Seems like you've changed too many things at once.?
A few guesses off the top of my head.
Have you hi pot tested the GS35b between cathode and grid? Are
you able to swap the old tube back easily?
Have you checked the heater feed through cap?
Was the heater transformer a like for like replacement?
Is there a DC blocking cap between the input network and the
cathode? If not, then check the input tune variable capacitor/s
for short/s.
Good luck, Alek VK6APK.
On 2/05/2025 5:07 am, Philip via
groups.io wrote:
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Hi All,
I am new to the Group, a friend of mine suggested to ask my
problem here as there are many capable Hams on this group.
I have a GS35 on 2m and has been working for years, I have
changed the tube during it's life and blown a bias transistor
here and there.
The problem I am having now is one I have never seen. When
I apply HT to the Amp usually the Amp is cut-off with the
cut-off resistor and no current flows. Now I get Negative Grid
current and Anode current starts to flow, and the more I
increase the Anode say from 1000v to 1500v the current
increases.
The things I have changed in the Amp:
Tube - New tested good tube installed.
Bias Board - tested adjustable from 0 to 55 v
Filament Transformer
HT & Heater feed-thru cap.
Usually when the Grid Bias transistor goes - I am using a
BDX66B from DL4MEA design (?
) the amp does not do anything so not sure that Bias is the
problem.
I anyone might have come across this negative grid current
problem please let me know.
73 Philip
9H1PA
