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 Post subject: Re: Silvertone 1448
PostPosted: Aug Tue 13, 2019 1:38 pm 
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Posts: 4866
Location: Gainesville, Florida
you can drill out the rivets. you might need to drill a pilot hole first then use a drill bit large enough to cover the rivet head and round it out carefully. otherwise you would have to match a new transformer primary to the 50C5 plate load impedance and 4ohm secondary


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Tue 13, 2019 2:56 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20204
Location: Warner Robins, GA
A typical AA5 using a 50C5 is usually around 2.5K primary impedance so any transformer with a 2.5K to 4 ohm impedance will work.

Impedance doesn't have to be 4 ohms though as it can be whatever impedance you choose to use for the replacement speaker.

https://www.tubesandmore.com/products/t ... ngle-ended


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Tue 13, 2019 5:12 pm 
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Location: Gainesville, Florida
here is another similar amp diagram using 50L6. notice that R15 is where the volume control should be. R14 is probably tremolo intensity http://schematicheaven.net/bargainbin/kay500.pdf


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Tue 13, 2019 11:30 pm 
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Joined: Aug Sun 11, 2019 10:02 pm
Posts: 10
Thank you both so much! I'll check it out.

Today I just received the 1449 Silvertone, 2 pick-up guitar and case/amp. This amp has the isolation transformer and an 8" speaker. I believe it puts out 5 watts. Funny, this one has a working speaker, but the amp is dead. All the tubes glow, but no sound. Go figure. I really love the tone on these babies!


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Wed 14, 2019 1:28 am 
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Location: Gainesville, Florida
no sound? no hum or scratchy noise? you are plugged into the input and not the foot switch jack? something may not be connected


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Wed 14, 2019 6:42 pm 
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Joined: Aug Sun 11, 2019 10:02 pm
Posts: 10
I think it was making a quiet crackling sound when i turned the volume knob, but no guitar signal. Then, I took the amp out of the case and turn it and sat it on its base. Turned it on and suddenly I could hear a general amp hum the tremolo noise/sound through the speaker. So, I plugged in a guitar and it worked! When I put it back together, it's not functioning.

My plan is to purchase a new set of tubes (I'll keep the old ones as spares) and do a bit of trouble-shooting.

If it's not a tube, then, I'll check for a loose component (that I can easily find by poking around with a wooden chopstick)


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Wed 14, 2019 8:26 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 441
Location: Copake,NY
Sounds like the input is getting grounded or some other connection/component is when its put into the case.For now,assume the tubes are ok since they worked when the chassis is out of the case.


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Wed 14, 2019 8:41 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4866
Location: Gainesville, Florida
something is getting moved when the chassis is being put back in the case. look for bare lead touching another, tubes moving, something getting pinched when you are securing the chassis


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Thu 15, 2019 12:05 am 
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ok, will do. Thanks guys!


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Tue 20, 2019 6:40 pm 
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Joined: Aug Sun 11, 2019 10:02 pm
Posts: 10
Tube Radio wrote:
A typical AA5 using a 50C5 is usually around 2.5K primary impedance so any transformer with a 2.5K to 4 ohm impedance will work.

Impedance doesn't have to be 4 ohms though as it can be whatever impedance you choose to use for the replacement speaker.

https://www.tubesandmore.com/products/t ... ngle-ended


So, back to this part...

I finally read through some things and tested the existing output transformer on the speaker.
I used a 24 VAC wall wart I had lying around and it supplied 27.6 VAC to the primary and it measured 1.125 V on the secondary. Based on some formulas I located elsewhere, I found the following:

Turns Ratio is 25:1
Impedance Ratio is 602:1
Multiply Numerator, 602, by 4 for the 4-ohm speaker = 2,408 : 4
So, I'm looking for an output transformer a ~2.5k ohm on the primary and 4 ohms on the secondary.
EXACTLY AS YOU SUGGESTED!! how about that?

My next question is about the bias current going through the transformer. Which transformer is best to use from those listed in the link you provided?

Since the amp has a 3-watts of output, would the 3W / 25 mA suffice?
https://www.tubesandmore.com/products/t ... ngle-ended


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Tue 20, 2019 7:51 pm 
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Posts: 4603
Location: Vancouver Island, Canada
Why not just search around your area for an old AA5 radio? If it is 1950's to late 50's, it will have the single ended 50C5 output and the transformer you need. Plus a spare tube or two.

I have some here, but shipping will add up to $20 each. :x

_________________
Watch the doughnut, not the hole.
Burl Ives, RIP, oldtimer.
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 Post subject: Re: Silvertone 1448
PostPosted: Aug Tue 20, 2019 7:53 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 20204
Location: Warner Robins, GA
https://frank.pocnet.net/sheets/049/5/50C5.pdf

The datasheet lists a max plate current of 50mA for a single 50C5 tube so whichever transformer is rated at 50mA or higher will work fine.


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 Post subject: Re: Silvertone 1448
PostPosted: Aug Wed 21, 2019 4:43 pm 
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Joined: Aug Sun 11, 2019 10:02 pm
Posts: 10
Yeah, looking for an AA5 radio would make sense too. I do have one with a 50C5 in it, but it works well and I don't want to mess with it. I'm using this amp project to gain as my official start with amp circuits. I want to understand how they work. I've made some ribbon mics and some tube mics, but never really got into the PSU or amps before.

I think I should connect the original Transformer and measure the current coming out of the 50C5 with the proper load. Its max is 50 V, but couldn't it run at a lower level? Or is it ok to have a transformer that can handle more current than needed? Just don't understand how these things affect the sound.

So, to recap, I still have to add the isolation transformer and a properly grounded three-prong cable to make this safe, remove the death cap as it won't be needed anymore. I have the new 6" speaker, need to order the output transformer and see how to mount that. Then it's time to rock out some sweet tones on this thing.

I bought this one so I could build a 2nd from scratch..I have a 1448 guitar and case that was missing the amp. So, I'd love to build another one in there with all modern components and possible hot rod it to have higher gain.

You guys have been so helpful, I can't really express how much fun I'm having with this and your assistance has made this possible.


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