Demco 750 customers on the bench.
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- Опубликовано: 13 сен 2024
- This one has been here before and back again. A customers Demco 750 that was only doing 150 watts. The customer then put new final tubes in it and same results. He then had me test the driver tubes and most were bad, 50% and below, but 2 tested at 60% and 1 at 55%. I put those best of the worse in and away it went. If I tune it for max dead key, it will do 450 and stand still. If I tune it for max rms swing it keys around 300 and swing to around 600 and does around 900 peak. Not too bad for 1/2 flat driver tubes. The driver's are 6jt6/6jr6'6jg6 type baldie tubes and 6kv6 are the preferred subs. They won't do more but will hold up better with 6kv6's. Demco makes a decent amp for a sweep tube CB amp, some things I like, some things I don't. Since I have most things Demco but not this, I wouldn't mind one for the collection.
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I do not know much at all .I just learned how to use a multimeter.I think tube stuff looks like glass art especially when it glows like Frankenstiens Lab.
Real amplifiers Glow.
My neighbor was visited and got his junk confiscated a few yrs back.
Wow, where was that?
Baldies, like me🤣
Nice amp. Since tubes are becoming scarce, the owner is probably better off running that at 3/4 power to make it last. Have a great Sunday Doc.
I always like to run my stuff low and cool. Interesting to me that I can use an amp for years, sell it and it takes the new buyer a week to blow it up.
A lot of people here and on the net hate modified radios, especially the dial-a-watt. One guy recently here said his buddies had Pride 100's and they sounded like crap and they all ran their radios stock. Well, one of the very reasons dial-a-watt came about (I was not the first but one of...) was that in most cases when using an amp, it can be used to better drive and tame the amp. Even with this Demco 750 in the vid with a mud duck 3 1/2 watt radio driving it, its being hit too hard. As I said in the vid, if I tune for dead key is will run around 450 and stand still. Tuning it for swing, it dead keys 300 and swings to 600. I would use a radio with dial-a-watt, and dial that dead key down to about the 150 area and let it swing up to 600 from there. That is around the 4:1 sweet spot, easier on the amp, easier on the radio and would sound better too. Same with the guy who said the Prides sounded like trash with a stock radio driving. Put in a dial a watt and turn that radio's dead key down to better drive that amp. However, many purists who know a lot more than me hate dial-a-watts and run their stuff 'Stock'.
@@tramdr Like most folks tune an old amp for peak watts then DETUNE it... They don't realize how bad that is for a sweep tube amp. I learned the hard way years ago ! Nice amp Doc but my Eagle 750 has it's daddy ! Lol
i miss my demom 150...that was a talker...shoot skip many a nights early on got called on the band. i believe it was 3 tuber but could have been a 4 tuber...6jt6 style tube or 6jk6 that i remember. or 6kd6...idk. but i had that bad boy hooked into a cobra 1000 ..cira 2010 i gotta dig into my photos i know i got pictures of her...anyways...i have a special heart for the demco brand! you already know, No Name! lol
I've got a special place for them too. I hope to get them all before I go and that includes the one Demco Unicorn I am searching for LOL.
Nice lookin kicker.
Thanks, I like it too.
What do you recommend for a tuned tester? Brand wise? I’m gonna be checking 8950 tubes for a maco 750
The best thing you can do to test a power tube is run it in an amp and test it for power. I use my converted Palomar 1 tube amp as my 12 pin (8950 and 6lf6) tube tester. 2nd best is to use a mutual dynamic tube tester which doesn't fully test for power, but it does test for gain. The BK-747 and Sencore MU-140 or MU-150 are the best for that, but they are not cheap. 3rd is a more common tube tester which are only 'emission ' testers. An emission tester is the most common and a lot cheaper, but they basically only test 'emission'. Emission is the cathode which the filaments heat up and once heated, the cathode releases or 'emits' electrons. An emission tester only tests for the correct amount of electrons released. It does not test the grids, or the plate or the full working capability of the tube. With emission testers, they will often test good (emit good) but the grid or plate will be bad and the tube is actually weak or bad. Sencore makes many dependable and fairly cheap emission testers. You get what you pay for.
@@tramdr well I have enough new tubes to replace them all. But my issue is all light up nice and orange at idle. When I key and modulate all of them but one has a little blue color to them. The one that doesn’t have blue to it doesn’t not change at all (the orange stays the same).
blue usually means the tubes are gassy or leaky.
There are some nice military surplus tube testers out there too. Fair Radio Sales sometimes has them. Even at that, my Elmer proved to me that substitution is best. When I hit a brick wall in fixing my Mark III Eagle, he subbed a tube and got the receiver working. It tested great on my expensive tube tester.
Although I've never heard the tubes with the metal caps on top referred to as, anoids, I am fairly certain that is the technical name for those tin caps (Anoids.) Close?
No. The 'Plate' or the output of the tube is called the anode no matter whether it is on top with a plate cap or on the bottom thru a normal tube pin.
@@tramdr very good. Thanks for the detailed knowledge.👍
Thats an interesting amp. Id definately toss that coax runner on the side install something cleaner and less lossy RG400 or RG142bu or something of the like.
I don't like the long output run,layout or the plug in relay for starters, but I'm going to leave it alone.
how about loosing the mouth noises? cant believe no one told you at your age. it's quite abnoxious
at least I can spell!
Sure you're name isn't RICARD? The Dr. Is one of the few ones left out there that knows this old stuff.