Stereo to mono by paralleling outputs?

[TonyTecson]

to parallel, use both inputs to be fed from a mono source, then parallel the hot leads from both channels.....

if you want more power.....
the SY Impasse preamp The ImPasse Preamplifier | audioXpress, has both inverting and non inverting outputs...
you can use to feed the two channels of a stereo amp and then take the outputs from the hot leads from each channel, this completes the bridging of your tube amp..

 

[PRR]

Full MO200A plan here.

The MO200A was internally two amplifiers, but strapped together in and out so, as-stock, it worked as one amplifier. (Yes- converting to 2-channel is trivial.)

Bogen had a range of such amps which were *designed* for parallel operation. It wasn't a major design change. Most low-NFB tube amps will parallel OK. The Bogen adds a "CP" jack which parallels the internal NFB points for less fighting.

There was a bigger 300 Watt amp I used a lot, and it shipped as two channels of 150W each. It was trivial to strap for one channel, and to soup-up past 300W; however I mostly ran mine as five 175W channels (one OT was burnt when I got them).

These amps were 99.9% reliable making FULL power ALL day at 59Hz to drive telecines. (The 0.1% flame-out is why they fell into my hands; and that was a no-solder "joint".) They probably were flat to 8cps at 1 Watt; certainly not 200W at 8cps!! The "Frequency Response" does not say what the power level was. The 117V output implies it will do big power at power line frequency. I never hit them hard below 50Hz.

> For various reasons you can't successfully run PP valve amps in bridge mode.

This is quite possible, assuming outputs are common ground. Simplest is to add an external phase splitter or out of phase drive. With internal access you can cross-connect NFB.

 

[Pano]

Hi,
Can I put a stereo signal into a tube power amp and parallel both channel's outputs into a single speaker?

As I clearly said, the MO200 has TWO inputs.
They are connected together to make a MONO input.

Well then it's not what the OP asked, is it? (see above) And it's not what people on the thread were objecting to. There wouldn't be any out of phase signal going to the Bogen power stages, right?

 

[6vheater]

There wouldn't be any out of phase signal going to the Bogen power stages, right?

Well if you can read circuit diagrams, you can clearly see that is the case.
You can put the stereo input into the 2 phono jacks, and the amp converts them to mono.

As for running valve amps in BRIDGE mode, there are many reasons why you shouldn't do that.

1/ You get no more power than putting them in parallel - which of course is exactly what Bogen did for their line distribution systems (70v/140v)..
In fact they recommended doing this, by adding more and more booster amps in parallel, if PA required such high levels.
Bogen were/are experts in this domain as were Peerless.

2/ Trying to run such amps in Bridge mode, means you will get nasty assymetric phase shifts which get multiplied x 2, making them inherently unstable, with unstable A-A loads at varying freqs..
If a speaker goes open circuit, you will likely destroy both amps.

3/ If one amp goes down, you will lose all signal.
There are more reasons, but those are the main ones.

Amps made of sand can be run in bridge, as they have often low PSU voltages,- eg in cars.This doubles the output power.

 

[Pano]

Sure. But the point was that the OP asked about the parallel connection of stereo outputs, and you replied telling him it's OK to connect mono outputs. And then you berated those who said that connecting stereo outputs together was not a good idea. Your answer was not to the original question; their answers were.

I just want to make it clear to those reading from the sidelines that the original question and your answer and not directly related. The question was stereo - your answer was mono.