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Oddwatt Push Pull Tube Amplifier Projects
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Author:  Trackhappy [ 29 Apr 2018, 03:34 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

The journey begins...

Attachment:
ValveAamp1.jpg


Got a lot more done this weekend than I thought. In the middle ground I plan to have a couple of vertical metal plates with the 317 heatsinks attached.I figure keep all the hot stuff upstairs, and the walls might help shield magnetism from the OPT's. Pre-amp valves middle foreground. I was going to mount the OPT's at 45 degrees, but my internal design consultant said no.. ;) I like the idea of 6550's as outputs, but a 500mA transformer might not handle it. I will use AC heaters for outputs, but regulated DC for the pre-amps an regulated B+ for the pre-amps also. The main B+ will be duplicated from the diodes onwards to limit cross-talk as much as possible.

Some questions:
1. I was going to use a combined IEC connector with built in EMI filter. Are they recommended or even useful?
2. Should I rubber mount the power transformer?
3. Will a 500mA transformer handle 6550 outputs? (I don't need the power, but they just look sexier than flat sided EL34's).
4. Do I bother with the delay circuit?

Thanks,
Glenn in Australia.

Author:  zyu [ 29 Apr 2018, 06:25 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Good afternoon!
First - the body looks good. Neat and symmetrical - I like it!
Now for questions. I will write everything that I tested myself in my example.
1 Yes, using such a connector is a good idea, as this will additionally help to deal with possible problems.
2 I believe that this must be done necessarily. The possible noise will depend on the thickness of the transformer cover. I believe that edcors quite thick. But with additional rubber the transformer becomes absolutely noiseless.
3 I would say yes. The fact is that the amount of current here is set not by a lamp, but by a current source LM317. For tubes 6550 2 resistors are connected in parallel 10 ohm and 22 ohm, together giving resistance of 6.87 ohms.
LM317 has 1.25 volts at the output, so the current will be 1.25 / 6.87 = 182mA for pair. Accordingly, for four tubes 364mA.
Of course, another part of the current will be spent on input tubes, raising the heater potential and so on. But, in general, should suffice.
4 In my understanding - yes. But I, for example, prefer mechanical delay. I just use a three-position toggle switch. Completely off, only heater, heater and high voltage are switched on.

Author:  gofar99 [ 29 Apr 2018, 08:50 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi Glenn, It should work fine. Good layout. I have used similar layouts on projects.

Good listening
Bruce

Author:  ILoveHiFi [ 29 Apr 2018, 15:29 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Looking good Glenn
A EMI filter will help reduce noise from mains, if theres some non legal noisy switch mode operating on your same mains, that noise will go into your amp.
The EMI filter will prevent this from happening.

With my electoric bike charger from china, many noise is observed when its charging and I am using my oscillie scope without any input

I would personally go with a sold steel mount for the transfomer, its not moving so a plastic mount will make the mounting less solid

Personally I do not belive in cathode stripping and all of that, so I wouldn't go with a start up delay.

Author:  gofar99 [ 29 Apr 2018, 16:31 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, I don't believe in cathode stripping either....however the delay in the big Oddwatts has a second purpose. With a solid state power supply the voltage on the filter caps goes to the peak value immediately. It will be about 550-570 depending on your actual AC mains input. This is a bit much for 500 volt caps. The delay allows the tubes to get warm and be ready to conduct immediately thus pulling down the voltage nearly instantaneously to around 430-450 and protecting the caps. You can naturally do the delay manually with a switch.

Good listening
Bruce

Author:  Trackhappy [ 29 Apr 2018, 18:01 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

I have in mind to use a Microchip PIC processor for the timing (10F322 probably). I tinker with them for fun and they are a tiny 6/8 pin chip that does that job easily. I have visions of making a small board and mounting it on an octal valve base. The icing on the cake would be a blank glass over the top and some LED's to make it look cool. Only two issues, finding a suitable relay to fit inside, and glass tube. Meantime, a switch might be in order. :)

Author:  gofar99 [ 29 Apr 2018, 18:48 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Hi, That would work, but the good old 555 does the job quite easily and are cheap. Small relays that will work are a problem. Apparenly the AC rating is more important than the DC. Ones I use and are in the kits are by OEG (OSA_SH_212-DM5) they are not made any longer but according to the manufacturer (now TE) the PCH-112L2M should work. Both are rated at only 277 VAC, but none have ever failed in one of the commercial amps. The AC there is about 400. Many have been in service since 2008. Go figure. The relays are small and could fit inside something like you have in mind.

Good listening
Bruce

Author:  Trackhappy [ 29 Apr 2018, 19:49 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

The thing about the little processor is there is no maybe's no capacitors to do the timing. It runs at 1Mhz, tell it what you want based on that clock and it does it every time. They are about $1.50 I think (cheap), but you need to add a vreg. In addition, you can use the other outputs to drive LED's in any pattern you might wish, or have an input (jumper?) to change its behaviour somehow. Once I have the code done, happy to share or send pre-programmed processors for anybody interested. I might even make a little board specifically for the purpose with an output to drive a relay.
On the physical layout side, I was thinking of putting air holes under the transformer as well to promote some flow. Might try without rubber mounts and see what transpires I guess. I need to identify some suitable switches and neon's to go on the front that look good. Have to bear in mind I will be wrapping it in some nice timber after it is running.
Next step is finish bolting everything down and start planning the wiring... oh, and find some suitable heatsinks. I am thinking heatsink black fins about 2 inches by 3 inches mounted vertically to promote air flow, is that enough?
Thanks,
Glenn.

Author:  ILoveHiFi [ 29 Apr 2018, 22:07 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Personally I belive its more simple and fast to use a plain 555 timer or rc delay with relay driving the b+.
I've done microcontrollers and I have done coding before

Author:  Emsworth [ 04 May 2018, 03:23 ]
Post subject:  Re: Oddwatt Push Pull Tube Amplifier Projects

Quiz question - where did the volts go?

I completed the second channel power supply of my 'dual-mono' amp last weekend and have been enjoying glorious stereo sound since then. Final tasks included 'power on' and 'HT on' indicator leds (old hands can probably guess where this is going...).
There being an unused 3.9V secondary on the power transformers, the 'Power On' led was very easy.
The HT hasn't worked yet :( There are 488 or 215 VDC available once the standby is switched and the led only needs a couple of volts - this should be simple enough, shouldn't it?
The led needs very little current so, reading up on voltage dividers and using the 215vdc supply, I tried 10R and 1k resistors in series to the led tapping off between the resistors for the plate supply.

Results, as they say, were mixed. The led was happy, but the plate voltage was WAY down - what really confused me was that the DC voltage measured before the 10R resistor was now reading around 50V. Where did the volts go?

Being in the territory of 'a little knowledge is a dangerous thing' here and reluctant to experiment further, I'd appreciate advice...

Denis

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