Greetings, thoughts on loud and clean Dumble style amps(SSS)

[Chrome Dinette]

Hello, I am more or less new here, though I have been lurking for a while. My background is in sound reinforcement and audio installation, though nowadays I seem to spend more time working on nurse call and fire alarm equipment.

Anyway, I play guitar and have worked on my own amps for years now, and built about 8 of them, as well as effects pedals and tube synth stuff. In fact, the only guitar amp I currently own that I didn't build is a Crate Powerblock that I carry around in the event my main amp blows up.

So far, my experience with Dumble type circuits has involved putting a Dumble style tone stack in a sort of Marshall/Sunn Model T hybrid I built using the xfmr's from an old Sound City head and also a low powered high gain amp using a single 807 for the power tube. On that one, I followed the ODS special type of circuit up until the PI. I also used octal preamp tubes, just because I found a ton of them at flea markets over the past few years.

Anyway, I plan on building a SSS inspired amp at some point. I have read these threads:

https://tubeamparchive.com/viewtopic.ph ... &start=165

https://tubeamparchive.com/viewtopic.ph ... =inductors

and it seems like a good starting point is the first part of an ODS type amp into a PI followed by a driver stage feeding the power tubes. The SVT style has been mentioned here and I have also seen some hi-fi schematics with this type of post PI driver. I have a bunch of 12bh7's I could use, though I might also try a 6sn7 for the power tube driver.

I have also seen inductors mentioned in relation to the SSS amps. I was thinking of trying something like the circuit in the following link between the normal Dumble tone stack and the PI:

http://www.gyraf.dk/gy_pd/pultec/gy_pd_sch.gif

Obviously I might have to change some things to make it guitar friendly and I wouldn't be using interstage xfmrs, but I think it is worth a try.

At any rate I have enjoyed lurking here and hopefully I can add something to the discussions.

[Structo]

Welcome,

Yeah, the SSS amp has a few unknowns as it stands although a few guys have figured them out, but they ain't talking....

Looks like you have been doing the research necessary to build one.

Remember it wasn't that long ago that the guys were guessing how the ODS was designed.

Everything that has been discussed here is in most of the threads dedicated to the amp. You just have to find it.

Frankly I don't see the attraction to an amp that powerful and clean but to each their own.

[Bob-I]

Frankly I don't see the attraction to an amp that powerful and clean but to each their own.

I'm with you, but Funk and Fuchs both have loud clean amps like this. I played both at the ampshow, almost knocked someone out of a chair 50 feet away from Brandon's amp, and they sound great.

Fuchs claims they're good sellers because some folks simply want to use pedals. Each to his own, I prefer the ODS type overdrive myself.

[marcos]

Several years ago I had the pleasure to try a Steel String Singer side by side with a ODS, and I have to say it´s a totally different animal.Yes, loud and clean but also warm and singing, very unlike Fender clean.You have to experience this to understand why many people want this type of amp.No way to get the exact same thing thing out of an ODS, or any other amp.BTW this particular amp did not have Tone Filters, but Reverb and Tremolo.Dear Santa Claus........

[Chrome Dinette]

I still haven't gotten around to my project, but I may get moving on it soon. An interesting amp sort of fell into my lap. A friend of mine was given a home made mono block hi-fi amp. He managed to cause it to stop working(turned bias pot until fuse blew).

Anyway he gave it to me to look at. He has basically given me his blessing to turn it into a usable guitar amp. There is plenty of room in this thing to add a tube and I am going to give a "clean Dumble amp" a shot.

FWIW, the tubes this came with are very cool. Real Gold Lion KT88's, Amperex GZ34's, Amperex and Telefunken preamp tubes. Hopefully my friend didn't kill the Gold Lion's when he blew the fuse.

pictures:

[img]http:1]http://i.ixnp.com/images/v6.23/t.gif[/img]

[img1200]http://jschreckengost.files.wordpress.c ... 3/amp5.jpg[/img]

[img1200]http://jschreckengost.files.wordpress.c ... 3/amp3.jpg[/img]

[img1200]http://jschreckengost.files.wordpress.c ... 3/amp6.jpg[/img]

Note use of 2 prong AC outlets as speaker connections.

[Chrome Dinette]

Hmm, maybe that site doesn't allow hotlinking. Here is the link, scroll down a little:

http://jschreckengost.wordpress.com/

[BobW]

The monoblock looks to be an old Dynaco Mark III. The filter caps also look original, and that's probably what blew the fuse.

The Mk III was the first amp (kit) I built back in 69, and still own it.

[Chrome Dinette]

It is actually not quite a Mk III. They didn't have 2 rectifiers or a voltage regulator tube. They also used a 6an8, which is half pentode, half triode. This has a 12au7 and a 12bh7.

Obviously the caps need to go, but I am afraid my friend just couldn't leave well enough alone and started playing with the bias pot, until the amp quit. I hope the power tubes survived, real Gold LIon's aren't cheap to come by.


mk 111 schem:

[img:825:1056]http://www.triodeel.com/dynamk3.gif[/img]

[Chrome Dinette]

So, below are my hastily traced schematics of the amp, as is. I think the caps are pretty well shot, though the transformers seem to be ok. I didn't measure voltages, because I couldn't get it to run with the rectifiers without blowing a fuse(unless I used a series outlet).

The PT puts out 425-0-425 with no load. I will probably add a tube and wire it up as the clean section of an ODS. I will then feed that into something very similar to the current PI/Driver setup.

There is room for a choke, and I have a couple, so I will probably do away with the UL taps. I haven't decided whether or not to use two GZ34's or go to silicon rectifiers.

The bias supply is derived from it's own small transformer.

I also have room in the amp to put in a FET stage. I believe I can use a GGG Stratoblaster board I have laying around to wire up the D-Style fet circuit.

I know when I am done, it won't be an SSS, but I think I can get satisfactory results of some kind.

[img:800:581]http://i15.photobucket.com/albums/a352/ ... amp001.jpg[/img]

[img:800:581]http://i15.photobucket.com/albums/a352/ ... effamp.jpg[/img]

[Structo]

I haven't worked on any dual rectifier amps but I wonder what that does to the voltage?

As in, do you get twice the voltage drop when using two?

Or since they are in parallel is that different?

[Chrome Dinette]

I don't think you get any less voltage drop. You generally use more rectifiers if one isn't rated for the current you need.

The amp should sag a little less and one can also use twice the capacitance following the rectifiers. I will probably just go with diodes.

[David Root]

Two rectifier tubes in parallel is really nice in that style.

It sags but doesn't woof, depending on your OT, I last used two GE 5AR4s in parallel in my Dumbleized 5F6A 100W w/two 8417s and 6SL7 preamps and it sounds very nice, except for a little fizz on the OD which is because I didn't Dumbleize the layout.

[Chrome Dinette]

I was finishing up(or so I thought) this morning and everything looked good. Bias is there, I put the rectifier tubes in, and voltages on the appropriate pins were where they should be with no tubes. I had also checked all grounds, and just about everything I could think of.

I put the tubes in and plug the amp into a series outlet(I always do this first). The bulb lights up and goes dim, so far, so good.

I plug it into a normal outlet and turn it on and the fuse goes immediately. I replace the fuse, pull the power tubes and this time, the amp stays on. I check the voltages, everything seems ok. I have the bias voltage high(biased cold) to start.

I put the tubes back in and turn it on and it stays on. I had unplugged speaker and power when I flipped it over to put the tubes in and I forgot to plug the speaker cable in.

I shut it off, plug in the speaker, turn the amp on and the fuse blows. I try it again with the series outlet, but it doesn't show a problem.

I try a different set of tubes, pulled from a working amp, fuse blows. Those tubes work when put back into the amp they came from(and I am using the same speaker cable and cabinet to test).

I check everything connected to the power tube sockets. The output xfmr seems fine. I get almost the same resistance from each plate to ct. There is no short between primary and secondary.

The only thing I can think of is that the fuse I am using is too small. The hi-fi amp was marked for a 5 amp fuse, assuming slo-blo.

I am out of these and was using 4a fast-blo, planning to run out and get some when Radio Shack opens. Could the inrush of current when turning the amp on be enough to take out a 4a fuse? And if so, I wouldn't have thought having the speaker connected would make much difference.

Oh, I also thought that I might have screwed up the negative feedback, so I completely disconnected that, as well.

I am going to step away from the amp for a few hours and take another look later.

[Bob-I]

Straight answer to the 4a normal fuse, yes the on-rush current can take it right out. Get the right fuse and try again.

[Chrome Dinette]

I was leaning in that direction. I will probably straighten it out later tonight or tomorrow.