maco 300

[oldmanriver]

can anyone offer up some insite on why a maco will not show output,,new tubes,,has 900 volt hv ..new ohmite chokes..,rechecked wiring over and over..what am i missing,,also hate to say this but it will bite you BIG time if you hit the anode caps,,,ask me how i know..

[MDYoungblood]

New tubes, (6LB6, 6LF6, or 8950), they are worth more than the whole amplifier. Check the keying circuit, possibly at one time it was hooked up backwards and blew the diodes or the relay itself just wore out. Check the resistors, (ceramic block ones), because you got zapped (filter caps) and are alive to talk about it might mean they are weak. Eyeball every wire, might see or feel one that is fried or broken inside the insulation. I usually go to each component and check to see if their value is still within spec, if dark, burned or unreadable, replace it.

3’s

Greg

[oldmanriver]

Thanks greg for the info...i guess what i really need is a progression of output from tubes to antenna...some where i am losing rf...since im asking questions that tells folks im not a tech..so any help i get is appreciated

[MDYoungblood]

Asking questions is the only way to learn, the other way (trial and error) costs more, I am no expert, just a novice myself but have 60 years of “oops” under my belt. I’ll try posting what I’ve done in the past and hope one of the amp guys see the thread.
What radio are you using on this setup? Are you using a dummy load, I hope. Which tubes are in the amp and you need to check if it is properly wired for those tubes, old swing tube amps aren’t “plug and play”.
It has been quite a few years since I even saw a Maco, if in standby, key the mic and the radio should go straight to the antenna, watt meter should read its output. Switch from standby and key, you should hear the relay click shut. Hearing a click means at least the keying circuit is working but it might not be switching power to the tubes. What reading are you getting then?

3’s

Greg

[443 Arizona]

the tubes that zap you is a good point to start, look at the tube sockets, upside and underneath, any close wires can be grounding out to each other, even the insulation can fray, short to another.
if you can find a way the tubes can be checked, do it, could be shorted internally and still light up.
have also seen tubes that have to have a ground on the "hat", either way, you got a lot of tinkering to look fwd to. hot tubes give off a bacon smell when you grab them,,

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Post Merge Complete

Added 4 minutes 16 seconds after previous.
after re-reading your original post, it occurred to me that maybe some of the di-electric grease is not doing its job, so again, you got alot of tinkering to do.