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Speaker Impedance
#85916 Sun Dec 12 2004 08:38 PM
Joined: Jun 2000
Posts: 2,773
Fred T Offline OP
Shop Shark
I'm trying to hook up a radio out of a 62, has transistor power supply with a vacuum tube output. I have found the speaker to go with it, and just tried a 4-8 ohm speaker, but didn't get enough volume. Any ideas on what to try?

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Re: Speaker Impedance
#85917 Sun Dec 12 2004 09:20 PM
Joined: Mar 2002
Posts: 9,030
Master Gabster
Normally one would work from the circuit diagram, and check all the posted voltages with a high impedance voltmeter. However, you could try swapping tubes out, if you have spares. What tends to happen in these old radios is that the capacitors dry out, start to short and sometimes burn out or damage resisitors.

If you are asking if the impedance is the problem I would think not. I don't know that particular model but 8 ohms was uaually pretty common.

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Re: Speaker Impedance
#85918 Sun Dec 26 2004 03:58 AM
Joined: Jan 2001
Posts: 198
If you have a tube output in the radio, it will have an output transformer, the resistance of the output of the transformer should be the same as the speaker you should use. If you ie measure 2ohms across the output transformer, then measure the resistance of a 8ohm impedance speaker, for comparson (resistance may be around 4ohms) which will give you an idea as to what impedance (AC resistance) speaker to use, this will allow the output tube to deliver the maximum power possable. May also be an idea to check the condition of the output tube(s) and any paper capactors for shorts.

Re: Speaker Impedance
#85919 Sun Dec 26 2004 04:43 AM
Joined: Oct 2001
Posts: 3,459
Extreme Gabster
DC transformer resistance and speaker resistance really have little to do with ac impedance (which is usually measured at 1 kHz for speakers).

Impedance is the algebraic sum of the DC resistance and the AC reactance, which is 2*pi*frequency*X*i, where X is the inductance of the coil. I is the square root of -1, which means the inductance is 90 degrees out of phase from the resistance.

It is desirable from a fidelity and electrical power loss standpoint to have as low a DC resistance of the coil/output of amp as possible. The AC impedance is all that applies in this situation.

For optimum power transfer the output impedance of the amp should match the impedance of the speakers. I won't go into the math, as it is boring and hard to follow in text.

Most old stuff was 16 to 8 ohms. If you are experiencing low output you may have faulty output tube(s) or some other problem. Power tubes lose gain as they wear out resulting in low volume and/or distortion.

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Re: Speaker Impedance
#85920 Sun Dec 26 2004 04:56 AM
Joined: Jun 2000
Posts: 2,773
Fred T Offline OP
Shop Shark
Most old stuff was 16 to 8 ohms.
That is what I wanted to know. I took some EE classes in college. Even built my own ham radio, but that was 30 years ago. eek Thanks for the replies.

52 3600
69 C-10

Moderated by  Rusty Rod 

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