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Old 12th November 2009, 08:04 PM   #1
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Default Vulcan Channel Meld

I know this is probably illogical but I have an Admiral amp out of an old console stereo system. Single ended, 6EH5 tubes.

My situation is such that I want to drive one 2-way speaker from both A and B channels of this monster amplfier. I'd like to combine both channels coming out of the Admiral to drive the speaker. It's my observation that the speaker output terminals would be the easiest point to access. What would happen if I wired the terminals together to drive the speaker. I'd wear safety glasses and I have a fire extinguisher!

I'd also like to use the phono input of the Admiral unit to accept the RCA lines out of a cheapy CD unit.

Please don't yell at me about mismatched impedance. I know this idea is not optimal but can it be done?
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Old 13th November 2009, 10:52 PM   #2
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I take it the phono is the only input?
Here's how you can do it.
Combine the channels on the output of the CD player, follow this diagram:

117.PNG

I'm not completely sure about the resistor values but 220K seems close - experiment but don't go below 100K.
Attach this to the phono input on one channel ONLY, drive the speaker from that channel.

Done.
Good luck.
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Old 13th November 2009, 11:30 PM   #3
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I strongly expect that the phono input is for a crystal cartridge so is essentially a line level inpput.

Paralleling or seriesing the output amplifiers may require some remidial circuit work. (series for sure will require you to lift the grounds on the OPT secondary... parallel possibly not. What impedance were the original speakers?

dave
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Old 13th November 2009, 11:49 PM   #4
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If line level, using 10K resistors would be ok.
Sounds like he just wants this thing to make some noise Dave.
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Old 14th November 2009, 12:02 AM   #5
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indeed. I built a 50EH5 amp (50V heater version of the 6EH5) and it sounded surprisingly good despite tiny OPTs.

Click the image to open in full size.

5-Buck Amp

dave
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Old 14th November 2009, 02:07 AM   #6
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Good stuff Dave.
I'm not well versed on tubes (many other things too, actually ) - what are those black things around the tubes? Heatsinks?
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Old 14th November 2009, 02:47 AM   #7
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PEARL tube coolers. Also help with microphony. Floor sweepings from helping Bill pack an order headed for the UK.

Pearl Tube Coolers

dave
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Old 14th November 2009, 05:14 AM   #8
wwenze is offline wwenze  Singapore
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Hmm neat. Not just a 5-Buck amp, but a 5-Buck tube-amp.

Tube coolers... sounds good.

Imagine if somebody just need to spread the word on other audio forums and soon people will be flocking to buy them, as long as someone says it sounds nicer.

This is potentially dangerous.
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Old 14th November 2009, 02:47 PM   #9
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Thank you Guys for your consideration. . .

. . .and yes, I am a freshman to this stuff but I find it fascinating. It's great to imagine how you folks see these questions/problems in terms of solutions in these diagrams. I'm a retired machinist. The more I play in this stuff the more I am able to also see but I'll never see as brightly as you guys. My hat's off to youall. . .

Mr. MJL:
Thank you for the diagram. Very handy.

Are the resistors to impedance-match with the phono inputs of the amplifier?

I can see how this would work Mr. L and it is a simple solution to my question but there is something inelegant about having a channel of the amp sitting idle. I might want to try something more.

Dave:
Yeah, it used a "crystal cartridge". Probably mid 60's vintage.

On the speaker terminals on the back of the amp there are 2 commons and two positive outputs. What would happen if I connected the 2 8ohm + terminals off of the amp's terminal block to the two speaker terminals of the speaker' xover. I'd then connect the two commons together on the amp's terminal block. I can see how the phasing of the two amp outputs would null each other. Can the polarity be reversed between the two channels coming out of the amp. Couldn't I simply undo the connection between one channel pos output and the speaker and turn it upside down to reverse polarity?

Original impedance of speakers is not noted on them but the ohmagege on the amp's speaker outputs is marked 8 ohm.

I really like your little amp. Exactly what I have in mind. Mine also cost 5 bucks.

I still haven't figured out how to send attachments.
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Old 14th November 2009, 04:17 PM   #10
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Quote:
Originally Posted by LikaComet View Post
Mr. MJL:
Thank you for the diagram. Very handy.

Are the resistors to impedance-match with the phono inputs of the amplifier?

I can see how this would work Mr. L and it is a simple solution to my question but there is something inelegant about having a channel of the amp sitting idle. I might want to try something more.
You're welcome
The resistors are for dropping the output voltage and work as a low rent mixer to combine the channels of the CD player. If the phono input is near line level input, then use 10k resistors.
Leaving one channel idle is better than both channels not working You could use it this way until you get another speaker (why only one?) and then use both channels and get rid of the "mixer".
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