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previous: Darren Okies, thanks for the suggestions, ... -- 3/5/1998 7:46 PM

Re: Damn, not enough B+

3/10/1998 10:19 AM
Stephen	Re: Damn, not enough B+ Darren, Sorry about delay in replying to this...I was sidetracked by other things at this end. It makes a nice change to find items and services which cost _less_ down here than they do in the US. One-off transformers seems to be one of these. $100-150 is about what I pay for a typical tube amp PT, depending on rating, and how much copper and iron. If you plan to use your amp for hours at a time, then check that the offered tranny is rated for continuous use, not intermittent domestic use. Also transformer design includes a permitted temp rise above surrounding air. In a tube amp - and especially in a combo amp with the usual inverted chassis in the top of the cab- there may be little air-flow, and the air surrounding the PT may easily reach 30 degrees ( make that 50 degrees if you're playing a desert gig The design temp rise goes on top of that - It's quite easy to end uo with a PT which is running too hot to touch! This may be ok with modern tranny materials, but I have chosen to get my combo-amp PT's designed for a lower temp-rise in continuous use. I am sure tranny designers in Oz have learned to allow for the high ambient temp in some parts of the country, but maybe you should let them know if your PT will also be working in a limited air flow and/or in raised local air temperature. They might say that's ok, or they might suggest the next size up for a few $$ more. Toroids: I'm still a bit cautious about toroids for tube amp power supplies. There _are_ people who understand about high-voltage windings on toroids, but IMHO too many products rely too much on the integrity of the wire varnish insulation. I still like to see a physical barrier between windings. Your old (1989) standard for separation of windings on a toroid was C126 ( maybe changed now) and I don't know whether it also covered separation of HV and heater secondaries from each other, as well as from the input winding, You'd have to ask the people who quoted you. - Stephen

3/10/1998 10:19 AM

Stephen

Re: Damn, not enough B+

Darren,
Sorry about delay in replying to this...I was sidetracked by other things at this end.
It makes a nice change to find items and services which cost _less_ down here than they do in the US. One-off transformers seems to be one of these. $100-150 is about what I pay for a typical tube amp PT, depending on rating, and how much copper and iron. If you plan to use your amp for hours at a time, then check that the offered tranny is rated for continuous use, not intermittent domestic use.
Also transformer design includes a permitted temp rise above surrounding air. In a tube amp - and especially in a combo amp with the usual inverted chassis in the top of the cab- there may be little air-flow, and the air surrounding the PT may easily reach 30 degrees ( make that 50 degrees if you're playing a desert gig :-)

The design temp rise goes on top of that - It's quite easy to end uo with a PT which is running too hot to touch! This may be ok with modern tranny materials, but I have chosen to get my combo-amp PT's designed for a lower temp-rise in continuous use.
I am sure tranny designers in Oz have learned to allow for the high ambient temp in some parts of the country, but maybe you should let them know if your PT will also be working in a limited air flow and/or in raised local air temperature. They might say that's ok, or they might suggest the next size up for a few $$ more.

Toroids: I'm still a bit cautious about toroids for tube amp power supplies. There _are_ people who understand about high-voltage windings on toroids, but IMHO too many products rely too much on the integrity of the wire varnish insulation.
I still like to see a physical barrier between windings. Your old (1989) standard for separation of windings on a toroid was C126 ( maybe changed now) and I don't know whether it also covered separation of HV and heater secondaries from each other, as well as from the input winding, You'd have to ask the people who quoted you.
- Stephen