Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: zapped on September 01, 2011, 02:08:48 pm

Title: NOS Stancor PT ???
Post by: zapped on September 01, 2011, 02:08:48 pm

I found a NOS Stancor Plate an Filament transformer in the junk shop. Its 250-0-250 @70 ma. 6.3@2.5a and 5v.@ 3a. Would the 500v output be too low after rectified  for SE Champ/vibrochamp or Princeton build? Thanks Ed

Title: Re: NOS Stancor PT ???
Post by: jjasilli on September 01, 2011, 02:39:42 pm

I think it would make for a great amp with lower, vintage value plate voltage.  250 X 1.414 = about 350VDC; for tube rectifier 250 X 1.2 (e.g.) = 300VDC.

Title: Re: NOS Stancor PT ???
Post by: stingray_65 on September 01, 2011, 02:45:49 pm

OK,

For an SE amp, you might consider going solid state for the rectification. They do not experience "sag" like PP designs do so tube rectification or solid state will sound the same, there will be less draw on the PT because the 5V tap will not be used, in the end it is cheaper.

So, for a 250-0-250 PT and full wave diode rectification, you'll get about 320 VDC.

sounds about right for a small SE amp.

BTW those stancor's sell at a premium on Ebay. You'd likely get enough for a Fender PT or Mag Comp PT plus some change for other parts.

Ray

Title: Re: NOS Stancor PT ???
Post by: zapped on September 03, 2011, 01:37:36 pm

Thanks for the info. If used for a Push-Pull Tweed Deluxe type, how would the reduced voltage (b+) effect the overall sound?? How low is too low for 6v6gt's??

Title: Re: NOS Stancor PT ???
Post by: stingray_65 on September 03, 2011, 02:41:39 pm

70mA is way to low of current for a PP 6V6. A pair of 6V6's in AB1 draw about 95mA with just 285V on the plates.

It is about perfect for a 5F2A Princeton.

My math was a bit conservative, expect closer to 350 as JJasilli suggested with diodes in full wave.

5F2A circuit can be found here:

http://www.el34world.com/charts/Schematics/files/fender/PRINCETON_5F2A.pdf (http://www.el34world.com/charts/Schematics/files/fender/PRINCETON_5F2A.pdf)

With voltages, try this:

http://www.el34world.com/charts/Schematics/files/fender/HARVARD_6G10.pdf (http://www.el34world.com/charts/Schematics/files/fender/HARVARD_6G10.pdf)

The 5F2A may well be my favorite amp, definitely my favorite tweed!

your 70mA will give you enough power to add another gain stage. or a 1 tube reverb or likely both.

This is (IMHO) the best amp to experiment with, different tone stacks, NFB and Presence circuits, different gain stages like these:https://taweber.powweb.com/store/cascode_schem.jpg

Ray

Title: Re: NOS Stancor PT ???
Post by: HotBluePlates on September 03, 2011, 02:50:26 pm

I too would vote for a SE design for this PT.

Title: Re: NOS Stancor PT ???
Post by: DummyLoad on September 03, 2011, 03:59:04 pm

single tube class A1 operation with 6BQ5, 6V6 or 6L6GB gets my vote. be different, use a 6BG6G. ;)

--DL

Title: Re: NOS Stancor PT ???
Post by: jjasilli on September 04, 2011, 11:07:33 am

2X 6V6 at max signal -- overall current draw will be about 100mA.  A little less than 50 percent of its current rating.  IMHO the Stancor can handle it. It will sag which is desirable for the right build.  So I think PP is a possible option.