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Old 7th Nov 2017, 10:35 pm   #21
Boater Sam
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Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
Default Re: Oh No! Not another howler.

There is no approach to howling really, it seems takes off as soon as there is enough signal into the EL41 to amplify and hear, I suspect that it is oscillating all the time really.
The various extra decouplers were grounded on an assortment of chassis grounds, there are around 7 or 8 around the valve bases. One is on the electrolytic can clamp mounting, and it is the neg for the caps too, the can is not isolated, not a good idea, but the bolts are tight and clean
I will try monitoring the AGC with the EL41 out, that is a good idea I had not thought of.
The reason I think its the IF amp regenerating is that when the wavechange switch is in gram, the RF valves are positively disconnected because the oscillator becomes 1st AF stage, and then there is no trace of oscillation anywhere yet the HT is still being applied the the frequency changer and IF amp.
There is so little in this chassis that Its improbable that its the wiring or layout, and as I said its all virgin.
With it in oscillation I could still receive the stronger stations but the audio was heavily modulated, but the motorboating slight reduced until it went off tune.
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