Transformer quote.

[al newall]

I just got a price for a little custom made toroid, from Airlink transformers.
240v primary. 115v and 12v secondaries. 37VA.

Quoted price £21.30, doesn't say if VAT is included or not.

Sounds ok to me but could i do better? What do you think?
Only downside is 4 weeks leadtime.

[Andrew]

Hi Al,

For a 12v 3 amp toroid wouldn't RS/Farnell be cheaper? Or am I missing something obvious.

cheers,

-- Andrew

[Andrew]

Sorry, just got it, you've got dual secondaries.

Are you using the 12v for heaters?

I think mixing heater and rectified B+ can cause problems, Nick and I found at his place that the noise from the rectifiers was getting capacitively coupled back into the secondary and appearing a grunge on the otherwise OK AC he was using to heat a pair of D3A.

Now if you're DC heating or its for another use then you could be OK.

cheers,

-- Andrew

[pre65]

Hi-does that apply to the 5V rectifier heater supply as well ?

[al newall]

Yep, DC12v for heating and 115v for HT from twin ss rectifiers.

Finding a 12v toroid no problem. In fact i already have one.
Finding a small 115v toroid, different matter. Unless someone knows different, in which case i'm happy to listen.
The idea of two secondaries from one toroid, appeals due to space constraints though..

[Andrew]

If you plan to DC heat then I reckon there's no issue, or if your AC heating a rectifier valve as in Philip's question, then again, you're going to rectify anyway so noise isn't an issue.

Sure, in any TX that shares a dual primaries, one for heating and the other for B+, then the noise will still be there but any following rectification and smoothing process will override it and should eliminate it.

So, in summary, if you plan to AC heat a signal valve use a separate TX, if not then go-ahead.

cheers,

-- Andrew

[pre65]

Hi-thats good,cos the transformer i was looking at (just looking-honest )had only HT and 5v secs,not 6.3v.