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Old 26th Dec 2011, 2:14 pm   #101
Don_Zalmrol
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Default Re: Stereo valve amp not working.

Thx, I will look in to that subject of audio processor for studios.
But won't those devices be very expensive?

In the attachment you can see the headset input.

I now have some measuring clamps and will adjust the voltages to 25mVDC to give an output current of 25mA.
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File Type: pdf headset input.pdf (196.5 KB, 114 views)
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Old 26th Dec 2011, 2:45 pm   #102
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Default Re: Stereo valve amp not working.

I've adjusted the bias to give a voltage of +- 250mVDC over the 10R/1W resistors.
It seems that whenever I turn the adjustable bias the voltages changes a bit over the resistor.

When I leave the current config the valves stay stable and no overheating occurs in valve #2, which is in place of socket #2.

If I wait a bit and then measure the voltages over the resistors (or pin 8) the voltages have changed by themselves by 1~2mVDC on all of the valves.

Is this normal?
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Old 26th Dec 2011, 2:46 pm   #103
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Default Re: Stereo valve amp not working.

Hi Don, They can be expensive, even second hand, but if you watch the auction sites you can see what is available and what might work for you - sooner or later you will find a bargain. You will certainly find a good processor cheaper than a valve power amp.

I have looked at your pdf, thanks, but it doesn't show the circuit accurately. Never mind, I'm sure I understand what is going on.

Peter
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Old 26th Dec 2011, 2:50 pm   #104
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Default Re: Stereo valve amp not working.

Hi Don, All sounds normal to me.

Peter
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Old 26th Dec 2011, 2:52 pm   #105
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Default Re: Stereo valve amp not working.

I know it doesn't add much to the schematic. But this is what Piet gave me. And I do not doubt his knowledge about valve amplifiers, but I think he thought I was going to use this amp also for playing music trough the speakers and only trough the headset at night so to speak. Thus the output was choked, but not as long as intended…

I now learned that I accidentally bought the wrong amplifier for the wrong use…
So I will remove the headset input from the circuit and use this one only for speakers.

I will now test the amp with some music and see how the valves react to it.
Now the amp is still on (with the new config) and the valves seems to be operating normal.

Also valve #2 is not overheating at the moment!
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Old 26th Dec 2011, 3:01 pm   #106
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Default Re: Stereo valve amp not working.

I don't understand the diagram of the headphone socket either. However if pugging in the headphones disconnects the speaker, which we're told it does, then nothing you can do with a 470R resistor will present a good load to a valve amplifier.

I think you'll find your amp will work fine when used with speakers

This will be my final post in this thread.
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Old 26th Dec 2011, 3:05 pm   #107
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Default Re: Stereo valve amp not working.

New voltages read-out:

Valve #1:
P1: 250mVDC
P3: 436VDC
P4: 438VDC
P5: -40,3VDC
P6: 435VDC
P8: +- 250mVDC

Valve #2:

P1: 257mVDC
P3: 436VDC
P4: 436VDC
P5: -41,4VDC
P6: 434VDC
P8: +- 253mVDC

Valve #3:

P1: 252mVDC
P3: 436VDC
P4: 437VDC
P5: -39,8VDC
P6: 0VDC
P8: +- 251mVDC

Valve #4:

P1: 280mVDC
P3: 432VDC
P4: 432VDC
P5: -40,8VDC
P6: 0VDC
P8: +- 246mVDC

When I listen to the speakers I hear a hum emitting from the right channel, the left channel is silent. Does this have something to do with 0V on P6 of the valves 3 & 4?

@Graham: Ok, Thank you for your help!
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Old 26th Dec 2011, 3:45 pm   #108
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Default Re: Stereo valve amp not working.

Hi Don, Pin 6 is not connected internally to the valve so it is probably being used as a convenient tie point for components with valves #1 & #2. That is, the voltage on pin 6 is irrelevant.

Test the amp with music and see how it sounds on each channel.

Peter
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Old 26th Dec 2011, 4:48 pm   #109
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Default Re: Stereo valve amp not working.

The headphones input is removed and I'm playing some music from the radio, everything is normal so far. Just a hum trough the speakers. But this was there in the previously also hearable before the fault of valve #2.
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Old 26th Dec 2011, 4:53 pm   #110
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Default Re: Stereo valve amp not working.

Ionisation seems also normal like previously stated, #2 has a bit more ionization, but I think this is normal for this valve, maybe a production error or some wear?

sound still normal, valves operating normal, sound is very clear, no errors or strange side sounds…
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Old 26th Dec 2011, 6:07 pm   #111
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Default Re: Stereo valve amp not working.

Amp still playing clear & cheery!
No more overheating on valve #2, problem solved so it seems.

I'm looking now for a complete valve headphone kit to build myself.

I'm looking at the VT-86PP (has a headphone jack and outputs to speakers) costs €330' but Herald1360 says it's overkill.
http://jukebox-revival.eu/index.php/...ersterker.html

But when I look at other amp kits like the Bottlehead S.E.X. amp kit which is to expensive for me to be honest… €469' and I still need to get it here in Belgium from the US so shipping and taxes will be a high cost…
http://www.bottlehead.com/et/adobespc/S.E.X./SEX.htm

Making it from scratch is also a problem for since I do not have the tools to make my own PCB or circuits…

So this is now my new pickle problem…



Thank you all for your help!
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Old 26th Dec 2011, 7:17 pm   #112
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Default Re: Stereo valve amp not working.

I make no recommendations, but maybe something like this?

http://www.ebay.co.uk/itm/Mini-dual-...item3f0f04b59c

It uses a couple of miniature Russian military valves as preamps to give the "valve sound" followed by transparent solid state output stages. It sounds (sic) plausible
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Old 26th Dec 2011, 7:29 pm   #113
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Default Re: Stereo valve amp not working.

Don,
I'm glad we've got to the bottom of this, and your amp is actually ok.

You seem keen and interested, and I would really encourage you to have a go at building it yourself.
For that price you could obtain all the parts you need (not necessarily brand new), the amp I built recently cost me around £60 in parts, including a pair of new British made output transformers.
With the change, buy yourself the tools you need, maybe even some test gear.
PCB's - don't need 'em, drill holes and wire it up the old fashioned way.
Chassis - I'll fold you one up Free Of Charge to help you on your way.
Circuit - There are plenty out there, but all variations of a theme. Think about what you want your amp to do first, inputs and outputs, tone controls, EQ etc. This will dictate the gain and hence the number of stages (ie valves) required and power requirements. Find the nearest similar circuit and at that stage feel free to ask here.
What you will learn and what you will need to learn building this I think you would find invaluable.
You might even enjoy it!
Best regards,
Rob.
p.s. maybe you ought to start a new thread re. headphone amp.
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Old 26th Dec 2011, 8:13 pm   #114
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Default Re: Stereo valve amp not working.

@Herald1630:
Thx for the link.
The device seems nice, but I think it won't give a high quality sound (I think it's more a hype-device…).

@Glowinganode:
Thx, I am interested. I will look up some more information about building it myself.

Why aren't PCB's allright? I find them to be clear in fault-finding and very sturdy (if you use thick PCB's of course)

Chassis is not a problem, at home we got ourself a small manual bending machine/ press.
But thank you very much for the offer!

The reason of why I like kits, is because they are tested and the manufacturer knows that it works. And don't have the hassle of my own circuits in PCB making or classical floating connections and thus minimizing the possibility of errors. Unfortunately they come at a price…

When I got more information, I will start a new topic here to verify my information/ facts and start building one of my own.

And thank you all again for your help!
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Old 26th Dec 2011, 9:13 pm   #115
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Default Re: Stereo valve amp not working.

Quote:
Originally Posted by Don_Zalmrol View Post
Why aren't PCB's allright?
Nothing wrong with PCB's for a mass produced item to a finalised design.
I just prefer to do it the old fashioned way, it makes it easier to make modifications, or tweak component values as required.
Rob.
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Old 26th Dec 2011, 9:51 pm   #116
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Default Re: Stereo valve amp not working.

Ah, ok.
This new amplifier would be a finalized system. If I would tinker with it, I would make an experimental board for testing and such…
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Old 26th Dec 2011, 10:08 pm   #117
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Default Re: Stereo valve amp not working.

Quote:
The reason of why I like kits, is because they are tested and the manufacturer knows that it works

Erm, I wouldn't stick to this rather bold comment - Kits, especially small volume ones can be a real faff to get working properly - Home built stuff can be as well, but you normally have not invested anywhere near the cash!
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Old 26th Dec 2011, 10:46 pm   #118
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Default Re: Stereo valve amp not working.

Sorry, I meant if I would implement a home-brew schematic without an PCB or something similar.

Also some of the schematics are a bit confusing for me, always one side of the channels is described
and I am a bit afraid for making a huge fault with mixing them (L & R) and so ruining the whole system then to buy the whole list again
and so to speak, pay again +- €100…

I know that with a kit the problems aren't gone or that no installation errors could occur, but to say it's a safer bet for me.

Last edited by Don_Zalmrol; 26th Dec 2011 at 10:58 pm.
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Old 26th Dec 2011, 11:20 pm   #119
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Default Re: Stereo valve amp not working.

Hi.
Well I have been at work and haven't been able to post. There is absolutely no reason why you cannot use the amp with phones if done correctly (although it's overkill) when you plug your head phones into the jack the switching should immediately put a load onto each channel in the order of 5-20 ohms and capable of dissipating 40 odd watts per channel, you also need an attenuating network so the headphones and your ears are not ruined. If this is done you will have no problems in that department.
If it was my amp though I would not even consider an output for headphones.
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Old 26th Dec 2011, 11:41 pm   #120
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Default Re: Stereo valve amp not working.

I've removed the headphones-output from the amplifier, I now know that this is overkill.

So I've started a new topic in the home-brew section whether to build a kit from scratch or to buy a kit which gives me the direct possibility to use my headphones or speakers or an amplifier only for my headphones

The topic is here.

The problem is solved with the amps #2 valve overheating, this is from the usage with the headphones, if I didn't noticed this earlier my whole amp would probably be on the fritz…
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