Silvertone 1483 questions

[EETStudent]

Correct me if Im wrong, but it looks like there is another stage after each half of the split load phase inverter, right? I love the way these silvertones sound, and Im trying to capture some design qualities that give it that sound. I like the idea of arranging my preamp to have those extra stages after the PI. Other than extra drive, what else is accomplished with this?

Also, I know this is a bass amp so it would need to be tuned a little for guitar use. Im thinking of going with a typical fender tone control circuit. Any other recommendations that would improve the circuit for guitar use?

[Rob Mercure]

ES.

You're not wrong - there's is another gain stage after the phase inverter. Remember that the split load PI provides no voltage gain so you can either feed the SLPI with a high level signal - and take a chance of distorting the PI input - or make up the slight loss with a "driver" stage. And in higher powered amps that draw grid current (the number following the letters - "Class A(1)" not drawing grid current while "Class A2 does, etc.) the driver is often a cathode follower to provide a low impedance current source (and sometimes sourced to a high current negative supply).

And yeah you'd definitely have to retune the tone controls for guitar - these are very low selective. The "strangest" thing - assuming the schematic is complete - is the choke in parallel with the output transformer secondary/speaker. A choke in series with the speaker isn't uncommon but the three in parallel is a might odd - still thinking about that one.

Rob

[EETStudent]

Hey Rob, thanks for the reply. Heres what Im thinking about doing. Ive got my first two stages set up like any ol' Fender, followed by a long-tailed PI. Would you recommend adding a stage just before the PI(for PI disortion as you mentioned) or do something like the 1483, with each signal half getting another stage?

With respect to altering the circuit for guitar use, I knew for a fact already that I would have to do something. Are there any other areas aside from the tone controls that should be tweaked? thanks man

[EETStudent]

In addition to my most recent post, do you think the SLPI is a big factor in giving the silvertone that sound?

[Rob Mercure]

ET.

By the time time you add Fender type tone controls and add a LTP PI what do you have left that might sound Sears 'cept that funky choke in the OT secondary? I think the TC s add a lot to the amp's sound so if you remove 'em you're back in the Fender/Marshall/Vox or Edwards/Bax or "cut control" territory. I forget to mention that the reason I think they're getting the gain post PI is to limit distortion in a bass amp - a state before the SL PI is more familiar.

Do you have this amp and are in the process of restoring/converting it? If not I'm not sure why you're "modelling" it as it is somewhat atypical while note being "iconic."

If you've got lots of stages to work with (after all, how many times do you see more than one person playing into a single any more?) you might try Fender type TCs on your first few stages and then "true Baxandhall" just before the PI (Pete Bax's designs used his tone shaping network in the feed back network around a triode or pentode and were quite "active" - the results are fairly "dramatic" for "global" tone controls with more focused TMB type distortion shapers).

But I'm far from the world's expert on distortion and distortion tone shaping - I've just messed with a few topologies and was lucky to stumble into what I like.

Rob

[Sweetfinger]

The choke is there to keep the original 15" Jensen from bottoming out. If you're not using the original speaker, I'd just disconnect it. The 1483 is already a great sounding guitar head with useable tone controls. When looking at its circuit, its hard to believe that it was designed AS a bass amp! The Twin Twelve has more power and is probably a better amp for bass anyway.
If you want to mess with the tone controls, do it on one channel, and leave the other stock. I have two of these heads and have done a little to both. The standby switch on these doesn't cut the high voltage off, it just shorts the inputs of the power section together. On one, I merely replaced the switch with a pot, for instant post PI master volume and on the other, I rewired the standby switch to switch in/out a cathode bypass cap on the recovery section. I messed a bit with changing out ceramic caps for mica or foil, and changing some resistor values closer to 'Fendery' values, but mostly left the things intact because they are pretty good as-is. If you feel the need to modify more than just one tone section, then that indicates that you want a DIFFERENT amp, and should maybe trade the 1483 in to someone who would appreciate it for its inherent coolness.

[Sweetfinger]

I'm rereading the initial post- If you're building an amp based on this design, most of the sound of these is in the output section, i.e. the low voltage, 5Y3 rectifier, crappy little output X-former, and the inverter/drive circuit. It almost doesn't matter what's before the recovery stage. You should also realize that this circuit used the 6CG7 and 6L6's because they would be very reliable and long lasting in this amp. Sears didn't want any returns! I think 6V6's would probably work fine in a new build. It might be really interesting to hear a BF tone stack in front of the 1483 power section. please report your findings!

[David Schwab]

When looking at its circuit, its hard to believe that it was designed AS a bass amp!

One can say the same for the Fender Bassman! How many bass players use that amp? Makes a great guitar amp with the tone stack just as it is.

[nek314]

Question about choke

I also have one of these amps and stupidly removed and then lost the choke that's in parallel with the speaker. Does anyone know what value it is? It's not specified in the schematic.