PT considerations for a 5F10 Harvard?

[rp]

From the layout it's got only ~300VDC off the 5Y3. I'd like to hit that within 10-15V but absolutely not drop below 300V...

-if only for the academic exercise to see what fixed bias 6V6s sound like at this low V.
-I don't want it to sound too much like my 5E3.
-if it was good enough for Cropper it should do me fine.

It's my understanding that you can't hit it purely with math as it depends on the PTs regulation, final load, and the individual tubes. I know it's 1.3 (or 1.4?) X the secondary minus the rectifier drop but I'm always off by 20-30V in the end so I just go for an educated guess. People here are better educated and might provide a more precise guess.

My PT choices are (I need Euro taps) a Hammond @$104.00 and the TDS Lighning/Spitfire PT at $79 on ebay. The money matters a bit right now. The TDS is laydown and requires steel chassis chopping.

-Hammond HX-370EX Universal 100/110/120/200/220/240 119VA - 550V CT - 125 ma - 5V CT@ 3A - 6.3V CT@ 4A

-TDS: 580V center tapped (290-0-290) no load, at .1A DC, 5V at 3A, 6.3 at 4A. http://cgi.ebay.com/Matchless-tube-amp- ... 255830586b

My Math:
Hammond: 275V x 1.3 - 60V (NOS 5Y3 drop) = 297V
TDS: 290V x 1.3 - 60V = 317V

Also, the current, is 100mA (TDS) and 125mA for the Hammond enough? I ask 'cause at ~300V I can probably push this real close to class A. The TDS seems too low though they claim it's underrated. Hammond offers a 150mA version the HX-370FX @$113. I hate heat but I don't want to deviate too far from the original with too stiff a supply. I'd guess Fender used a dinky PT in the original but maybe someone knows for sure. And, I hope Hammond is accurate with that 120V tap and it not really 115V like all their 200 series.

Gonna order something on Monday, which would you go for?

[tubeswell]

I make it

PT
280-0-280 @ ~120mA with 50V Bias tap
6.3V @ 2A CT
5V @ 2A CT

OT
15WPP Interleaved
8k Pr

[David Root]

I built one six years ago, using all 7-pin tubes. I used a Mercury Magnetics FDP20 PT and an MM FBFDR-O OT. I used a 9H Hammond 156G choke.

The PT is a BF Deluxe Reverb PT with some extra laminations. The OT is the standard (for MM) BFDR OT.

Both of these would be stiffer than the original tweed iron. Also the 9H choke reduces sag too. It still sounds pretty tweedy with the right speaker.

For your build I would check out Magnetic Components 40-18017 at www.triodeel.com. This is a 120/240V Deluxe PT for $54.26. 330-0-330, 120mA, 6.3V at 3 amps and 5V at 3A. It is a laydown type but their iron is arguably the best value out there right now.

You will get about 360V quiescent so if you want squeeze the 6V6s closer to Class A you have the voltage to sacrifice and still have 300V plates quiescent.

[rp]

I make it PT 280-0-280 @ ~120mA with 50V Bias tap 6.3V @ 2A CT 5V @ 2A CT OT15WPP Interleaved 8k Pr

Tubeswell, I was hoping you'd reply, I read something by you and a Harvard build elsewhere, maybe old an Ampage post, it was one of my references in starting this. I'm not going to find a 280V PT unless I have Heyboer do it custom, so it's either 275V or 290V. I’d really like to know what you wound up with on the plates with that 280V PT and did you keep the power string the same? NOS 5Y3? How'd you bias it, did you try it very hot? What'd you settle on? My guess is that Fender just did their standard ~60% percent dissipation and nothing exotic, and that this is how people recording with it like Cropper or Garcia used it. BTW did you keep the 6AT6/6AV6?

Sounds like you used a better than stock OT. I was going to use a 108 OT clone like a 5E3 'cause I have a spare, assuming that was what was in the Harvard. Correct assumption? Was the 108 interleaved? If the amps comes out sounding too much like a 5E3 I might later try a 6.6K Deluxe Reverb OT.

For your build I would check out Magnetic Components 40-18017

David, MC was the first I looked at as this is a totally budget build to use up parts I have, but I'll eventually be in Italy and that 240V may not be right. I'm also leery of using a 330V PT as if I decide it sounds best biased at 70% I'll be stuck with too high a B+ for a proper Harvard.

Anyone got a real Harvard or Victoria Ivy League in their hands they can blueprint? The YouTube clips of either sound very good. An old Harvard plugged in today would have higher voltages too, so more to wonder about.