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 Post subject: Silvertone Model 1484 Guitar Amp
PostPosted: Jan Thu 28, 2016 4:54 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
A friend of mine heard that I liked restoring old tube gear and asked me if I wanted an old Peavey amp. Of course I said "sure do". At first I was a little disappointed that it was "just" a Silvertone 1484. A quick scan of the tube compliment yielded (3) 12AX7's and (2) 6L6GC output tubes (I assume in push pull). The little bit of searching on YouTube and the internet seems to indicate this is a well regarded vintage amp. Not super powerful but generally liked for it's sound. Unfortunately the cabinet and it's 12" Jensen's is gone. Like the head, it was made of crappy particle board and fake Tolex. He thinks he knows where the foot switch is though.

I don't like to start anything before I finish a work in progress (a Zenith in this case) but I'm looking forward to bringing this back. I already cleaned the fake Tolex and soaked the knobs in warm soapy water There's a lot left to clean up. It's been sitting for a long time. Here's how it started:

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Jan Thu 28, 2016 6:41 pm 
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Joined: Aug Sun 01, 2010 1:12 am
Posts: 8431
Location: Minnesota
Oooh that PT looks a little scary. Hopefully it's OK. Most of Sears amps were made by Danelectro or Valco. Either of which can be a sweet little tone machine. I suspect that one is Danelectro.


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Jan Thu 28, 2016 7:00 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
ggregg wrote:
Oooh that PT looks a little scary. Hopefully it's OK. Most of Sears amps were made by Danelectro or Valco. Either of which can be a sweet little tone machine. I suspect that one is Danelectro.



Yeah... I haven't put on on the PR-57 and checked current draw. I want to look under the chassis first. I'm hopeful that I can fix the transformer with a little evapo-rust and black paint. We'll see

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Jan Sat 30, 2016 12:41 am 
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Joined: Jan Sun 20, 2013 12:41 am
Posts: 216
Location: South Portland, ME
Under specced output transformer is the weak link in those amps, but probably contributes to the unique voicing.. that and the low screen supply.
I love the way these sound.

The original red Planet electrolytics are "Guaranteed for one year". Might wanna replace those :lol:

Also, be sure and check output tube bias -- they can run very hot, and a nice trick is to run the bias supply into a voltage doubler and trim pot.


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Jan Sat 30, 2016 1:19 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
hylaphone wrote:
Under spec'd output transformer is the weak link in those amps, but probably contributes to the unique voicing.. that and the low screen supply.
I love the way these sound.


I have a Mercury Magnetics output transformer made for the amp. It's got 4, 8, and 16 ohm output windings. I'm not going to install it right away

Quote:
The original red Planet electrolytics are "Guaranteed for one year". Might wanna replace those :lol:


A whole year! :)

Quote:
Also, be sure and check output tube bias -- they can run very hot, and a nice trick is to run the bias supply into a voltage doubler and trim pot.


I'll cross check against the schematic to look for mods and I will definitely checked the output tube bias and power level.

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Jan Sat 30, 2016 8:49 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
I've got a couple of different LCR meters and when I measured the power supply filter choke it comes up around 50H and it should be 7H. My Fluke shows it to be open and the VTVM on the Rx1 scale shows it is open. I guess that's pretty open... Mercury Magnetics has one though.

I wasn't going to work in this yet but it just keeps calling me...

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Jan Sat 30, 2016 9:36 pm 
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Joined: Jan Sun 20, 2013 12:41 am
Posts: 216
Location: South Portland, ME
Mike6158 wrote:
I've got a couple of different LCR meters and when I measured the power supply filter choke it comes up around 50H and it should be 7H. My Fluke shows it to be open and the VTVM on the Rx1 scale shows it is open. I guess that's pretty open... Mercury Magnetics has one though.

I wasn't going to work in this yet but it just keeps calling me...


huh.. the last one I worked on had an open choke too!
I just used an off the shelf Hammond 5H, worked fine.


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Jan Sat 30, 2016 10:07 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
The power supply in the amp is a tad different. I already ordered the choke from Mercury Magnetics so I'll just go with that. At this point I think I'm going to go with the upgrade to the 4/8/16Ω output transformer and install 3 jacks for the speaker vs leaving the long cable installed.

In order to clean the amp up "properly" I'm going to disassemble it a lot more than I wanted to but that will probably cut down on the bad language in the long run :)

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Mon 01, 2016 9:04 pm 
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Joined: Sep Sat 15, 2012 2:19 am
Posts: 56
Voltage doubler


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Tue 02, 2016 3:25 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
RattleCat wrote:
Voltage doubler


Series voltage doubler. The filter caps "add" up to 25mF... But I simulated it and it seems to be fine at that.

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Tue 02, 2016 7:25 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4852
Location: Gainesville, Florida
use a current limiter dim bulb if you have one. easy to make. saves the power supply :|


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Wed 03, 2016 3:48 am 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
I have a dim bulb tester and variac but most of the time I just use a Sencore PR57 so I can watch the current draw on startup.

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Sat 06, 2016 8:58 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
I have some capacitor questions

I'm working on the power supply "board" and specifically on the components in red for this section of the tremolo circuit

Image

Te resistors had drifted a little but not out of spec. I changed them anyway since I had desoldered the lugs to test the caps.

C23 is a Sprague .47µF / 200V paper cap. It tested great. Capacitance was almost dead on and leakage was nothing at max voltage on my Eico 950). Since it's not in the power supply circuit I decided to leave it in. Thoughts on that decision? If it were in the power supply or in an AA5 I would change it just because.

C24 is a .047µF / 600V cap. Capacitance is also almost dead on but leakage wasn't "perfect" up at 500V. On the other hand, the eye tube looked very similar with a new cap installed so maybe my Eico isn't working as well as it could be. ESR was low. So, the plan is to leave it alone. Thoughts on that decision?

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Tue 09, 2016 4:45 am 
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Joined: May Thu 01, 2014 6:00 pm
Posts: 89
Location: Taneytown, Md.
If it were me, don't mess with it till you fire it up. If the trem works, it works. :)


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Tue 09, 2016 2:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4852
Location: Gainesville, Florida
2ND that motion :|


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Wed 10, 2016 1:44 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
Due to a full schedule at work I'm a couple of weeks away from power up.

On another note:

I was reading the first chapter of Designing Tube Preamps for Guitar and Bass. Actually... I skipped ahead to 1.24 thru 1.26. I'm going to start over at the beginning this evening. It looks like a decent book :D

I tend to buy metal oxide resistors for my AA5 and test equipment repairs. I have some carbon comps but tend toward using the metal oxide resistors for just about everything. The author says "Metal oxide resistors are similar to metal film, but are usually avoided for audio because they can cause low-level distortion and are fairly noisy. They may still be found in the power supply however." Elsewhere he makes the recommendation for metal film. Wirewound seems to be preferred overall but finding lower wattage wirewound resistors seems to be an issue. And they are expensive. Thoughts?

So far I haven't found any resistors that have drifted out of spec. so the it may not be an issue.

_________________
It's hard to solve an equation if every term is an unknown.

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Last edited by Mike6158 on Feb Sat 13, 2016 4:37 am, edited 1 time in total.

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Wed 10, 2016 4:49 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4852
Location: Gainesville, Florida
hope you take a vacuum cleaner to it first so it will look good for the occasion. some time take the transformer bell ends off for rust removal and paint. maybe some Rust-Oleum black or glow in the dark paint. could use Ospho on the transformer segments. turns rust black. can get real crazy with aluminum polish on the valve covers :|


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Wed 10, 2016 11:32 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
tubeAMP wrote:
hope you take a vacuum cleaner to it first so it will look good for the occasion. some time take the transformer bell ends off for rust removal and paint. maybe some Rust-Oleum black or glow in the dark paint. could use Ospho on the transformer segments. turns rust black. can get real crazy with aluminum polish on the valve covers :|


I'm pretty well along with cleanup. The transformers are pulled and waiting for "de-rusting" and paint. The chassis is stripped of anything that's in the way. I'm going all out with cleanup. Under all that grunge is a nice amp. I plan to keep it so I'm making it right for the long haul. I'll post pics when I get it back together

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It's hard to solve an equation if every term is an unknown.

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NE5U

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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Feb Tue 16, 2016 4:48 pm 
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Joined: Nov Sat 27, 2010 6:15 pm
Posts: 5449
Since you are going to all that trouble, why not just replace all the old caps and carbon resistors. Some of these old parts behave differently once they heat up in the cabinet and can be difficult to diagnose. You should have a nice amp when done if the iron is good!


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 Post subject: Re: Silvertone Model 1484 Guitar Amp
PostPosted: Nov Mon 19, 2018 9:24 pm 
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Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2009
Location: Weimar, Texas
You know how they say not to start something and then put it off until later? Yeah... I did that. I have a few days that I can spend on it so maybe I'll get it finished this week. Then I can tackle a few other "almost done" projects :?

Current state

Front

Image

Bottom (power supply board is finished but not installed yet)

Image

Top. Somehow the reverb tank "strap" has grown in width.

Image

_________________
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