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[Amps] problem with homebuilt GS35B 70cm amp

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Subject: [Amps] problem with homebuilt GS35B 70cm amp
From: Benedikt Sveinsson <>
Date: Tue, 7 Oct 2014 16:26:39 +0000
List-post: <">>
Hi all

I have been building a 70cm GS35B amplifier and it's not working

Here are pictures of the amplifier

So - I have done and noticed:

* turned on the amplifier with HV
*When I started the amp for the first time the anode trip on the GM3SEK 
 (video: )  <- first time I turned 
him on with HV
Perhaps I did a mistake there of clearing the alarm - bit anxious.

* When keyed - it draws around 200mA current on Plate.
* When keyed and and driven (10-20W) no changes on the plate/grid meter (grid 
meter never moves)
* input tuning works - I can tune to low SWR 
* Grid meter never moves (all calibrated using methods in the Triode manual by 
* 12V AC (bit low) filament measured on the feedthrough capacitors into the 
input compartment.
* When I was driving the amp - the PSU tripped a 16A breaker few times - but 
after letting the amp sit with
Filament + HV for some time - (1hr) it stopped doing that - this must have been 
a arc inside the tube - I really cant find what would have caused this.

When writing this I notice that I don't have any capacitor on the filament 
transformer. - is that perhaps key? 

I notice in my design there is no RFC on the output - I would assume that is a 
major safety issue.

Or could this be a faulty tube ? It went through some knocking when getting the 
cooler off (it was supposed to go into a 2m amp)

And a bonus question 
* if you look closely at the picture of the power supply - I put a 4 way 
ceramic switch on the AC output of the Peter Dahl transformer so I can switch 
from approx. 2kv-4kv
* CAN I move this switch with HV on ? (have not tried it!)

73, Benni TF3CY

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