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 Post subject: Looking to learn!
PostPosted: Sep Tue 14, 2021 3:58 pm 
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Joined: Aug Sat 28, 2021 10:32 pm
Posts: 7
Hello folks!

I'm new to the forum and the world of tube audio (aside from my guitar amplifiers), but have a keen interest! I've been purchasing late 1950s and early 1960s consoles for the past year and am curious if there might be anyone in central Minnesota who might be willing to help guide and or mentor me. I have found a couple of places including a shop in St. Paul and one in St. Cloud that work on tube audio, but I'd also like to learn myself. I'm fairly handy and can solder (many years working on guitars), but can't read or really understand a schematic.

This past weekend I purchased a late 1950s Motorola SK14M with matching speaker cabinet from member Jukebox Denny (wonderful guy and visit!). I also have a 1957/58 Magnavox Berkshire, 1957/58 Magnavox Continental, Magnavox S-48 speaker cabinet, and RCA SHF-8. I would like to restore all of them to working condition. I've spent quite a bit of time reading this forum gleaning information which I really appreciate! I look forward to any information anyone can provide!

Many thanks,
Adam


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 Post subject: Re: Looking to learn!
PostPosted: Sep Tue 14, 2021 7:26 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 13508
Location: Fernandina Beach, FL
I can't recommend any help with working on those lovely looking consoles. But I can say, "Welcome" to the ARF.

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Don


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 Post subject: Re: Looking to learn!
PostPosted: Sep Tue 14, 2021 8:26 pm 
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Joined: Jan Fri 27, 2017 8:41 pm
Posts: 380
Location: Springwater, NY
anewname wrote:
....I'm fairly handy and can solder (many years working on guitars), but can't read or really understand a schematic.


Adam, welcome. Jump in and start...that's the only way. Help is here. Perhaps set aside your restorations for now and pick something and build it. Since you like guitars, dig in and build a 5F1 or 5F2A Champ. Like this:

https://www.amazon.com/MOD-102-DIY-Guitar-Amplifier/dp/B00493YF8W

There are several similar kits. There is nothing difficult about it and you'll learn to read and understand a schematic. You will learn the function of all the key parts. You will learn about safety.

To save money over a commercial kit, the Antique Wireless Association sells their '48 Special guitar amp PCB (with schematic, chassis template, and parts list), which is inspired by the Fender 5C1 Champ amp. I think the total price works out to be about $140, without a speaker cabinet. Nice clean tone and very nice breakup. The have a help desk.

Or search the archives here for a 6888 Tube AM Transmitter that you will find useful later on with your restorations. Or pick some other project to build. Just get started and build something.


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 Post subject: Re: Looking to learn!
PostPosted: Sep Tue 14, 2021 10:09 pm 
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Joined: Aug Sat 28, 2021 10:32 pm
Posts: 7
Many thanks! I do have an account with CE Dist./Antique Electronic Supply and so starting with one of the Mod kits (or something similar) could be a great jumping in point. I appreciate the suggestion and look forward to digging in.


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 Post subject: Re: Looking to learn!
PostPosted: Sep Wed 15, 2021 7:50 pm 
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Joined: Jul Sun 21, 2019 3:32 pm
Posts: 384
Location: Upstate NY by the big lake!
I found that the videos on YouTube by "Uncle Doug" where he teaches tube theory, and schematic reading to be very helpful.

Learn how AC gets converted to DC, and that capacitors block DC, and allow AC to pass, creating a bridge for the signal to pass from stage to stage.

Mike


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 Post subject: Re: Looking to learn!
PostPosted: Sep Thu 16, 2021 2:44 pm 
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Joined: Aug Sat 28, 2021 10:32 pm
Posts: 7
Thanks Mike! I watched a couple of Uncle Doug's videos and found them very informative and I appreciate his style of teaching. His excitement is contagious and the channel seems like a new time bandit for me.

Kind regards,
Adam


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 Post subject: Re: Looking to learn!
PostPosted: Sep Sat 18, 2021 2:45 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10867
Location: Beaver Falls, PA. USA
Welcome to ARF! The biggest problem with old amps is defective capacitors, both electrolytic and paper types. In the 1950s, many manufacturers used molded-paper capacitors which are just as bad, or worse, than the wax variety. Many of us have long experience with tube amps, so don't hesitate to ask questions. Do you have any test equipment?

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Tim KA3JRT


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 Post subject: Re: Looking to learn!
PostPosted: Sep Sat 18, 2021 3:58 pm 
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Joined: Aug Sat 28, 2021 10:32 pm
Posts: 7
Thanks for the insight, Tim! I just have an inexpensive multimeter, but was thinking I should upgrade. I was considering a Klein one as I've good experience with other tools made by them. Do you have any suggestions on other test equipment I should consider?

I was thinking that I would try and tackle my RCA SHF-8 as it appears fairly simple (I obtained a schematic from RadioMuseum.org). It currently 'works', but has a nasty hum which I understand to suggest that the filter caps are bad.


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 Post subject: Re: Looking to learn!
PostPosted: Sep Sat 18, 2021 4:12 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 23703
Location: Haledon, NJ, usa
Welcome!
Here's a link to Fun with Tubes... where there are many areas to browse through and select an area you want to start learning about. Such a Audio Amplifiers- How they work etc.
https://www.angelfire.com/electronic/fu ... index.html
These old tube radios had 5 tubes and were known as the All American Five radio.
https://www.angelfire.com/electronic/fu ... AA5-2.html
That's a nice area to start if you want to understand how to fix a tube radio.

But lots there to learn from... enjoy

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To be a man, Be a non-conformist, Nothing's sacred as the integrity of your own mind.
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 Post subject: Re: Looking to learn!
PostPosted: Sep Sun 19, 2021 3:25 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 10867
Location: Beaver Falls, PA. USA
With test equipment, the sky is the limit, depending upon your budget, and what you want to do with it. For 1950s phonographs, you can get by with a good DMM or VTVM, and a tube tester. A signal tracer is another nice thing to have, both for amps and radios. Some folks like to have a good capacitor tester, as well. If you plan to work on radios and tuners, a good RF signal generator is the next thing to get. FM and multiplex repairs require specialized generators, if alignment is needed.

For serious work on HI-FI, theatre, broadcast, and PA equipment, you will need a good audio generator, an oscilloscope, AC VTVM, and a distortion analyzer. Don't forget a dummy load! All this equipment can be found on the used market, and there are some bargains to be had, if you don't mind having older stuff. Be aware that the older test gear itself may need some work. Hamfests and radio swap meets are good places to find test gear, as well as the ads here in the Classified section.

"Elements Of Radio Servicing" is available for download on this site; it's a good book, and much of the information also applies to amplifiers and phonographs. It's located in the Archives section; go to the home page to get there.

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Tim KA3JRT


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 Post subject: Re: Looking to learn!
PostPosted: Sep Mon 20, 2021 4:49 pm 
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Joined: Aug Sat 28, 2021 10:32 pm
Posts: 7
Many thanks for the information! I have a friend who has multiple older DMMs, an oscilloscope, frequency generator and other tools he's considering selling. He said that all have been gone through and function properly. I really appreciate you sharing your knowledge with me!

Kind regards,
Adam


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