014, 09:17:18 PM »

Peter: Correct on both accounts!  (I didn't mention the screen voltage because he had already determined that it was to be removed and was thinking of installing a switch in the HV line.)

Thanks for the jerk back to reality Peter.

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N8CBX
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Posts: 159




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« Reply #5 on: September 29, 2014, 02:08:27 PM »

You should never run a beam power tube - or a pentode - with screen volts and no plate volts. That over dissipates the screen grid.
That is very, very true.
Kenwood has a screen on/off switch, and besides removing the screen voltage, the switch applies about -100vdc to the screen. You can pick off the -100vdc from your grid supply. I install a screen switch on my Tempo radios, they didn't have any either. It helps a lot doing neutralizing.

Jan N8CBX
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Dayton Ohio - The Birthplace of Aviation
G3RZP
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Posts: 4727




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« Reply #6 on: September 29, 2014, 02:46:14 PM »

Yet the Marconi Marine Commander marine HF SSB tx had a plate fuse and no screen fuse.....When I took my marine operators examination, they put a u/s plate fuse in. So I switched the volts on and off for short periods while checking. When the examiner asked why I did that, I explained and he was shocked to find someone that knew and didn't want to cook the PA tubes. Although the PA tubes were really crap, being basically three 807 cathode/grid/screen structures and a big carbon anode and  absolute 500% swine to kill the parasitics on!

Marconi were good at that - they had a military transmitter that had around 600 volts on the plate of 5894 driver and the screens of a pair of 4-250s. The 5894 screen was fed from a separate 300 volt line.....the 600 volt line was fused and if the 600 volt line fuse blew the, 5894 lit up like a lantern - but not for very long....

So 'professional' rigs weren't immune from nasty design coc*-ups......



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KB3MDT
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« Reply #7 on: October 16, 2014, 09:01:29 PM »

Hi,
   You could use a Fuse Holder and Fuse (I.e. "Little Fuse" Glass Fuse) in the HP-23 or the HW-100 as a way to disconnect and reconnect the Hi voltage.  Just pop out the fuse when you want to disable the High Voltage. 

   I'm getting ready to neutralize finals in an HW-101 and have been thinking about doing this.

73
Ken
KB3MDT
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G3RZP
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« Reply #8 on: October 17, 2014, 01:05:39 AM »

DO NOT FORGET!!! Removing the plate supply and leaving the screen supply on is a sure fire way to ruin the tubes.

Far better to remove just the screen supply and put a temporary ground on the screens. If you leave them open, they can float and give problems.
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N8CBX
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Posts: 159




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« Reply #9 on: October 22, 2014, 02:56:27 PM »

DO NOT FORGET!!! Removing the plate supply and leaving the screen supply on is a sure fire way to ruin the tubes.
Absolutely.
Guys, the 6146 tube is a tetrode tube.

Jan
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Dayton Ohio - The Birthplace of Aviation
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