[ARC5] Receiver audio impedance

[Robert Downs]

The only one of the five models to have a tap on the audio output transformers was the SCR-274-N.  And that one only on the –B models.

 

Robert Downs

 

From: arc5-bounces at mailman.qth.net [mailto:arc5-bounces at mailman.qth.net] On Behalf Of J Mcvey via ARC5
Sent: Friday, March 15, 2019 20:29
To: arc5 at mailman.qth.net; Richard Knoppow
Subject: Re: [ARC5] Receiver audio impedance

 

You can also pop the bottom off and check which tap is being used. The tap positions are described in the manual.

 

method 2:

using a low amplitude tone output from the radio, check the open voltage, then put a variable resistor across the output and adjust for 0.707 time the original voltage. remove pot from the circuit and measure the resistance.

 

Jim

AC2EU

 

On Friday, March 15, 2019, 8:28:26 PM EDT, Richard Knoppow <1oldlens1 at ix.netcom.com> wrote: 

 

 

    You can measure the output impedance by finding the value of 
load that gives you the maximum output. Then, for a pentode or 
beam tetrode reduce the load to about half that value for minimum 
distortion. For a triode the value should be greater than the 
load for maximum power usually about twice or more for minimum 
distortion. Since you expect this to be either 600 ohms or 8K 
ohms you have some idea of what to expect from the measurement. 
Once you have the correct value you can make a variable pad to 
feed the power amplifier. The values are not very critical. It 
should be easy to tell an 8K from a 600 ohm output.

On 3/15/2019 4:32 PM, AKLDGUY wrote:
> My ARA 6-9.1 Mc receiver has an audio output transformer of the 
> original type which I want to terminate correctly and feed to a 
> solid state amplifier. What is the correct termination?
> 
> Apparently the ARA and AN/ARC-5 sets were 300-600 ohm headphone 
> impedance, but how can I be sure an SCR-274N transformer (4,000 
> ohm) hasn't been fitted. All transformers were stamped 5634 
> weren't they?
> 
> Neil ZL1ANM

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL


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