Cheap power iron at the e-place (the ten pounders)

the thermionic watercooler

Postby burnedfingers » Fri Oct 22, 2010 2:34 pm

So these are a typical 70volt commercial speaker step down transformer?
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Postby EWBrown » Sat Oct 23, 2010 2:47 pm

I've used the SPECO 7010s in parallel feed applications (as does Bottlehead in their original entry level 2A3 based "Paramour" and 6DN7 based "SEX" amps, these work amazingly well for what was then a $4 transformer. It just happens that this particular brand and model of line matcher trannie is a lot better than most low cost line matchers.

FWIW, Radio Shark used to sell a very similar line matcher, I am not sure if they still carry that model or not.
Our 70 volt 10 watt line transformer has wattage taps. It has 10, 5, 2.5, 1.25, and 0.625 watt taps. It also offers color coded leads.


To figure out the equivalent primary impedance, just divide 5000 by the wattage "tap", for example, 0.625 W is 8K; 1.25W = 4K; 2.5W = 2K; etc.
These have both 4 and 8 ohm secondary taps. Where did I get 5000? That would be 70.7V squared, and Z = V^2 / P.

These trannies are not designed to be used as series feed OPTs, as the primary current ratings, and more importantly, the insulation between the windings is not rated for high voltage or direct current. They may be OK for a low voltage (150V or less) B+ applications, but it would be best to try out a "breadboard" prototype first, before committing the design to hard metal..

In parallel feed, the plate current is fed through a choke, and then the audio "AC" signal is capacitor coupled to the OPT's primary winding. This assures that no DC is present on the primary winding, and that no core saturation can occur. For 8K, 1uF is a good value, 4K, 2.2 uF is good, and for 2K, 4.7 uF.

These SPECOs work best in an "auto transformer" mode, in which the "cold end" (black wire) of the primary winding is connected to the secondary's 8 ohm lead, and the speaker output can be taken off either the 4 or 8 ohm output as required.

This "autoformer" connection improves the bass response, and reducees the internal losses to some degree. Bottlehead discovered this trick, I can't claim credit. As they say, " O:) imitation is the most sincere form of flattery"

I've used these SPECOs as 4K (1.25W) and 8K (0.625 watt) OPTs, with a 10H to 30H plate choke, with sufficient current capability for the power tube's requirements.

HTH

Update 29 Oct 2011:

SPECO has significantly changed (let's just call ir "cheapened") these line transformers, and unfortunately, they are no longer suitable for use as parallel-feed OPTs. THis has forced Bottlehead to re-design their 6DN7 based "SeX Amp" and to design new OPTs for them.


/ed B
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Postby EWBrown » Sat Oct 23, 2010 3:27 pm

I've progressively loaded the E-bay trannie with more and more wattage, using 120V bulbs connected in series, as I have "only" 160W worth of 230V bulbs (four 40 watters).

With two 100W, 120V bulbs connected in series, on the "red" secondary, and four 6AV5GAs on the "green" 6.3V filament winding, it barely gets warm after a couple hours' run time. So this is about 850 mA on the red secondary, the unloaded voltage is 235 VAC, and with 200 watts (850 mA) it drops to 228VAC. Translated to voltage doubler service, that is well in excess of 240 mA @ 600VDC, or with a fullwave bridge, 480 mA @ 300VDC. (using the multiplier factor of 3.6X for the doubler, or 1.8 for the FWB) This "7019" trannie is definitely a "beast" (666) (666) (666) and for $20, a real bargain. I have been working up an interesting "monster" PSE design that requires this kind of B+ voltage and, more importantly, current.

If I can dig up some more octal relay sockets - I have LOTS of these, just have to figure out which box they're hiding in - then I can go all-out ballz to the wall, heavy duty testing with all the windings being loaded. I'll take it easy on the "blue" 44VAC winding, as it isn't intended to generate much current, and its DC resistance reflects this.

/ed B
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Postby DeathRex » Sat Oct 23, 2010 5:30 pm

He's out of the 7019, but still has plenty of the 7018. Since the 7019 is good for 235 volts at 850ma, the 7018 with 170 volts is probably good for an amp. Might be able to use it as a tripler, quad, or more with plenty of current for those 845/GM70 amps.
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Postby EWBrown » Sat Oct 23, 2010 7:45 pm

The 7019s moved fast, and I bet most of them were bought by DIY-tubers here (lol) and at DIY Audio - they were mentioned there, and the original selling price started out at $15 each. =:o

I might go for a couple of the 170V 7018s, just to have them for future possibilities, at the cheap price, why not...

/ed B
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Postby burnedfingers » Sat Oct 23, 2010 8:35 pm

What would be a good project for the 7019 without a voltage doubler?.

Now that I have them I don't know what to do with them. (lol)
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Postby DeathRex » Sat Oct 23, 2010 8:43 pm

6C33C as an OTL. You can run 4 of them. Might need more filament power though.
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Postby EWBrown » Sun Oct 24, 2010 1:33 pm

What would be a good project for the 7019 without a voltage doubler?.


Anything that needs a B+ voltage between 300 and 320VDC, the more the current consumption, the lower the voltage (using a four diode full wave bridge. Might be good for a bunch of 6V6GTs or their TV vertical sweep derivitaves, like 6JB5, 6JC5, 6HE5, or 6MF8, 6LR8, 6LU8) the latter 3 tubes ending in "8" have a triode and a pentode, much like a beefier version of a 6BM8. This trannie coupd easily handle a PPP stereo configuration, with 4 pentodes per channel.

If you are into tube rectification, then use a 5U4GB, 5AR4, and then use two SS rectifiers for the negative half of the bridge. THis will deliver somewhat lower B+ (275-300V) but it allows for the nice slow and gentle tube-rectifier warmup. Though the maximum current will be limited by the rectifier tube's capability, and any of the 5V rectifiers will require an extra 5V 3A filament trannie, or you could use 6V TV damper diodes, on those two "extra" 6.3VAC filament windings, along with two SS rectifiers.

/ed B
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Postby burnedfingers » Sun Nov 07, 2010 1:35 pm

What about putting the two transformers I bought in series? Wouldn't putting the two secondaries in series give me 470 VAC? @ 850 mA?
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Postby EWBrown » Tue Nov 09, 2010 5:08 pm

What about putting the two transformers I bought in series? Wouldn't putting the two secondaries in series give me 470 VAC? @ 850 mA?


That would be a serious "overkill" and may also exceed the insulation voltage ratings between the windings. These are designed to be used with voltage doubler or FWB rectifiers, and connecting two of these in series as voltage doublers may have some truly unexpected and undesirable consequences.

If you want the 600VDC B+ just use the voltage doubler PSU design, with 1N5408 or higher-current rectifiers..

If you REALLY need the huge amount of current (850 mA) then it should be possible to connect the HV secondaries in parallel, or use two transformers and separate voltage doubler circuits, and then use one for each channel ( as in dual monoblock)

The (perennially in process) "Herniator" amp design was based on this concept , with two separate "main" PSU transformers (one for each power channel), plus a third smaller one for the VA and LTPI stages, and with two chokes for each PSU. Add in two OPTs, and that amounts to eleven pieces of heavy iron =:o [:) And then add in a total of nine tubes, it's gonna be a BEASTATRON =:o Just think of two MKIII bolted together :/

When a transformer or other electrical device is "hi-potted" for product safety testing (at 1500VAC or 2121 VDC) , the main concern is the separation / isolation of the primary (line) from the secondary (load) cirrcuitry, and the insulation ratings between the various secondary windings are not usually a consideration with this particular method of testing..

/ed B
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Postby burnedfingers » Mon Jul 04, 2011 7:08 am

Just got around to testing the transformer this morning. I got 313VDC output from a bridge rectifier. I am hunting up some capacitors at the moment to make a voltage doubler and see what I get for output. Does this transformer have enough grunt to run with a doubler and run a Stereo 70? Naturally resistor values would have to be changed to obtain workable B+ in the range needed.

My input voltage was 119 AC.
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Postby burnedfingers » Mon Jul 04, 2011 9:03 am

How do I do a voltage doubler using tube rectifiers? I have searched but cannot seem to find a schematic for it.
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tube doubler

Postby msmpe » Mon Jul 04, 2011 9:29 am

I think you need to use 2 halfwave rectifiers.
8>) Mike

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Postby DeathRex » Mon Jul 04, 2011 12:48 pm

Yep you need 2 rectifiers. If you look at voltage doublers on wiki, on the Greinacher circuit, the first diode going from the capacitor to the bottom of the secondary can be a 1N4007. The other diode would be a tube for slow warm up, but all the current will be going through it, so it's got to be a hefty rectifier, 6CE3, 6CG3, 6CE3 or GZ34 with the plates tied together.

A 6BY5 has 2 independant rectifiers, but probably not quite powerful enough.
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Postby burnedfingers » Sat Oct 01, 2011 12:58 pm

quote:
THIS AUCTION IS FOR A NEW OLD STOCK TRANSFORMER FOR A TUBE POWER-AMP. PROJECT. IT HAS A COPPER FLUX SHORTING BAND. DUAL PRIMARY. IT'S SECONDARY VOLTAGES ARE, RED to RED 235v NO CENTER TAP---BLUE to BLUE 44v --- GREEN to GREEN 6.8v with C.T.and THICKER WIRE ---YELLOW to YELLOW 6.8v ---ORANGE to ORANGE 6.8v. ALL VOLT VALUES UNLOADED. Not knowing the specs on this transformer. I proceeded as follows.

I loaded the secondary red winding to 200 ma. and filament green winding to 6 A. The voltages are now 607 VDC and 6.3 VAC., for 8 hours to check for temperature rise. I did not load the YELLOW or ORANGE winding thinking they are for tube rectifier filaments which probably no one will use, and BLUE is only for negative bias. I had a 35 degree C rise in primary temperature..DIMENSIONS ARE 3 1/2 x 4 7/8 x 4 1/4 HIGH


Do you think this transformer has enough power with a voltage doubler to use as a power transformer on a clone dynaco 70? I realize I would have to have a voltage dropping resistor in order to get the B+ down to the level that I want. The dynaco choke is only rated at 200mA. I figure worst case it would draw 220mA? I think the stock Dynaco stereo 70 is only about 250mA output .

Also I made a voltage doubler for the bias supply. At aprox -130 that would be too high but if I used the half voltage that would be available it would work I think.
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