PT 450V

[Smokebreak]

Pullin my hair out tryin to find a standup PT for 2X6L6 with SS rectification, to get 450-460V plates.
I've got a Mag Comp 650VCT that gives 480 plates, also a multitap 610/710 that gives 400/490, and a 290DX, 650VCT that gives 480.

Any ideas/experiences?

[matt h]

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[M Fowler]

How about this MC PT http://triodestore.com/40-18103.html

or http://triodestore.com/potrforhotro.html

[Stevem]

So you are looking for 480 with every thing up and running and the two 6l6s at idle between 50 and 70%?

If so than may be you can find a used PT (013895) from a silverface Fender proreverb, super reverb or bandmaster reverb , the ones with a master volume control, but this would have to be converted to stand up type!

[sluckey]

Pullin my hair out tryin to find a standup PT for 2X6L6 with SS rectification, to get 450-460V plates.
I've got a Mag Comp 650VCT that gives 480 plates, also a multitap 610/710 that gives 400/490, and a 290DX, 650VCT that gives 480.

Any ideas/experiences?

Is that 650VCT figure an actual voltage measurement? Is that 480 plates figure measured with all tubes in place and drawing normal current? I ask because a 650VCT (same as 325-0-325) can only put out max unloaded 460VDC on paper. Add a load to it and that can only go down.

If your wall voltage is high then the 650VCT will be high as well. I would think the 650VCT would be fine for a 2x6L6 amp if the current capacity is high enough. That 290DX is Hammond's SR replacement so it should be a good choice except you would need some L brackets to stand it up.

[Smokebreak]

Matt, that's exactly right. 122V wall here, and the MC are rated fully loaded @200mA. That multi tap has voltages published on the spec sheet, and they are ridiculously lower than real world idle voltages.
I'll look at some Edcor stuff. It's been a while. That 150mA rating makes me a hair nervous though.
Mark, I hadn't considered using a FWB with the deVille units. That's a possibility.
Steve(s) I'm looking for 450-460. As is, I'm having to bias all the way to 70% just to keep the plates at 480.
650VCT is not the actual reading, just the published rating. Real world is 720V! This is with the MC and the 290DX .With normal current pull from 2x6L6 I get 480V . Granted, with GZ34 I'm down to certain BF voltages.

Blackburn is sending me a heyboer. 600V CT that reads 608. We'll see where that gets me then adjust from there. I think it's custom time, as I can't seem to hit anywhere between 430-470 with anything off the shelf...for Fender stuff at least , w/ SS rectification.

[matt h]

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[Smokebreak]

Looking at the Hammond sheet, I see that ~120mA of current pull with FWB cap input would call for 200mA PT( 200 x .62). Unless I'm reading incorrectly, it looks like the calc for FW cap input would be 120mA? (120 x 1). That doesn't seem right.

I'm most concerned with how you'd come to the 180mA at full tilt number, which begs the question(let's assume the PT is not conservatively rated, and a true figure), why would you want to push the PT that hard? Even if it is conservatively rated, how do we know "by how much?"

[matt h]

(deleted)

[Smokebreak]

Matt, thanks for the great post.
The 376X may be a good choice, though pricey http://www.hammondmfg.com/pdf/EDB376X.pdf

[tony hunt]

Recently, in a pinch, I used a stand up 325/0/325 150mA IG Präzisions-Wickeltechnik IGMT-M45/50RS Plexi PT in a '64 Fender Concert and got bang on 450V at the plates biased about 65%. Those are no longer made, but it may be a direction to look into.

Mind you, I had to fiddle the bias supply of the HT Marshall style. But it works so well that I'm tempted to leave it in. The Hammond 290EEX is waiting on the shelf.

[matt h]

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[xtian]

I'm thinking about a 2x 6L6GC build using this inexpensive Fender HRD PT. But I'm planning a lower-wattage, lower voltage, home/recording amp. I want to experiment with 300-400 volts on the plates.

Hey, Matt! I want to take your advice on the MOSFET voltage regulator, as shown at the bottom of this page. This article suggests the voltage reduction is set by the voltage of the low-power Zener. So for a ~50v reduction, I'm looking at this Zener.

Next, I don't know how to spec a MOSFET. I was looking at this one, but don't know if the Drain Source Voltage has to match the Zener.

What if I want the option of -50 or -100 volts reduction? Do I have to swap both the Zener and MOSFET?

[Phil_S]

I don't think you actually said how many mA you need. If you can get by with 140mA, MPS makes a 330-0-330 with primary taps for 115 and 120, which may or may not be helpful; the 115 option gives you a 4.4% boost. I figure, with solid state rectification, you get 330 * 1.4 *96% = 444V. Goosing it for the factor of 122/120 line voltage should get this right on the money at 450. I use 96% as an estimate of typical loss and experience suggests this is reasonable, but less than perfect.

The 330-0-330 has a 5V tap that will go unused, reducing demand on the primary coil. It might allow for a bit more mA on the HT secondary, but that really is limited by the winding and the wire gauge.

http://www.musicalpowersupplies.com/products/

[xtian]

Thanks, Phil. But I really want to be able to experiment with a variety of lower voltages. Ill have two 12ax7 and two 6L6. Maybe this MOSFET idea isn't substantially different from Hall's VVR, and why reinvent the wheel?