silvertone twin twelve reverb issue

[unclerny]

HI Forum, this month's amp of mystery is a beautifully preserved Silvertone Twin Twelve.  It had a good bit of filth and what not from being stored for years but it's over all in great condition considering I'm used to seeing press board cabinets damaged by water and this one's not.

Anyway, I replaced the power caps and the 6L6GCs along with a new power cord, 3 prong, and removed that permanently wired speaker zip cord with a nice 3 foot speaker cord with new Switchcraft jacks.  Amp fired up and was well within bias so that's all good.

Customer brought it back a few days later saying the reverb started humming and had tones of reverb.

I found the reverb to be micro-phonic, picks up my voice from several feet away, and it has so much reverb it's like on maximum regardless of the pot setting.  If I turn the reverb off, switch on pot, the entire problem goes away.  Problem in reverb front end.

Being it still has the stock tubes I swapped them out first with known good ones from an Ampeg we have here.  The problem is still there.

I suspect I have a microphonic resister or similar.

Has anyone else ever dealt with this symptom?  I found the schematic on sch heaven.  Silvertone 1484.  It's too large to post but I can mail it if needed.

Best Regards, Tim

[rafe]

The reverb unit in those amps are crap and it may be the unit itself. the actual sound when working is not so bad but the unit is up inside the head it's a small silver box not a full sized pan with springs......

[tubenit]

IF I owned one ........... I'd replace the original goofy sounding reverb with the "One Tube Reverb".  So in light of that idea, I drew up a draft schematic showing how I would attempt that.  The SCH editable versions of the schematic are right here:  http://www.el34world.com/Forum/index.php?topic=593.msg1643#msg1643

With respect, Tubenit

[RicharD]

>a beautifully preserved Silvertone Twin Twelve.
>Customer brought it back a few days later

>IF I owned one ........... I'd replace the original goofy sounding reverb with the "One Tube Reverb".

That doesn't seem to be an option + a "cherry" Silverfish is flipping for >4x original value.  Yes the differential design is "different" and not what we're used to hearing, but it might be what the customer likes.  Any amp that is over 25 years old needs to face restoration vs. remodeling.  That's just my opinion anyway.

So  I agree with Rafe that it's probably the tank itself.  Make sure you didn't plug it in backwards.  I fought and fought with a Silvertone reverb and it turned out to be a bad cable.  If you don't mind, check all the plate and cathode voltages of both 1/2's of the 12AX7 and 6FQ7 involved in the reverb circuit.  That's a real good place to start to see if the tubes are sitting close to happy.   Try unplugging the input to the tank and see if it's still microphonic.  So check wiring, cables, tank, and voltages and let us know what you find out.  Please post your voltages.

-Richard
 

[tubenit]

Each to his own ......... I took a Dano Centurian with the same goofy reverb and changed it to the one tube reverb and enjoyed the amp waaayyyyy more than the original unuseable (for my purposes) reverb.  In fact, I did that with two different Centurions. You can see the reverb trannie and tank in one of the photos.

As you know the Silvertone were made by Dano & while the Centurian was a 6V6 version ....... it did have some similarities (at some level) to the 1484.

With respect, Tubenit

[RicharD]

>Each to his own

Absolutely.  I hope I didn't come across rudely.  I probably shouldn't post 1st thang in the morning.  I can't argue that the Silvertone reverb is the suck, but it's not his amp.  Now... if the tank is toast, which my gut instinct tells me is the case, then yes a remodel is probably the best solution, or perhaps he can convince the owner an improvement is worthwhile.  I've never been a fan of Silvertone, especially now after that last split chassis amp shocked the p1$$ outta me.

[sluckey]

Try unplugging the input to the tank and see if it's still microphonic.

I'm pretty sure that reverb unit is hard wired. No plugs involved.

[tubenit]

Hey, I have one of the old Dano reverb tanks still if you want it? It's been in a box in the garage for 3 plus yrs so I don't know if it's still works.  Check out the Centurian schematic on Schematic  Heaven and if you think it's the same just PM me and I'll mail it to you.

With respect, Tubenit

[unclerny]

Hey Tubenit, I may just take you up on that tank.  My deal with the amp is that I know the reverbs are the worst problem.  It was a wonderful coincidence the vintage guitar ran a must have article on this exact amp when it came into the shop so all the things it said to look for I did.

When the amp left the first time it worked perfectly and the reverb was an amazing surf reverb, incredibly deep wash, lush.  The overdrive in this thing is really outstanding for an amp not meant to last this many years.  It still has the stock Jensen speakers too, wonderful c12's, not sure of the wattage, didn't look that close.

So no one thinks it could be a resister?  Interesting.  I guess with those tanks being the Achilles heal of these amps I guess it could have failed from being moved around.  I've never had a tank cause this kind of problem.  Usually they just die but those are usually Accutronics or similar, modern Acc. tanks are made with some of the cheapest parts when they come as stock tanks in a new amp, sad.

Get back to me on how much you want for that tank.

Tim

[tubenit]

it worked perfectly and the reverb was an amazing surf reverb, incredibly deep wash, lush

I am wondering if it's the same reverb then. This sounded like something from a old Buck Rogers movie and I can only describe the reverb as something between bizarre and goofy?

However ...........

You can have the reverb tank at no cost.  However, let's check 3 things:  1) look at the photo I've attached ...... is that what yours looks like?  2) Compare the Dano Centurian schematic reverb to the 1484 & 3) I will check continuity on the tank and see if it has that.   My digital camera is out of state on a trip right now or I'd post a better picture.

If all that looks good, just leave me a PM with a mailing address you're comfortable with and I'll mail it out perhaps tuesday of next wk.

With respect, Tubenit

[unclerny]

Hi Tubenit, I don't think we have the same animal.  Here's mine

Tim

[rafe]

Yeah that's the one I used to have , I don't know why but I thought they were Valco's, not Dano's.
I think someone told me so and I believed them. Like I stated the reverb sounded Ok in mine, big iron
RCA 6l6's, nice jensens, nice tremolo ....I wished I'd have kept it. I gave it away when I moved to FL
 

[unclerny]

yes, bad move but we all made those decisions.  I once landed a Boogie Mkii with Jonathan Kane stamped on the bottom of it.  oops

Tim

[unclerny]

ok guys, for future reference I figured I should show what I'm talking about and the fix I believe has worked.

I eventually decided that the reverb tank had to be the cause but since it still appeared to be working but was micro-phonic or rather super sensitive I took it apart and the only thing I could note was the amount of power from the tape covering the metal piece that is inserted into the spring about an inch in from each end.

Pulling the spring off it was easy to see the wear on the tape so I left the spring laying on top of this metal bit and wired it up and found the reverb worked much better.

I decided to use a bit of mixer tape to recover the metal and replaced the spring back where it belonged, wired it up and it tested about as good as I'd expect a 45 year old reverb made this cheaply to sound.  I'm happy with it.

I attached a pix so you can visualize the whole affair.

Tim

[nichesound]

 1484 reverb troubleshooting and Adding a NEW REVERB TANK:
Doug Circuits
Silvertone used undersized plate resistors on the 6CG7. 125V across a 27KΩ resistor is .58WATTS, and Silvertone used 1/2-WATT resistors. If the voltage at the plate of the 6CG7 is close to 320-340V instead of 215V, the resistor has failed. Similarly, this can also be an indication that the tube has failed.
 
 The major difference between the M13 and the 1484 circuit is that the Silvertone "Tank" takes a push pull signal from a phase inverter that the 6CG7 (V2) provides in para-phase arrangement. The 6CG7 is a
 
 Can this circuit be easily modified to accept a common Hammond style tank?
 
 If we remove the voltage divider (R47 & R48), and instead let V2B's grid be tied to V2A's grid, both triodes will produce a signal in the same phase as the each other (instead of inverted). We can then tie the two signals together at the tank inside of the coupling caps, and send that signal to the tank.
 
 The current produced should be reasonably strong. This parallel arrangement of triodes is similar the M13's paralleled 12AU7, and the plate resistors are load enough that it should produce a strong current to drive the tank.
​The amperage draw does not change for the pair of triodes, so it'll have no effect on the power supply.
 
 R40's 560K will need to be reduced (or eliminated). R26's 560K values might need to be tweaked to get the wet/dry mix right. Otherwise, this would work!
 
 Another note about the 1484
 
 The other weak spot is the power transformer arrangement. These used an odd-ball power transformer (PT) that had two secondary 150V windings. They used voltage doubler rectifier circuits and stacked the two on top of one another to make the 480V of B+ to power the amplifier.
 
 I have searched for this article to add a tank reverb and found it...hope this helps anyone who wanted to add a tank to their Silvertone Amps....good luck...Johnne in Clallam Bay WA.