# Hammond PT's - input?



## DBS_180 (Oct 2, 2018)

What has your experience been with using Hammond PT's lately? I've read about some people experiencing noise/buzz with the 2xx series PT's.

Going to be doing a 5F2A build soon, was planning with going with either a 290AX or 270AX.

Thanks.


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## _Knighthawk_ (Mar 2, 2014)

I recently bought a hammond for a 5E8a build and it has worked flawlessly. I also have one in my 64 VV build - it has worked without issue for the last 14 months @ 4 to 10 hours of use per week


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## Lincoln (Jun 2, 2008)

The older 290AX didn't have a center tap for the tube heater circuit, and they very often did hum. The cure was to install a "virtual center tap". That consisted of two 100ohm resistors, one from each leg of the heater circuit, to ground. Problem solved.

Hammond has since started adding a center tap to its 290AX transformers. Anything you buy now, will have the center tap and you're good to go.


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## DBS_180 (Oct 2, 2018)

Ah, thanks. I suppose if I went with the 270AX, I could add the 6.3V virtual center tap.

Speaking of which, would the 270AX be sufficient for a 5F2/Champ? Single 6V6 & 12AX7, diode rectification so no need for the 5V secondary winding. My only concern is the 58mA and if that would be sufficient.


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## _Knighthawk_ (Mar 2, 2014)

I can recommend the 290AX if you decide to add the 5Y3 for rectification.


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## Lincoln (Jun 2, 2008)

DBS_180 said:


> Ah, thanks. I suppose if I went with the 270AX, I could add the 6.3V virtual center tap.
> 
> Speaking of which, would the 270AX be sufficient for a 5F2/Champ? Single 6V6 & 12AX7, diode rectification so no need for the 5V secondary winding. My only concern is the 58mA and if that would be sufficient.


with only 2 tubes on the 5F2, the 270AX should be enough transformer. Is it substantially cheaper than the 290AX? Are you using a pre-made 5F2 chassis?

Where I'm going with this is wondering how well the 270AX will fit a pre-made 5F2 chassis.


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## DBS_180 (Oct 2, 2018)

270AX is roughly $20 cheaper than the 290AX. Not using a pre-made chassis, so sizing shouldn't be an issue.

Is there a general rule of thumb for matching your total Plate Current with the PT HV current rating?

e.g. ~35mA 6V6 + ~5mA 12AX7 = 40mA Total (69% of the 270AX total current capacity)


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## Lincoln (Jun 2, 2008)

DBS_180 said:


> 270AX is roughly $20 cheaper than the 290AX. Not using a pre-made chassis, so sizing shouldn't be an issue.
> 
> Is there a general rule of thumb for matching your total Plate Current with the PT HV current rating?
> 
> e.g. ~35mA 6V6 + ~5mA 12AX7 = 40mA Total (69% of the 270AX total current capacity)


Perfect!


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## epis (Feb 25, 2012)

You should be fine, class A amps draw max. Current at idle, but $20 difference isn't significant. I would go with 290ax and tube rectifier. If you wanted to sell it one day


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## jb welder (Sep 14, 2010)

Aside from the current, there is also substantial voltage difference between the 270 and 290 (HV secondary). Just mentioning in case it was overlooked.


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## DBS_180 (Oct 2, 2018)

jb welder said:


> Aside from the current, there is also substantial voltage difference between the 270 and 290 (HV secondary). Just mentioning in case it was overlooked.


If I went with the 290AX, I'd use the 275-0-275 secondary for diode rectification. Would be nice to have the additional 5V winding as an option, for a $20 difference I'm just nitpicking :/


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