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Old 16th August 2010, 11:10 PM   #1
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Default Any thoughts on this transformer on eBay?

Greetings everyone,
Does anyone have any thoughts on this transformer on eBay? I know Edcor has one will similar specs and price.

160/200 watt Tube Output Transformer for 6550 EL34 etc. - eBay (item 110268290224 end time Aug-25-10 12:19:54 PDT)

Thanks,
Ray
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Old 16th August 2010, 11:18 PM   #2
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Hi Ray;

This one is rated for 160W for bass guitar, from 40 Hz to 15 KHz. I suspect it is made almost the same way that Schumaucher guitar transformers I have, i.e. like plain electric transformers.

Edcor transformers are specified from 20 Hz, and they are interleaved, so they are specified for 20 KHz.
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Old 16th August 2010, 11:43 PM   #3
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So am I correct in saying the Edcor is a better choice quality wise?
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Old 17th August 2010, 12:21 AM   #4
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Yes
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Old 17th August 2010, 12:40 AM   #5
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Quote:
I suspect it is made almost the same way that Schumaucher guitar transformers I have, i.e. like plain electric transformers.
I have a bunch of Schumaker "guitar amp" OPT's that are rated for "80VA from 80 Hz to 4 KHz". I also have a Schumaker automotive battery charger(14 volt 6 amp) that I bought in the early 80's. The transformers look identical.

I dissected one of the OPT's. There is zero interleaving. I bought them to make guitar amps and have built several. About 8 years ago I stuck one in a HiFi amp just to see what happens. I was amazed. I now have them in my Simple P-P's, my 300Beast, the red board and just about everywhere else that they will work. So, the bigger ones may be OK, or they may not. Someone will have to try them. We KNOW the Edcors will work.
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Old 17th August 2010, 01:01 AM   #6
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I use a pair of such Schumakers in a hi-fi amp, 40W per channel from a quad of 6L6. Sounds really nice, but I drive them by low impedance of slightly loaded tubes. I paid $50 per pair, local pickup.
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Old 17th August 2010, 04:08 AM   #7
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I got a couple of the transformers in question on E-pay recently. They are certainly impressive chunks of iron and copper for the price I paid. As is my custom, I threw one (actually placed it gently, as there's enough mass to dent any bench) on the bench and gave it my usual test with a 300Hz, 50V signal P-P (with a DVM on the secondary winding I'm assuming to be the 8 ohm tap) to measure turns ratio and primary inductance.

The transformers I have in house measured out at 7k:8 plate-plate to secondary. Since the spec as shown on Ebay is very elastic with respect to the secondary impedance that can be encountered, it meets the spec. NWIH is it 5k:8. This means that if you insist on an 8 ohm load, you're going to need high plate voltages (~700V) to extract really high output power from this transformer.

I have no idea about the internal construction, but some good news is that it appears that the primary inductance P-P is very high (660H, P-P, @100V, 300Hz). I had to crank the primary excitation up to 100V from 50V to get measurable primary excitation current. This means that it's likely you'll get some good bass extension out of this transformer. Since I have no idea about the internal construction (and no, I didn't test leakage) high frequency response is anyone's guess.

Moral of the story? If you're lucky, you get what you pay for. If you're expecting a Bartolucci/Electra-Print/Hashimoto/Tango, etc. for < $100 each, well, you're going to be disappointed. Otherwise, this is a good chunk of iron to have around if you're experimenting with high power sweep-tube based amplifiers. I may use this monster as a basis for options hinted at in a private e-mail from KYW that involve using a big chunk of iron in conjunction with a smaller HF transformer to cover the entire audio spectrum.
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Old 17th August 2010, 03:26 PM   #8
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You can figure out most of the typical data from the datasheet figures they gave.

Leakage L to 8 Ohm winding: 235 Ohm at 800 Hz or 2350 Ohm at 8000 Hz or 4700 Ohm at 16000 Hz. 3dB point would be when it reaches 5000 Ohm. Looks like the 3 dB point is about 16.12 KHz. Usually the 1 db drop off points are given for the bottom and top end spec. But the data specifies 40 Hz to 15 KHz for 2 dB.

From these data you can figure the leakage L from XL = 2*pi*f*Leak or: Leak = 235/(2*pi*800)

Primary LP from 630K Ohm at 800 Hz:
LP = 630,000/(2*pi*800)

The primary L would still be 6.3 K Ohm at 8 Hz, so thats not whats limiting the low end to 40 Hz. So Volts/turn is the limiting factor (ie, magnetizing current at saturation) From core tongue area 2.25 x 1.5 inch you should be able to calculate the actual number of turns (approximately) to get likely 17 Kilogauss (Guitar amp or power xfmr spec) at 40 Hz and the max AC voltage spec. for 160 Watts. For Hi-Fi the max Gauss is usually spec'd more like 10 Kilogauss, so min. freq. would be more like 70 Hz) Super Hi-Fi at 8 KiloG then at 80 Hz. Operating down to 40 Hz at full power will give you some bad magnetizing current distortion (a plus for guitar). Dropping the power spec though will allow Hi-Fi operation to the lower freqs. Vmaxrms = Sqrt (R* Watts) ...... (R is impedance).

Turns ratio (Primary to 8? Ohm) from Sqrt(630,000/650)
Turns ratio (Primary to 4? Ohm) from Sqrt(630,000/350)
or Turns ratio (8? to 4? Ohm) from Sqrt(650/350)
or just the impedance ratio (8? to 4?) from 650/350
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Last edited by smoking-amp; 17th August 2010 at 03:51 PM.
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Old 17th August 2010, 05:36 PM   #9
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This is all assuming that the really did the transformer that way - the spec is really loose as a goose. I suppose I could drag the transformer back into work and nail it with 300VAC (the max capability of my sine wave source) with some load, start cranking down the frequency, and see where the excitation current starts to take off.
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Old 18th August 2010, 08:54 AM   #10
Ian444 is offline Ian444  Australia
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I bought one of those trannies too, very large it is. I'm glad the Zp seems to be closer to 7K than 5K as I'm hoping to use 2 x GU50 tubes PP, hopefully with near 700V B+. But it could be possible, I was thinking, to fit 4 x GU50 sockets, and for PPP (4 tubes) I could double the load on the OPT, i.e. connect two speaker cabinets instead of one, or whatever it takes to double the load (4 ohm cabinet connected to OPT 8 ohm tap). I hope the "10lb of iron power tranny" with voltage doubler can supply the necessary power.

According to the Fender PA schematic that used this OPT, a 2.6 ohm load is required for 160W output with the special (Fender P/N 010309) 6550 tubes. Just thought I'd throw that in, if it helps any.

Last edited by Ian444; 18th August 2010 at 08:58 AM.
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