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# DIY Audio Projects Forum

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 Posted: 05 Feb 2017, 07:29

Joined: 05 Aug 2016, 14:35
Posts: 227
Suncalc wrote:
Ah... no. The math is correct. Please note:
Suncalc wrote:
(these are 3dB higher due to having two channels)
Two channels doubles the acoustic energy into the space and hence adds 3 dB.

The two speakers would have to be very nearly exactly two meters apart, and focused on a single location for this summation to be accurate. In a world designed around a 'sweet spot' - this may be a reasonable result.

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 Posted: 07 Feb 2017, 17:24

Joined: 29 Jan 2017, 17:55
Posts: 10
Hi guys! I had some rough couple of days at work so couldn't check the forums.
And can see (to my delight) that a lot happened

So, to clarify.
- when deciding on power I'm not concerned about volume. I don't think I've ever exceeded 100 dB and I don't think I ever will. I guess I'm usually within ~70-90 dB.
I just want to have enough headroom for my speakers to play safe and clean up to let's say max of 110 dB (probably never)

- from what I understood neither too low nor too high power is good for speakers.
Since, as Peter mentioned, difference lies in choice/price/size of components and not complexity of design I'll stick to 50W plan for now.
If it means that tubes will be "BIG" it's even better, I want end result to look majestic AF

- Gofar, I don't know why You assumed that I'm unhappy with my current setup. As I said in OP it's just the opposite - I like it very much and don't want to improve anything.
I just want to try and learn something new/different and scratch-building such beautiful item as tube amp is my way to go

- also final cost is not a big concern, experience I'm hoping to get in this project is priceless

- Peter, thanks for bench tools suggestions. For starters I managed to get from a friend some (nearly unused) equipment - EXTECH MN15 multimeter, some prototyping breadboards with handful of wires
and 30v regulated DC power source. Now a question about that power source. We are talking of ~500V in tubes, so is it of any use? I mean I know DC can be changed into AC
and voltage can be lowered and increased but will that be practical?

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 Posted: 08 Feb 2017, 07:41

Joined: 05 Aug 2016, 14:35
Posts: 227
- Peter, thanks for bench tools suggestions. For starters I managed to get from a friend some (nearly unused) equipment - EXTECH MN15 multimeter, some prototyping breadboards with handful of wires
and 30v regulated DC power source. Now a question about that power source. We are talking of ~500V in tubes, so is it of any use? I mean I know DC can be changed into AC
and voltage can be lowered and increased but will that be practical?[/quote]

The meter is a good start, probably all you need along those lines for now.
The bench power-supply is not going to be very useful. You will not be prototyping solid-state designs, nor is 30V a particularly useful voltage in tube designs. But that does not mean it should be deleted - just put aside for now. As an aside, one of the things you will discover quickly is that bench real-estate becomes precious quickly.

For my recent birthday, my wife gave me this device:

https://www.amazon.com/dp/B00GIKVP5K/re ... +hand+tool Don't ask me how she knew - but it will be incredibly useful. The alligator clamps are strong and the arms steady and go where they are told. A very useful tool for soldering fine items. I keep a Luxo magnifier light, so between the two and reasonably steady hands, I can do some very fine (small size) soldering work. Those two things together are great bench additions.

And, relating to light, I have a total of four articulating lights over the bench, including the Luxo. Meaning I can get shadowless light and light from many angles including UP from below. Light is good.

Prototyping boards will _always_ be useful. Think of them as you would yellow-trace if you are designing on paper, or shims doing cabinet work. 100% expendable proof-of-concept devices not to be saved when used up.

https://www.youtube.com/playlist?list=P ... yV5FIKdtOK In the little-steps-for-little feet department, these you-tube videos will walk you through many of the concepts used in tube amp design, how things go together, how one choice affects another - very useful stuff that will allow you to understand what you are doing as it relates to your final goal.

Above all, enjoy!

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 Posted: 09 Feb 2017, 06:43

Joined: 29 Jan 2017, 17:55
Posts: 10
Thanks for all great advice again! And that YT channel!
- What should I use to safe-power-test my designs if I don't want to invest into variac yet?
Is that "Bulb" current limiter device good enough?
- Are there any substantial differences between audio amps and guitar amps I should be concerned about?

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 Posted: 09 Feb 2017, 09:46

Joined: 05 Aug 2016, 14:35
Posts: 227

Mikuda wrote:
Thanks for all great advice again! And that YT channel!

The You Tube channel is useful to get a basic idea as to how things go, and how individual steps relate to each other.

- What should I use to safe-power-test my designs if I don't want to invest into variac yet?

The Variac is of far less import than an *ISOLATION TRANSFORMER* as it applies to your personal safety. I cut my teeth on AA5 radios (transformerless radios made from about the late 1930s through the 1960s), so I have always been aware of these things. You will need at least 300 watts, 500 watts (secondary) is better. Getting hit with 500 volts ac or dc is no fun at all - and if you look at a healthy, adult male over 150 pounds (68 kg) as being a 1/4-watt, 10,000 ohm resistor, you will see the point of a device that will protect you against many forms of shock. Not from stupidity or deliberately inserting yourself into the circuit. But many problems.

Is that "Bulb" current limiter device good enough?

Dim-bulb testers are for the protection of the item being tested, not for the protection of the user. Nor are they much more than crude indicators of the actual state of any item. They will NOT help you against shocks.

- Are there any substantial differences between audio amps and guitar amps I should be concerned about?

Other than the probability that an instrument amp is often an instrument in itself, and an audio amp purports not to be, no. Both use the same general means to the same general end.

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 Posted: 10 Feb 2017, 16:25

Joined: 29 Jan 2017, 17:55
Posts: 10
About that isolation transformer, I found such device schematic, is it what You are talking about?
(I guess it's "two in one" with integrated bulb tester).
Oh I forgot to point out that I'm in Europe, so 230V here.

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 Posted: 10 Feb 2017, 16:42

Joined: 05 Aug 2016, 14:35
Posts: 227
That schematic is a reasonably accurate representation of an isolation transformer with a few more bells and whistles attached.

Simple is good. If you an afford it, look for a unit large enough for what you are working on today, and are likely to be working on tomorrow. Writing for myself, I WOULD NOT be incorporating such a device with other stuff. Such stuff should stand alone so as not to become incorporated into any test inadvertently. I would also suggest using fuses rather than breakers *because* changing a fuse involves cost and a sequence of deliberate actions such that there is an opportunity for some thought before power is restored. Flipping a breaker is far to casual an action under these conditions.

Yeah - 240VAC, hot-to-ground. OUCH!

Enjoy! I will stop sending you links to exclusively US/North-American devices such as the Heath. But, if you can find a Euro equivalent, go for it. I find it immensely convenient to be able to control voltages in tiny increments and watch amps in equally tiny increments.

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 Posted: 21 Feb 2017, 17:18

Joined: 29 Jan 2017, 17:55
Posts: 10
Hello again! (I'm still not electrocuted!) Meanwhile I'm reading and watching and learning a lot of stuff and I feel I'm getting into it more and more.
I have two more questions about workbench:
1. I have some spare cash, opportunity and will to buy used oscilloscope (it's my dream since physics experiments at school when I was 13 anyway) I don't think I need anything fancy, but I'd like it to be suitable for my tube amp project. They have a lot of parameters I have no idea how to interpret, but since tubes run at ~400V I thought input voltage is one of parameters to look at. OR am I wrong and ~400V input is not necessary? Anyway here are 3 models I'm currently considering (and are within my reach):

VOLTCRAFT VC 630-2 This one is almost like new ~160\$

2 channels
300V input

SCHLUMBERGER 5228 ~250\$ - looks cool, has 3 channels but I'm confused about input voltages
3 channels
1 Mohm input 250V DC or 500V AC
50 ohm input 5V DC
more parameters in manual: http://bee.mif.pg.gda.pl/ciasteczkowypo ... UAL%20(eng).pdf

HP 54600B - ~160\$ Digital control and highest voltage input but I've read they are not good, difficult to use and not that accurate.
2 channels
500V input

Is any of them good? What would be Your advice? Any other suggestions up to ~300\$? What parameters should I look at?

2. About safety devices. We are talking about two: isolation transformer for my safety and bulb dimmer for equipment safety. Diagram I posted above is some sort of hybrid of them and I agree about simplicity. BUT If I build these two devices separately - Can they be used together or do they mutually exclude?
If only one can be used, I'm obviously choosing isolation option, but If I can use both, is there any particular order they should be connected? Like: "wall socket - isolation - dimmer - amplifier" or the other way around?

Lastly, please look at these sites. Some local stores selling tube amp parts. What do You think of their offer? Can I stick to them as suppliers?
http://www.ogonowski.eu/transformers/power/ - amplifier dedicated transformers
http://sklep.lampyelektronowe.pl/?lampy-mocy,33 - no English version but symbols and company names should by obvious for You. Selling tubes, capacitors, transformers, knobs, sockets and a bunch of other stuff also amp dedicated.

Thanks in advance for any replies!

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 Posted: 21 Feb 2017, 20:02

Joined: 05 Aug 2016, 14:35
Posts: 227
Tektronix, Fluke, Hewlett Packard in that order. Accept no substitutes.

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 Posted: 22 Feb 2017, 07:15

Joined: 29 Jan 2017, 17:55
Posts: 10
So, in short will HP 54600B be good for me? Despite its drawbacks? Was I right about input voltage concerns?
(Tektronix and Fluke are out of my range - found a few in reasonable price but in unknown condition)

Small update, how about one these two Tektronix:
https://www.olx.pl/oferta/oscyloskop-te ... 809443a447
https://www.olx.pl/oferta/oscyloskop-cy ... 809443a447

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