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Old 4th January 2011, 03:59 AM   #31
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Originally Posted by platplaas View Post
I can't seem to find transformers with the double 6.3v.
You should be able to parallel all three signal tubes (12AT7 and two 6BQ5) off a single 6.3 volt winding. The only time you really need separate filament windings is when you are using directly heated tubes.
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Old 4th January 2011, 04:23 AM   #32
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Thanks. Out of curiosity - does anyone have suggestions for how to order the power transformer such that it could be useful for future projects down the road? I'm wondering whether to oversize etc?
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Old 4th January 2011, 04:05 PM   #33
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Originally Posted by platplaas View Post
Thanks. Out of curiosity - does anyone have suggestions for how to order the power transformer such that it could be useful for future projects down the road? I'm wondering whether to oversize etc?

If you do a decent job building it, you could probably sell your RH84 (down the road). That could generate the $$ for the next bunch of parts.....

Your parts box will tend to increase in size with time as well - dumpster diving and scanning CL for old hifi gear, will build up your collection of power transformers.
So my advice would be to get what you need for the RH84 and let the next project fend for itself, for now.

John
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Old 5th January 2011, 08:04 PM   #34
Trout is offline Trout  United States
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Originally Posted by platplaas View Post
Now that I have the choke and output transformers settled....

I'm a little puzzled about the power transformer. The schematic calls for 600v (300-0-300) plus 6.3v x 2 for the filaments plus 5v for the rectifier circuit.

I can't seem to find transformers with the double 6.3v. I did find one at Edcor but it also has a 25v and goes for a fairly steep price: EDCOR Electronics Corporation. XPWR167-120

Hammond has the 372jx but the Hammond site seems to indicate that it only has a single 6.3v (vs Parts Connexion which seems to be worded such that it might be a double 6.3v)

If anyone can shed light on this it would be appreciated. I am a bit puzzled by the transformers because a lot of people talk about using old iron...but if it is so hard to find the right specs in even new iron then I'm not sure how they make old iron work?
You might look into this budget outfit for a transformer. I have used a couple of these for this exact amp and they work perfectly, Bonus, dual 6.3V taps
TUBE PWR XFMRS - Musical Power Supplies Inc.- Quality Tube Amplifier Parts You CAN Afford


Part number PT325.2
Click the image to open in full size.

Last edited by Trout; 5th January 2011 at 08:08 PM.
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Old 7th January 2011, 05:52 AM   #35
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Originally Posted by platplaas View Post
I am a bit puzzled by the transformers because a lot of people talk about using old iron...but if it is so hard to find the right specs in even new iron then I'm not sure how they make old iron work?
Sometimes you have to be a bit creative with the rectifier section to get the right B+....all part of the challenge.
For small amps usually old iron will provide enough amps on the 6.3v heater winding. It helps if you know what the power transformer was driving in its 'previous life'.

John
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Old 7th January 2011, 05:56 AM   #36
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Originally Posted by Trout View Post
You might look into this budget outfit for a transformer. I have used a couple of these for this exact amp and they work perfectly, Bonus, dual 6.3V taps
TUBE PWR XFMRS - Musical Power Supplies Inc.- Quality Tube Amplifier Parts You CAN Afford
I've dealt with MusicalPowerSupplies in the past. It would probably be a good idea to drop him an email to confirm stock on hand. (Sometimes he has stuff that isn't listed on the website as well. He was trying out some 'HiFi' ideas 1-2yrs ago.)

John
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Old 7th January 2011, 09:11 AM   #37
Doz is offline Doz  United Kingdom
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You can always place a capacitor across the choke to resonate it. This will improve the ripple on the DC.

There's some info here: Inductors and Capacitors Together

Take your AC frequency and multiple by 2 if using full wave or bridge rectification, then work out the value of C. Pick the nearest preferred value and place in in parallel with the choke (don't use an electrolytic!). I always get three caps, one nearest the calculated value and one either side, then pick the best! Most chokes lose a little inductance when passing current.
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Old 28th February 2011, 05:01 AM   #38
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The amp is built!

Sounds great - but I have a question. The edcor gxse transformers have a 40% tap for ultra- linear. Can I disconnect the screen resistor and use the ultra-linear tap instead? Or does the amp need more substantial modifovations?

Last edited by platplaas; 28th February 2011 at 05:02 AM. Reason: Typo
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Old 28th February 2011, 02:26 PM   #39
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Can I disconnect the screen resistor and use the ultra-linear tap instead?
Absolutely. I would suggest keeping a small resistor in series between the screen and the UL tap. Something about 100 ohms, 1/2 watt should suffice. It helps protect the screens during startup while the power supply stabilizes.

With the UL connection, you will get less power out of the amplifier.
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Old 28th February 2011, 04:27 PM   #40
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Great - I'm going to give ultralinear a try. What to expect for sound differences?
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