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Old 14th June 2007, 10:55 PM   #1
eeyore is offline eeyore  Australia
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Default Peter Millett's Uniamp with KT88

Just about to finish building the PCB version of Pete's Uniamp amp. I am currently selected some OPTX. Don't want to spend too much money, and came across these from Edcor CXPP60-8-6.6K 60 watt push-pull tube amplifier output transformer 6,600 ohms to 8 ohms. Anyone have opinions about the transformer/combination?

Finally, I am also trying to decide on a choke. There are cheap options for a 15H/100mA choke which seems nice, or a similar priced 3H/250mA choke. From simulations (PSU Designer) the average current through the choke is about 90mA, so I guess the 15H/100mA would be out. But would the 3H be too little? Or alternatively, are the suppliers out there with chokes in the 10H/150mA or higher range for around US$15. The other two chokes are at US$10 each.
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Old 14th June 2007, 11:02 PM   #2
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hey-Hey!!!,
The choke choice depends on what it is doing. In between two caps as the inductor in a Pi filter is a lot different from input service in an L-C filter.
cheers,
Douglas
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Old 14th June 2007, 11:10 PM   #3
eeyore is offline eeyore  Australia
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Hi, from the schematic, it does actually sit between two capacitor. The tube rectifier is followed directly by a capacitor, then the choke, and then it goes straight to the OPTX, then after that, there are about 4 more capacitors. So not sure it is function as a PI filter, given there isn't a capacitor between the choke and the OPTX. (See schematic on the site).

Reducing the value on the choke in PSU Designer seems to make the initial ripple peak less than having it a higher value.
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Old 20th June 2007, 06:55 PM   #4
wuffer is offline wuffer  Denmark
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how is the uniamp going???
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Old 20th June 2007, 11:27 PM   #5
eeyore is offline eeyore  Australia
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It's going alright thanks, just about to place the order for the output transformers, the Edcor CXPP60-8-6.6K . The chokes are going to be open frame Hammond's 159P 10H/125mA, and the power supply from DIY Club, which is a 380V-0-380V unit.

Will get around to posting the pictures some time (already taken some...)
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Old 22nd June 2007, 07:44 AM   #6
wuffer is offline wuffer  Denmark
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want to see pics

still looking around for the output transformers.. 2 pices of Edcor CXPP60-8-6.6K cost around 220 euro with shipment to denmark.. maybe there are some better choices...

sorry about the bad english
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Old 22nd June 2007, 07:46 PM   #7
Cobra2 is offline Cobra2  Norway
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I have built the boards too...
I found 2 irritating issues...the sockets mounts on the "underside", and there are no adjustable bias-circuit.
I still have not planned what trafos to use...

Arne K
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Old 24th June 2007, 10:40 PM   #8
eeyore is offline eeyore  Australia
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The Edcor are expensive once you add the postage, but any transformer will be, they are heavy... Have you tried Lundahl? LL1620 seems to be reasonably suitable? Perhaps they could do a custom one that would be cheaper overall? Just a thought...
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Old 28th June 2007, 10:28 AM   #9
eeyore is offline eeyore  Australia
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Here are some photos.

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Old 28th June 2007, 10:29 AM   #10
eeyore is offline eeyore  Australia
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I am still missing two resistors, and will have that soldered soon. The Output transformers and chokes have been ordered, and awaiting their arrival! Still looking for a good value power transformer. Anyone know of one that is suitable?
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