toroidal transformer + europe

[cedricb]

Hi,

I'm currently planning to build a European version of the ST-35.

Any pointers of which shop/manufacturer I can use for the toroidal transformers (power & ouptuts). I've sent an email to http://www.trafomatic.com to get a quote... I've just looked at http://www.amplimo.nl but I don't really know how to match the Z-565 spec and secondary of the PS-774... I found different standard power toroidal transformer with dual 6V secondary, can I use one of this?

Do I need to change anything in the PCB/components for the 230V power transformer?

I would like to "hide" the 3 transformers in the chassis (for personal view I found all the transformers a bit ugly) and leave the tubes outside, any advantage/drawback of this choice?

I was thinking to use a passive solution for the volume (for example with a DACT CT2 100K) and the input selection (DACT CT3), any drawback for these?

I'm a total newbie in term of tubes, so which tube do you recommend? the Russian one? I would like something which can last a little bit... :-)

Regards,
Ced.

[cedricb]

...anyone?

Can I use this power transformer?

http://www.tube-town.net/ttstore/media/products/0739076001125000029.pdf

[EWBrown]

That should work, the output windings are similar to those of the Hammond 272FX, which is commonly used for the DIY-35. Just cap off the 50V leads, as they are not needed in this design, and the 5V winding could be used for a GZ34 or similar rectifier, or just capped off as well.

150 mA is cutting it a bit close, as the total DC consumption of the '35 is around 148 mA. But I've used the 272FX with no ill effects it gets hot but not as hot as most PA774s.

HTH

/ed B in NH

[cedricb]

Thanks for the clarification!

Any though about my other questions? :-)

[Shannon Parks]

Do I need to change anything in the PCB/components for the 230V power transformer?

No. You'll be fine.

I would like to "hide" the 3 transformers in the chassis (for personal view I found all the transformers a bit ugly) and leave the tubes outside, any advantage/drawback of this choice?

I like the Tube-Town power tranny you listed. But I do worry about lack of ventilation derating the transformer output power limit. Maybe vent holes for the power transformer?

I was thinking to use a passive solution for the volume (for example with a DACT CT2 100K) and the input selection (DACT CT3), any drawback for these?

I don't see any.

I'm a total newbie in term of tubes, so which tube do you recommend? the Russian one? I would like something which can last a little bit... :-)

The EL84/6BQ5 tubes are very robust. You can't go wrong with any of them. I've only had one fail, and that was a Russian 6p14p at startup at about 7C.

[cedricb]

quote from Vista Audio for Trafomatic transformers...

Code: Select all

1. Power transformer, toroid, 180VA
Primary: 230V/ 50Hz
Secondary 1: 300-0-300V @0.2A
Secondary 2: 6.3V @ 6A
Secondary 3: 5V @ 3A
Quantity: 1
 
Price (standard): $74.00
Price (potted and shielded): $89.00
 
2, Output transformer, toroid, PP, 20W
Primary: 8k, CT
UL tap @ 40%
Secondary: 0-4-8 ohm
Quantity: 2
 
Price (standard): $52.00 each
Price (potted and shielded): $68.00 each
 
International shipping: $44.80

[cedricb]

EWBrown/ Separks: to optimize (reduce) the price on these toroidal transformers (PT & OPTs) from Trafomatic, can you please comment on the voltage/ ampere/ power/ ohms ?

[Shannon Parks]

Since Trafomatic has made some ST35 trannies before for Ed, can't you just tell him you want the Ed Brown special? Also, you can go to Triode's website and look at their datasheets for the PA774 and Z565.

[cedricb]

I've done my previously quote based on a mixture of the PA774/ 270HX:
- a kind of PA774 with an additional 5V for the rectifier tube
- an average of PA774/270HX for the high voltage --> 300-0-300V
and I've done a matched for the spec of the Z565

From what I've read on other threads, EdBrown has complained about too much B+ with these Trafomatic.
That's why I was wondering and asked for returned experience/ view...


Regards,
Ced.

[EWBrown]

I dod find excessive B+, but then my local AC voltage is usually around 123VAC, and sometimes as high as 128VAC :o

I was getting operating B+ over 400VDC, and as occasionally high as 420VDC. Unloaded B+ was approaching 450VDC. :o

I suppose one could emulate VTL (Vacuum Tube Logic) and turn the bias current down to 30 mA - they even do that with hefty tubes like 6550Cs... They also tend to run very high B+ voltages.

THe Trafomatic trannies have dual 115VAC primaries, and they really do mean 115VAC... If your power over in Europe is close to 220-230VAC, these should be good for the ST35.

OTOH, the power trannies run a LOT cooler than the PA774s or Hammond iron. I suppose that the 50 Hz rating allows extra margin for 60 Hz users.

The unpotted / unshielded trannies are a lot easier to mount below the chassis, only one mounting hole is needed to be drilled into the chassis for each one.

/ed B in NH

[cedricb]

EWBrown: could you post the specification of your Trafomatic PT & OPTs please?

Cheers,
Ced.

[EWBrown]

I'll have to dig up the supplied data sheet in order to check my figures, these were the "standard" ST35 transformer set, with no special requirements, I ended up getting two sets, (due to a minor screwup on Trafomatic's part, which ended up giving me the extra set for a bargain price) and now Shannon has the extras of them.

Their boxes were labelled as "ed brown specials" but they were just the standard ST35 set, as he (Boris Sasic) had described on his E-bay listings.. Just ask for the standard ST35 set, and add in any extra requirements you may want, like an extra 5VAC, 3A filament winding, 120VAC instead of 115VAC dual primaries (or single 230 or 240VAC primary), as shown on your posted quite. Trafomatic knows the various international requirements, but they as well as a lot of other manufacturers (Like Hammond) still believe that USA standard voltage is 115-117 and not 120VAC or higher.

The cost for one transformer set was comparable to the price a set of the Triode ST35 set.

IIRC, the power trannie has 2X 115VAC primaries, 330-0-330 @ 200 mA HV secondary, 2 X 6.3VAC (no CT) at 2.5 Amps. These trannies are 50 Hz rated, so they run nice and easy, and fairly cool temperatures on 60 Hz.
From my couple of hours of somewhat "overloaded" testing, this power trannie barely got warm. A PA774 in the same time would get very hot.

My problem is the "true" 115VAC primaries combined with my 123VAC average line voltage. I'm on an 11.5KV feeder line and the "pole pigs" serve two only houses, so I get extra "juice". The place in NC is pretty much spot-on at 120VAC, and with very "clean" power. Instead of 50 feet from the "pole pig", that lcation is about 600 feet back, with the heavy power cables going into and out of the transformer buried underground.

The OPTs are 8K CT, 20W, with UL taps at 43%, and 4 and 8 ohms (perhaps also 16, I'll have to recheck). I'd guess these could be pushed a lot harder for more power, if desired, as these trannies are seriously overbuilt.

All are toroidal, potted in some mysterious bright red material and shielded with a metal "can" on top, photos are posted elsewhere on this forum. The color code for the leads is very unconventional.

/ed B in NH