Vulcan Channel Meld

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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?
 
Disabled Account
Joined 2007
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. ;)
 
frugal-phile™
Joined 2001
Paid Member
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
 
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.
 
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?:cloud9:

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.
 
Disabled Account
Joined 2007
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".
 
frugal-phile™
Joined 2001
Paid Member
Thank you Guys for your consideration. . .

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?

I'm a bit over my head here so i'd check a bit deeper to make sure everything is cool.

Amplifiers like the Dynaco stereo 70 had a switch to convert them to mono. I believe that this allowed you 2 paralel the outputs. the 2 8 ohm taps would be connected and drive one speaker terminal, and the commons connected (in many amps unnecessary (yours likely included) as they are common with ground inside the box) to drive the other terminal. the speaker would ideally be 4 ohms.

The Decware Zen lets you series the outputs, it has the outputs of the OPT secondary floating (one terminal NOT connected to ground). Then you connect one red terminal to a black terminal and drive the speakers off the remaining terminals. Now best to have a 16 ohm load.

dave
 
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?

What are those two sets of terminals doing? They're connected in the circuit how?

Without knowing that, this could go very bad :-\

Cheers!
 
MJL. you said:
The resistors are for dropping the output voltage and work as a low rent mixer to combine the channels of the CD player

Does this have to do with impedance? How would I know if its not enough resistance? I like to use these kinds of questions to understand impedance better.

Geekdude and Dave you-all said:
What are those two sets of terminals doing? They're connected in the circuit how?

You are on the money Dave. The commons on the amp's speaker output terminals are wired together and then grounded to the case. And Geekdude. . . The terminals of the positives on the terminals go to the OPTs.

MJL:
The reason for all of this. . .
Recently I bought a EV/University Cobraflex folded horn midrange with a compression driver. I only have one. So, what I've done is I had a small two-way JBL bookshelf (model 2500). I disconnected the tweeter and connected the Cobraflex. Am driving this "thing" with a mono Sony table transistor radio. It sounds pretty good if I don't over drive the "thing". This concoction is what I listen to the news on and keep the cats company when I'm away from the house. The Sony's tone controls work pretty well to attenuate the Cobraflex to match the bass of the JBL. Does that make sense?

I have my Dad's old Marantz 8b and C pre-amp. It also has a setting for combining the two channels. If I can find it I'll look at the schematic of the pre-amp to see how they join the channels.

On the diagram on the attachment. . . Is this series or parallel? Also, If I reversed polarity on one of the channels would this work? If it would work how would I reverse the polarity? What would be accomplished by floating the ground on one of the OPTs (disconnecting the ground)?
 

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  • Admiral amp output.JPG
    Admiral amp output.JPG
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Geekdude. . . The terminals of the positives on the terminals go to the OPTs.

Brainfart... I thought you meant two terminals on the speakers :eek:


Given what you have for speaker, i would use one channel to drive the tweeter, and the other to drive the woofer. Balance control gives you level adjustment.

aka "How to turn two stereo amps into a true biamp system" :D

Cheers!
 
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