Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: audiocats on November 10, 2014, 04:14:08 PM

Title: HV current capacity of the PT-3 transformer ?
Post by: audiocats on November 10, 2014, 04:14:08 PM

Thinking about the possiblity of a Crack-Double-Dosage project, i.e. use two 6080 in the output stage, for lower output Z. Maybe something like this has been done before, if so please point me to it.

Anyway, at this point I have a little question for the bottlehead team:

say if I use the PT-3 for high voltage only (will use a dedicated filament transformer for the heaters), how much HV current can it safely output? will it do 70mA x2 ? The overall power handled by the PT-3 will actually be a little less, outputs around 21 VA (vs the ~27 VA in a standard crack).

Thanks for any inputs

Title: Re: HV current capacity of the PT-3 transformer ?
Post by: Paul Birkeland on November 11, 2014, 06:09:42 AM

We have indeed experimented with paralleled cathode followers.  I would suggest building something like this on a piece of plywood to be sure that you will be OK with the compromises that come along with this.

The PT-3 could probably handle the B+ duty, but you would most likely want a transformer that will produce slightly higher voltage to allow for the additional power supply filtering that such an amp would require.

-PB

Title: Re: HV current capacity of the PT-3 transformer ?
Post by: Doc B. on November 11, 2014, 08:46:34 AM

I am required to step in here and say that our license with Paul Joppa, the designer of the PT-3, limits our support of its usage to our own designs. The bifilar construction of the two separate high voltage secondaries of the transformer can lead to a failure if wired incorrectly.

Title: Re: HV current capacity of the PT-3 transformer ?
Post by: audiocats on November 11, 2014, 03:09:54 PM

Thanks for the warning Doc.

Caucasian Blackplate, thanks for the info, can you point me to the "parallel followers" mods? can you elaborate on "the compromises that come along with this" ? is it related to the sonic result?

Title: Re: HV current capacity of the PT-3 transformer ?
Post by: Paul Birkeland on November 12, 2014, 08:01:33 AM

Yeah, from what I have tried, the sonic penalty of the paralleled cathode followers is not worth the decrease in output impedance (which isn't quite enough IMO).

When you go through the exercise of pulling the parts together, the SEX amp ends up looking like a much better option (and the output impedance is as low as you'd ever need for headphones).

-PB

Title: Re: HV current capacity of the PT-3 transformer ?
Post by: audiocats on November 13, 2014, 05:54:43 PM

Thanks for the heads-up, I guess I won't bother with it then....

Title: Re: HV current capacity of the PT-3 transformer ?
Post by: mcandmar on November 13, 2014, 06:39:09 PM

Left field idea, if you want to lower the output Z try a Tung-Sol 7802.