Help with OPT choice....

[Steve O]

I'll look up the article, otherwise, you would have to ask mr Barbour...who knows what he's talking about in my book. Let me dig it up. I can tell you several built these and liked them, so there is something to it. Aparently that amount does not saturate them I guess. Of course you are only getting a watt or two at most.

russellc

That's pretty much it.

The original article was published in Glass Audio during the height of the revival of DHT amps in the US. At the time, everyone seemed to be going for 300Bs, 2A3s, 845s and the like. This could get expensive real fast. Barbour's logic behind the concept of Single Ended Glory... was low cost using what he believed to be mostly "junk box" parts and a good but low cost DHT (#45). Since decent but low cost SE opts weren't readily available, he proposed the use of a PP OPT in the 25-40 W class and originally designed for 6L6 or 7591 use. This got one a P-P impedance of 5-7K which would match up with the #45 nicely. Since the proposed #45 op pt is in the range of 35mA, Eric assumed that saturation woudn't be an issue with a 30 W PP opt running 2W of audio along with this. Based on numerous reports, apparently Eric was correct.

A major glitch with the SEG concept today is that the proposed PP OPTs came from things like Fisher 500s or Sansui 1000As...not particularly worthy of the term junkbox today IMO and certainly worth a lot more than $100/pair esp if on a restorable chassis.

FWIW, AA's amp appears to be an implementation of SEG.

 

[Russellc]

That's pretty much it.

The original article was published in Glass Audio during the height of the revival of DHT amps in the US. At the time, everyone seemed to be going for 300Bs, 2A3s, 845s and the like. This could get expensive real fast. Barbour's logic behind the concept of Single Ended Glory... was low cost using what he believed to be mostly "junk box" parts and a good but low cost DHT (#45). Since decent but low cost SE opts weren't readily available, he proposed the use of a PP OPT in the 25-40 W class and originally designed for 6L6 or 7591 use. This got one a P-P impedance of 5-7K which would match up with the #45 nicely. Since the proposed #45 op pt is in the range of 35mA, Eric assumed that saturation woudn't be an issue with a 30 W PP opt running 2W of audio along with this. Based on numerous reports, apparently Eric was correct.

A major glitch with the SEG concept today is that the proposed PP OPTs came from things like Fisher 500s or Sansui 1000As...not particularly worthy of the term junkbox today IMO and certainly worth a lot more than $100/pair esp if on a restorable chassis.

FWIW, AA's amp appears to be an implementation of SEG.

Yes, thats the article and I have found it. Its from 1995, volume7, number 3. Under the section about output transformers, he states: "The output transformers involve a trick that works only with smaller triodes like the 45."
"Since it pulls only 25 mA of plate current in this circuit (less than half that used by 2A3s, 50s, or 300Bs), you can use a push pull transformer." "The unit should be at least 20W, preferably around 4k-6k plate-to-plate." If the core is large enough, this small plate current and AC power output will not saturate, so you wont need the exotic single ended core with internal air gap."

I just happened to have a pair of 500C outputs in my junk box at the time.
I'll see if I can dig it out of my garage and post a pic. So to answer the question "What makes the 45 any "easier" on the outputs than any other tube running at 9 watts idle dissipation?" according to Mr Barbour is that it only pulls 25 mA of plate current in this circuit (less than half that used by 2A3s, 50s, or 300Bs), so is "easier" on them.

Hope this helps

Russellc

 

[Kegger]

For a few extra dollars, I believe Gery will put an extra tap on the primary at 50%. Might be useful if you ever want to play with a single ended ultralinear configuration on a pentode or beam tetrode type tube (EL34, 6L6, KT88, etc).

I would second this suggestion, not only for other pentode tubes down the road
but for other circuit options like running the driver power from the UL taps also.

If he charges a small fee an will do multiple taps I would suggest the usual 45-50%
and one at 20-30% as well.

 

[soundmotor]

Currently I am thinking about the Edcor XSE 15-8-5K or the Transcendar 5K.

I don't have any experience with Edcor's products but after reading about them, I like their style -

Edcor History

 

[analog addict]

I don't have any experience with Edcor's products but after reading about them, I like their style -

Edcor History

Still waiting to hear back from Gary of Transcendar.

In the meantime, Bricktop has kindly offered to send me a set of loaner Edcors so I can at least start listening, and perhaps make some comparisons. I guess I need to look at a way of clipping them in for temporary use....

 

[bricktop]

They have regular 0.25" male spade terminals on them, so ya just need some wires hangin out with female spades on it. They come in an insulated variety as well for safety :thmbsp:

 

[Redboy]

Anyone here have experience with Edcor's nicer offering, the CXSE Series? Looks like they would offer better frequency response and purty blue endbells, all at a still reasonable cost.

 

[ducati_EL34]

Anyone here have experience with Edcor's nicer offering, the CXSE Series? Looks like they would offer better frequency response and purty blue endbells, all at a still reasonable cost.

If they are anthing like the transcendar's freq. response over the Hammond 125ESE budget xformers, I am sure they will sound really nice. I am loving the great bass response from the Transcendars.

 

[jaymanaa]

That Micah's a hell of a good guy.:thmbsp:

 

[analog addict]

Peanuts....

$2.00 for an extra 50% UL tap. Sign me up...:yes:

And if the 20% tap is an additional $2.00, that also sounds like a no-brainer.....:thmbsp:

 

[dank]

magnequest RH40's

As I mentioned in that previous thread, not that I'm their spokesperson or anything, but for $200 bucks you can also get those magnequest RH40's. I'd let you know how mine sound but I haven't made the amp yet. They're 5k, 40ma, 8 & 16 ohm secondary. No end bells or leads (just solder tabs) and are $99 each. Anybody here have any experience with magnequest xformers at all?

Hi currituckco,
Yes, I have a pair of RH40's in my DIY 45 amps. The monoblocks I made are basically the Gordon Rankin Bugle 45 design. I can tell you that they sound wonderful. I started out with a pair of Hammond ESE125's and noticed a difference for the better with the upgrade in iron. Better on the low and high end. The Hammonds are pretty good for their low price, but if you can swing it, go for the RH40's you won't be let down.

Dan

 

[currituckco]

Hi currituckco,
Yes, I have a pair of RH40's in my DIY 45 amps. The monoblocks I made are basically the Gordon Rankin Bugle 45 design. I can tell you that they sound wonderful. I started out with a pair of Hammond ESE125's and noticed a difference for the better with the upgrade in iron. Better on the low and high end. The Hammonds are pretty good for their low price, but if you can swing it, go for the RH40's you won't be let down.

Dan

I already have them, ready for the Rankin design build. I'm glad they sound good for you! Now I just need to source a pair of 45s...

 

[analog addict]

Purchased the Transcendars today....

...with an extra 50% UL primary tap for $123.80 shipped. Apparently Gery can only do the one extra tap.

Hope he can come up with them fast, cause I am itchin' to get this amp up and running.....:thmbsp:

 

[coman61]

I talked to a former AK member/toob guru who doesn't want to shoot where you are standing, and he told me that even if the current primary is 3K, a 5K primary will sound better with 45's versus the 3K, and that I could roll the 5K unit in without any circuit changes.:

Usually pretty sound advise.:thmbsp:

 

[ducati_EL34]

Usually pretty sound advise.:thmbsp:

That is what I did for my 2A3 amp. 2500 ohms is the "usual" choice for primary impedance, but I chose 5000 ohms, after listening to my amp with both, thanks to the multiple primary impedance taps on the Hammond transformers. With the LaScala speaker efficiency, I still had plenty of volume with the 5K:8 transformers.

 

[analog addict]

Thanks Micah!

Edcors arrived today. I was just looking at the schematic. IIRC, there were only 4 leads used from the original transformers, and the Edcor has 5. I'll need to look at the remaining original OPT and try and figger out the wiring. Here's the layout of the original transformers from an earlier thread....

There are two leads from the OPT to the speakers. These are the secondaries.

There are two leads from the OPT to the circuit, one to the 45 tube B+, the other to one of the + terminals of some of the caps. These are my primaries....

The two primaries used from the original OPT were blue to the B+, and dark tan/brown to the + cap terminal.

So it appears I have an extra lead I need to figger out what to do with, most likely dead end for now. Here's the schematic of the Edcors....

Anyone want to offer an opinion?

TIA.....:thmbsp:

 

[PabloL]

Anyone here have experience with Edcor's nicer offering, the CXSE Series? Looks like they would offer better frequency response and purty blue endbells, all at a still reasonable cost.

I do, I bought some of these for my KT-88 SE amp and love them. I buy all of my transformers from edcor, unless I need something they don't make, then I usually get Hammond. But for OPTs I go with Edcor...

 

[PabloL]

Edcors arrived today. I was just looking at the schematic. IIRC, there were only 4 leads used from the original transformers, and the Edcor has 5. I'll need to look at the remaining original OPT and try and figger out the wiring. Here's the layout of the original transformers from an earlier thread....



The two primaries used from the original OPT were blue to the B+, and dark tan/brown to the + cap terminal.

So it appears I have an extra lead I need to figger out what to do with, most likely dead end for now. Here's the schematic of the Edcors....

Anyone want to offer an opinion?

TIA.....:thmbsp:

The Extra lead is for the screen tap, you don't need that for a 45, just cut it off or wrap it up and wire nut it...

 

[Kegger]

The Extra lead is for the screen tap, you don't need that for a 45, just cut it off or wrap it up and wire nut it...

What he said, the one for the "screen" is not needed for a triode.

If you were running a pentode that would be your UL tap, just tape it off.

 

[bricktop]

Success?