Univox SS to Tube amp

[punkykatt]

Hey Guys,  I have this 1970`s SS Univox 1-12 combo amp with a 4 ohm 30 watt alnico 12" speaker that is begging to become a tube amp.  The controls on the faceplate are: Volume, Tone, Reverb,  Speed , and Intensity. The cabinet looks to be well constructed(no partical board crap anywhere). The chassis is painted steel 15"x 6.5" x 2.5". (too small for a Princeston Reverb). Im thinking maybe a Princeston 6G2 and adding Tubenits one tube reverb?  Question: Will adding the one tube reverb suck the tone and balls out of this amp? The reason I ask is because looking at the Princeston Reverb schematic it shows a triode gain stage before the 12AT7 reverb driver. Or is that gain triode there to make up for the gain loss of the preceeding tone stack?  Getting old can`t remember this stuff anymore LOL.
For iron i have kicking around to use: a  Hammond 270FX PT , 275-0-275(actually reads with 120v line 307-0-307), one of Doug`s 18 watt Marshall OPT 8K -  4/8/16, all the other parts are in inventory, all i will need to get is a short reverb 8AB _ _ _ _tank.  Any suggestions and ideas are welcome and appreciated.

http://www.el34world.com/charts/Schematics/files/fender/princeton_6g2_schem.pdf

http://www.el34world.com/charts/Schematics/files/fender/PRINCETON_REVERB_AA1164.pdf

[Tone Junkie]

Im thinking my friend that you would be fulfilling the SS amps ultimate fantasy in becoming a tube amp. All kidding aside looks perfect, just need a 5e3 type tonestack, and do one of those sweet powertube bias tremolo,s. hope i said that right, but you know what I mean.
Bill

[eleventeen]

Biased (pun definitely intended) as I am towards Princetons (with reverb) my humble but offhand suggestion/preference would be to go with the proven design in a box that's a little tight rather than try to debug in a box that's a little tight.

The stock PR is 19.75 wide, subtract 2 * 3/4" for the cabinet and you have 18.25. Your chassis is 15" long. And yes, that's tight. Me, I would lose the tube recto, lose the tremolo & mount the reverb transformer out of line with the little tubes and IMO you could do it. Incidentally, and I am sure it is apostasy, you could use PC-mount style (eg; radial) electrolytics as the filter section (easily available) and MUCH cheaper than axial (traditional/both-ends) caps. Take up less room. Glue/silicone 'em in on a plastic square block. Remember that a Princeton uses a 3-in-one can versus the Deluxe doghouse, but I am assuming you'd use individual caps.

Controls: Vol, treb, mid, bass, reverb. Just talking about changing the  6.8K (?) fixed resistor under the tone stack to a 10K pot. Now you have 5 knobs for the five holes.

btw; losing the tremolo does not save you a tube, you'd still need four 12a_7...but it would save some component space.

[jjasilli]

You can add an extra chassis with its own filament tranny to power the extra bottles.

[eleventeen]

Speaking of Princeton Reverbs....here's my next project. Shouldn't be too bad at all. This is a CONN organ chassis....with twin channels 12AX7 driving 12V6 tubes. The plan is to lose the tube recto (only makes 337 B+ w/5U4  ) thus pointing to a SS recto. Although I tend not to like open trannies, the output trannies are pretty fat...like Deluxes, so they should be fine. Stay with the 12V6 outputs. Swap positions of the 12V6 row and in their place throw in 4x nine pin sockets. Maybe 5, on the theory that given that there's enough room, install a dummy socket for later mods, maybe another gain stage or sumthin'.

Not all organ chassis are suitable for ampin'. This one seems to be wide enough to handle a parts board & controls. And, it will cough up a nice spare output tranny.

[kagliostro]

If you haven't enough space for your project on the original chassis

you can use it for the preamp section

and use a new chassis for the power section

on the bottom of the case as HotBluePlates did on his Standel

http://www.el34world.com/Forum/index.php?topic=14263.0

K

[eleventeen]

I'm not fully convinced you "don't have enough room" (for a single chassis execution)....but I admit I don't have the parts & chassis in front of me. Yes it will be tight. But you have a standup power transformer, no choke...the output trans can be moved to the opposite end of the chassis & the reverb trans can be mounted anywhere. The leads may have to be spliced and run over the surface of the chassis in a carefully constructed and well secured bundle. I did this with my silverface PR that I hotrodded with Dynaco 35 transformers. Make sure, of course, that you allow for the amount of chassis surface that the baffle board eats up.

[punkykatt]

Thanks for the replys Guys.  If I really really wanted to squeese a PR in that chassis I could. But it would be a lot more work than I may want to do reason being the aluminium faceplate(see pic 1st post) is in good shape except for a few scratches at the guitar input jack and plus the bottom lip of the faceplate goes over the top and front of the speaker baffle. To make a new faceplate or relable this one? Is it worth it?  Which brings me back the the question I asked in the 1st post.  Will adding a single tube reverb to the 6G2 Princeton circuit alter/suck the tone and performance of the amp? 

[jjasilli]

It further occurs to me that:

* I don't see why a reverb circuit should suck tone. 

* I plan similar projects and will use the Traynor "cap driven" reverb circuit -- see, e.g., the Traynor Guitarmate schematic.  One tube.  No reverb tranny.  And the reverb tube's output impedance matches the input impedance of the little spring reverb tank stock to the SS amp (if your amp already has one).  Granted this is not lush Fender reverb, but works for me in such a project.

* Belton sells a reverb chip so you can build a SS reverb circuit, taking up little space & no tank needed.  There is an old thread here somewhere if you search the Forum. 

[eleventeen]

Can you just flip the front panel over...?! Or is it glued onto the chassis (vs being held on by the pot shafts) and thus removing it would warp it out?

Me; I wouldn't touch the front panel. You're the one who's going to use the amp, you'll know what the controls are.

I don't mean to harass you; my vote is for the PR and the feasibility is IMO strictly the net real estate available once the chassis is mounted into the cabinet. Yes, I understand the overhang of the chassis over the baffle board eats some room, sometimes a LOT of room, and is VERY important to take into consideration when it comes to mounting the power transformer (and of course all the other non-back-row mounted trannies) ....which affects how much room will remain IN BACK OF the PT, and yes, whether there is enough room to mount some tubes aft of the PT.

One thing I do it reach inside the amp w/the chassis installed, and with a pencil (or sharpie) draw the "limit line" of how far forward you can mount the PT. That's your drop-dead limitation: the amount of space eaten up by that overhang.

I wish I could tell you about the single tube reverb. I frankly do not know.

[tubenit]

I essentially built a 5E3 with a "one tube reverb" for my son yrs ago and thought that it sounded great.  I've used a one tube reverb in my Carolina Blues Special amp also. Both of those have a concertina phase invertor like the Princeton. And I added it to several DanElectro 275 Centurians which is similar to the Silvertone 1482 and uses a 6Au6 vibrato which has been my favorite vibrato. I tossed the goofy piezo reverb and stuck the one tube reverb in it's place.

http://www.el34world.com/Forum/index.php?topic=565.0

I've been happy what it did for me tone wise and felt like it added a warmth and musical depth that the amps did not have with the reverb turned off.

Having said that, I think the one tube reverb is somewhat easier to implement on an amp with LTPI.

Please keep in mind that this type of reverb is NOT going to do "surf reverb". It tends to add a little more reverb to the mids than Fender does also.

I typically had the dwell pot on 5-7 and the reverb pot maybe around 3 or slightly less.  Anything above that is too much reverb for me.

I think of this more as adding a seasoning to a great meal more than a major intregal ingredient (as I use reverb sparingly).

No, I can't imagine the reverb "sucking tone" used in a manner like I've used.
My experience has been that it adds tone.

BTW, the Carolina Blues Special is still one of my favorite amps and my best friend and son in law own ones that I've built yrs ago. Still love to play them. They're a reasonably clean amp but you get some break up on double stop notes and such. I think the CBS sounds sort of like a cleaner version of the 5E3 Deluxe.  I say that based on a jam where I used the CBS and HotBluePlates had his Deluxe with him.

With respect, Tubenit

[loogie]

Belton sells a reverb chip so you can build a SS reverb circuit

You can also use an LM386 to drive the tank.  You can make that as surfy as you like.  Don't knock it 'til you try it.  Its a five minute breadboard job.

[tubenit]

OK,  I remembered I have a sound clip of the Carolina Blues Special with the one tube reverb. The CBS has a concertina phase invertor like the Princeton but doesn't have the tremolo.

http://soundclick.com/share.cfm?id=6775767

Both rhythm parts and the lead is the CBS with the reverb on. So maybe that will help you guess whether it might be worth it to you or not?

With respect, Tubenit

[Tone Junkie]

Belton sells a reverb chip so you can build a SS reverb circuit

You can also use an LM386 to drive the tank.  You can make that as surfy as you like.  Don't knock it 'til you try it.  Its a five minute breadboard job.

Not to high jack the thread or anything but loogie do you have a schematic of what your talking about Im up to learning new things about reverb.
As to the one tube reverb I thought it was quiet sufficiant for everything I do and I like the tone maybe it was as Tubnit said it enhances little more of the midrange which I like.
I put it in in the first TOS I built.
Bill

[loogie]

Its funny, I just did a google on 'lm386 reverb driver' and the first hit was my old post here:
http://www.el34world.com/Forum/index.php?topic=10589.0

I started messing around with it before I did any reading other than the TI datasheet:
http://www.ti.com/lit/ds/symlink/lm386.pdf
I had some power supply issues (thanks FYL and PRR) because my low grade wal-warts are hummy.
I quieted the hum and I'm still tinkering with it, but I think it sounds nice.

This is good:
http://sound.westhost.com/project34.htm

If you use a wal-wart be sure to add the bypass capacitor from pin 7 as shown in the TI application notes.

[punkykatt]

OK Guy`s, thank you for all your input, and thanks Tubenit for that clip of the CBS, that is a nice sounding amp.  I finally made my up my mind.  Since I do play several surf songs at every gig I have decided to go the Princeton Reverb route.  Since I will be using all standup trannys it will give me the extra room inside the chassis. I will be using a JJ 40/20/20/20 cap can mounted on the inside of the chassis. Things will be tight but doable.  I will move the Volume to where the organ input jack hole is, the treble where the volume is, and the bass where the tone is. I will let you know how it works out. Punky.  Fun stuff
Thanks again

[tubenit]

 

Since I do play several surf songs at every gig I have decided to go the Princeton Reverb route.

That is a much better choice if you play some surf stuff than the one tube reverb.  And I think you can make a PR fit with a stand up PT.

I'd recommend experimenting with 4.7uf cathode caps instead of the 22uf cathode caps in the preamp so you have a little more headroom.
I had an original Princeton Reverb years ago.

With respect, Tubenit

[punkykatt]

Thanks Tubenit. I do have a few of those 4.7uf`s in my stash. HAPPY 4th of July  everyone.  Don`t blow any fingers off with those cherry bombs and M-80`s.  Be safe.

[sluckey]

all i will need to get is a short reverb 8AB _ _ _ _tank.

You may be able to use a long tank mounted vertically on a side wall. Do you have 16.75 inches between the bottom of the cab and the chassis?

If you do go with a short tank I'm very interested to hear your opinion of a short tank in a PR.

[punkykatt]

You may be able to use a long tank mounted vertically on a side wall. Do you have 16.75 inches between the bottom of the cab and the chassis?   

GREAT IDEA!!! sluckey.   Can`t get out to the shop till tomorrow to take  a measurement, so I did a google search on that amp. I can`t believe I found the dimensions on line. Height is 22".  So (-) 1.5" for the top and bottom panels = 20.5" (-) 2.5" for chassis height = 18" inside deminsion. A long tank should fit no problem.

[sluckey]

Any progress? Take a look at this layout. Will this work in your chassis? The board is only 8" long. I've got a complete board layout but I need to tweak it a little more. If this is of use to you I can post the complete details later this week.

[punkykatt]

Thanks sluckey for that compact board and layout.  Things are coming along nicely.  Im already populating Dougs style PR board I made and shortened it leaving off the two 100 R`s,(PT has  Htr CT).  The long reverb tank fit nicely on the side (vertical)of the cab.  Gutted the chassis and drilled all the necessary holes, got the tube sockets installed, PT in and htrs , rectifier, IEC connector, fuse, power switch and light wired up. Heater voltages at 6.9vac, no load, line 123+vac. Hopefully with all tubes in and AC calms back down to 120vac they will drop to within reason.
I gave up on reusing the original Univox faceplate.  I used some hammered spray paint direct on the chassis and it looks great.   I want to use all the available holes on the front of the chassis.  Im thinking of adding a Midrange control between the treble and bass using a 250kA pot like Allen Amps did.  I think Topbrent may have spoke about that a while back.   Has anyone ever put a 250kA midrange pot in a Princeton Reverb? How did it work?
I have a very busy day tomorrow, If I get a chance I will try and take some pics and post them.
Punky

[sluckey]

Im thinking of adding a Midrange control between the treble and bass using a 250kA pot like Allen Amps did.  I think Topbrent may have spoke about that a while back.   Has anyone ever put a 250kA midrange pot in a Princeton Reverb? How did it work?

I put one in a Deluxe Reverb and also an AB763 Lite. I didn't put it between the treble and bass though. It replaced the 6.8K at the bottom of the bass pot. Most call it a Raw pot because it kinda lifts the tone stack from ground, boosting the gain and giving a more open sound. I like it.

I'm very interested in your project and would love to see some pics. Did you get a reverb tank that was meant to be mounted vertically, or are you just using the more popular 4AB3C1B?

[punkykatt]

Man what a busy day this has become, worst than i expected.  sluckey thanks for the info on the mid/raw control.  I have a 4Ab3A1B (Gibbs)on hand, im gonna see how that works for now. Pics will come tomorrow perhaps. Got a lot of unsuppected repairs to do. Big T storm on the way gotta shut the PC down. Later

[zapped]

 I hope you will show this build to completion. I have a very similar Univox amp( except for 2x10 speakers), that I have had since 1973 and have been thinking about the same conversion to a Princeton Reverb-ish amp. Good luck with the amp...   Ed

[punkykatt]

Here are some pics of what I have done so far.

[punkykatt]

Hey guys, does it make any difference where the foil side leg of a cap in the tone stack gets connected to? I know when used as a coupling cap the foil side leg goes towards the preceeding plate.

[eleventeen]

Looks pretty nice! We're rooting for your success...I know I am! Think you're gonna get away with the voltage drop through a tube rectifier? Don't get me wrong---it's a heck of a lot easier (and smarter) to install the recto socket at the construction stage and if the B+ isn't enough, you can always diode it up. What you're doing is very closely my notion of what should be done with dead SS amps...with either 6V6 or 6L6 power bottles. Yes, very conventional...but nobody should complain about having an extra Princeton Reverb around when your jammin' pals come over. Nice!

[Willabe]

Looks really good!

I bet she flies!


           Brad     

[PRR]

> where the foil side leg of a cap

No.

[tubenit]

Sluckey,

Man, that layout board you drew up looks excellent!  I like it.  I wish I had done something like that on my new build.

PunkyKatt,

Your board proximity to the 9 pin sockets is the same situation that I have on my new build the D'MoSo56.  The stretch between my LTPI socket to the board is rather lengthy and runs by the power tubes kind of like what you've got in your chassis. I've been somewhat concerned that it may create oscillation problems.

I mention that because tomorrow, I'll fire my amp up and find out how it sounds and IF there are any oscillation problems with the layout design. Check in on my thread for the verdict IF you're interested? 

With respect, Tubenit

[punkykatt]

PRR,  Thank you.

Tubenit,  thank you for the oscillation consern. I checked out your layout and you do have long PI runs from the bd.  My PI runs will be much shorter than yours.   All those turrets and eyelets on the left of my bd are for the bias supply and power tube screen grid resistors and chathode 1 ohm resistors.  Just for drill,  I rerouted the OPT secondaries to run out side the chassis and come through closer the speaker jacks .

[punkykatt]

Input jack is in and wired up, pots installed with ground buss, board populated and wired.  Tomorrow with fresh eyes I will recheck everything, install the board and finish wiring it up.  We may have lift-off by tomorrow afternoon? The anticipation is building up fast. This is what got me hooked 11 years ago. Punky

[eleventeen]

Lookin' really good! I'll take a teeny bit of credit for pushing you towards the PR but you are the one doing the work and doing a nice job of it!

[punkykatt]

Its ALIVE, Its ALIVE.  Everything is working. Trem is real strong and rich sounding, reverb I have a 12AU7 in the driver for now to calm it a bit, Voltages a bit low for a std PR but I expected that with the Hammond 270fx PT.  With  the Allen Amps Raw control 250kA mid pot in place of the 68k resistor on the bass pot, the amp kinda farts out more that I want it to when turned up. The first twin triode bypass caps are both 4.7uf. Im wondering if the PI is wimping out with the lower voltages.  I will try the Stokes mod moving the PI plate B+ from node C to B and see if that helps. Im going to list the voltages so you guys can see.

http://www.el34world.com/charts/valve/ValveData.php?e=view&f=15830

[Willabe]

Its ALIVE, Its ALIVE.  Everything is working.

Yes, she flies!


       
           Brad     

[sluckey]

How does that Univox speaker sound with the PR circuit?

[punkykatt]

I tested a bunch of speakers to day and my ears are ringing!!.  In the univox cabinet I tested a Cannabis Rex, Texas Heat, Celestion V12-60 Silver series, and a 1967 date coded Fender labeled Utah speaker. Other tests included plugging into a Fender Twin Reverb cabinet with JBL speakers, a homemade 1-12 semi openback solid oak cabinet with a Celestion Sidewinder 150w speaker and a Silverface Princeton Reverb cabinet with a 12" Celestion Vintage 30 speaker.  The set up with the most tone control function was the home made oak 1-12 cab with the Sidewinder speaker.  The original 30w AlNiCo speaker was the wimpiest  of all the others with the earliest break up.  The break up was like a bassy fuzz box distortion from the 60`s. If you didnt crank up the amp that speaker will do fine.  While testing all the other speakers and cabs, if  you cranked the amp up and turned up the bass and or the raw control past half way that same bassy fuzz box distortion happens.   Im gonna take a break for a couple of days(other work came in) and then experiment with the Stokes and the Paul C mods in the PI circuit.
Punky

[eleventeen]

"... if  you cranked the amp up and turned up the bass and or the raw control past half way that same bassy fuzz box distortion happens."

Don't know about the "raw" control but it is entirely normal (in my experience) for a bass setting of say 6 or higher to mush out the sound of any Fender blackface amp. At higher volumes, this is sure to happen earlier, eg; at 4.5 or 5. I do not play cranked (the amp, I mean!) any more but when I did, I definitely recall I had to keep the bass control low. And that is with JBLs/Altecs.

You're doing a load of work flipping those speakers in & out. Shouldn't be any sort of surprise to find the orig "no name" speaker the least satisfactory.

[punkykatt]

I did the Stokes mod on the PI connecting the 56k plate load resistor to node C rather than node D on the PS increasing the voltage to the plate. This helped  reduce the bassy fuss box distortion I was getting before.  Since the overall amp voltages are low because of the 270FX PT, i reduced the first 18k dropping resistor (between B & C nodes) to 3.7k.  This helped even more with the bassy fuzz box distortion and put more life into the amp.  I have played the amp at two gigs so far and Im really liking it now. Sings like a bird!!!!  That original Japan AlNiCo speaker that came in the amp is starting to really warm up too.  I believe that speaker got little to no heavy use as a solid state amp.  
I think Im done tweeking for now.