new build: 18 watt lite IIb

[xtian]

New 18 watt lite IIb build, using a variety of schematics and layouts as reference, including Brown Note, Mark Huss, docereryamps, Ceriatone, and even Spitfire for comparison and options.

I'm using a Hammond 125E for OT. I want to make sure I'm wiring this right. I believe I want a primary impedance of 8k ohms for a Marshall 18 watt build. With that given, I'm looking at Hammond's table, and I have two choices for secondary pairs:

5&3 (4ohm secondary) = 8,800 primary
5&2 (8ohm) = 8,200
5&1 (16ohm) = 10,200

or

6&4 (4ohm secondary) = 6,400 primary
6&3 (8ohm) = 6,800
6&2 (16ohm) = 8,000


Did I read the table correctly? Which is my best choice?

[Phil_S]

Is it too late to get something else? IMO, you've got some compromises there that are less than optimal. Look here: http://www.musicalpowersupplies.com/3.html at the OT20PP or the OT15PP. Reasonably priced and better suited to what you are seeking. Neither one of these is a faithful reproduction of the 18W OT, but neither is the Hammond. I've used MPS iron before and it's good stuff. As he says on the website, "...the most bang for the hobbyist's buck. You may find you like it too....it's not $85, try one." Pricing is here: http://www.musicalpowersupplies.com/6.html

[xtian]

Should have mentioned: This is a cheap-ass-bastard build, made from beaks and feet--whatever parts I had laying around. Trying to keep cost near zero.

With this in mind, will the Hammond OT work?

[Gee]

Yes but it might sound a bit beaky.

[xtian]

Yes but it might sound a bit beaky.

Then I'll have to give it an appropriately fowl name.

[Phil_S]

Do you have 6V6's or 6AQ5's? I think they will be better than EL84 with the 6 terminal as the common. With EL84's I'd pick the combinations with the 5 terminal as common.

[xtian]

Do you have 6V6's or 6AQ5's? I think they will be better than EL84 with the 6 terminal as the common. With EL84's I'd pick the combinations with the 5 terminal as common.

I'm using EL84s pulled from an old stereo (Packard Bell!). Thanks, Phil.

Progress photo attached.

[surfsup]

The 125e is rated at 80ma and that's pretty much idle for two el84s in pp, at idle, right? So wont it get exceeded? What can we expect in a situation like this?

[Phil_S]

Progress photo attached.

Hmmm. Everyone has a style for doing the heaters. If this was mine, I'd run the red wire on V1 and V2 right over the middle of socket straight to pin 9 instead of looping around. That way, it will be out of the way of B+ and signal wires.

[Structo]

Those transformers are reasonably priced.

Unfortunately, it doesn't do much for our economy......

Phil have you used any of those trannys?

[xtian]

More progress, with photos of my heater wiring just for Phil. I usually put my heaters near the chassis, with everything else floating higher.

[Gee]

Yes but it might sound a bit beaky.

Then I'll have to give it an appropriately fowl name.

[img:634:692]http://www.thepoke.co.uk/wp-content/gal ... notice.jpg[/img]

[Phil_S]

Those transformers are reasonably priced.
Unfortunately, it doesn't do much for our economy......
Phil have you used any of those trannys?

Yes, I've bought iron from Matt. I have used an older model OT that is no longer offered. It has a bifilar secondary, offering 4 ohms on one winding and 8 ohms on the other winding, with a 6600 ohm primary. I put it in an Express-like build using a pair of 6AQ5's. In that build, I used his 275-0-275 PT. I probably should have used a tube rectifier to bring plate voltage down a bit, but I ended up at around 330VDC and decided to leave it. I have no idea what a real Express sounds like, except maybe what I can get on YouTube, so my frame of reference is less than perfect. Casting aside the compulsion for comparison, I think the amp came out great. I used the same model OT in a 5e3-ish build. I know that one should use an 8K primary, but, it is what it is, and I like that one, too.

I'd add that Matt is an all-around nice guy. I have two stories that I think are worth telling.

I had a bit of trouble with my Express build and ended up blowing the PT, my fault entirely, doing something bone-headed. Matt reduced the price of the replacement PT by sending me one without the end bells, which I canibalized from the blown one. As an aside, I was able to sell the blown PT on eBait (advertised as blown and needing a rewind) for about $10, LOL, I got out of that one better than I expected.

My other experience with Matt was some great advice and a number of pointers about how to fix a vintage OT that had lost one secondary lead. He told me what I needed to do the take it apart and where to get some of the things I needed (like varnish), and how to properly reassemble it.

As for offshore production, what can I say? I think this is always a tough one. He can't get it produced domestically for those prices or I feel certain he would. Increasingly, we will need to come to grips with the changing nature of the global economy. At least he's up front about the country of origin and I think that says a lot, as he really doesn't need to disclose it on the website, and certainly not so prominently. His message is clear -- nothing is free. Offshore production is the cost of low pricing to the end user.

I'd buy MPS iron anytime. It's good stuff.

Phil

[Phil_S]

More progress, with photos of my heater wiring just for Phil. I usually put my heaters near the chassis, with everything else floating higher.

Ha! I see. Like I said, everyone has a style and there is more than one way to get it done right. I usually do the opposite, heaters in the air, signal wires on the floor. If you know what you did will work, just go for it. I guess that lone red wire looks like trouble to me, but heck, that doesn't mean I'm right about it.

I love the bone pile builds. I think it is real inspiration. If you are free to write a check (or swipe the plastic) you don't need inspiration. I'm pretty sure this will turn out to be a magical amp it its own way and you'll get a great sense of satisfaction from doing it.

Let us know how it turns out.

[xtian]

Finished wiring. Powered up without tubes, and PT got warm very fast. Realized I have a 3A fuse in there. Put in an 1A fuse to test the theory, and it blew immediately. So I've got a short.

Guess I'll take a breather and look at this later. Let me know if anything occurs to y'all.