Advice: Hammond PT for a Two-Stroke (Rev 2) Amp

[Maccullt]

I am a first time tube amp builder and I would like to use a Hammond PT to build 2nd revision of the Two-Stroke Amp from Dave Hunter’s book.

I want to use Hammond PT because I live in Canada, have a local supplier (NextGen) and Hammond have a good reputation.

I am undecided which transformer to pick and I am looking for help from experienced builder especially ones that have built this amp.

The Tube Amp Network hosts a copy of the layout and the schematic and the revised layout

The book suggests one of:

Mojo760
Secondary: 330-0-330 VDC @ 75mA
Filament: 6.3V @ 4A
Rectifier: 5V @ 4A

P-TF22772
Secondary: 325-0-325 @70mA
Filament: 6.3V @ 2A
Rectifier: 5V @ 3A

Weber 125P1B
Secondary: 330-0-330 100mA
Filament: 6.3 V @ 4A
Rectifier: 5.0 V @ 3A

Or any transformer for a tube amp with:
Secondary: 310-0-310 to 330-0-330 VDC at least 70 - 80mA
Filament: 6.3 V @ 4A (note: the schematic from the Tube Amp Network says 2.7A)
Rectifier: 5.0 V @ 3A

Hammond Transformers
Starting with the Fender replacements at the Hammond classic 290 series I see :

Hammond 290 AX
Secondary: 325-0-325 VDC @100 mA
Filament: 6.3V @ 2.25 A
Rectifier: 5 V @ 3A


The filament voltage is low but according to the Hammond site this is the replacement for for Fender parts 125P1B and 022772.

Would 2.25A be too low for this amp? (this would be powering the power lamp + 12ax7 + one of 6V6/6L6/EL34)

Hammond 290 CX
Secondary: 325-0-325 VDC @207 mA
Filament: 6.3V @ 4A
Rectifier: 5 V @ 3A

The filament amperage is correct but the secondary is amperage is high 207ma vs the 100ma or less for the other PT. Would this cause a problem?

Hammond 290 CBZ
Secondary: 325-0-325 VDC @120 mA
Filament: 6.3V @ 4A
Rectifier: 5 V @ 3A

This seems to be closer to what I need according to the original spec.

Looking at the Hammond classic 200 series

Hammond 272 DX
Secondary: 300-0-300 @144 mA
Filament: 6.3V @ 4A
Rectifier: 5 V @ 3A

The 300-0-300 is lower than the spec’d 310-0-310 minimum


Looking at the Hammond classic 300 series I didn’t see anything closer …

 

[Printer2]

The EL34 is listed at 1.5A, the 12AX7 at 0.3A, 6L6 at 0.9A, 6V6 at 0.45A. It would seem that either combination would have you under Hammond's 2.2A spec.

 

[leadbelly]

As Printer2 said, the Hammond 200 is fine. There have been reports that the 200 series can run hot, and can even buzz IIRC, so if you are the type who wants extra quality and is willing to spend more to get it, then the 300 series is better.

 

[Maccullt]

Thanks to everyone one who chimed in on Guitars Canada , Tube Amp Network , diyAudio, and TDPRI

The consensus is that the Hammond 290 AX should be fine for the Two-Stroke.

Some other interesting observations:

“There have been reports that the 200 series can run hot, and can even buzz IIRC, so if you are the type who wants extra quality and is willing to spend more to get it, then the 300 series is better.”​

The 291AEX is an “upgrade” version of the 290AX and in addition to supporting export voltages
“291AEX uses high grade 29M6 magnetic steel laminations for reduced losses, more surge output power, cooler operation & longer life.”​