Discussion in 'Amateur Radio Amplifiers' started by G3YRO, Aug 5, 2017.
One transistor powers the other. The schematic fails to connect the dots.
I realise that !
But the first transistor drives the first relay, and the second transistor drives the second relay, via the first transistor . . . why bother with the second transistor?!
It is a AND gate. Can I say "If you will", Or is that to old school ?
If they did not do it that way, You would have nothing to fix.
Roger, the keying circuit is the way it is timing purposes. Trust me, it's important that the timing is accurate for that amp!
Ah I see . . . I didn't consider that.
I wondered why they used two separate relays . . . so with the time constant the top one hangs on slightly longer than the bottom one. Presumably so that the Output is still connected to the Load until AFTER the input drive is removed and the Valves are turned off . . .
Thanks for pointing that out !
Well I've fitted the new Relay . . . and it works fine !
I also fitted a 1 amp fuse in the HT+ supply . . .
It's quite easy to fit a 20mm fuseholder like this on the Power Supply PCB, using one of the existing mounting screws.
So the AL-811H is all back together and ready to take back to the owner!
Hopefully the things I've discovered about these Amps (mainly from W1QJ) while fixing these two different units will be useful to someone else!
I hope you didn't do what I think you said you did.
You put a plain 1A fuse in a 1500V B+ line???
Yes . . . why not?
A lot of Amps fit them . . . hopefully it will save more destruction if the Valves arc over.
Not the high voltage side they don't.
I guess you have never seen when you take a regular glass or ceramic fuse and exceed the current rating and have that fuse blow. The arc will cause the glass fuse to explode and there may be a fire.
The Ceramic fuse packed with sand will arc also and you will have the same result unless the fuse is rated for the voltage.
Don't do that, there is not only very bad engineering practice but Hammy Hambone wouldn't even do it.
Well even if it does, surely that's better than all the damage caused inside the Amp by an arcing Valve?!
I know very few Amps fit them originally . . . but a lot of people suggest fitting one as an aftermarket mod.
I would appreciate it could be a problem if this was 25kV . . . but at 1800V I wouldn't have thought it was an issue.