• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Please confirm my transformer math.

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leadbelly

leadbelly

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Joined 2002
#1
The background is that I have some old output transformers that came out of an SS amp, VERY old. They are 2500 ohm primary / 3.2 ohm secondary. They look like they could be used in a spud amp because they are reasonably large, say at least an inch in every dimension (I don't have them with me right now). So the 6C45Pi is suited to a 5K primary OPT. From RDH4 (attached image) it looks like using an 8 ohm speaker would offset the drop in primary resistance WRT distortion. Is that correct?
 

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#3
Re: Re: Please confirm my transformer math.

jeff mai said:
Yes, but it isn't the only consideration. The primary inductance of the trans may not be sufficient to ensure full bass extension.
Click to expand...

Thanks! Yes, I fully expect this to be bass-challenged amp. I was more concerned from a will-work/won't work at all point of view.
 
#5
I hate to be a spoilsport, but a cautionary note is in order. Trafos designed for use with BJTs have insulation that can tolerate battery voltages. It's quite possible that the insulation in those old trafos will break down when the CT is connected to a tube B+ rail. Don't forget that the lamination stack will be at ground potential.
 
#6
Eli Duttman said:
I hate to be a spoilsport, but a cautionary note is in order. Trafos designed for use with BJTs have insulation that can tolerate battery voltages. It's quite possible that the insulation in those old trafos will break down when the CT is connected to a tube B+ rail. Don't forget that the lamination stack will be at ground potential.
Click to expand...

So if I ran a long burn-in session with a small fuse in series with the primaries, wouldn't that address that issue?
 
#8
leadbelly,

Those old SS trafos are constructed for low voltage service. I get no comfort from a fuse.

There is a SURE FIRE way to be safe. Build your amp with parafeed topology. CCS load the plates and cap. couple the plates to the O/P trafos. Ground the CTs of the trafos.
 
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