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adwsail 10th May 2010 02:45 PM

Paralled output monoblock PP
Can the simple PP output transformers outputs be paralled to create a monoblock amp in a similar fashion as the SE (not the simple SE)?

Tubelab_com 10th May 2010 05:15 PM

Yes, the inputs and outputs of both channels can simply be tied in parallel to make a mono block with one channel at twice the power. To get the power doubling you need the load impedance to be half of the impedanc of each individual channel. In other words you parallel the 16 ohm taps and connect an 8 ohm speaker. I have done this with two Simple P-P boards for a stereo amp and it works.

I then started thinking, why do I need 4 OPT's for a stereo amp? So I paralleled the output tube plates and ran them through a single OPT per board. My OPT's are large enough to support the power level. Again you need to halve the load impedance. In order to accomplish this I just connected my 8 ohm speakers to the 16 ohm taps on the OPT's. This works too, maybee even better than 4 OPT's. Your results would depend on the OPT quality.

I then started thinking about using one 12AT7 to drive all 4 output tubes. I found several ways to do this, but I must wait until I can perform some more testing to see which way works best.

I have also discovered that some EL84's and old 6BQ5's can live with a lot more than 300 volts on their plates and crank out some serious power with excellent sound, but a seperate screen regulator board is needed. These experiments must wait until I return home from a trip that I am on but I have a 100+ watt amp almost done that uses two Simple P-P boards.

The concept was proven a while back and mentioned in post # 209 and 298 here:

And # 36 here:

There is a discussion of an external circuit being added to SY's RLD amp in place of the bank of LED's. I am testing a version for use with the Simple P-P.

adwsail 10th May 2010 05:32 PM

Outstanding George, thanks alot. While I'm still chasing the unstable bias problem on my 300b SE I figured I might as well go ahead and stuff up this PP board I got from you some time ago and see how it does as a sub driver.

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