very low powered tweed

[cminor9]

hey all, I have thinking about something as of late, and would appreciate ideas.

I am using a 5E3 to play jazz gigs, and its perfect except I cannot turn up enough to get that nice singing verge-of-OD tone I like from the 5E3 for jazz (not all out cranked, just a gritty voice, almost sax-like). I still want the warm cleans, but I'd like to be able to crack open the guitar's vol pot to get a bit more sizzle for certain things. At this point, it's all clean for me. The amp is always about 1/3 up on both channels, and guitar vol is on 2-ish. If I turn the guitar's vol up to 5 or so I get the tone I want, but it's too loud for the venue and the stand up bass and that is just gauche.

This is pretty much the antithesis of all those questions about "how do I make this 5E3 loud enough to keep up with a band that plays too loud?!"

Some thoughts I had: Clever tube swapping (maybe a 12ax7 in v1 to give me earlier grit, which I tried but it didn't quite get me there). Build a 5F1, but that lacks the 5E3's wonderful clean. Wire a switchable dummy load in parallel with the speaker to soak up some of the output (might work). Build a mini-5E3, with something like 6K6 output tubes (expensive and could compromise the 5E3 tone I love). I realize I could use a power brake or something, but I'd rather build another amp than use one of those (I like a very simple rig - a guitar, an amp, and a cable.) And it seems to be an interesting problem, IOW, fun to solve. Use a power, brake, well...that's no fun.

Or am I just striving to beat one of the inevitable trade-offs one encounters when designing something?

[ThermionicScott]

What speaker are you using? A less-efficient speaker would have you turning up a little more to get the same volume, causing the amp to compress sooner. (But you probably knew that )

Dropping the 6V6 screen voltages a bunch could work, too, but you might then need to implement a split B+ rail to keep the preamp voltages from being too low.

- Scott

[pdf64]

Both of Scott's suggestions are good.
Another idea is to have seperate 560R cathode resistors for each 6V6. Switchable dual pole bypassing with 100 or 220uF caps (needs to be bigger than stock as not getting the benefit of signal cancellation from linking the cathodes). Unbypassed ~ halves the clean output power (and reduces the gain a little). Though the overdriven tone isn't quite as compressed as when cathodes are bypassed. Bypassed the tone and performance is as per stock.

[Diablo]

You could add a Vari-watt.

Page Title

[Bruce / Mission Amps]

Look at the art work here....
With a real NOS 5Y3GT rectifier, remove the 6V6s and use two 6K6s instead.
It wouldn't hurt to reduce the B+ to the amp when using 6K6s....

[cminor9]

appreciate the responses, guys.

I think replacing the speaker would work, but would also prevent me from using the amp at blues/rock/r&b gigs where the extra volume is needed. And I don't want to lug around another piece of gear just to lower the volume. I can pick up my jazz rig with two hands and go (and I don't have to leave any gear unattended when loading/unloading )

From what I have seen here, it seems like the simplest solution is wiring a (large) resistor in parallel with the speaker. This would give me the best of both worlds if I were to make it switchable. Thanks for the artwork, Bruce! A simple drawing but it makes the point.

Looking at a 6K6 datasheet, getting the B+ low enough would be a chore. I set my amp up to run at 370V B+ with a sovtek (zenered the voltage down a bit). Even if I dropped in the NOS recto, it would be really pushing it.

[cminor9]

also, the variwatt sounds interesting, it looks like it uses a few wirewound resistors to accomplish something similar. I don't know that I need that much precision, I just need somewhat of a shotgun approach. I think I could pick up a few large resistors at a local surplus place for under $5. That might be the way to go.

[Bruce / Mission Amps]

I've run 6K6s in the 5E3 with a small string of three 10v zener diodes in the center tap of the PT and bypassed with a switch right above the power cord entry on the chassis.
With a NOS 5Y3GT, the B+ should be around 300vdc and they will run for a long time like that... plus they are super cheap compared to NOS 6V6s.
This will reduce the power quite a bit but still sound like a 5E3... still kind a loud though at around 7-8 watts output.
I hate to say this but with two 6K6GTs and the zeners, I've even soldered a 5Kohm 10 watt resistor onto lug 3 of one power tube sockets and on to ground.... then pulled that 6K6GT tube out. I know... dumb, and slightly hummy but it worked and I was really trying to get the volume down.

[Diablo]

also, the variwatt sounds interesting, it looks like it uses a few wirewound resistors to accomplish something similar. I don't know that I need that much precision, I just need somewhat of a shotgun approach. I think I could pick up a few large resistors at a local surplus place for under $5. That might be the way to go.

The Variwatt doesn't use wirewound resistors to control B+. It uses a Mosfet circuit. I've got the fixed bias version on a 5E8A, which also adjusts bias voltage automatically as you change B+. For the cathode bias amps, he has a less expensive version without the bias adjusting circuit.

[Steve Conner]

I've even soldered a 5Kohm 10 watt resistor onto lug 3 of one power tube sockets and on to ground.... then pulled that 6K6GT tube out. I know... dumb, and slightly hummy but it worked and I was really trying to get the volume down.

Couldn't you just disconnect the drive from the PI to one of the tubes? Seems to me that it would do the same thing as taking the tube out, but you could make it switchable.

Mesa amps used to have a power reduction switch labeled "Full power/Tweed power"... so what would a tweed amp have?

[GrungeMan]

Want early breakup and crunch use a Weber 12F125-0 20watts, 12F150-0 25watts or 12F150-W 25watts. These lower wattage versions will give it up earlier than the 30 or 50watt versions of the same.

Turning the amp up will only make the crunch tastier for rock n roll blues.

The W is twangier than the O.

All the cabs I build for my personal use are loaded with these in varying numbers of 10"s, 12"s, and 15" speakers.

Check out Weber's speaker product page.

Grungy

[Bruce / Mission Amps]

Couldn't you just disconnect the drive from the PI to one of the tubes? Seems to me that it would do the same thing as taking the tube out, but you could make it switchable. ...

Sure I guess so. As a matter of fact, another trick I've been doing for a long time harp amps I build and mod, is;
replace the two 220k to 270k grid load resistors (which ever they are) with two 470k resistors and then parallel them using a 500K L pot with it's outside legs connected to the power tube end of the coupling caps and the ground the wiper if the amp has cathode biased power tubes, or, connect the wiper to the -v bias supply or use DC blocking cap(s) from ground or the -Vdc bias supply.
You can attenuate or mute one or the other power tubes to, On, Off, on a little, on a lot... etc.
It can really throw the "balance" of the driver off with it set up lopsided... and sounds good to harp players who don't know any better yet.
Nobody can patent this idea 'cause it's old school tube stuff for balancing the output of phase inverters and I've taken it to the extreme of, left or right muting, unbalancing and anything in between, Done this for years and the art work is all over to many of my customers... you all know who that comment is for.

[ThermionicScott]

Another idea is to have seperate 560R cathode resistors for each 6V6. Switchable dual pole bypassing with 100 or 220uF caps (needs to be bigger than stock as not getting the benefit of signal cancellation from linking the cathodes). Unbypassed ~ halves the clean output power (and reduces the gain a little). Though the overdriven tone isn't quite as compressed as when cathodes are bypassed. Bypassed the tone and performance is as per stock.

Shades of the Carr Viceroy! With separate cathode resistors and caps, you could even safely yank out one of the output tubes.

- Scott

[cminor9]

Mesa amps used to have a power reduction switch labeled "Full power/Tweed power"... so what would a tweed amp have?

heh, good question. If I could somehow turn my 5E3 into a generic sounding, overpriced, overhyped, way too loud amp with too many knobs, maybe I could put a tweed/mesa switch on it.

*ducks*

[Steve Conner]

you all know who that comment is for.

The man who, legend has it, used his first pocket money to patent himself and sue his parents?

The point I'm trying to make is that yanking one output tube unbalances the output transformer, because it has DC in one winding but not the other. I imagine this would saturate it and make it sound a bit funky.

If you use a resistor as a dummy power tube like Bruce did, or like I suggested leave the tube in, still passing idle current but without any signal, then the DC in the OT gets cancelled.