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Sears/Silvertone 40XL solid state amp schematic

Started by galaxiex, October 10, 2016, 12:37:47 AM

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Quote from: Loudthud on October 11, 2016, 05:30:12 PM
Are you sure about Q3? It would make a lot more sense if it was a PNP.

Ahhhh... hahahaha!   :o ??? ::) :P :-[ :-\ :'(  :duh <mixed emotions!

So I had to go and look....

Its a 2N4248 PNP and looks *exactly* like all the other small 2N5133 transistors on the board!
I just assumed..... and the laugh is on me now.  :lmao:

Sigh... Ok... one more time.... I'll fix the schem....

What would I do without you guys!

Thanks!  :)
If it ain't broke I'll fix it until it is.


Soooo, just to be sure...

Would the orientation of Q3 be the same as Q7?
Emitter of Q3 to the base of Q4?

Or the other way around?
If it ain't broke I'll fix it until it is.


B, E, and C connections of Q3 are correct. Emitter current comes from the output through R21 and Collector goes to the Base of Q4.


If it ain't broke I'll fix it until it is.


Ok, reeeeely...... hopefully.... the very last time I post these....  :duh

To avoid confusion I removed all the earlier schematics and layouts.
If it ain't broke I'll fix it until it is.


So I unhooked the P/T out of curiosity to check the unloaded AC voltage.

20-0-20 vac

No idea of the VA rating.
Its marked,

PTR 222
If it ain't broke I'll fix it until it is.


A meter reads resistance, not impedance, so an 8 ohm speaker measures 6-7 ohms usually.

A 4 ohm speaker would at most be 3 decibels louder.  Just about enough to notice, but not enough to cause a "where did my volume go" situation.

J M Fahey

26V single supply is same (as power is concerned) as 13+13V rails.

A TDA2006 fed +/-12V has a power output of 8W into 8 ohms, 12W into 4 ohms (and that with 10% distortion, somewhat beyond visible clipping) so his amplifier can supply about the same.



Alright, so I've done some small tweaking/experimenting to this one and have got it where I like it.  :)

Simply changed the volume pot arrangement at the inputs.

As it is, Ch1 is much louder than Ch2-3. (same as before the change)

Since the "effects" channels would likely get the most use, I thought to add a pre-amp to make it the same loudness as Ch1.

In the pre-amp schematic is there a good technical reason to *not* use the simple capacitor coupling C1,2 as drawn?

Do I need to use mixing resistors?

I have bread-boarded this and it "seems" to work ok.

I'm ready to etch a pre-amp board for this, but thought I'd better ask first.  ;)

If it ain't broke I'll fix it until it is.


Well, this post is to say a big THANKS to Mr. JM Fahey!  :)

I read a post (some time ago) where he recommended the Jensen MOD series of speakers.

I had never tried them before....

I decided to take a chance and ordered a MOD 10-50 4 ohm speaker for this amp.

WOW! AMAZING! This thing just came ALIVE!  8|
It has a unique tone like I have never heard before.
Its also now quite loud for a bedroom/practice amp.

So Thanks again JM.  :) Those MOD speakers seem to be a very good value.  <3)

You could gig with this if you mic'd it up and ran it thru the PA.
On its own it might even keep up with a drummer in a rehearsal space.
If it ain't broke I'll fix it until it is.

J M Fahey

Gee, thanks :)

MOD speakers are a hidden in plain sight secret.

They are made by SICA, the exact same Italian Factory , an impressive quality Hi Tech one which also makes the "official"  Jensen speakers, but since these do not have the "expensive sticker" glued to their backs, have same quality but lower price tags, what´s not to like?

for a Factory tour


Hey JM, Thanks for that link, very interesting.  :)

Ya, those MOD speakers are great! (based on my 1st time using them)
I kinda dismissed them before because of the low price!
What an idiot I am!

I'll be using more of them in the future.  8)

Getting back to this amp...

I was not happy with the reverb.... I repaired the original tank, but it was a tiny thing and not much use.
With the original tank, the reverb was very tinny sounding and just not very usable. Horrible sounding, really.

So I bought this....  https://www.amplifiedparts.com/products/reverb-tank-mod-8fb3c1b
As a full size tank would not fit the existing cabinet.

With this tank the reverb was waaaaay over the top! Just tooo much echo even at low settings.
Also it sounded kind of "far away" if that makes any sense.

So the attached schematic shows...

I changed the Volume pot wiring back to original...

and then moved the input to the Reverb circuit (C16 - 20nf) from the wiper of the volume pot to the junction of R25 and R3.
Basically to the top of the Depth pot.

Much better! Of course I don't expect the reverb on this to sound like my Deluxe or any other Fender for that matter.
But at least now it is usable! Even with the Reverb control on max it is quite nice.
The whole range is usable.  :)

As a teaser... I have 3 more obscure Japanese 60's - 70's cheezy low watt amps on their way to me that shall be tortured to reveal their secrets!  ;)

Soooo.... this "should be" the final version of this amp!
As it is right now, I can't find anything to not like about it!
The MOD speaker,the reverb tank and Reverb wiring change, and the input buffer
turned this one into something I will take to our rehearsal place to shock my band mates!  8)


oops, EDIT;

Here is the Pre-amp schematic I ended up using.
I did not install C3 10uf as the gain was already plenty.
J2 input is approx the same loudness/volume as J1.
J3 input is somewhat less loud, maybe usable for high output pickups.
No matter, I will probably only use J2 most of the time anyway.
If it ain't broke I'll fix it until it is.

J M Fahey


Has anyone found or created a schematic for the SS 40XL Silvertone amp?  I have one with a tremolo.