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Linear Amplifier repair for dummies 101 part 1
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- čas přidán 8. 01. 2024
- My first class or thoughts on repairing a tube linear amplifier for dummies. First off,
WARNING WARNING WARNING WARNING WARNING WARNING
Tune Linear amplifiers contain LETHAL voltages, and one wrong move will take you out, permanently. A small JB-12 almost took me out as a kid, 50 years ago.
With that said, today just going thru the simplest of amps in engineering and design. A single stage 2 tube grounded grid amplifier, a Browning Golden Eagle Mark 100 which is an earlier version of the Browning 180. It is as simple as they come. No thrills, no spills, just an amp that takes four watts in and does about 50 watts out. No preamp, no turbocharging, no 'Supermod', no bias, no screen, not even a Tuned Input Circuit.
The Browning 180 just has a power supply that provides about 800v's for plate voltage, 6vac to light the tube filaments, and a high voltage center tap at 400v to run the tube keying circuit. That's it for the power supply. When in operate mode, the HV is on the tubes at all time. However, the Tube cathode which is basically the ground, is only grounded when the keying relay is keyed. When the relay is keyed, the choke L1 which is connected between the radio input and ground is now in circuit as the radio Input and choke both are connected to the Tube Cathode when the relay is keyed.
So enough about this amplifier, here is my very simplified thoughts on repairing an amplifier.
First and foremost, one should determine what exactly the amplifier is either not doing right, or is doing wrong. Common things are:
It blows fuse
No power at all
Tubes not lighting
No Output
Low Output
With Ham amps that usually have meters that read Voltages, Plate Current, and Grid Current, it is a lot easier to see what is going on with the amp, However, since hardly any CB amps have meters for that, we have to use a little common sense and get creative.
If an amp is blowing a fuse, you have a short. Shorts are usually easy to find. Just start disconnected stuff until the short is no more. With Tube amps, the most common cause of a short is a shorted Tube. Hence take the Tubes out, fire up the amp and see if the short is still there. If it is, start working your way backwards. Next disconnect the HV power supply cap bank. Still short, check the power supply diodes for a short, and even if you don't find a shorted one, disconnect the diode bank and try it. If the amp is still shorting out with the Diodes disconnected, sorry to tell you, cancel Christmas, you probably have a shorted Transformer. Replacement transformers usually aren't easy to find, nor cheap.
No Output? I've said many times in many video's the first thing I would check is your Input SWR. Just to pick a point, under 3:1 you ae probably good. A little higher, it may be the problem and a lot higher, it is a problem. If your radio has a SWR meter built in, you can use it. If it doesn't or you are using a driver amp to drive the amp you are working on, put an SWR meter inbetween the radio or driver and see what it reads. There are other clues too. If your amp had an amp meter or grid meter, those should be reading correctly if the amp has HV and is getting drive to the tubes. If the amp had a HV meter, it should drop a little if the amp as getting drive. If you had an external line amp meter, which I wanted to show in the vid, but I ran out of time, it should show that you are pulling good amps when the amp is getting drive. If all the voltages are there and the amp is getting drive, the tubes should be getting hot, especially if there is no output. I look at all these things and check my Input SWR after I made sure my voltages are OK.
Filament Voltages. With glass tubes, if the Tube has the orange glow inside, the filaments are ok. If not, the most likely suspect if a bad connection between the Tube and the Tube socket. Most likely culprit is a dirty tube pin. I use a Dremel with a soft brass wire brush head and a very light touch. I want to Brush away the dirt and grime, but keep in mind, most tube pins are coated with an extremely thin coat of conductive material. You brush too hard, which is not hard at all, you remove the conductive material. Old school Hams did not like Brushing tube pins at all for that reason. Also look for broken wires and cold solder joints if not lighting.
No output is probably the hardest to track. If the tubes have voltages and drive, but no output, they are eating that output and should be getting hot. could be a short or open in the Tank or output circuit, and even more likely, a bad connection at the relay contacts. Clean those relays. For bad ones, I use a Dremel with the soft brush again. Check the output circuit, Tune and Load cap, and coil for shorts, bad connections etc. I have also seen bad coax and wiring cause the output to fail.
I had more, but I am out of space, so more to come. Good Luck.
Great video! I'm an old rookie and love learning about these old tube amps. I have a Varmint XL450 and she's needing some love. I have a input SWR of 5 with the amp on and the she puts out 100 watts AVG on AM. Tubes all light up and look good and relay keys up. I know it should do more. Thanks for pointing me in the right direction.
I have a Galaxy 1000, “1feeding 4”. I also have about a 1000 tubes I got from buying a ham opener out. I want to fix it and your video is going to be useful. Thank you for taking the time to share your knowledge and talents. Wish I could talk with you.
Thanks
Thank you very much for taking the time to make these videos,ive been learning and building transistor amps ,and wanted to start learning tube amps,so thank you very much for this.
Thanks
This was so helpful my friend. All stuff that I normally check first as well. Just keep in mind folks that you are dealing with high voltage and you must take it seriously !
Agreed.
Man I am ecstatic i found this video, as i aspire to build amplifiers one day soon. Thanks!
@RL-521 Have you started your build yet?
I also am interested in building one just for my use and to be able to say "I built this"! I have some knowledge in electronics but need help in the process for sure.
@Don.E.63 not quite, actually not sure where to get started. Where's the best place to purchase components i.e. tubes, transformer, capacitors, resistors, etc. Unfortunately I don't have a nearby mentor, I've read and watched tons of videos, even obtained my Technicians license; now it's time to execute. 😑
Thanks for posting and sharing all these videos with information hands on. Best regards and happy 2024!
Same to you!
A very good explanation Doc! You should have been an electronics teacher. Trouble is that kids today don’t want to learn electronics. That’s why I got out of the teaching profession.
Btw, I found a relay in a linear that was sticking on. Turns out that some guy sprayed it with some type of lubricant. It concentrated from heat and made the clapper stick to the core of the relay. A good cleaning with a non-lubricant cleaner and it worked fine again. God save us from technician want-a-be’s.
That can happen, or have seen relays sticking from arc'ing and/or pitting, but that's not usually the case.
Love the video as always..... fantastic information. You had me dying at "infinity" swr. hahahaha
Great video. I'm currently struggling with a D&A and a Varmint so this is a lot of help.
Glad I could help!
I have a lot of the 6jg6 and 6lq6 tubes for my d&a amps. The 70s were awesome for cb innovation.
Yeah, 70's was lit.
Thank you thank you so much 511 NE. New Jersey appreciate you happy 2024😊
Thank you too
Excellent. Thanks Professor.
You are welcome!
yeah I'm going to try to get back and work on my little brown in 180 that's what the problem is with it has a tube keying circut good info and troubleshooting.
Good Luck.
Thank you. Yes, very helpful. To those that will talk shit, you teach like the ole school radio guys. Keep them coming.
Thanks
I'm old school. You have the gift of teaching in how you come across. Don't listen to those who are jealous of that. God bless and keep them coming.
I appreciate your time.
Thank you for your lesson and tube amp tutorial. Just picked up a transformerless amp with 3 30kd6 tubes. Tubes light off good , relay is keying, receive pre amp works but zero on the watt meter . Load side variable cap shaft is stripped so I moved it with a plastic screwdriver, went too far where the fins were open and keyed it and it puts out 15 watts or so. Not sure if it's a dirty relay only pushing power when there is no load or if that variable capacitor is my culprit. The stripped barrel on the cap makes me nervous tho so I'm going to order one and change it to be safe.
Probably that cap is shorted. Be careful, you know the nickname for those amps, right? The Widowmaker.
100% correct!! I always get a chuckle when people say "the relay is sticking just replace it" hahaha! like you said, the keying circuit is the problem or theres oscillations ocurring in the amplifier keeping the relay latched! Relays dont stick they either work or dont!
100% correct!
@@tramdr what your 20
Detroit
great video, I have a RMKLV 350 twin tube amp, every now and again the relay starts chattering (clicking very fast) when i de key the mike, Could the cause be RF feedback? If you could possibly cover this problem in a video or maybe just a short explanation I'd be very grateful
Yep, those are not the best built amps. Feedback and/or a bad Input SWR. Long coax into may actually help this problem. Yeah, I know, I'm not a real believer in coax length, but I have said that its like putting a Band Aide on a big open wound. It's not what you really need, but it may get you by in a pinch.
Thank You sharing your knowledge.Great Stuff!
My pleasure!
Thank you for making these videos 😀
Glad you like them!
Thx for good basic info..With most GG sweep tube Linears producing relatively low 8 to 10x gain per Stage, have you tried running any Beam tubes with adjustable B+ on Screens rf Bypassed with disc Caps ?? ....Just thinking the screen + Bias V design would give More useful Gain per stage...
Ummm have you heard me mention 'Turbocharged'? That's the term I use for amps running in Tetrode mode, which is running voltage to the screen instead of Triode and/or Grounded Grid mode. Also, as you said, you need Bias when running in Tetrode mode. So now instead of Grounded Grid mode where you only need the HV, you need Screen and Bias and with those, if you don't sequence it right, or lose one, often the whole thing will let the magic smoke out. Hence, you won't hear me get deep into that here on my Linear Amplifier for Dummies channel.
On a d&a phantom 12 tube it won't key down with mic but you can push relays down and it works. What do you think. And how to go about fixing it
D+A's used both an early Tube type keying circuit and later a transistor keying circuit and in many, the transistor circuit used negative voltage and there were many changes and revisions. If its transistor, it is probably the keying transistor, however, I just replace the whole keying circuit with the Nomad Radio keying circuit. However, you would have to convert the - Voltage to positive to do that. www.ebay.com/itm/115811469907
Thank you for this video. I learned a lot.73
thank you!!! Keep'm coming!
Thank you.
You're welcome!
🎉very nice man very nice! Gatekeeper Said that
Thanks
I have a 2 driving 4 linear amplifier. Can I add 2 tubes and make it a 4 driving 4?
No
Is that basically the same amp as the old ABC Electronics, or the Kris Boomer, or Hy Gain after burner?
or Contex, or D+A Hawk, or Lafeyette HA series, or Sonar or.......
Thanks for this video. I picked up some equipment recently that included a 4 Band Palomar tube amp with 6 tubes in it. I am trying to decide if I should send it in for testing and repair or sell it as is.
Good Luck, but nowadays, not a lot of people doing repairs and also repairs can get very expensive.
If it is a Palomar 350z, as I suspect, be very careful. That amp has the tubes keyed all of the time. A considerate amount of current flows through those tubes, even when the amp isn’t keyed. The amp has long been known as a fire hazard. I rebuilt mine so the tube current is off when it isn’t transmitting. That and some proper biasing of the tubes resulted in a great amp. But it took a lot of time and effort to fix those design problems. Doing that also greatly extended the life of those expensive tubes.
Nice video.
I have a amplifier I'd like to get working again. Palomar 300a
Sorry, only rolling my own.
So you don't work on equipment for the public? How bout advise?
I can try but it not easy to advise on a repair without seeing the amp myself. Whats the problem with the amp?
@@tramdrI appreciate all your videos, I have one that needs repair I accidentally hit mine with the power up, messing with swr on an old antenna. it's a 2 pill, mrf 454s it slightly smoked one of the 11 ohm resistors, I replaced both but still not putting out. Do you think it damaged the pills? How can I test them? Thanks in advance
10:28 Does this mean that you're losing 2.5W, then the amp is on standby or turned off? 🤔
Yes. That 'Cheater' inductor is connected all the time, even when the amp is in Standby or even Off.
I like this video thank you.
Glad you enjoyed it!
@@tramdrI like to learn more so I can hopefully fix my own one day. I always watching 73 till the next one.
🎉man I've been looking for something like this bad in Downloading these and I dont download much I want to learn how to build these starting off with 42kn6 tubes
Hope it helps.
If a transformer was bad in my tube amp,what would be the symptom?
If the transformer had a short, it would blow the fuse as soon as you turn it on. If the transformer was open, it wouldn't put out anything.
511 N. Jersey where are you located? I have a swollen tubed amplifier 1200 X would like for you to look at.
I am in Detroit, however, I don't do others.
Interesting. An amplifier with tubes with no plate cap.
thank you
You're welcome
I need some help with a jb200 mobile unit
Oh ohhhh, those are touchy. Whats it doing or not doing?
would love to talk with you sometime if you are available
I'm not a talker but you can email me Tramdr at Yahoo.com
Good job! thank you. 💥🎛💥
Thank you Bro, very informative stuff 💯, how can I contact you, Soldier boy (101) on CZcams,I have a copper which I think you capable of turning into Gold.73s
Tramdr at Yahoo.com