Thoughts on a fresh SE build?

[mike9]

I have this nice little chassis from an Epi Galaxie 10 that died. I like heads so this happens to be punched on the top for two 9 pin and one octal socket. Front panel has on/off, standby, jewel, five knobs, and input.

I'm thinking about a 5F2-A type circuit with a 6L6, a diode rectifier, one, or two 12ax? preamp tubes, volume, tone, master volume and adjustable NFB pot. I'm thinking about a cathode bias with a pot for substituting a 6V6GT for the 6L6.

Power Tranny's I have in mind are the Hammond 272DX - it's 300-0-300 @ 125ma. I thought about the 270EX at 275-0-275 @ 125ma, but not sure that would swing a 6L6. Any thoughts on this? The stock Epi tranny is just tiny and I'll be using a Hammond 125ESE for output.

Thanks for any input. Hard enough learning this stuff on your own, but having a community like ours (and others) makes it feel doable.

[Phil_S]

With a full wave bridge, B+ will be around 420v @ 385v @ ~60-70mA to the plate depending on which tranny. The preamp tubes call for a small draw, conservatively 5ma each. Either PT has plenty of juice for your project. If in doubt, choke input will provide more mA than cap input. You need .9A + (2*.3A)= 1.5A for the 6.3v filaments. I don't imagine that's a problem for either one of these PTs, but I don't know the spec.

IMO, the Epi OT is not up to the job on a single 6L6. It is too small (5W) and the primary load resistance is too high. I think you are looking at output of more than 10W, but less than 15W. The 125ESE is probably a decent choice. Look at the OT10SE here as an alternative: http://www.musicalpowersupplies.com/2.html and he's got PT's also. It probably makes good economic sense to source from one place or you pay 2x for shipping.

[Cygnus X1]

Phil...have you ordered much from MPS?

Somehow the looks of that place scares me...perhaps it's the perpetual "out of stocK", and the stories of not being able to source suppliers etc.

[Phil_S]

Yes, I've ordered from Matt at MPS more than once and exchanged email with him a few times, as well. All my experiences with him are good.

There was a blown OT (all my fault) that I had from him. He sold me one without the end bells for a discounted price. That was really decent of him to do.

I don't want to speak for him, but, from what I gathered, he designs the transformers and sources them offshore at a rock bottom price. He was making them in China for a while, but I think he's got a factory in Central or South America that he's been working with. I'm not sure. This clearly isn't his "day job". Apparently, his goal is to make a few bucks on the side by providing good stuff at low prices. Like it says on his website, at these prices, there isn't much risk.

I think the reason he is frequently sold out is that he makes a good product and sells it at a very competitive price. Basically, his stuff flies off the shelf.

I think he keeps his website up to date. If you want an item that is out of stock, just email him to find out if or when he will have it. Production schedules probably vary and he works to keep the production cost low and the quality high.

I put his iron in a 'wreck xpress deviant, with a pair of 6AQ5's, B+ around 335. I am very happy with what I got from him.

[jhaas]

The "Beast Champ"' from over at SEWatt.com (currently offline) might be an option. SS Rectified, one 12AX7 and one 8-pin power tube of choice. The schematic uses the two hammond trannys referenced here - 272DX and 125ESE

I recently built a pair of EL34 Champs but those are rectified w/ a 5AR4 (8-pin) so that wouldn't meet your needs. I did use a 272DX PT, which supplies enough juice for three tubes. I used an Allen Amps TO11C OT, which is a "Heavy Duty" single ended OT made by Heyboer.

BTW, the 272DX at AES (tubesandmore.com) has gone up $14 (over 30%) since I ordered it a month ago! Has hammond raised their prices?

[joebob]

I used one of those MPS OT10Se in my p1_ex and used a 6L6 it sounds good. Several folks on the Hoffman forum have used those OT & PT and liked them. Also in the Hoffman schematic section there are several SE versions of amps you might want to check out. Edcor has some nice transformers too.
Yes, Hammond has raised prices, Radio Daze used to have decent prices for Hammonds.

[davent]

Hello,

In the spring built something similar to what you described, a 5F2a based amp to use as a tube auditioner. Used a Hammond 270EX and a Doberman (Heyboer) 20watt OT. Put in parallel preamp sockets so i'm able to sample 12a?7's, 6eu7 and 6S?7's or have run with a couple of those paralleled. Can be biased variable cathode or fixed so can run any octal I've got on hand. Switched 4k/6k primary on the OT. Rectified with diodes. Switched caps on the first triode cathode, a switched 1uF cap on the second triode cathode to get lots of crunch. Switched adjustable NFB. Also put in a master volume but it just stays up all the way all the time. A VVR or some other power scaling would be a better option but i can't see anyplace to shoehorn it into the chassis. All in all a fun little double duty amp!

http://dobermanamps.com/?pg=transformers

[IMG:640:480]http://i216.photobucket.com/albums/cc30 ... G_0953.jpg[/img] [IMG:640:480]http://i216.photobucket.com/albums/cc30 ... G_0954.jpg[/img] [IMG:640:480]http://i216.photobucket.com/albums/cc30 ... G_0828.jpg[/img]

Take care,
dave

[KT66]

Here's some clips Mark Huss posted at SEWatt of his "Beast" If I can figure out how to post them.

Nice work Dave, that amp looks sweet.