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Old 8th November 2009, 05:29 PM   #11
rmyauck is offline rmyauck  Canada
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Hi,

(4) ONLY ship USPS, and the most they will charge is a $5 brokers fee. A lot of times 0$. They will charge PST & GST especially over $100. Depends on which customs it comes through. Shipments from retail stores always taxed. Old tubes and electronic parts seem to be taxed especially if over $100. Maybe forms have to be filled out as antique parts. If possible ship First Class Mail International, a bit slower and no insurance, but can be many $ less. Priority Mail can be double in price. Go to USPS.com. I don't think may will steal old electronic parts as they will have trouble selling them. I have had small items shipped First class from many internet sellers and never had a problem. Most retail stores will only ship priority and lot of times insurance is still optional extra $. Lesser than years past only ship Fedex, UPS, Purolator etc. Heavy bulky items may only ship priority, and if so $ can be saved by using USPS shipping boxes, but size is limited to their different sized boxes. Can be less $ to ship heavy transformers individually this way, as heavy items are more likely to be dropped and damaged especially if they bang into each other or delicate items in the same box. Well packed items solves problem, but does not always happen because of time, costs & knowledge.

Good Luck!

Randy

Last edited by rmyauck; 8th November 2009 at 05:46 PM.
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Old 8th November 2009, 06:49 PM   #12
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#1) Any choke (within reason) is far better than no choke. The choke must be rated for at least 150 ma, 175 or more would be ideal. The DC resistance should ideally be 80 to 150 ohms, but anything from 40 to 250 ohms will work. The inductance should be 4 to 10 Henries, but I have used a 1 Hy choke, and it still worked better than using the resisitor.

#2) a film resistor is made by depoisting a thin film of resistive material on a ceramic substrate and then laser trimming the resulting resistor to the desired value. The resistive material can be a metal alloy (metal film) or a metal alloy that has been oxidized (metal oxide film).

The metal films are more conductive so less material is needed for a given resistance value. This makes them more suited for low power resistors, and they tend to exhibit lower noise and higher stability than a metal oxide film. The metal oxide film is uaually thicker and can often handle more power than a metal film resistor, but it will usually contribute more noise to a circuit than a metal film resistor, and be more prone to value change with a temperature change. These are broad generalizations and modern manufacturing mathods has blurred the lines between these types a bit.

I usually use metal film resistors for all of the small (1/4 watt and 1/2 watt) resistors and metal oxide films for the higher powered parts. There is another type, the wirewound resistor which is made from resistive wire. These are good for higher powered resistors and used for R1, R17 and R27.

3) The old IXYS parts work fine. The newer ones (made in the last 3 or 4 years) will fail in this circuit. The Fairchild Stealth Diode # ISL9R8120P2 will work just fine. The FRED diodes are only needed if you want to use a solid state rectifier, and may be omitted with a vacuum tube rectifier.
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Old 8th November 2009, 07:25 PM   #13
DougL is offline DougL  United States
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Quote:
Originally Posted by ciagon View Post
I have a couple beginner questions as well.

I just recently learned about motor run capacitors but I don't fully understand why people use them. They seem to be much larger and more expensive that electrolytics. Is there an advantage of using them (other than cool looks)?
Capacitors have several "secondary" parameters that may affect the performance in a particular circuit. Besides Capacitance and breakdown voltage, there is ESR (Effective Series Resistance), Inductance, Dielectric absorption, temperature, microphonics, to name a few.
Motor run capacitors are designed to have very low ESR, and when used as the last cap in the power supply can lower the power supply impedance. Its your job to decide where their advantages outweigh the cost and size penalties. Isn't DIY grand?

I see Tubelab beat me to it. To Obi Wan you listen.

HTH

Doug
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Old 8th November 2009, 10:14 PM   #14
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Quote:
Originally Posted by tubelab.com View Post
3) The old IXYS parts work fine. The newer ones (made in the last 3 or 4 years) will fail in this circuit. The Fairchild Stealth Diode # ISL9R8120P2 will work just fine. The FRED diodes are only needed if you want to use a solid state rectifier, and may be omitted with a vacuum tube rectifier.
Hi,
Would this work for the FRED?
Digi-Key - APT30DQ120KGMI-ND (Manufacturer - APT30DQ120KG)
I try to limit the number of distributor to limit the shipping/handling cost.



Thanks
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Old 8th November 2009, 10:59 PM   #15
hwong is offline hwong  Canada
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Just like nickolas812 “…I have absolutely no idea what i am doing. I just thought it would be fun to try and build a tube amp…” I am starting to build this amp also and this will be my first ever attempt to build an electronic device.

For now I have a couple of questions regarding parts. For sure I will have more questions as the build start.

I intend to build the amp using tube rectifier and will be using KT88. Currently I have a P-P integrated amp (purchased not build) using quad KT88 (EH) and I have spare (quad) OEM Chinese KT88 that came with the amp that I can use as guinea pig. I definitely wanted to try out the EL34 later with this amp. So

Parts that I have purchased so far:
PC board – Simple SE
Power transformer – Edcor XPWR035 (really big and heavy)
OPT – Edcor CXSE25-8-5K (really big and heavy)

I’ll be ordering the following:
Choke – Hammond 193H
Rectifier tube – 5AR4
Coupling cap – AuriCap

and the remaining BOM from the list on Tubelab site.

Where I am not sure:

1) Motor Run Cap – Is this the same as “Supplemental Capacitor” in Tubelab’s document? I have read in a thread about one (100uF 370 VAC ASC) For my setup, do I need 100uf? 370 or 440 VAC?

2) Inrush current limiter- can someone provide a diagram where they will go. I got the Digikey part # from another thread (KC009L-ND) but not sure where they will go.

3)KT88 turbo switch – also read from another thread of putting a “1k ohm” in parallel with the 560ohm (R17,R27) with a switch and turn it on for KT88 and off if using EL34. Are we talking 1k ohm 5W wirewound resistor same type like the 560? Any ideal what is the best way to hook them all up?

4)Semiconductor – (D1,D2,U10,U20) Do I still need them if I am using the tube rectifier?
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Old 8th November 2009, 11:32 PM   #16
DougL is offline DougL  United States
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Quote:
Originally Posted by spacemen12 View Post
Hi,
Would this work for the FRED?
Digi-Key - APT30DQ120KGMI-ND (Manufacturer - APT30DQ120KG)
I try to limit the number of distributor to limit the shipping/handling cost.
Thanks
1200V @ 30 Amp is very robust. Looking at the web page, it specifies 1200 PIV, and you have that right. While lower amperage parts may work fine and be less expensive, those should do it.

HTH

Doug
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Old 8th November 2009, 11:47 PM   #17
DougL is offline DougL  United States
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Quote:
Originally Posted by hwong View Post
Where I am not sure:

1) Motor Run Cap – Is this the same as “Supplemental Capacitor” in Tubelab’s document? I have read in a thread about one (100uF 370 VAC ASC) For my setup, do I need 100uf? 370 or 440 VAC?

2) Inrush current limiter- can someone provide a diagram where they will go. I got the Digikey part # from another thread (KC009L-ND) but not sure where they will go.

3)KT88 turbo switch – also read from another thread of putting a “1k ohm” in parallel with the 560ohm (R17,R27) with a switch and turn it on for KT88 and off if using EL34. Are we talking 1k ohm 5W wirewound resistor same type like the 560? Any ideal what is the best way to hook them all up?

4)Semiconductor – (D1,D2,U10,U20) Do I still need them if I am using the tube rectifier?
1 Yes. AC rated capacitors can be conservatively rated at 1.4 times their AC rating. 60 mF or more would great. If you can get the 80 mF or 100 mF, those would be ideal. If your power supply is going to be designed to be above 460V, get the 440V AC caps. If not the 370 are good to 516Vdcor more.

2. Put it between the fuse and the transformer primary.

3. Use solder? Sorry, couldn't resist. If it were mine I would do a little perf board with solder lugs. Cut the jumper for one, solder in the jumper for the other. And yes, use a 5 watt part.
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Old 9th November 2009, 01:19 AM   #18
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Quote:
Would this work for the FRED?
Digi-Key - APT30DQ120KGMI-ND (Manufacturer - APT30DQ120KG)

1200V @ 30 Amp is very robust. Looking at the web page, it specifies 1200 PIV, and you have that right.
The IXYS parts are rated for 1200 volts and 12 amps, yet they blow up. It turns out that the diodes can deal with the voltage and the current just fine. They blow when the amp is switched off! Why? The power transformer stores energy in its magnetic field which can be released as a brief spike when the power is shut off. This is the same principal that is used in an automotive ignition coil. This spike will blow a diode that is not rated to handle it. The APT diodes do have an avalanche rating of 20mJ which is the same as the Fairchild parts, but I have not personally used them.
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Old 9th November 2009, 03:51 AM   #19
DougL is offline DougL  United States
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Quote:
Originally Posted by tubelab.com View Post
The IXYS parts are rated for 1200 volts and 12 amps, yet they blow up. It turns out that the diodes can deal with the voltage and the current just fine. They blow when the amp is switched off! Why? The power transformer stores energy in its magnetic field which can be released as a brief spike when the power is shut off. This is the same principal that is used in an automotive ignition coil. This spike will blow a diode that is not rated to handle it. The APT diodes do have an avalanche rating of 20mJ which is the same as the Fairchild parts, but I have not personally used them.
Really! That makes sense. That's a good example of parts substitution is not trivial because the important parameters are not always obvious.

Best wishes to your family.

Doug
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Old 9th November 2009, 05:04 AM   #20
hwong is offline hwong  Canada
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Quote:
Originally Posted by DougL View Post
1 Yes. AC rated capacitors can be conservatively rated at 1.4 times their AC rating. 60 mF or more would great. If you can get the 80 mF or 100 mF, those would be ideal. If your power supply is going to be designed to be above 460V, get the 440V AC caps. If not the 370 are good to 516Vdcor more.

2. Put it between the fuse and the transformer primary.

3. Use solder? Sorry, couldn't resist. If it were mine I would do a little perf board with solder lugs. Cut the jumper for one, solder in the jumper for the other. And yes, use a 5 watt part.
Thanks Doug,

For the Inrush current limitor, I read in another thread, can't find it anymore, that there should be three, does that mean putting all before the trans primary?
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