Maco 300 looks rough but with 7 good 8950 tubes.....
HTML-код
- Опубликовано: 27 авг 2024
- old Maco 300. Has surface rust but looks very good underneath. Has 2 driving 5 very good 8950 tubes. A good 8950 can fetch $50 or more so often people will abandon these amps when the tubes go bad. I always recap an amp before I play with it. Found it has no bleeder resistors so I put some in it. I use 220K 3 watt resistors for bleeders. Fired it up and heard the original open frame fan grunting and moaning. It was froze. I put in a new modern box fan and with the good tubes and new caps, away it went. Dead keys 250 and swings to 450 average (Bird watts) and 700 Peak watts. Pretty good eh? Quite a few asking is it for sale. $400 plus the ride.
Very good brother! The 8950s are expensive but they are historic. I prefer to keep them if possible. In the near future we will have a generation of youngsters who have no understanding of tube technology.
Yep, LDMOS are the new thing, but for me and for the base, tubes rule.
I have a maco 300 with the 8950’s the final section has five parasitics and only one transformer. New muffin fan was a must though.
I agree. In a lot of these old amps with the open frame fan, the fan is either weak or bad. New fan improves air flow and helps the amp out a lot. Saves those very expensive tubes.
@@tramdr what is the part specs or number or name of the piece on back of the maco 300 metter the one that connects the + and - side of meter i need it please i dont know what that thing was...... its smoke now i installed a new meter now and need that part have no clue what that was.
I'm selling stuff left and right to hustle up for this one, got to have it!
I'd sell it cheap....without the tubes!
@@tramdr I really like what it's doing the way it is, I will get the money together. There is an old closed TV repair shop in the next town I will find out if there are still tubes inside that he might sell if he does I will let you know
Great video, I have a special place in my heart for the ol macos
Well I got a special place for them and the Palomar, Blackcat, and D+A amps too. I was a kid and found those amps fascinating.
@@tramdr I'm only 39, but those are all great amps, the tried and true 4 tube elcon, in it's complicated screen drivin design are also fun and tough amps. Mobil tube amps are also fun bring back the fun ol times with those. I'ma old soul.
I got a 4 tube 12dq6 Elkin base I am working on right now. Problem is there is no schematic for it. I got the complicated screen figured out, but now I am trying to figure out the also complicated Bias circuit. Uses 3 one watt Zeners series. Can't figure out what one of the Zeners is.
@@tramdr if I remember right, the bias is controlled a several way on this thing, there is a TIP 47 ( might vary from a 47 to a 50, but it's like a 300v regulator. It's located right under the tubes and a stand off. And they had a diode going band end to chassis right need the front of the amp when Its upside down of course. It's a 4007 I've seen um with two in series before, and last but not least the adjustable pot where the big 5 watt resistors are. Give me a bit and I'll turn the one I have over and see what that one is, I know 4007's but they was like a glass diode at the beginning. I think you can sub it for a 4007. But I'll check when I get home
@@tramdr just got the bottom of this one, it has two diodes series 1n4007, and a glass diode on the adjustable pot it is a 1n4749
Back in the day I had a buddy that used one of these and he always sounded great with a lot of modulation. Thanks Doc
Jeff think this is the video I told you about
Hmmm.
You can use Maas metal polish to get all the rust off of it. The stuff really works, and I used it to clean the front panel of a 101 with the other day... :-)
That thing works great.
I just found an LA-1000 from Amp Supply. Looking for tubes to, its very clean, the manual says the amp wants between 100-150 watts in to run, I only have a 20 watt radio but 20 watts drive, it makes 100 watts. I thought that was great until I saw your Maco make 500.
LA-1000 is a decent amp. It will do better when you drive it properly.
@@tramdr That's what I hope to do with my next transceiver,
@@tramdr Yes I believe it will, it was actually used very little and is extremely clean. Keep up the good work on your channel.
Howdy Tramdoc, Did maco make a 400 or 500 tuber? I used to run a maco base tube amp years ago. The cab had been repainted black so the maco lettering was long gone. I bought it as part of a package deal back in the day to get the Courier Centurion 40d with digital VFO and 4x250b Davemade base amp. Had zero interest in the little maco but damned if that little box wasn’t a duck stomper. It would key somewhere around 50 bird and do around 250-300 bird. Wish I till had the Maco and Courier 40d lol I was told the Maco was a 400 but like I said it had been painted and for the love of Christ I can’t remember what tubes was in it,I wanna say say it was 2 driving 4 or 2 driving 6. But it was a talker,talked a lot of skip with that setup both on my old Astro-plane and 4 element Maco beam up on 2 sections of tv tower. Miss those days,things were simpler back then 😂
Here is a list of Maco's I made.
Maco
Mini Brute DC 1 6JR6 X 2 8950
Brute (75) 1 M-2057
Brute II 2 X 5 8950
75 1 M2057
Super 75 2 M2057
Duster (DC) 2 M2057
100 4 6JT6
200 1 6LB6 X 3 6LB6
300 2 6LB6 X 5 8950
300M DC 2 6LB6 X 3 8950
500 Browning 4 6JT6
500 1 2057 X 4 M2057
750 (1 8950) X 2 6LB6 X 6 6LB6
KW (1 M2057) X 3 M2057 X 8 M2057
She's a crusty one but she does the watts!
Yep, I guess sometimes old and crusty beats the young fresh dumb ones lol!
Tubes worth more than the amp.
Yep, I bought the amp for the tubes. Same with that mobile Palomar 500 with M2057's but the seller didn't pack that one and killed the tubes :(
Just picked up a 300.....looking for a KW
I am working on a Frankenstein KW but its a long term project.
@@tramdr they're around and coming avail. People are looking for easy cash and selling old amps just to move them out. I just missed out on a pumpkin KW at a swap a few weeks back....working, and for a really good price.
Maco's are plentiful, but Maco KW's are almost unobtainium.
Well it looks like I'm the only one that owns one or have ever seen a Maco KW Plus. It's got to be worth something
Can you explain the knobs for tuning ? The two on the front and the one on the side and the order they are used .Thanks
Front are the final Tune and Load, Side is the Driver Tune. Not really critical which is first, but tune fast as you can, never ever detune an amp, always tune for max. With that said, here is the order I go in....
Final Tune on front first, Final Load on front 2nd, then repeat front Tune and Load, then Driver Tune on side, then retune all 3 for max until no more output can be seen.
I tune the output Tune first as IMHO that is the most critical to the health of the final tubes. I do the Load 2nd as again, I want my output going out, before I max out the drive going in (Driver tune). To me, it makes a lot more since to tune the output before tuning the drive. BTW, to all the Hams and expert operators, I know about overcoupling, but to that I say, know your audience.
Do you know where I can find the rear transformer for that type of amp
Sorry, no.
@@tramdr thank you
How come some have 2 transformers and some only have 1?
Cost. To simplify, it's cheaper to use two 1 amp transformers than one 2 amp transformer.
@@tramdr thanks.
How does the high low switch work? Plate voltage? Bypass drivers?
Dual tap on the HV transformer.
@@tramdr how many drive watts pep can one of these take . Or even per 8950
Very nice :)
Is this still for sale?
Yes, contact me at Tramdr@yahoo.com
What value are those bleeders? As my amp needs some.
I put in 220k ohm 3 watt flame proof resistors (2) One across each HV capacitor. However, I modded the capacitor bank. It originally had 3 100uf 350v capacitors in series, and I used 2 100uf 500v capacitors. The 2 originals in series would give a total of 33uf at 1050Volts and the 2 I put in would give a total of 50Uf at 1000V. Whether you use 2 caps or the 3 caps, 220K should be a pretty good all around figure. Will bleed in about 90 seconds. More bleed (lower resistance) will bleed faster, but will suck away more watts. Those bleed watts are wasted heat watts when the amp is in use. Higher resistance like 330k or 470k will waste less watts and heat, but bleed time would be raised to 3 or 4 minutes.
Speaking from television experience, it's always good practice to apply a ground wire to the high voltage after a few minutes. Bleeder resistors can and do fail open.
true but I run a resistor off each cap, so even if 1 goes, the rest of the bleeders will still drain the caps except for the one cap that the bleeder opened on. I also use 3 watt resistors were the actual bleed wattage used is around 1/2 watt depending on bleeder resistance and voltage. I figure 6x safety margin should for the most part help stop the resistors from opening up. But, as you said, I still ground first too before I stick my paws in there.
@@tramdr , I'll share with you and everyone a saying that enabled me to retire after nearly 50 years of working with voltages from low DC to 138 kV: be a skeptic with electric. The WW2 vets that I apprenticed under told me that pilots and electricians have something in common: there are old electricians and there are bold electricians, but there are very few old, bold electricians.
Truth be told, ANYTHING that plugs into the wall can kill you! Knowledge and experience in this arena is a matter of luck until you start doing it for a living and are trained in how to protect yourself.
Looking back, all of my big shocks were when I was a kid, still in school. Working on radios, TVs, appliances, and tools all had their own unique hazards. Through stories I've tried to pass what I learned on to my apprentices. Time will tell if it made a difference.
@@tramdr would it be possible to add a indicator bulb of some kind to prove the voltage is no longer present ?
Do you want to sell it?
It's listed on my "amplifier rafters full" video for $350. Those tubes ain't cheap.
For sale?
$400 plus the ride.