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 Post subject: Re: Amplifier question
PostPosted: Apr Wed 24, 2019 1:11 am 
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Joined: Apr Thu 14, 2016 8:25 pm
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Location: pensacola fl
And the 6DY7 is 2 6L6 tubes in one bottle pinned out like the 6DZ7. Not the GC version.


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 Post subject: Re: Amplifier question
PostPosted: Apr Wed 24, 2019 1:31 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Warner Robins, GA
Very nice.


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 Post subject: Re: Amplifier question
PostPosted: Apr Mon 29, 2019 6:10 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Rochester NY USA
One thing not mentioned - most speakers need a low drive impedance to avoid a lumpy frequency response; pentodes have a high output impedance. With a high drive impedance there will be considerably more output at the speaker's low-frequency resonance, and there will be a rising response due to inductance at the high frequency end. Two possible fixes: Use triodes (triode wiring the 6V6s reduces max output by half or more) or employ negative feedback. This requires a gain stage or two; the output impedance (and distortion) is reduced along with the gain.

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 Post subject: Re: Amplifier question
PostPosted: Apr Mon 29, 2019 6:49 pm 
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True, although the older speakers like the ones I may use with the amp may have been designed with that in mind and may work best with a tube amp.


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 Post subject: Re: Amplifier question
PostPosted: May Fri 24, 2019 3:31 pm 
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I decided on a whim to try the idea since I had the amp in the house as I had used it a few weeks ago for its B+ voltage as I needed to test something to know what transformer voltage I needed before I ordered a replacement for it.

Connected the amp to a Grundig speaker I had laying around and connected the amp input to an AKAI EIE pro USB sound card which has balanced outputs.

As expected the volume isn't very loud perhaps maybe a watt or two maximum which with the right speaker could be a good bit louder.

If I decided to go through with building a pair I would use a dual triode as a gain stage in each amp.

I just had to see how well it would work.

Another option would be to use an Edcor balanced/unbalanced to balanced/unbalanced transformer to drive the tubes as I could get a 600 ohm to 15K transformer which would provide the necessary step up in voltage and would permit both balanced and unbalanced inputs to be used, although the amp would then only be good with low impedance sources which if I used the balanced input the source would be low impedance anyways as that's how most balanced sources are.

I am seriously tempted to find another set of the 15" Jensen woofer and three 5" tweeters someone had pulled from an Emerson console, put them in a proper open back box, build a couple amps to power them with then set them in the room I have my main stereo in with my current stereo speakers sitting on top of the speaker boxes. I would then drive them with the output of the sound card as it has four balanced outputs. I could then select between the two sets of speakers based on what I'm listening to and my mood.

Now when I tested the Jensen 15" speaker in a cardboard box the bass seemed to be ok and I know it will be much better in a proper open back box and I won't need a powered sub with it.

I'll either build two of these amps with a driver and either

1. Transformer input if that can drive the amps good enough and not impact frequency response
2. Triode stage as driver
3. Triode stage as driver and transformer for balanced or unbalanced inputs if it doesn't impact frequency response.


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