• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

bridge mono tube amp

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diyAudio Senior Member
Joined 2002
BUILDING BRIDGES

Hi,

You will require a phase inverter for one channel.

You then send the signal to both channels and hook up the speaker to the + terminals of the amplifier.

If you need to drive an 8 Ohm speaker the 4 Ohm taps of the OPT should be used.

Cheers,;)
 
Transformer Polarity Inversion......

Car audio retailers (and wholesalers) sell line level transformer coupled DC isolation boxes.
These can be modified to provide polarity inversion of one channel WRT the other.
This will cause the two amplifiers to run in anti-phase, and with the 4 ohm tap arrangements that Frank mentions, you have a cheap and easy means of bridging.

Eric.
 
Does anyone happen to have a inverter/tube circuit? Anyone can make a bridging circuit out of op amps. How about a real burn your fingers circuit for this application? In a brigded situation with tubes how much is to be gained by bridging? With solid state amps the power is multiplied by a factor of 3 or 4 times depending on the power supply and the circuit makeup.

Joe
 
diyAudio Senior Member
Joined 2002
GOLDEN GATE

Hello,

Actually, if it did, you could get over it by using 2.

Exactly that I had in mind.

Does anyone happen to have a inverter/tube circuit?

I do have a Counterpoint SA Pi phase inverter...never got around to drawing the circuit diagram.

Actually it uses one ECC88/6DJ8 as an anode follower with almost no gain.
There is a little trimpot on the frontplate to adjust gain setting but I can't hear any difference any way I turn it.

You can easily build your own with just a dual triode,all you need to know is that any single amplifying stage will invert absolute polarity.

Cheers,;)
 
Cheap, Easy And Good Phase Inverter....

On my workshop system, I have one with reversing switches that I fitted on the primaries, and it works just fine for AUS$12.00 plus switches.
The secondaries need to be resistively loaded to avoid peaking in HF, but distortion is not noticeable, and I find the system is long term nicer with the transformer coupling.

Eric.
 
diyAudio Senior Member
Joined 2002
BURNING BRIDGES

Hi,

I don't think it's a good route for HiFI.

I agree,although you will get a 6 dB gain and increased power,distortion levels tend to increase as well.

How well it works will depend a lot on how the PSU is designed.

What you do when bridging a stereo amp is pretty much the same as running it in balanced mode.

If the amp was designed for that kind of use right from the outset (as some sand amps for subwoofer use and HT are) you'll be OK.

The Dynas were never designed for it.

So I would rather opt for biamping the LS than to bridge the amp if I had a set of two stereo amps.

Cheers,
 
diyAudio Senior Member
Joined 2002
HORSES FOR COURSES.

Hi,

On my workshop system, I have one with reversing switches that I fitted on the primaries

Yes,but your use of the xformers is rather different,isn't it?

If I recall it correctly,you use them to reverse absolute phase at the flick of a switch + you have the added advantage of isolating ground currents as well.

Cheers,;)
 
1002 Uses For A Transformer.....

"Yes,but your use of the xformers is rather different, isn't it?"

Yes, I am usually using them in stereo mode with selectable polarity reversal, but with a Y-lead I can feed the same signal into both primaries (with one channel in the inverted switch position), and connect an on-test speaker between the amplifier active outputs.
I sometimes use this setup for feeding reasonably high power (250W) into cabinets as I need to, and this setup works fine.

Yanamps does not mention if this higher power bridging mode is for a center channel or sub or something.
If so, then the transformer soloution is a quick and cheap means of trying it out, and I don't mind transformer sound, and it will likely work well for him.

Eric.
 
There are numerous ways of producing inverted phase, arguably the best is using a quality transfomer. One question though. How critical will be matching phase gain? This also involves matching each amps gain quite accurately as there is no global feedback to compensate for this.

cheers

peter
 
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