[Collins] Need advise on diode load tube amp AC/DC

[C E]

Thanks.  I intially examined the input to the amplifier. The input is coupled directly to the gain control before it hits the first (perhaps the only) amplification stage. Cal. 

--- On Wed, 10/28/09, Dr. Gerald N. Johnson <geraldj at weather.net> wrote:


From: Dr. Gerald N. Johnson <geraldj at weather.net>
Subject: Re: [Collins] Need advise on diode load tube amp AC/DC
To: collins at mailman.qth.net
Date: Wednesday, October 28, 2009, 10:50 AM


On Wed, 2009-10-28 at 05:35 -0700, C E wrote:
> All:
> I recently picked up a salvaged AC/DC type tube audio amplifier from an RCA record player. I intend to use it as a diode load amp for my R-390A and 51J-4. 
>  
>  I have two concerns: 1) can I get away with physically isolating the amplifier from the chassis without an isolation transformer while preventing any AC voltage leakage when interconnecting the radio and amp together?

Generally not. Chassis is often hooked to one side of the AC line.

> 2) I suspect the input to the amplifier was using a magnetic phono cartridge.  Will this be an unsuitable impedence input to the amp when tapping signals from the diode load output. Thanks. 

The impedance will be OK, but the gain will be too high and the
frequency response not flat. It will have a bass boost and a high cut;
the RIAA playback curve.

You would have a better result hooking the diode load audio in at the
gain control or just before it at the tone controls if any.
>  
> Cal, n6KYR/4
> 
> 
>       

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer

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