Mid 60's Valco (Supro) S6450 "Royal Reverb" schematic needed

[rrozell]

Brian,
I replaced the 3.3k resistor you referenced earlier with a 47k. The guy on the internet used a 33k and the Gretsch 6162 uses a 68k. I figured between the two was a good compromise. I hooked up the reverb section that I had clipped the leads to while troubleshooting. I now have an output coming out of the speakers, but the volume is much, much lower than the maximum I get on Channell 1. As I suspected, I have multiple problems. It's hard to tell if the tone control works because the signal is weak, but I think it does. The reverb does not work nor does the tremolo. I'll press on tomorrow...
I'll probably have to draw the whole schematic up, but I'd like to get it working first.
Thanks again,
RR

[rrozell]

Enzo,
S'Cool. I live and work with a bunch of Redskins fans and they can be irrationally fanatical. A couple of guys at work get so worked up I have to tell them, "Dude, it's just a game at the end of the day. No one's going to die."
I'd rather spend Sunday cranking one of my Jacksons through my little Fender Blues Jr. turned all the way up.
RR

[Glasgow]

Hope you feel better soon!

Brian

[Glasgow]

I'll probably have to draw the whole schematic up, but I'd like to get it working first.

RR,

You very well may get it working quicker if you take a little time to get the schematic together first.

Old hands don't need them as much because they have seen and worked with this stuff so much, but you can often get a clearer picture by seeing the circuit diagrammatically. Having an accurate schematic will also help us help you because we can see what you are really working with.

Start with something close like the 6162 (or whatever you find is closer) and make some adjustments so that it matches your amp.

Brian

[rrozell]

Guys,
I found it. someone had taken a terminal strip apart to replace the bias cap for V2 and soldered the last .01 cap before the 2nd volume pot to the plus side of the cap resistor bias pair instead of to the leg of the 2nd volume pot. I was following the signal down the 6162 schematic and ran into it where the signal went south again. The tremolo works. The reverb works, but is barely audible. Probably need a new tank. It's not easy to find something like that without knowing what someone else did.
Both channels sound really warm and full of harmonics. I'm going to replace the rest of the tube sockets and put the original tubes back in. I would like to get rid of the hum later on...maybe buy a reverb tank. I wish the 2nd channel was a little more fuzzy, but all in good time...it definitely has that 60's warm, crunchy tone when turned up. Groovy baby!
You guys are awesome for helping me.

[Glasgow]

Good find RR.

Enjoy your new obsession!

Brian

[rrozell]

Brian,
I will. I would never have found it without you guys helping me. Is it possible to add a 3 wire grounded power cord to these two prong amps?
RR

[Glasgow]

Is it possible to add a 3 wire grounded power cord to these two prong amps?

Not only possible, but highly recommended!

I believe the best practice would be the following:
* Remove any circuitry on the primary side of your PT including ground switches, caps, etc.

* Connect the black (hot) wire from your new cord to your fuse, then to your power switch, then to one side of your PT primary.

* Connect the white (neutral) wire directly to the other side of the PT primary.

* Connect the green (ground) wire directly to your chassis. This could be mechanically through a bolt/nut or soldered to a lug. Make sure you have a great connection! You may find a high wattage iron helpful if you try to solder to your chassis.

Brian

[rrozell]

Brian,
I take it I should not reconnect the caps or other circuitry on the hot side of the primary transformer?...other than the fuse, of course...?
RR

[Glasgow]

Fuse and power switch.

Brian

[Enzo]

Fuse and switch. NO grounding cap, no ground polarity switch.

DO not assume your reverb pan is bad. FIND OUT. Measure resistance across the jack at each end. 99.99% of the time, it will either be open (bad) or have continuity. (good) The resistance won;t be wrong, it will be open or good. Now the pan could be the wrong type for the amp, but that won;t be the pan's fault.

Turn the amp on, pull the cable out of the OUTPUT jack of the pan, turn the reverb up half way, and touch the tip of the plug with your finger. A loud hum should result. If so, the recovery circuit is working. If nothing, pull out the other plug and touch it. If that one makes the hum, then the wires were backwards, so fix that and see if it works. The one that hums goes in the jack marked OUTPUT.

[rrozell]

Enzo,
The reverb tank is hooked up correctly, but I checked it as you suggested. The coax cable goes to the output jack. There's hum on the coax if I put my finger on the jack.The other footswitch cable is a single conductor. The output jack of the tank reads like 200 ohms. I was going to pull the little reverb tank out of my Blues Junior as a test before I ordered another tank. When I turn on the reverb pot and the built in switch goes closed to engage the reverb circuitry, I lose signal level from CH2. Not a lot, but it definitely drops. I just noticed there's no bias voltage on that 6973. Pin 7 has no volts. I could swear it was like 18 VDC when I started working on this. Gotta check that cap. Man, this amp has lots of issues, but I'm almost there.
I'll cut out the giant .01 cap on the 120v and do away with the reversing switch which is not needed. The 3rd wire ground cut out lots of noise and added safety.
I'm thinking about upping the ground resistor going into the 3rd 12ax7 from 47k (originally 3.3k) to 68k as it is in the Gretsch 6162. Waddaya think?
I read lots of opinions about keeping the old tubes in there for "vintage" sake. Others say pop in all new tubes. Opinions? I'm saving all the old parts regardless.
RR

[Enzo]

In my shop we have a rule:

Fix it before you start to modify it. Make it work right before you start pplaying with changing values of parts. Once it is as good as it gets, then you can start top play around in it. If that resistor change makes the reverb more livable then so be it, just make sure everything around it is 100% first.

SOunds like the output end of your pan is OK, check the input end as well though. If your reverb is timid, turn the reverb up midway, then rock the amp to crash the reverb spri8ngs, or brush them with your fingers. Does the reverb spring noise come out strong, or still timid? if the noise is strong, then your drive circuit maybe weak or faulty. If the noise is weak, then your recovery circuit is bad in some way.

Old tubes for vintage sake? What nonsense. Y0u want to keep old worn out crappy noisy tubes in an amp for old times sake? DOn;t forget to leave the original strings on your guitar too.

It will be great to have a pile of original old crappy tubes in the bottom of the amp when you go to sell it to a collector, but nice fresh new WORKING tubes in it also demonstrates that the amp works. And the bonus is that you can use the amp between now and the time you sell it.

[Tom Phillips]

...I read lots of opinions about keeping the old tubes in there for "vintage" sake. Others say pop in all new tubes. Opinions?....
RR

My philosophy is to replace tubes only if they are bad (weak, noisy or just not correct for the circuit) Some vintage tubes will outlast several sets of "new" tubes. The derision is made on an individual tube by tube basis.

Many times I have had a customer bring in an old vintage amp they just acquired. They say, "it's not working and I already replaced all the old tubes."
A real waist if they didn't save the old tubes. If they did save them, they were often better than the new tubes and we put them back in the amp if they were good but not just because they were vintage.

Regards,
Tom

[rrozell]

It's not the tank. I tried the one from another amp and same symptoms. I can barely hear a very, very slight delay with the reverb all the way up. I don't think the 6973 is doing its job of amplifying the reverb signal. Put the newer tubes back in. You're right old tubes makes no sense. Ithink some people are more concerned with restoration than actually using the amp. I want to use it.
If I put a tube driver preamp in the chain before the amp, this thing just screams and I can't even crank it up in my condo. Running the guitar straight in is very nice as well. It has that Stevie Ray Vaughn kind of clean bluesy tone
RR