Besides Hammond, who makes a 25 watt OT with 4-8-16 taps?

[rooster]

I know some of you have built an EXP with the Hammond OT I refer to. It has a primary impedence of 7600 ohms, you know the one. I have been thinking that it would be a better build if I could find an OT that more closely matched the Pacific/Heyboar iron, 6600 ohms, but in a 25 watt version - not the 35 watt norm.

Has anybody run into something? Thanks. The 25 watt Hammond iron is working out very well power-wise actually, but am starting to wonder if I could have my cake and eat it, too. And yes, I do want to hang with the EL34s so I am 'halving' the speaker load to change the primary load - or - said differently, I am running the OT so that the EL34s are seeing 3.8K, and not 7.6K. (.........And here's where it gets weird, actually. The Hammond actually has a 4-8-16-20 tap for 6V6s, which translates to 2-4-8-10 when I run the EL34s. With me? Anyway, this means I am stuck running my 16 cab on the 10 ohm tap, maybe not an ideal hookup.) [/b]

[joebob]

http://www.musicalpowersupplies.com/index.html
http://transformerdesignandsupply.com/
http://www.vibroworld.com/parts/tech5.html#transformers
http://www.tedweber.com/

There may be something here.

dave

[rooster]

Dave - Thanks for your suggestions. All these suggested sellers look to be offering something not quite right somehow. I am nervous about the Chinese product for one, and two, the perfect OT does not jump out at me from these links. But I will make contact with two of them and see if I am reading their offering pages correctly. Still, I thank you for posting a suggestion!!!!!!!! You rock!

[Bear]

It at least used to be the case that Edcor would take custom orders for multi-taps. And for not much more money. Probably worth a call or email to find out.

Bear

[rooster]

Bear - Thanks for that link, I didn't know of them. They make a 7600/25 watt 4-8-16, too, just like the Hammond. Hmm, nice company from the looks of it. I will contact them on Monday. I see, too, that they are into ribbon mic trannys - not an easy product to produce in quality. Interesting company...

Thanks again. You Rock!!

[muchxs]

Ross, While I have misgivings about "Chinese quality":

Weber's HiPot test procedure makes his product more reliable than some expensive handwounds. I'd try the multitapped Bassman or high headroom Marshall. It sounds like you want to lean towards core saturation which was my initial inclination. I currently use oversized OTs whenever I can. The exception would be recycled SE transformers, those are on the small side.

One of my associates used to buy handwounds from a "reputable vendor". The guy ("reputable vendor") apparently doesn't HiPot anything because the handwounds all came back sooner or later with open windings. If size were any indication the handwounds should last forever, these didn't.

[rooster]

Eric - Hey. Yeah, I have some big iron on some of my other builds and they do a job - a loud job. Which is fine once every decade for me if then. The real desire for me at this point is that saturation thing at a 'reasonable level'. The EXP is so evenly balanced from front to back that its a perfect candidate for smaller iron as far as I'm concerned. So that's the game plan. Glenn seems to get the job done with speakers which is actually very interesting to me. But then, he has an original and you know he's not going to bugger that up! Me, I'm wide open.

On that subject, using the 25 watt Hammond has been very cool. I am not unhappy with it at all, except I can't help but wonder what the circuit would sound like with a slightly different primary impedence. Forgetting for a moment the potential interaction of the primary and the pwr tubes, to my volume ear, things would be just a bit better if the amp broke up a little bit later than it does. Not much later, just a bit. I can't help but wonder if a different primary would be the ticket, something with a little more headroom somehow. For example, I would love to try a 25 watt OT with a primary impedence of 5K or slightly higher, just to see what happens. Do you know what I mean? And here I suppose I might run into a larger difference with just swapping manufacturers, bullocks to the primary impedence? But I would still like to try it.

BTW, in my search for such a tranny, it has become clear that tranny manufacturers are thinking that 25 watts is more mated to 6V6 usage. All I can find - with 4-8-16 taps - are 7600 ohms. Kinda weird to discover actually. And yes, I am kinda stuck on that 16 ohm thing based on my cabs of choice.

OK, enuff explaining and whining. That Edcor company that Bear suggested is pretty interesting to me at this point. As to Weber (who's speakers I am fan of) and the Chinese iron? Hmm, you could be completely correct, and actually someday that may be all there is to pick from. For now, however, I am still looking at North America. We have a pretty rich amp culture here in the US. Until I asked on this forum, I had never even heard of Edcor! Is there more? Thanks for checking in here, Eric, you get around, I know. And I do value your input! You Rock!!

[muchxs]

The 25 watt Hammond has been very cool. I am not unhappy with it at all, except I can't help but wonder what the circuit would sound like with a slightly different primary impedence. Forgetting for a moment the potential interaction of the primary and the pwr tubes, to my volume ear, things would be just a bit better if the amp broke up a little bit later than it does. Not much later, just a bit. I can't help but wonder if a different primary would be the ticket, something with a little more headroom somehow. For example, I would love to try a 25 watt OT with a primary impedence of 5K or slightly higher, just to see what happens. Do you know what I mean? And here I suppose I might run into a larger difference with just swapping manufacturers, bullocks to the primary impedence? But I would still like to try it.

BTW, in my search for such a tranny, it has become clear that tranny manufacturers are thinking that 25 watts is more mated to 6V6 usage. All I can find - with 4-8-16 taps - are 7600 ohms. Kinda weird to discover actually. And yes, I am kinda stuck on that 16 ohm thing based on my cabs of choice.

Here are my picks:

The W404248. Listed as 4k into 2/4/8 ohms that works out to 8k into 16 ohms. At $46.00 (current retail) it's cheap and available. Strap in in there, wire it up, see what it does. It's a cheap education at the price.

The WO18343. Same as above but larger @ $58.00 current retail.

The WOT45HHR. 50 watt Marshall High Headroom by any other name. 6800 ohms into 4/8/16/32 ohms. $58.00 current retail.

By mixing and matching speaker taps you have 3.4k, 4k, 6.8k and 8k primaries readily available between these transformers. We can't quite hit your ideal of 5k with these choices. There are other factors at play like core size and winding style.

If you want later breakup larger iron at a precisely matched impedance is the direction I'd go in. I'd swap a 5751 into the preamp before I warmed up the soldering iron. One tube, three possible positions. Time to play and experiment!

OK, enuff explaining and whining. That Edcor company that Bear suggested is pretty interesting to me at this point. As to Weber (who's speakers I am fan of) and the Chinese iron? Hmm, you could be completely correct, and actually someday that may be all there is to pick from. For now, however, I am still looking at North America. We have a pretty rich amp culture here in the US. Until I asked on this forum, I had never even heard of Edcor! Is there more?

I'd be the last person to promote WeberVST if the product wasn't sound. I'm not saying everything over there is The Mutt's Nuts. I wouldn't argue with Ted about anything having to do with speakers, he's the expert and he's the best in that department. He's managed to work with his Chinese vendor (and they're not easy to work with IMHO) to bring us usable iron at a reasonable price.

[Bear]

I get the impression that Edcor can do some fairly custom stuff fairly cheaply, so you might inquire about a different primary impedance than they list. I've never gotten the idea that they do paper interleaved or anything like that, but all the reviews I've seen are positive. Heck, doesn't Mercury use plastic bobbins on several models?

Oh, and on the ribbon mic transformer front, you should also be aware of Cinemag and Lundahl -- a bit more, but generally better report on the mods.

Bear

[lewilson]

Ive used some of the musical power supplies power and output transformers. Very nice and efficient. the 0t18 output sounds nice. I am working on another amp with the opt40 watt transformer. At 25 or 30 bucks you cant go wrong.

[skyboltone]

I'm in the process of testing half a dozen vintage OTs in that power range. When the best one is selected I'm sending it off to Heyboer for cloning. They will be in the 7200 to 10500 primary range. If you want a 6600/4,8,16 with M57 iron, just order it from Heyboer. He'll have it ready for you in about 2 weeks. Single run pieces with M57 will run about $90. Mine will be some time before they are ready but they will be available on the forum. I may start a poll on if one needs a 4 ohm tap or not. I just can't think of any reasonable speaker combination that can't be wired for 8 or 16 ohms. Adding the 4 ohm tap requires bigger wire and changes the OT tonal properties.

I currently have 120V primary 235-0-235 200ma PTs with a single non center tapped 4A 12V filament tap. They are perfect for a two hole Liverpool or an EL-84 Express. Wire the power tube filaments in series of course. I have 5 to sell at $70 plus shipping. I make a whopping $10 each on the deal.

[rooster]

OK - That's a lot of info. Let's start with Eric. Eric, my Man, I don't want BIG iron, I want LITTLE iron, 25 watts is the target. I have the 35 watt Heyboar TW OT here and it is too big.

Bear, yes, I am running a Lundahl with my CascadeMics Victor mic, great iron. It was $74 delivered I think. Edcor was less than half of that but I can't find a review. I may never try it, but it impresses me that this Edcor Co. is making PT, OT, AND ribbion mic trannys. That's unique and may be indicative of a progressive Co. intent on cornering a market share. These guys deserve a better look. Tomorrow for them.

Skyboltone, yes Heyboar is already the TW iron @6600 ohms primary - at 35 watts. Where's the fat 25 watt iron? - that's my point. Yes, I think they can and will do the custom piece. However, that being said, I am currently running one from them in the 25 watt, 6600 range, with two taps 4 & 8, from Allen Amps. It is a good sounding piece of iron on so many levels, but oddly enough, it lacks bottom. ?? I swap the 35 watt piece in and I have bottom, the 25 watt piece, no dice. So I am kind of miffed by them at this point. Too, I will point out that the 35 watt TW piece is BIG, and the 25 watt piece is kind of small. (The Hammond piece is bigger in comparison - and has bottom, BTW.) No, I am not smart enough to understand or say conclusively that its the shear weight that makes the bottom happen, but I am noting the facts.

OK, all of this said, it has occured to me that I may have a better conclusion to all of this. I will check this out tomorrow but I suddenly considered something that I overlooked regarding the stock EXP with the 35 watt iron. Everybody is biasing them pretty hot, around 45 ma for EL34s. I run my smaller OT one at 40ma. But it has occured to me that I should try something a little colder, say 36 ma or even 34 ma, to see if this doesn't put things in line. Right now my amp will start to break up pretty good at 10 o'clock, and not the 1 o'clock that the bigger iron is known for. This altered biasing may be the ticket for my smaller watttage build. We'll see tomorrow, my day was jam packed with honeydo's, if you follow....

Thank you all for the input, again, YOU ALL ROCK!!!

[rooster]

OK, I'll skip to the chase. Re-biasing to a colder setting was the help I needed. 34 ma om a set of J/J KT77s. Everybody has an idea here but it finally did occur to me that most to the cats running the EXPs are biasing them a bit hotter so they can use them in a club or recording situation. In other words, helping the amp to breakup a little sooner by biasing them a little hotter. Now, some may just bias their amps on the hot side at all times, or feel that 45ma here is not hot at all. ? Sure, OK, your amp, your decision, no worries

However, in the case of the EXP that I run with the 25 watt Hammond OT, all the headroom is pretty much gone at that setting, unless you keep the volume at 9 o'clock or lower - or lower your gtr volume, of course. With a lower bias setting, the amp is more predictable with typical settings and not something I have to ride the gtr volume pots with as much. YMMV, but this way is much better for me - and it still does that Bluesbreaker kind of grind when you dig in. Cool. I'll try my Siemens tomorrow, and then my Mullards, as well, but hey, I actually like the J/J KT77s in this amp. Thank you all for your ideas and suggestions, BTW, I did not mean to waste your time. BTW, I will still check the Edcor Co. out, Bear, count on it.

[rooster]

OK, this is a total boring post for all of you at this point, but I did want to add one other thing regarding the smaller OT and power tubes.

Today I switched to the Mullard EL34s that I had in a Marshall plexi amp - that I rarely use - too much power. Funny thing is, I had tried them in my 35 watt EXP build and, where I thought they were great tubes in so many ways, I decided on the KT77s from J/J - because they are very decent sounding tubes and they are available for OK money. Soundwise, don't shoot me, but it wasn't the 'sound' of the Mullard that was better to my ear. Instead it was the 'feel' of them. They were very smooth somehow at the top of the note/attack. They made the EXP feel like a 'broken-in' amp is what I want to say, I guess.

Anyway, I remember that I biased them to 40 ma, keeping in line with what I had read here. (Which is still conservative from the 45 ma that most go with here as far as I understand.)

OK, so in keeping with my thought that the smaller iron needs to be biased on the colder side of of 45 ma, I was running the J/J tubes at 34 ma. And this sounded great actually, an improvement in headroom and overall tone. I was very happy with it this way.

And then I tried the Mullards....

I started at 35ma because this is where they happened to sit with the amp being biased for the J/Js. It was OK, kind of more of the same actually. Then I dropped the bias down to 32ma. Something happened in the midrange area that surprised me at this point. Turning the 25K pot past 12 noon, the amp just came on like a roar! I never had this with any tube combination or bias point I had tried. FWIW, I have to add that I have never had any amp do this, period. My plates went from 401 to 400, BTW, with the two bias settings. I thought, WTF, I would try 30 ma to see what the plates would do. 399VDC. I then played the amp for about an hour. Unbelievable.

What I think is happening is that the circuit and the Mullard tubes are mated incredibly well - and - that the smaller iron saturates in a most perfect way if you don't overbias it. ....So when you read somewhere that the Mullard EL34 has this 'really beautiful midrange content', and you will, believe me I do finally know what they are talking about. For me, it took a TW with a 25 watt OT to showcase this, YMMV.

Oh, I am running a 2/12 VOX cab with a tuned back, not open back, not exactly closed, with two Weber alnico 50 watt blue bells - this probably accounts for some of it. too.

[Wayne]

I'm missing something - or maybe just tired - why is your plate voltage decreasing as you bias colder? I would expect the opposite to occur.

W