What could I do with a Stromberg Carlson Signet 70?

[benoit]

Got this from a class mate. Powered a church system for a while, then sat in a garage for a while. Runs a pair of 6550s (of which there is a pair of old GEs in good shape). Preamp is 3 12ax7s and a 6U8 (a triode and a pentode in one envelope). Tube rectified (a 5Y3GT and a 5U4GB). It's got 2 mic ins and an rca in.OT has 4, 8, 16 ohm taps and a 70v as well. Speaker jacks include screw posts and an octal socket. There's no cabinet, just a cage that goes over the tubes, and I have to say, it looks awesome.

What I'm wondering is this: what could I realistically build in there? It definitely needs to be gutted, though there are plenty of salvageable parts (old film caps, carbon comp resistors, and of course tubes and trannies).

Chassis is 16.5x9x2.375". PT is laydown, so that's a bummer. There's a choke mounted inside but that could easily be moved outside.

I'd love to get a wreck in there but I don't know if the chassis would allow for good lead dress. I'm also not sure what my other options might be, besides maybe an old marshall circuit. Maybe I'd be better off going with a 6l6 amp but I really want to use those old 6550s if I can.

[jaysg]

I have an older S-C PA amp. The iron is good.

[10thTx]

I probably play this amp more than any that I own. If you replaced the 6U8 with a 12AX7 you could build this.

It gets really nice cleans. The PAB and NFB switch give both give it a huge boost with some nice smooth tweedish overdrive. You could lose the local feedback circuit.

Just tossing it in the mix with other ideas to consider.

I've gutted a number of Bogens and used inexpensive terminal strips paralleled to rewire the amps. Never had oscillation problems doing that.
You can mount the tone stack on the pots using terminal strips also.

With respect, 10thtx

[10thTx]

If you could move the OT (?) to the top of the chassis, you could use terminal strips or maybe even a tagboard & modify this layout. I do think PTP wiring would work also.

You have room on the front panel to have vol, trbl, mid, bass and mstrvol on front. Several Bogen rebuilds I did had the input jack on the back panel. It worked fine.


So you could put the input jack on the back panel along with the reverb pot and dwell. You could also use a 1M to ground and skip the dwell pot.
OR .......... you could use the 4th tube for a buffered effects loop instead of reverb with controls on the back panel.

IF ....... you're actually interested in this schematic and layout with an effects loop I can redraw it.

With respect, 10thtx

[sliberty]

You could send it to me

When rebuilding old PA's like this, I usually search for circuits that use a similar tube compliment, because then I know that the iron will be appropriate. In this case, the pair of 6550's are the key. If you can't find a circuit that uses 6550's, you can certainly do something with a pair of EL34's since 6550's draw more heater current (so the iron can easily handle the EL34's). In fact, if you can squeeze it in there, you could do an Express (just ignore the 6U8). You may have to offset the impendance settings though. You could also probably do a Marshall circuit (early Plexi).

I love doing PA conversions. Currently I have a Lafayette PA that is setup as an EF86 channel from a DC30 coupled with an AC15 power section, and I have a Brentwood PA that I converted to a Z28. Cool projects.

Keep us posted.

[M Fowler]

Ben,

I like it just the way it is. If you decide to get rid of it let me know the next time I see you in the store. Maybe I will get the Dynaco from Jerry for fun.

Mark

[Structo]

A lot of possiblities with that chassis.

I wish I could find stuff like that.

Years ago before I knew anything we used to go to the 2nd hand store and buy old amps like that for $10-15 and then just hook up a guitar. If it sounded good fine but when something blew or a tube went we'd just throw it away......

I'll bet I did that to 4 or 5 amps....

Young and dumb.

[M Fowler]

About 6 years ago I got a Stromberg-Carlson roller rink amp that used 6Sn7, 6N7, 4-6l6, and dual rectifier tubes for free. It worked very good had dual inputs and volume controls. The schematic was glued to the bottom plate.

I too used to be able to go about anywhere and pickup those single 6V6 or dual 6V6 record player amps that I used for guitar amps. Got rid of all that stuff in 2003 and wished I had kept them. Also got rid of my Plush 100 in blue metal flake with 3 -15 bottom, silvertone amp and guitar and all of my PA gear. Why?

Where the heck have all this fun stuff gone to. I did get an old radio at an auction sale recently but not sure what to do with that rats nest.

Mark

[6G6]

If ya need a bass amp, it could be a Sunn 200S.

[gldtp99]

I've got the same type of S/C amp sitting in my "old PA amp" pile---- except mine is branded "General Dynamics".
I've had it for some time and all i've done with it is to pull the like-new Sylvania 6550's for use in my '81 JMP 2204--- they sound good.
I'm thinking of using the S/C iron to build another vintage Orange clone---- maybe i can use the OD green/Black orig chassis/cage for this--- it would be a cool look....................gldtp99

[Ronsonic]

My first experiment would be as minimal a change as possible. Try to dig up a schem, or just trace and experiment with the various inputs and see if there isn't one that doesn't have an appropriate gain level for guitar. Or one that's close anyway. A lot of those old PA mics had some drive and the amp inputs for them are only a bit gainy and bassy for guitar. Then I would tweak that input a bit according to what I heard and didn't like or thought there should be more of.

Why gut it and start over when there's already a well engineered amp in there.