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Bias of SET amps


rplace

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I have my first set of SET amps. Wright Sound 3.5 mono-blocks. I don't see any obvious place to set the bias, nor do I know the values if I could find where to adjust them. I bought the amps used and they did not come with a manual. When I search for a manual online I see several others trying to find a manual, but no solutions. Also some people online say that when they had a Wright 3.5 manual in the past it did not have much information beyond the "obvious" whatever that is.:rolleyes:

 

Got me to thinking do you not typically adjust the bias on SET amps?

 

Any and all help greatly appreciated.

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3 hours ago, wdecho said:

It depends on how the amplifier is biased. When there is no bias pots the amplifier is cathode biased. 

 

This Gent is well ahead of me circuit wise. And maybe Tube Fanatic can add to this. I do know that many 2a3 amps also incorporate hum pots to adjust tube hum/buzz to minimum. What I don't know is why some need or use it while other do not. Obviously the Wrights use neither.

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8 hours ago, wdecho said:

I just checked out your website, http://www.itishifi.com/. I really dig it. 

 

Thank ya hopefully big changes coming up.

 

I talked to George Wright a few times and he was a very genuine person who answered even the most basic questions. I was hoping to meet him at one of their Oregon happenings but never happened... Bummer

 

 

 

 

 

 

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Thanks for the help and info guys!

 

I also have a GW preamp to go with the 3.5s. Its been a lot of fun checking out the differences between a relatively high powered tube set up (60 WPC) and these flee powered 3.5 amps. I like them so much I had to build a way to make the permanent in my set up not just swap out the amps from time to time. With two preamps and two sets of monoblocks I incorporated a Niles switch box (below Wahoo LP in first pic below) so all I have to do is swap my phono outs between the two preamps and push the button and I can easily swap between an all GW set up and my original pre/Amps.

 

Next up is a slight mod to my TT platform to allow the phono pre under it and hide the mess of wires in the 3rd pic. Don't pay any attention to Heresies they are HT surround backs...not part of the vinyl/tube set up.

 

IMG_20180223_151336.thumb.jpg.351f7579357bfebd049f33e2b117fee6.jpg

 

IMG_20180223_151138.thumb.jpg.1e00349d95ff1bc7760c7e4b5594ec31.jpg

 

 

IMG_20180223_151243.thumb.jpg.92c900888788c91350315d7677837069.jpg

 

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On 2/28/2018 at 12:37 AM, seti said:

These George Wright amps are superb. I've spent alot of time with them. I also had the GW WLA12A and it is one of the preamps I most regret parting ways with. George Wright was one of the good guys..

 

 

 

 

 

@seti any idea with that GW pre if it is possible to connect amps to both the high and low output as long as you only use one at a time? I can't imagine why not. I'm guessing that switch on the back simply switches where the output goes.

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Rich,

 

 Should be pretty easy to figure out what the switch does get me a close up shot of the switch area inside. Also if your using the preamp right now and only have one set of amps attached flick the switch and see if the sound goes out to the attached amps.

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2 hours ago, rplace said:

 

@seti any idea with that GW pre if it is possible to connect amps to both the high and low output as long as you only use one at a time? I can't imagine why not. I'm guessing that switch on the back simply switches where the output goes.

 

 

The switch on the back is different gains.

Voltage Gain: 12 to 20dB, switchable on back

 

This is what I got from George on the WLA12A

Tube Compliment

2 x 6SN7

1 x 6EM7

1 x 6X5

Specifications

Very Linear 6 SN7 voltage and driver stages

Frequency Response: Better than 20 Hz to 20 kHz , plus/ minus 1 dB

Distortion: Less than 0.4 percent total harmonic distortion

Input Impedance: 100 kilohms, nominal

Output Impedance: 2 kilohm, nominal; will drive loads down to 600 ohms with some loss of output level

Voltage Gain: 12 to 20dB, switchable on back

Noble Audio Mastering pots

Hovland Musicaps© in line stage

Tube rectifier and regulation for truly quiet operation

Output Level: 1 volt PP nominal; will drive up to 20 volts PP

Stereo-mono-stereo reverse switch

Output level control: 0dB- -10dB- -Full mute

Tape record and playback compatible

Size: 6 x 10 x 5 inches

 

 

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On ‎3‎/‎3‎/‎2018 at 2:57 PM, NOSValves said:

Rich,

 

 Should be pretty easy to figure out what the switch does get me a close up shot of the switch area inside. Also if your using the preamp right now and only have one set of amps attached flick the switch and see if the sound goes out to the attached amps.

 

Craig, no inside pictures but I can report that with it connected to either the left or right set of outputs flipping the switch from down to up made it get louder not go silent like I kind of expected. See the picture below there are two sets of pre-outs as well as not totally in picture 4 inputs and tape in/out. The behavior I was expecting was that left set of outputs would receive the high output when the switch was up and the right side of outputs would receive the lo output with the switch down. It appears there is no difference between the left or right outputs. Just a difference based on the high/low switch up or down.

 

Since it has both tape in and out what would be the reason to have two set of preamp outputs that do the same thing?

 

@seti Thanks for all the info above. It is a pretty sweet sounding little pre and it dead silent.

IMG_20180303_181717.jpg

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3 minutes ago, rplace said:

 

Craig, no inside pictures but I can report that with it connected to either the left or right set of outputs flipping the switch from down to up made it get louder not go silent like I kind of expected. See the picture below there are two sets of pre-outs as well as not totally in picture 4 inputs and tape in/out. The behavior I was expecting was that left set of outputs would receive the high output when the switch was up and the right side of outputs would receive the lo output with the switch down. It appears there is no difference between the left or right outputs. Just a difference based on the high/low switch up or down.

 

Since it has both tape in and out what would be the reason to have two set of preamp outputs that do the same thing?

 

@seti Thanks for all the info above. It is a pretty sweet sounding little pre and it dead silent.

IMG_20180303_181717.jpg

 

Rich --

No, no. 

If memory serves the L and R you are seeing is for the entire top/bottom row of inputs - right channel, left channel. Has nothing to do with the hi/lo switch. That is for hi and lo gain if needed to bump the source signal. You should easily notice the edition all volume needed when set to lo compared to hi. Plus the sound is more subdued, less in your face on lo. Hi is extremely detailed in comparison. And remember I mentioned it not wise to use this switch in powered operation or be prepared for a rather eye popping sound from your efficient KHorns. 

You are more than welcome to ask me but for whatever reason you choose not to --?

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Rich-B, I (Rich-P), am not avoiding you. Just figured the more the merrier on the info side for discussion sake. Also figured there had to be a few former and present wright owners since they are a natural for efficient speakers. I do remember you saying there was a loud noise when flipping the switch. That is actually what got me to thinking about all of this.

 

I was kind of thinking/hoping that since there was two set of outputs that switching the high/low might make  the other silent. Not having done it I was curious how you got the noise from it. My plan if it worked the way I hoped was to have VRDs on the high output and Wright 3.5s on the low output and simply power down one set up amps and the pre, flip the switch, then power up the pre and other set of amps. Guess I still could but scratching my head now on why two sets of outputs.

 

Also you are correct in that the right left lettering is for all inputs and outputs across the entire preamp's back panel. Since it has such a small footprint I was guessing the labels served two purposes. I did not guess correctly.

 

I only did it once on each set of outputs but flipping the switch with music playing give a pretty good thump but nothing crazy loud or violent. Still not something I'm likely to do again.

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2 set active outputs are used for power subwoofers or when bi-amping. Not all that unusual at all. 

 

I think you will be able to use both set of amps as long as you're careful. I would confirm that having both sets of amps attached is not causing a load down/impedance problem with the preamplifier by pulling the RCA cables from the preamp for the UNUSED set of amps while you are listening to music to see if you can hear any audible difference or sound level when you lift the inactive set of amps from the preamplifier. If pulling the RCA cables while listening gives you pause then your going to have to use your ears and AB the setup.

 

                                         Craig

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3 hours ago, NOSValves said:

2 set active outputs are used for power subwoofers or when bi-amping. Not all that unusual at all. 

 

I think you will be able to use both set of amps as long as you're careful. I would confirm that having both sets of amps attached is not causing a load down/impedance problem with the preamplifier by pulling the RCA cables from the preamp for the UNUSED set of amps while you are listening to music to see if you can hear any audible difference or sound level when you lift the inactive set of amps from the preamplifier. If pulling the RCA cables while listening gives you pause then your going to have to use your ears and AB the setup.

 

                                         Craig

 

I ran both of these sceneraios. I biamped when I had the WLA12A and also tried with a sub. Very cool preamp.

 

 

 

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Thanks for all the info and help! I'm always afraid to plug and unplug things when powered up since I don't fully understand what I should and shouldn't do.

 

Here is my results. VRDs and Wright amps both connected to Wright pre. Switch on low output. Both sets of amps turned on. With music playing on wrights I pulled the pre-outs at the preamp to the VRDs. No chance at all. With music playing on VRDs I pulled the pre-outs to the wrights. No change. 

 

Final test with both sets of amps connected and powered up I switched between VRDs and wrights using the -10 on the pre and adjusting the volume. Nothing blew up, popped or smoked.:emotion-21::D. both sound very nice but easy to tell the difference...beyond just the loudness/level

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Amps with and without hum-null pots:

 

The Wright 2A3 single-ended amplifiers are designed with low impedance driving the output stage via a larger than customary interstage coupling capacitor, as well as incorporating a different filament hum reduction approach, using fixed resistance rather than a variable potentiometer to balance the AC filament supply for minimum 60 cycle hum.   When using three element tubes such as the 2a3, 300B, 45, etc., the cathode is also the filament, so hum is more problematic than a tube with an indirectly-heated cathode.  The power supply is also unique -- I talked with George Wright about it years ago.  Such a gentleman, he was.

 

The other more simple solution around AC filament hum is to use filtered DC instead.  The Moth si2A3 as designed by Craig Uthus uses regulated DC for all filaments, and is thus an inherently very low noise amplifier.  Every time I compare the two (AC and DC filament supplies), I always tend to prefer AC; and so installed dedicated AC supplies in the Moth amp for both input and output stages.

 

OP:  As others have already pointed out, you don't need to adjust the bias on those amps.  Enjoy them, they are marvelous amplifiers.

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