SuperSonic 22 conversion

[tubenit]

I'm trying to make sense of this circuitry in RED?   Not sure what it's purpose is or where it goes to in the schematic?


I can see the bias circuit next to it, but am puzzled by the RED wiring?


With respect, Tubenit

[shooter]

It's a split rail lo-volts PS, typically for IC's n relays

[sluckey]

Look on page 1 of the schematic pdf and you will see the +15v and -15v power supplies all over the page, anywhere you see ss components.

[tubenit]

Thank you for the helpful responses!  I appreciate it!  And the answers made sense.


Next question ................ any reason the reverb transformer and reverb tank can't be used for a more "normal" traditional reverb circuit without all the other gizmos and such added like on the SuperSonic 22?


I can't see any reason why they would not be OK for something more traditional in a Fender reverb?


With respect, Tubenit

[sluckey]

Next question ................ any reason the reverb transformer and reverb tank can't be used for a more "normal" traditional reverb circuit without all the other gizmos and such added like on the SuperSonic 22?

This is the same as a "normal" fender reverb circuit, except this uses FETs rather than a mechanical switch to turn the reverb on and off. The advantage of this over the original circuit is that you don't have to run the low level reverb signal out to the footswitch and back. Kinda like using footswitch controlled relays. This circuit is much improved IMO.

We really need to know what you have in mind. Is this just a brain exercise? Do you actually have this amp and want to "improve" it?

[tubenit]

No,  I don't actually have this amp.  Someone who owns it but doesn't like the amp all that much is pondering about converting it into something different.  So, I'm looking at what can or should be reused from the original design.  Considering a turret board and removing the PCB boards.  They looked into selling it but never were able to get a good offer for it as is so they're thinking about keeping it and changing it into something they may like better.


It's not a classic or vintage Fender amp.



With respect, Tubenit

[sluckey]

Now I understand. You can reuse the transformer and reverb tank to build the old style circuit.

[tubenit]

Thanks for the help!   

[tubenit]

I am not familiar with these diodes in a fixed biased circuitry?   What purpose do they serve?   And are they needed for the bias to work OK?


With respect, Tubenit

[sluckey]

That's just a full wave rectifier circuit. Those two diodes are absolutely needed. The two diodes that are not circled are not absolutely needed but diodes are cheap. I recommend to build the circuit exactly as drawn.

[tubenit]

Very grateful for the response!  I would've blown it on that one and left them out thinking they weren't needed.


With respect, Tubenit

[tubenit]

Thought I'd better check out another question to make sure I don't make another error in my thinking.


Can I cut those two wires shown and simply put tube shrinking over the ends and have the bias circuit still work properly?


I should actually have the amp in my hands tomorrow to open it up and take measurements etc...........   


Thanks, Tubenit

[pdf64]

Yes, cutting those wires out shouldn’t cause a problem for the bias supply.

That's just a full wave rectifier circuit…

Are you sure? I don’t see it, it looks like a 1/2 wave to me.
I’m not sure what D43 is doing, possibly just snubbing spikes?

[sluckey]

Can I cut those two wires shown and simply put tube shrinking over the ends and have the bias circuit still work properly?

No. All that stuff is on a PCB and will disappear when you pull the PCB. If you will not need the +15V and -15V power supply, I suggest you reduce that whole section of the schematic to this...

[tubenit]

Super super helpful!!   THANK you so much, I truly appreciate the guidance.


IF the conversion is a "go",  it may need some relay switching and I am familiar with Doug's and like it alot and have it in several amps.


However, the SuperSonic 22 only has one 6.3v  filament for heaters.  So I am thinking of adding a second one to run the relays.  Does this attached version look proper to you for that
purpose?

I am thinking two of Doug's relays will use less than 1 amp?

This will likely be my last question until I get the amp in my hands and can open it up.


Thanks,  Tubenit

[sluckey]

Are you sure? I don’t see it, it looks like a 1/2 wave to me.
I’m not sure what D43 is doing, possibly just snubbing spikes?

Yes, you're right.

[sluckey]

That transformer will work. And of course you can always use the existing filament winding if you float the relay power supply.

[PRR]

...That's just a....

Is a voltage doubler. IMHO D13 is not strictly needed (but diodes ARE cheap). With the rise of computer simulation we can see a BIG back-bias on that cap on the first half-cycle. But it is rarely used, apparently because that cap does not in fact blow-up from one half cycle the wrong way.


Same but opposite polarity and minimum parts:

[tubenit]

This amp was NOT working properly and was not "playable" in it's original form.  The owner wanted it converted into the Carolina Overdrive Special of mine after he played the COS.  This is about as close as I can get to that.  Overall, I am reasonably encouraged with how the conversion is going.  It was a shame it did not work in the original form.  I heard some YouTubes of the SuperSonic 22 and that it was an OK amp.

Voltages checked out OK with the PT and the B+ rail and plates of the preamp tubes.

It will be cathode biased just as my COS is.  It will have 6V6's instead of 5881's  (although I use 6V6's in my COS occasionally). It may have a PPIMV although my COS doesn't have any master volume at all.

I have a matching layout to the schematic.  Both editable.  The original chassis layout was designed around the PCB, so there was alot I had to change to fit a paralleled turret board in there.  I don't ever remember a Fender amp with tubes in the middle of the chassis AND a few tubes on the back edge?


With respect, Tubenit

[tubenit]

Some progress .....................


I'm trying to keep the outside appearance as close to original as I can in the cab.


With respect, Tubenit

[tubenit]

I am trying to wrap my thinking around this type of diode rectification and can't make sense of it?


Q1)  Does someone have another drawing of this that is easier to visually make sense of? 


Q2)  What kind of rectifier is this?


Q3)  Are the capacitors needed across those diodes OR can I leave those out?


With respect, Tubenit

[shooter]

the caps are transient spike caps.  The "switching" action of a diode can create spikes.
 

[sluckey]

This is a Full Wave Bridge rectifier. The caps are not needed but are an improvement because they eliminate any switching noise created by the diodes switching on/off. I've built several projects with a FWB and have never used the caps. Plan your layout so you can easily add them later if you think they are needed.

Hoffman sells a 1000V/3A FWB that is compact, cheap, and layout friendly. Use one screw to fasten to the chassis or the board.

PS... Here's a pic of Hoffman's FWB in my revibe...

     http://sluckeyamps.com/revibe/revibe_02_big.jpg

[tubenit]

Gentleman,  thanks for the helpful responses!   


The Fender drawing of the full wave bridge rectifier was throwing me off and I wasn't following it.   However, with Steve's drawing ............... it does make sense now.


The other thing that was throwing me off was the 156VAC noted above one of the red wires and yet having around 420v at node A?


Dividing 420 by 1.4 was giving me something closer to 300-300 for the PT wires?    But maybe I am not thinking about this properly and it would be more applicable to 300-0-300 PT?


I have a full wave rectifier on my HoSo56 "the Minimalist" and I've not noticed any switching noise beyond the mechanical switch itself.


With respect, Tubenit

[thetragichero]

i have no idea why fender draws their bridge rectifiers like that... maybe their draftsmen get paid per line?

is the purpose of d51 and d52 just some sort of crude 6A fast blow fuse?

[shooter]

Guessing;
if you measure wire to wire on the AC side of the bridge the 156AC might be higher? 


I just called them "steering" diodes, but they do work well as fuses

[sluckey]

The other thing that was throwing me off was the 156VAC noted above one of the red wires and yet having around 420v at node A?

Dividing 420 by 1.4 was giving me something closer to 300-300 for the PT wires?    But maybe I am not thinking about this properly and it would be more applicable to 300-0-300 PT?

That voltage at TP1 is in reference to chassis ground. It's also a bit misleading. The important thing is that there is 300VAC   ***BETWEEN***   the two red leads.

Fender doesn't draw all their FWBs like that. Here's another more conventionally drawn FWB...

     https://el34world.com/charts/Schematics/files/Fender/Fender_65_twin_reverb_manual.pdf

D51 and D52 don't do much. One end is connected to chassis ground and the other end is connected to circuit ground.

[PRR]

...the 156VAC noted above one of the red wires and yet having around 420v at node A?

If 420V were the peak-to-peak of the AC sine, then 148.5V is the RMS. Or 441V for 156VAC, implying sag.

The 420-440V is the p-p of the AC. However most bench meters will not read 156V there, because the AC is riding on DC, and because most AC meters have hidden assumptions. Here I would suspect a VTVM, peak-to-peak detecting, calibrated /2.828 to read "RMS".

If you have the four hundred volts of DC there is little reason to question the AC.

OK, when you go to buy a different transformer for the same purpose. But you would normally buy a stock part, and look at the suggested application to see if (with the suggested rectifier scheme) it comes out 420V.

[tubenit]

Thanks for the replies!  ALL helpful information.  Grateful your knowledge and generousity in sharing it!


With respect, Tubenit

[tubenit]

How does this look for the PT wiring? 


Any issue with the 8200pf cap being located after the standby switch & before the full wave rectifier and using just one 8200pf cap?


With respect, Tubenit

[sluckey]

That looks fine. I'd delete that 8200pf cap.

[tubenit]

Thank you!  Grateful for the help.  I got that 8200pf location from the other Fender link you shared regarding the full wave rectifier and was just copying what they did.  However, I can leave it out as a starting place.


With respect, Tubenit

[tubeswell]

Re the 8200pF, if ringing does occur, you can just put the snubbing cap back in.

[tubenit]

Slowly getting there.  Much easier to start with a chassis blank then a chassis with tubes in the middle and PCB boards all over the place.  Probably won't do another conversion like this ever again.  The chassis is only 6 inches deep compared to the 8 inch blank chassis I normally use.


With respect, Tubenit

[tubenit]

Does it really matter where the standby switch is located?? 


One shows to ground  (Twin Reverb re-issue)


One shows to one leg of the red HV PT wiring


Is one actual "better" than the other or is it a preference thing?


With respect, Tubenit

[sluckey]

Switching the PT AC lead is easier on the switch (less arcing). Marshal was fond of using a DPST switch to switch both PT legs. I like this idea.

[tubenit]

Thanks Steve!!   Greatly appreciate the help and the answer!  I will do it that way.


With respect, Jeff

[tubenit]

Got this amp done today!  I am very impressed with the tone.  Very transparent, very touch sensitive in my opinion.  Clean is beautiful.  OD is smooth sounding and with the James tone stack, you can dial in some pretty nice different OD tones.


Probably the most complicated build I've done given the smaller chassis to work with and an already punched laid out arrangement for the chassis which I had to redo and think through what would help lower noise and improve tone.


Did this for a friend who is a remarkable player with a great ear. Free labor for the conversion, he just paid for parts that I didn't have on hand which totaled around $220.  Given the amp originally wouldn't hardly play louder than my cell phone this is a great improvement.


It might benefit from a different speaker on the OD such as a Warehouse ET65.  However, the Fender Jensen sounds great on the clean channel.


Despite the messy wiring and odd layout ................. the amp is amazingly quiet!  And the passive FX works well with the delay pedal I tried.


Don't recommend attempting this for others as it was ALOT of work, planning and research.  However, for a friend it's definitely a meaningful project.


With respect, Tubenit

[sluckey]

Nice work! You're quickly becoming the go to guy for these conversion projects.

[John]

Well done! Always like following your projects!

[tubeswell]

Imaginative adaptation!


What does the OD sound like?

[tubenit]

Finished amp.  Had to make a new baffle and remove the previous "glued in and stapled" baffle. UGH!  Old baffle didn't have clearance between speaker and OT.


I should mention there was a goal of maintaining as much of the original SuperSonic 22 look as possible.     


The amp sounds lovely and I hope to post sound clips in the next handful of days or so.  Very touch sensitive to picking attack.


with respect, Tubenit

[tubenit]

What does the OD sound like?

I like the overdrive on this amp quite a bit!



There are two amp demos here:   Carolina SuperSonic amp demos (el34world.com)


The one that has a lead to a backing track has a sample of the overdrive at about 2:10 into the 4 minute song.


With respect, Tubenit