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leadbelly 10th March 2005 11:52 PM

Please confirm my transformer math.
 
2 Attachment(s)
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?

jeff mai 10th March 2005 11:58 PM

Re: Please confirm my transformer math.
 
Quote:

Originally posted by leadbelly
Is that correct?
Yes, but it isn't the only consideration. The primary inductance of the trans may not be sufficient to ensure full bass extension.

leadbelly 11th March 2005 12:01 AM

Re: Re: Please confirm my transformer math.
 
Quote:

Originally posted by jeff mai
Yes, but it isn't the only consideration. The primary inductance of the trans may not be sufficient to ensure full bass extension.
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.

planet10 11th March 2005 01:45 AM

Those should also work with 50EH5...

dave

Eli Duttman 11th March 2005 01:55 AM

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.

leadbelly 11th March 2005 02:47 AM

Quote:

Originally posted by Eli Duttman
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.
So if I ran a long burn-in session with a small fuse in series with the primaries, wouldn't that address that issue?

Colt45 11th March 2005 04:00 AM

Go for it. Put a fuse in the power supply and hope she doesn't blow up.




edit:

Oh, you're in alberta eh?
Im in saskatoon. email me or something.

Eli Duttman 12th March 2005 12:52 AM

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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