NEED HELP WITH OUTPUT TRANSFORMER TO BOOST POWER OF EXISTING AMP

[leftu2]

So with the help of some of you guys on my last post about helping to tightening up my amp, I got my amp tightened up by increasing the power supply filtering. It's dang near perfect for me, been playing it all day. Thanks to all that helped me out.

I did install some clipping diodes in a asymmetrical configuration (a 20v and 15v). I love what it does but it pulling too much volume. To get the same volume as when the clipping diodes are not running, the end result is the output tubes start over-driving and my "tight" amp starts going to mush.
 
My amp is based on the 6V6 JCM 800 that Rob Robinette did. It's only 20 watts, built in a princeton chassis.
https://robrobinette.com/images/Guitar/Marshall/RR2104_Master_Volume_Micro/RR2104_Master_Volume_6V6_Layout.png

Id' like to get to 50 watts to get a little more headroom before over-driving the power tubes.
I'm thinking I'll do El34s. Pins 1 & 8 are connected with 1k 5watt screen resistors as the amp is already set up to run el34s. The allen OT is set up to run el84, 6v6, 6l6 & el34 tubes (with a amp and speak mismatch when using the 6l6 or el34s)

I know I won't double the volume of the amp. I just want a little more headroom.
From what I've seen, 20 watts is 75ish % as loud as 50 watts. I'm hoping the extra 25% will get me where I want to be....

I don't want to get into the "change to a more efficient speaker" thing. I know it makes a difference but I'm not regulating this amp to certain speakers;)

With el34s needing 400v minimum at the plates  ( I believe that's right ), I think I should be good on the power transformer as I'm measuring 430ish volts on the plates right now with the allen PT

Here's the allen PT specs from the data sheet I have:
310-0-310 @150ma
50v bias tap
6.3v @ 4.5A center tap


If I'm already meeting the el34 plate voltage requirements, can I just swap the output transformer to one rated at 50 watts and that's it?
Not sure if any other components/values in the amp need to be changed...
P.S my choke is a 5H 120ma

I'm looking at the hammond 1750N output transformer that's it says is made for a marshall jmp 50. 
https://www.hammfg.com/files/parts/pdf/1750N.pdf

[kagliostro]

A 50W amp is all one other amp

assuming preamp can be the same you require a new PT (don't remember well wich will be the DC requirement in current for a PP of EL34, usually PT spec refers to AC current, not DC), new Power Tubes, new OT

as you can see it is a BIG difference, wrth the effort to apply a mod or it will be better to use a new chassis and build a new circuit

what you can save is the cabinet (and the Speaker if it can afford the new power level) and decide if you keep the old complete chassis or you want to sell it

Franco

[pdf64]

… I did install some clipping diodes in a asymmetrical configuration (a 20v and 15v). I love what it does but it pulling too much volume. To get the same volume as when the clipping diodes are not running, the end result is the output tubes start over-driving and my "tight" amp starts going to mush…

I can’t make sense of the second sentence above. Could you try rephrasing it, explaining the issue in more detail?

[Latole]

To boost or to have more headroom, you need more than a more powerful transformer or powerful output tubes.
You need a preamp circuits to push more power at first with the right power supply.

It is another amp

JCM800 Power transformer JCM 800*, JMP - 50* Watt   -   120/220/240 VAC 50/60 Hz.   690Vct @ 200 mA   6.3Vct @ 5A   
More powerful  than your.

The Marshall JCM800 Model 2204 Power Amp ;; https://www.ampbooks.com/mobile/classic-circuits/marshall-jcm800-2204-power-amp/

[kagliostro]

About the preamp as it is planned to drive 6V6 tubes that has a sensibility of 3.75mA/V and EL34 tubes are in the order of 11mA/V I think you don't require to use a different one, the swing will be enough to push the EL34 to their maximum, instead, may be you must tame a bit the signal from the preamp to the power section

Franco

[leftu2]

… I did install some clipping diodes in a asymmetrical configuration (a 20v and 15v). I love what it does but it pulling too much volume. To get the same volume as when the clipping diodes are not running, the end result is the output tubes start over-driving and my "tight" amp starts going to mush…

I can’t make sense of the second sentence above. Could you try rephrasing it, explaining the issue in more detail?

clipping diodes add compression and gain. they will pull the volume down. I'm running the preamp gain wide open with a tube screamer on the front end. When I say "mush", I don't want added power tube distortion added in, which is what happens when I try to achieve the same volume as when the clipping diodes are not engaged. I need more headroom in the power section before power tube distortion occurs. 

[BrianS]

Clipping diodes "add gain"?

[HotBluePlates]

I did install some clipping diodes in a asymmetrical configuration (a 20v and 15v). I love what it does but it pulling too much volume. To get the same volume as when the clipping diodes are not running, the end result is the output tubes start over-driving and my "tight" amp starts going to mush.

Try this:

   -  Bias this amp (however you normally do that) just the way it is now.

   -  Measure the DC Volts at Pin 5 for each power tube.

   -  Get a string of diodes that are higher total-volts than what you have now, but less than the voltage you measured at your output tubes.  For example, if you have -37v at Pin 5, maybe you use a "20v diode" and a "15v diode" in-series as a "35v diode string" that allows a bigger signal to get to the output tubes.


If you don't increase the voltage at which those diodes clamp, you could have 4x 6550s and you won't get any louder than what you have now.  They clamp the signal into the power tubes, and don't allow any larger drive signal.  The drawback of using clipping diodes is there is basically "one loudness level" where they work really well.  You're gonna be married to that loudness level for as long as you rely on those clipping diodes.

My amp is based on the 6V6 JCM 800 ...

Id' like to get to 50 watts ...
I'm thinking I'll do El34s. Pins 1 & 8 are connected with 1k 5watt screen resistors as the amp is already set up to run el34s. ...
...
With el34s needing 400v minimum at the plates  ( I believe that's right ), I think I should be good on the power transformer as I'm measuring 430ish volts on the plates right now with the allen PT

Here's the allen PT specs from the data sheet I have:
310-0-310 @150ma
50v bias tap
6.3v @ 4.5A center tap

Connect Pin 8 ---> Pin 1 ---> Ground
Connect 1kΩ screen resistor to Pin 4.
Strongly consider not using any other socket-pin as a mounting point for parts.

Your PT specs should support EL34s.  And yes, the Hammond 1750N is suitable for EL34s.