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PostPosted: 26 Mar 2012, 20:43 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, Thanks Paul for the assist. It has been told to me many times that in the US we have an easier time getting parts from Europe than folks that live there. Economics 101 at work in a twisted way. Often cheaper as well...go figure.

Good listening
Bruce

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PostPosted: 27 Mar 2012, 04:33 
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Joined: 16 Mar 2012, 11:15
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Location: UK
Paul and Bruce. Massive thanks for the advice. I'll order the caps now then I'm ready to start building. After seeing Paul's point to point wiring I'm sure I can manage that and negate the need for veroboard. I've seen a few people stating that veroboard isn't a good idea anyway as it increases the amount of connections is the system.

Huge thanks for the Maplins numbers and for the image of the underside of your amp Paul. That's helped massively.

I'll be taking images along the way of the various stages of the build so I'll keep you posted.


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PostPosted: 08 Apr 2012, 13:01 
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Joined: 16 Mar 2012, 11:15
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Location: UK
A quick question for anyone who may be able to answer. The power switch I'm using has an inbuild LED ring which runs off 12V DC.

This kind of thing:

Image

Is it possible to run this off the 12V line for the valve heaters as this is only source of 12V DC. Or will this destroy the valves as they have to be a floating circuit?


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PostPosted: 08 Apr 2012, 20:52 
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Location: Arizona, USA
Hi, Normally this is OK. I use some similar in the Oddwatt Kits.

Good listening
Bruce

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PostPosted: 09 Apr 2012, 04:03 
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Location: UK
Cool, cheers Bruce. I didn't want to cause any issues with the valve heaters for the sake of a £5 switch. I did consider using an extra bridge rectifier to run the LED's from but if it's not necessary I won't bother.


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PostPosted: 28 May 2012, 07:51 
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Joined: 23 Apr 2012, 14:17
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Hey Bruce & Fellow Builders

The names Mark and im from the UK.

I'm new to tube amp construction, but i have an electronics background in college and the occasional tinkering on the simple stuff however i work in IT now so im a bit rusty. Im pretty confident on the construction and safety aspects for building an amp but there are a few things im unclear on.

I'd like to build this design from scratch, mostly because my account manager (wife) would rather i didn't spend a large amount in one go on a kit... but also because i have some asthetic design ideas id like to implement whilst im building it.

so questions..

1. the heaters must not be grounded.. this means that the heater power supply output must not be connected to or come into contact with the chassis or any other circuit right ? where the negative of a DC circuit might normally be connected to chassis.

2. signal ground. is / can this be chassis ?

3. do the tubes have to be arranged as laid out in the photo's for reasons such as interferrence etc, i was hoping to do a triangular format, the 2 EL84's at the back and the 5751 front center for each channel. I notice in the photo's a thick copper wire joining the centre pins on the valve bases is that connected to anything else and could you explain what it does?

4. i've seen tubes working on old equipment but i've never really known just how hot they get, i wanted to paint my case and i was hoping to use some clear 4 - 6 mm acrylic etched decoration on my case under the actual valves, are they hot enough to melt this ?

5. I'll have to order the transformers from edcor direct Bruce you mentioned that a 180-0v transformer (cheaper :) ) could be used for this project with a full wave rectifier.. im pretty sure i know what this means but could you tell me exactly how this would work so i can be definate?

Any help would be massivly appreciated. i hope to have this running quite soon.

Many Thanks in Advance

Mark


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PostPosted: 28 May 2012, 08:42 
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Joined: 25 Oct 2011, 17:46
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Not meaning to tread on Bruce's toes, but as I'm surfing the forum right now...
maxpdaddy wrote:
1. the heaters must not be grounded.. this means that the heater power supply output must not be connected to or come into contact with the chassis or any other circuit right ? where the negative of a DC circuit might normally be connected to chassis.

Correct

maxpdaddy wrote:
2. signal ground. is / can this be chassis ?

Yes

maxpdaddy wrote:
3. do the tubes have to be arranged as laid out in the photo's for reasons such as interferrence etc, i was hoping to do a triangular format, the 2 EL84's at the back and the 5751 front center for each channel.

Triangular is fine. i built mine triangular.

maxpdaddy wrote:
I notice in the photo's a thick copper wire joining the centre pins on the valve bases is that connected to anything else and could you explain what it does?

Ground bus bar. Everything that needs to attach to the ground goes to this bar. It's a common grounding system. You don't have to use it... it's just an option.

maxpdaddy wrote:
4. i've seen tubes working on old equipment but i've never really known just how hot they get, i wanted to paint my case and i was hoping to use some clear 4 - 6 mm acrylic etched decoration on my case under the actual valves, are they hot enough to melt this ?

Under it should be fine. They get hot but heat rises... it might warp it or make it go cloudy after prolonged use.

maxpdaddy wrote:
5. I'll have to order the transformers from edcor direct Bruce you mentioned that a 180-0v transformer (cheaper :) ) could be used for this project with a full wave rectifier.. im pretty sure i know what this means but could you tell me exactly how this would work so i can be definate?

See the attached file for details. The schematic on the left is for a 180-0-180 PT and the one on the right is for 180-0

All the best,
Paul


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PostPosted: 28 May 2012, 10:52 
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Joined: 23 Apr 2012, 14:17
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Thanks Paul,

Im sure Bruce will have many other questions to answer shortly, as i said im very rusty :D ... I've just ordered the transformers from edcor, that made my credit card sting a little !! and im dreading the customs charges.

I was wondering what sort of rectifier i should use in the tube supply with the single type transformer, i've found up one that is rated at 200v 10A but the RMS is 140.. this is where i get confused. Im possibly even way off the mark here.

Regards

Mark


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PostPosted: 28 May 2012, 11:26 
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Location: Arizona, USA
Hi, Welcome to the forum. Thanks Paul for answering some of the questions. In one area I differ with your answer. I do not recommend connecting the signal and power supply ground directly to the chassis. This will in many cases cause a ground loop and hum. They used to do that in the old days ...but then way back not many systems could really reproduce 60HZ all that well. I always use a type X2 (designed for use in AC applications) capacitor in the range of 0.1uf to 0.22uf with a parallel fixed resistor in the range of 120 to 150 ohms (neither is all that critical - lower value capacitors with higher value resistors for lower powered equipment and the opposite for higher power units that tend to have more leakage currents). These components go between the signal/buss ground to the chassis. The chassis can then also be connected to the AC mains earth ground directly. Using this arrangement has proved to keep ground loops from forming between the signal circuitry and what ever you have attached to it. I find that one of the worst and hardest to find loops can be formed between two pieces of equipment that have the chassis used as circuitry grounds. Difficult to fix as well. I also highly recommend an input line filter on any audio gear.

I do recommend the use of a ground buss. It can be a simple piece of bare copper 12 gauge wire.

For rectifiers I like to use UF4007. They are generally rather inexpensive and work as well as any other type of fast rectifier I have used. Do not use the much slower 1n400X series. They will put noise into the power supply that will need to be filtered out.

The tubes will run rather warm, but your stuff will probably be OK.

Nearly any arrangement of the tubes is fine. Just try to place the 5751 away from the power transformer so it won't pick up hum directly from it. Keep the output transformers at right angles to the power transformer with at least and inch of separation. Allow for ventilation around the rectifiers, especially the ones in the heater circuit as they will have to dissipate some heat. You can use AC on the heaters instead of the DC as shown in the schematics. I have found that after much testing the difference is minimal in hum and noise. This is because of the elevated heater potential from the dc reference circuit. It raises the heaters about 65-80 volts above the signal ground and reduces the hum and noise by a significant margin. The newest commercial Poddwatt kits will use AC on the heaters because of this. I would personally use the AC heaters. Remember though that no part of the heater circuit can be attached to any ground. If you use AC on the heaters all the rectifiers, and filter caps can be eliminated. You do need to keep the small (.1uf) caps across the individual heaters as this filters out noise.

Good listening
Bruce

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PostPosted: 04 Jun 2012, 15:20 
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Joined: 05 Nov 2010, 21:07
Posts: 702
Location: South East US - Tennessee
Hey Bruce!
I was wondering if you've ever tried a 12AT7 in the PoddWatt in pace of the 5751?
I've added the PoddWatt to my "bucket list". I plan on using a GPX10-8-10k instead of the 10-6-10k.

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We cannot solve our problems with the same thinking we used when we created them. - Albert Einstien
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