Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Tubes and Hybrids => Topic started by: galaxiex on May 31, 2017, 09:19:28 PM

Title: New amp day! Silvertone 1481
Post by: galaxiex on May 31, 2017, 09:19:28 PM
New Amp Day!

Look what landed on my doorstep today!

Thought I'd put this here since its a tube amp.  :)

Found this on Reverb for a good price.
It sounds great considering the speaker cone is a little soft. Farts a bit on low notes.
Speaker looks original, as do the tubes.
The 6X4 rectifier is a JAN Phillips, not sure if that would be original.

Is that really how they hooked up the speaker back then?
Right off the O/T winding?


Title: Re: NAD!
Post by: galaxiex on May 31, 2017, 09:21:09 PM
More pics...
Title: Re: NAD!
Post by: J M Fahey on June 02, 2017, 07:46:12 AM
Thought I'd put this here since its a tube amp.  :)
What makes you think that?  :o
Last time I checked, site name said "SS"  :o
Title: Re: NAD!
Post by: phatt on June 02, 2017, 08:44:52 AM
Well it is under  *Tubes and Hybrids*  ;)
Phil.
Title: Re: NAD!
Post by: galaxiex on June 02, 2017, 08:16:27 PM

What makes you think that?  :o
Last time I checked, site name said "SS"  :o
[/quote]

Well it is under  *Tubes and Hybrids*  ;)
Phil.

Ummm, yes this is the area of the forum for tube amps.

I guess this forum doesn't get much traffic from tube amp folks.

Oh well, mods please feel free to move this thread as you see fit.
I guess it would have been better in players corner.
Title: Re: NAD!
Post by: teemuk on June 03, 2017, 04:12:17 AM
Quote
Is that really how they hooked up the speaker back then?
Right off the O/T winding?

Speaker load is the secondary side circuit so how else should they make the connection? Since I see no features such as extension speaker jacks or alike isn't that the shortest and most logical method to connect the speaker?

Theoretically there could be a speaker out jack and a plug in the speaker wires ...but why? Now its solid connection to load and additionally they manmaged to make the cheapie model even cheaper.

IMO, this one isn't even an oddity. You probably haven't seen those vintage amps yet that have their tiny, tiny OTs riveted right to the speaker frames...?
Title: Re: NAD!
Post by: Enzo on June 03, 2017, 05:47:11 AM
teemu, I could be wrong, but I think what he found odd was the enamel winding wires from the transformer soldered directly to the speaker.   As opposed to the winding wires going to a terminal strip and then the speaker wires connected there.  So the physical arrangement rather than the electrical aspect.  At least that is how I read it.


Actually, on old amps like that, it was not uncommon to see the small output transformer itself mounted right on the speaker frame.  Then the (typically) blue and red wires of the primary went back to the chassis.

Like this old Gibson (Jensen speaker in Gibson amp):
(http://www.chambonino.com/work/gibson/gib2c.jpg)
Title: Re: NAD!
Post by: phatt on June 03, 2017, 07:04:24 AM
Hey chaps,,, if you go back far enough, before magnet materials became economical speakers had a big Electromagnet wrapped around the voice coil of the speaker.
IIRC simply called Electromagnetic speakers which came with a Field Coil which created the magnetic field for the VC.

I think the field coils may have been wired out of phase to reduce hum,,,, so maybe humbucking was understood long before the idea was used in PU's  8)
Phil.

a couple of links showing the idea;
https://www.youtube.com/watch?v=Pq64-ayRyfs

https://www.youtube.com/watch?v=rHhSqEMyzIs
Title: Re: NAD!
Post by: galaxiex on June 03, 2017, 08:08:47 AM
Quote
teemu, I could be wrong, but I think what he found odd was the enamel winding wires from the transformer soldered directly to the speaker.   As opposed to the winding wires going to a terminal strip and then the speaker wires connected there.  So the physical arrangement rather than the electrical aspect.  At least that is how I read it.

Yes, this is what I meant, the physical arrangement I had not seen before.
It makes sense to do that in a budget guitar amp where they are pinching pennys.
The question was sort of rhetorical.
Sorry, I should ask questions where I actually expect an answer, rather than "thinking out loud".

For the record, I am familiar with field coil speakers,
well... familiar in the sense that I had on old "portable" record player (my Dads) long ago that I took apart to "see how it worked".
(ahh, curious youth)
It had field coil speakers.

I stripped it down to attempt to build a rather crude guitar amp.
My Dad didn't mind, he had bought a fancy "new" stereo music system. ;) 

I knew enough to know that the guitar input would have to be hooked up where the needle cartridge was connected.
It didn't sound very good....   :lmao:
Title: Re: NAD!
Post by: Enzo on June 03, 2017, 08:18:57 AM
I doubt field coils were wired "out of phase" because they ran on DC.. If you have two coils wired one reverse the other, they form opposing magnetic fields, a weak result.

In my example, the field coil is a separate issue from the speaker frame mounted transformer.
Title: Re: NAD!
Post by: g1 on June 04, 2017, 12:00:36 PM
  Though not hum-bucking, the field coil does often also serve as a choke for the power supply.  So it is dual purpose in that sense.
However, I do vaguely recall some speakers that did in fact have an extra hum-bucking coil?
Title: Re: NAD!
Post by: joecool85 on June 08, 2017, 02:03:29 PM
Ummm, yes this is the area of the forum for tube amps.

I guess this forum doesn't get much traffic from tube amp folks.

Oh well, mods please feel free to move this thread as you see fit.
I guess it would have been better in players corner.

You are correct, this is where this post belongs - no worries!  :tu:

Also, neat amp!
Title: Re: NAD!
Post by: galaxiex on June 08, 2017, 10:03:28 PM
Thanks Joe!  :)
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 18, 2017, 05:09:45 PM
Well time to start working on this....

First look inside the chassis shows someone replaced the 2 wire power cord..... with a newer 2 wire power cord....  ::)

So I installed a 3 wire power cord and clipped the death cap.
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 18, 2017, 05:14:17 PM
Arrrgh!

After installing the 3 wire cord and a speaker jack....

The amp no longer works!  :grr

Quick inspection reveals the O/T primary is now open! Rats!

Seems this is common on these amps (google search) so I ordered a Hammond replacement O/T for a Fender Champ.

Mercury Magnetics has a Silvertone 1481 O/T listed, but the price is triple the Hammond.

I'm sure the Hammond will be just fine....
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 18, 2017, 05:23:11 PM
On to other things...

Need a new speaker baffle, so a short time in my shop with the table saw and jig saw and we have this...

First, the old baffle and careful removal of the grille cloth.

Transfer dimensions to a piece of 1/2 inch plywood.

Cut relief on the corners so the new baffle will slip into the cabinet.

Then drill some holes and paint flat black.
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 18, 2017, 05:26:59 PM
Here's the old speaker (original?) and O/T.

Someone put some goo around the cone at the edge surround trying to "save" it.
It's done.
Cone has a small tear and makes crunchy/crackling noises when you touch it.
The paper is very dry and brittle.

For the record... this speaker did "work" when I got the amp, but it definitely needs a recone.

Meanwhile, I have a few 8" speakers I can try out once I get the baffle installed. (waiting for paint to dry)
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 18, 2017, 07:45:32 PM
There!
Speaker baffle done!

I think I'll call this amp "Bruce"  ;)

Now the 2 week wait for the new O/T to get here...
Title: Re: New amp day! Silvertone 1481
Post by: Enzo on June 18, 2017, 09:21:56 PM
How about a thorough inspection.  measure for primary resistance right at the transformer wires.  it may have opened, but there is nothing inherent in changing to a grounded power cord that would stress a transformer.
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 18, 2017, 10:36:41 PM
Thanks Enzo,

Yes, I should do more checking.... however...

I'm embarrassed to admit.... "I" may be the cause of the failed transformer.

You see, I drilled a hole for the secondary wires to go inside the chassis so I could install the speaker jack.

Foolishly I did this with the transformer still bolted in place... do you see where this is going....

That's right, the tiny pilot drill I used, punched through the chassis and nicked the winding's.  :grr

I then of course, removed the Tx and made the hole big enough to install a grommet for the wires.

Then inspected the Tx carefully with a magnifying glass and did not see any real damage, but the drill bit did go a small ways into the winding.

Fairly sure I screwed it up.

Title: Re: New amp day! Silvertone 1481
Post by: joecool85 on June 19, 2017, 06:05:50 AM
Thanks Enzo,

Yes, I should do more checking.... however...

I'm embarrassed to admit.... "I" may be the cause of the failed transformer.

You see, I drilled a hole for the secondary wires to go inside the chassis so I could install the speaker jack.

Foolishly I did this with the transformer still bolted in place... do you see where this is going....

That's right, the tiny pilot drill I used, punched through the chassis and nicked the winding's.  :grr

I then of course, removed the Tx and made the hole big enough to install a grommet for the wires.

Then inspected the Tx carefully with a magnifying glass and did not see any real damage, but the drill bit did go a small ways into the winding.

Fairly sure I screwed it up.
Bummer. However I feel for you. I did a similar thing where I was putting a heat shield back onto my wife's car. I had to drill a hole for the rivet and it was to go into the spare tire housing...I didn't remove the tire first. Made for a funny moment at the tire shop when I told them I drilled the tire LOL.

Sent from my XT1055 using Tapatalk

Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 19, 2017, 09:01:47 PM

Bummer. However I feel for you. I did a similar thing where I was putting a heat shield back onto my wife's car. I had to drill a hole for the rivet and it was to go into the spare tire housing...I didn't remove the tire first. Made for a funny moment at the tire shop when I told them I drilled the tire LOL.

Sent from my XT1055 using Tapatalk

Thanks Joe, that's a funny story.   :)

Ya, I'm sure anyone that works with their hands has messed up somewhere, sometime, and done something boneheaded.
I know I have, and not just when working on music gear.

I've been in the transmission repair industry for nigh on 40 years now and have witnessed, and done, some really stupid things.

One doozy I'll never forget....

Taxi cab came in the shop cuz the tranny is not working... Ford Crown Vic rear wheel drive.
Ok, so pull the tranny out see whats broken...

The guy pulling the tranny removed every single bolt holding the tranny in the car and it refused to come out...???
Like it was "stuck" up in the car... WTH.

Turns out the driver had it at a place to install "Taxi cab gear" you know, the meter and radio and such...

Well they mounted it on the transmission hump and.... surely you can guess now...

Yup, they use reeeely long screws and drilled and screwed right down into the transmission to install the meter and radio. DOH!

Glad it wasn't me that did that!

(you didn't think I was gonna tell of any of my boneheaded screw ups, didja  ;)
this one with drilling the Tx was enough.
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 19, 2017, 11:12:41 PM
Just thought I'd throw up a schematic for this...
Title: Re: New amp day! Silvertone 1481
Post by: J M Fahey on June 22, 2017, 08:47:20 PM
Probably wire was quite corroded and barely held for the initial tests, then any knock might have finished it off.
Look closely , inder good light and with good glasses, you might have it split very near the terminal, simply because only the wire end gets scratched for soldering, the rest is still covered in protective enamel.

The point being that maybe 1/2" or less of fresh copper wire saves your transformer.

As of the enamelled wires directly being the external connections, it´s often done in low voltage transformers (think 6V or 12V) , it saves some assembly seconds and is relatively safe,since that wire is usually thick.

It woud be dangerous on primary fine wire, and VERY frustrating.
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 22, 2017, 09:52:50 PM
Thanks JM,... but

Naaaah  the transformer is gakked!

I peeled back some of the lacquered paper and the drill bit went in right between the thick sec wind and the tiny primary.
With the paper peeled back I can see several broken primary winds right in the middle.

Only way to save this one would be a rewind. Probably not worth it.

I'll keep it with the amp for posterity.  :)
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 23, 2017, 10:29:42 PM
Sooooo, as per the schematic attached above, the original O/T secondary went straight to the speaker.
No connection to the chassis.

Since I am installing a speaker jack,
I have the option of installing an insulated jack that obviously, would also not make any connection to the chassis.

If I were to install a non-insulated jack, would it then make some difference as to which side of the secondary should be connected to the ground side of the jack?
IOW, is there a phasing issue that I need to be concerned about?

TIA
Title: Re: New amp day! Silvertone 1481
Post by: Enzo on June 23, 2017, 11:13:46 PM
Phasing really only matters when the same signal is fed to multiple amps.

There appears to be no negative feedback loop, so phasing doesn;t matter there either.

usually output transformers identify hot and cold lead by color.  SO good practice would be the cold side to chassis.
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 24, 2017, 02:09:02 AM
Cool.  8)

Thanks Enzo.

Hopefully when the new O/T gets here, it will have something to ID the leads.

Edit; Oh... yes it does...  I ordered this one...

https://www.amplifiedparts.com/products/transformer-hammond-output-replacement-fender-5w-7k (https://www.amplifiedparts.com/products/transformer-hammond-output-replacement-fender-5w-7k)
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 29, 2017, 09:18:15 PM
New output TX came in.

Amp is working again, Yay.  :)
Title: Re: NAD!
Post by: jfetter on June 30, 2017, 03:52:25 PM
Thought I'd put this here since its a tube amp.  :)
What makes you think that?  :o
Last time I checked, site name said "SS"  :o

its kinda funny, i've put up a lot of diy data on hybrids on another site and it gets no love , even the students get upset. if i put test plots and schematics in SS they cry, then if i put in Tube section they cry. Its hybrid and homeless. Nice to see a hybrid section here.

congrats on your amp find.
Title: Re: New amp day! Silvertone 1481
Post by: galaxiex on June 30, 2017, 04:16:36 PM
Thanks! :)
It sounds pretty good with the Weber speaker (originally intended for the Vibro Champ).
Not very loud tho...

That's ok, it could keep up with a moderately loud rehearsal.
Title: Re: New amp day! Silvertone 1481
Post by: lotus1 on December 28, 2017, 08:48:52 PM
Rotate speaker 180 degrees, tightens it right up...they sag over time, try it.