• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Best PP OPT 30-100W range

Howdy, Folks:

For the amplifier currently in the conceptual stage, I'll want a new manufacture PP output transformer, and for budget reasons it should be an off the shelf as opposed to a custom (unless someone knows of a competent custom winding house that is competent compared to off the shelf).

The topology is still up in the air but most likely it'll require separate screen windings with about a 20-30% ratio relative to the plate windings. Not ready to specify the complete transformer yet, just wanted to give y'all an idea of the class. This is for HI FI.

So, the question: who are the off the shelf providers out there with whom any responder has experience and what are the respective opinions about each?

Thanks!

Rene
 
I have a pair of 30W PP Transcendars on the way for an EIclone. I will report back when I finally get it put together. The one I hope to build is a clone of the Eico Hf-87 as per the diytube.com website. My reference will be the JE Labs 300b mono blocs which sound beautiful but not enou power right now. WAF prevents true high efficiency speakers....

JP
 

45

Member
2008-12-18 2:29 am
UK
Howdy, Folks:

For the amplifier currently in the conceptual stage, I'll want a new manufacture PP output transformer, and for budget reasons it should be an off the shelf as opposed to a custom (unless someone knows of a competent custom winding house that is competent compared to off the shelf).

The topology is still up in the air but most likely it'll require separate screen windings with about a 20-30% ratio relative to the plate windings. Not ready to specify the complete transformer yet, just wanted to give y'all an idea of the class. This is for HI FI.

So, the question: who are the off the shelf providers out there with whom any responder has experience and what are the respective opinions about each?

Thanks!

Rene

Depends on what "for budget reasons" means. Custom made transformers with those specs are not going to be cheap.
Off the shelf you can buy the Sowter 8994 that is a replica of the Acrosound TO-350. Of course if you can find a pair of original Acrosound OT's they still are very good as well, although modern magnetic materials are a lot better.
A pair of Sowter 8994 cost about 500 British pounds!
Primary impedance is 6.6K plate-to-plate with separate UL windings at 43%. The Sowter is rated 100W (but the frequency is not specified), the Acrosound was specified for 100W from 20Hz to 20KHz, FR 7Hz to 70 KHz +/-1dB, max DC current for each tube 175 mA, max DC unbalance 10% of the previous value.
These transformers where specifically designed for tubes that could not withstand high screen grid voltage like the 6146, however I think that the separate winding is beneficial for any tube....
 

45

Member
2008-12-18 2:29 am
UK
Looks like there is some misurdestanding here: separate windings for UL is not the same thing as UL taps.
Separate windings are usually called tertiary windings and, as the name suggests, are indipendent. This allows to apply a different DC voltage to screen grids. This is not possible with the vast majority of UL output transformers, regardless of their cost and performance. As the winding geometry becomes more complex and the work nearly doubles the cost increases accordingly.....
 

TonyTecson

diyAudio Moderator Emeritus
2003-05-29 2:57 am
Maybunga, Pasig City
Howdy, Folks:

For the amplifier currently in the conceptual stage, I'll want a new manufacture PP output transformer, and for budget reasons it should be an off the shelf as opposed to a custom (unless someone knows of a competent custom winding house that is competent compared to off the shelf).

The topology is still up in the air but most likely it'll require separate screen windings with about a 20-30% ratio relative to the plate windings. Not ready to specify the complete transformer yet, just wanted to give y'all an idea of the class. This is for HI FI.

So, the question: who are the off the shelf providers out there with whom any responder has experience and what are the respective opinions about each?

Thanks!

Rene

i suggest that you pm BudP, Bud Purvine, who is member here, he can surely help you out, if i recall correctly, he is from the Washington state area...
 
I have used two pairs of 1650R OPTs so far and have been very pleased eac thime with the sound. The R version was first recommended to me by Douglas Picard (Pak Protector) for his E-Linear design, and I later learned it is used by at least one custom builder whose PP monoblocks sell for over $30K. I can't say that it is the very best sounding OPT because I haven't compared it to others using the same circuit, but I can say that it sounds very good.
 
thanks for all the input so far, hope it continues! OK, I'll reveal a bit more: My design will be using sweep tubes which generally means lower PP load resistance than other tubes (lower plate voltage at higher current). I'm almost convinced that this will be a conventional G1 drive but I do want to operate in UL mode. Rather than a tapped or tertiary winding transformer, I'm leaning toward a MOSFET circuit to allow adjustment of both the nominal G2 voltage and the percentage of plate swing which will be coupled to the G2. All the simulations I've run plus a considerable amount of investigation by others in this group have convinced me that the optimum "tapping" is somewhere in the 20-30% and not in the 40% range.
with an off the shelf unit, if all else fits, I can always simply ignore any existing G2 taps.
I'm encouraged by the endorsements of both Edcor and Hammond as they are inexpensive units, bears more investigation. The kicker may wind up being the low load Impedance (I think in the order of 3K or so, still running what ifs on that), the higher current and whether CFB will be incorporated.
Keep them coming! This hopefully is helping others in their thinking process.

Rene
 

45

Member
2008-12-18 2:29 am
UK
There is no magic % for UL operation. There are some historical values that soon became standard but actually the percentage depends on device first of all.....
If cathode feedback is used I am not sure that a mosfet follower driving G2 is a better solution than a pentode with regulated screen voltage.
 
Power.

How much power, what class of operation. How much low end response. Which tubes at what voltage = plate impedance calculation. etc.

Otherwise it is just a list of manufacturers.

The actual specifics *change everything*.

20-30w PP iron is easier in general than 100watt+ iron... for example.

The ideal spec is like 10Hz -- 100kHz. Good luck.
But it could just about be done... in general you'd want to reach for that limit... for maximum performance.

Don't forget core material counts too...

In short, everything is a variable and every transformer is a trade-off.
Choose your poison!

_-_-bear
 
Thanks for the comments, all. I would like to get back on topic which is: what are the best PP transformers in the 30-100W range. Based on personal experience, not just hearsay.
My reason for revealing a bit about the topology under consideration was to aid in the flow of input regarding transformer sources.
So, yes, a list of manufacturers but put thru the filter of individual experience. That will be greatly appreciated!
Thanks again!
Rene