I want to add an extra tube/gain stage to my plexi reis head

bmf5150 · Post by **bmf5150** » Sat Apr 24, 2004 7:48 pm

Have any of you guys done this?since finishing my plexi 67 clone i want to turn my plexi reis into a high gain head with sustain and note definition!Just not sure about adding a gain stage?
stan

Post by **VelvetGeorge** » Sun Apr 25, 2004 4:14 pm

Stan, are you dead set on this?

There are options that don't require an extra tube.

Of course, by saying that I now have to list those options. Right?

OK let's get started......

Will you be using a MV?
How many channels?
How much gain? Using say a 5150 as a reference.

My take on hi gain is that it's better to get it in the preamp. Then run it through a well behaved (stable) tube output section. That's where the mud comes from quite often. You might even think about using 6550's or KT-88's.

George

bmf5150 · Post by **bmf5150** » Mon Apr 26, 2004 12:27 am

Im not dead set on doing anything yet.just want to keep it tight and some what articulate.I dont know if i will use a master volume yet,or not.depends on how it sounds!!i have the idea of using both sides of the v1 tube for extra gain and put an aditional 5 or 10 uf cap on the v2 for extra gain.now i can keep things tight by raising the power filtering or through the feedback resistor.i havent tried this yet.just an idea.Yes,what would you have in mind?
stan

gnugear · Post by **gnugear** » Mon Apr 26, 2004 12:59 pm

I asked a similar question in the metroamp section and George said increasing the 100k resistors on V1 to 220k will add some extra snarl.

Can you do other things to get 5150 type gain without adding an extra tube? I'm going to try this with my reissue as well ... as soon as I'm done with my 100 watter that is!

Would you recommend a pre or post phase inverter master?

flemingmras · Post by **flemingmras** » Mon Apr 26, 2004 3:21 pm

Actually I would recommend a type of master that isn't even installed in the amp.

It's called a Power Brake. And for a great price I'm sure George would be more than happy to install his special "rhythm/lead) mod!

Jon

Guest · Post by **Guest** » Mon Apr 26, 2004 3:45 pm

I have tried the 220 k in the v1 about a year ago and it didnt sound good.i have a hotplate and want more gain..so what ideas do you have george?
stan

flemingmras · Post by **flemingmras** » Mon Apr 26, 2004 4:57 pm

Hey Stan. OK my thing with the hot plate is is that it's a RESISTIVE load whereas the Power Brake is an INDUCTIVE load. Here's the difference. If you start reading this and it turns out that you already know what I'm about to say, just skip it and reply so that you don't think that I'm implying that you're...not intelligent or something. LOL

Anyway, a speaker is an inductor, which has impedance, which is the resistance to AC current(a guitar signal). Inductors and resistors differ in the fact that a resistor maintains the same resistance no matter what the frequency of the AC signal whereas an inductor changes it's resistance to AC current according to the frequency of the AC signal.

A Hotplate is a resistive load, meaning that regardless of the frequency of the amp's output signal, it maintains the same resistance, so it doesn't act like a speaker like the amp wants it to. However a Power Brake is an inductive load due to the fact that it uses a big stepping transformer to drop the signal's amplitude. Since it is an inductor, it acts just like a speaker just like the amp want's it to. So as far as your amp is concerned, the amp thinks it's hooked up to a speaker so the amp is gonna sound exactly the same as it would hooked straight to a speaker, just at a lower volume. Whereas on a resistive load the amp acts much differently so it doesn't sound the same. IMHO it sounds thin and lacks punch on a resistive load and there's a much better chance that you could blow your amp's output section on a resistive load than there is on an inductive load. And since output transformers are designed to drive inductive loads and not resistive loads, the Power Brake IMO is much safer for your amp as well.

As far as adding more gain, have you tried some kind of a gain pedal(like a clean boost) or even a tube screamer? I've heard great reports about the TS pedals. I don't use one simply cause I run EMG pickups which have a much hotter output, on top of the fact that I use my wireless receiver for a little more gain(most receivers have about +4dB extra gain when maxed out on the output level control).

See if you can take your amp to a music store if you haven't tried a Power Brake already and try one out. I guarantee you'll love it much more than a Hot Plate. Plus George offers his rhythm/lead control mod on Power Brakes only so that you can get a little more volume to get over the band volume when you go to solo! WAY COOL!!!

Hope this helps.

Jon

bmf5150 · Post by **bmf5150** » Tue Apr 27, 2004 12:08 am

No,actually i did not know the diference between the two.i was all ways told the marshall was un safe..thanks for the info.I have tried the pro co rat and the sd1.i havent been impressed with either.
stan

flemingmras · Post by **flemingmras** » Tue Apr 27, 2004 1:07 am

Actually the Marshall is the safest of all because of the fact that it makes the amp think it's a speaker.

The dumbasses that think otherwise do two things wrong. First, they use GUITAR cable in place of SPEAKER cable on the amp's output. THIS IS A HUGE NO NO!!! Especially when cranking. The second thing is is that they mismatch the load by doing one of three things:

1) Running a 4 ohm load, which the AMP can handle but the Power Brake cannot. The lowest load you can run with a brake is 8 ohms and there is a selector switch on the back for either 16 or 8 ohms unlike a Hotplate.

2) Incorrectly setting the impedance selectors on both the amp and the brake. The impedance selectors must not only be in the same position, but whatever load you have it set for you must be sure that this is the load that you're running.

3) Mixing and matching different impedance speakers, which creates an "off value" load(a non-standard load value that the amp cannot be set for)

Basically Stan as with any power soak, EVERYTHING MUST BE RIGHT!!! Gotta make sure you're not running tubes that have been in the amp for years on end and make sure the amp doesn't have any other inherent problems. Make sure you use SPEAKER cable from the amp to the brake and from the brake to the speakers and make sure that the impedance selectors are in fact properly set and you should be fine. George runs his amps on 10 all night with no problems.

However, I take it 1 louder by cranking to 11 all night through one and not only that, maxing out my wireless receiver and running EMG active pickups and my ST Marshall takes everything I give it with no problems. The other Marshall is down due to a bad OT that would only cause problems when ran on the brake due to that damn Jager bomb getting spilled in it a few weeks ago. But I just got the new OT today so as soon as I'm done installing George's Power Brake mod I will be fixing that head and she'll definitely be able to handle the brake once again!

Jon

Post by **VelvetGeorge** » Tue Apr 27, 2004 2:23 am

Hey Stan, are you against cascading the gain stages like a mastervolume amp?

You basically want a plexi style amp with a ton of gain right? Unfortunately, it's bound to get mushy on you.

You could try changing the cathode follower stage (right before the tone stack) into a gain stage. But you lose some Marshall-ness this way.

Have you tried any clean boosts? It seems like I remember you saying you have.

If you want the Soldano thing, that's like 4 gain stages in a row. But they produce only about the same gain as a hot JCM 800.

I guess I just need to design you an amp from scratch......

George

bmf5150 · Post by **bmf5150** » Tue Apr 27, 2004 7:13 am

how would i go about changing the the cathode follower stage before the tone stack to a gain stage?I dont want to re design a whole amp..i can counter some mushy through the negative feedback resistor and power filtering adjustments!
stan

flemingmras · Post by **flemingmras** » Tue Apr 27, 2004 7:30 am

Hey Stan. All you gotta do are four things. DON'T FORGET TO DISCHARGE THE FILTER CAPS BEFORE WORKING ON THE AMP!!!

1) Add a resistor between the plate and the B+ on pin 6 V2(or it might be pin 1...whichever pin the B+ wire is coming in on). A 100K should suffice however you might want to experiment with this. The rule is the higher the value the higher the gain and vice versa.

2) Disconnect the cathode resistor from the tone stack. Connect the pin on V2 that you just added the plate resistor to to the tone stack input(where the 500pF cap meets the 33K sloping resistor). Reconnect the cathode resistor to pin 3(or it might be pin 7...whichever pin the tone stack used to be connected to).

3) Considerably lower the value of the cathode resistor. I'd say down to between 1K and 10K...experiment with the value. The lower the value the higher the gain. You may also add a capacitor across it to tune that stage.

4) Add a coupling cap between pin 2 and pin 6(or again it might be pin 1 and pin 7...whichever two pins were jumped by the plate resistor mounted on the socket) . Again experiment with the value. The higher the value the lower the cutoff frequency will be for frequencies allowed to pass to this stage. I would say start with a .022uF cap and go from there. Also add a 1 Meg resistor between this grid pin and ground. This will be the grid load resistor and it must be there for the tube to bias itself.

As with anytime u perform mods on any tube amp, recheck the bias on the power tubes just to be sure.

Hope this helps.

Jon

bmf5150 · Post by **bmf5150** » Wed Apr 28, 2004 12:00 am

Wow,thanks jon!!i will give it a try!!
stan

gnugear · Post by **gnugear** » Wed Apr 28, 2004 4:21 pm

bmf5150 wrote:Wow,thanks jon!!i will give it a try!!
stan

Stan, have you tried it yet??

I just talked to George and I'm might try some KT88s to help firm up the bass.

bmf5150 · Post by **bmf5150** » Wed Apr 28, 2004 5:45 pm

chris,
No i have not! i havent had the time!
stan